HomeMy WebLinkAbout01 - Appendix C Part 1APPENDIX C
HYDROLOGY AND WATER O UALITY
WATERSHED ASSESSMENT REPORT
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Prepared By:
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Fuscoe Engineering, Inc. J -III,
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16795 Von Karman, Suite 100
Irvine, CA 92606
949.474.1960
Prepared for:
NEWPORT BANNING RANCH, LLC
1300 Quail Street, Suite 100
Newport Beach, CA 92660
Date Prepared: June 30, 2011
�,; Project No.: 821 .01 .02
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT
Design Applications for Hydrology,
Flood Control, Water Quality, and
Low Impact Development Features
City of Newport Beach, CA
FINAL DRAFT
Prepared for:
NEWPORT BANNING RANCH, LLC
1300 Quail Street, Suite 100
Newport Beach, CA 92660
a
FUSCOE ENGINEERING, INC.
16795 Von Karman, Suite 100
Irvine, CA 92606
Contact: John Olivier, P.E.
949.474.1960
June 30, 2011
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT— FINAL DRAFT
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WATERSHED ASSESSMENT REPORT— FINAL DRAFT JUNE 30, 2011
TABLE OF CONTENTS
Section
Paae
ACRONYMS & ABBREVIATIONS ............................................... ...............................
vii
EXECUTIVE SUMMARY .............................................................. ...............................
ix
1.0 INTRODUCTION .................................................................. ..............................1
1.1 PURPOSE OF STUDY .............................................................. ..............................1
1.2 PROJECT AND SITE DESCRIPTION .......................................... ..............................1
1.2.1 Location ........................................................................................ ..............................1
1.2.2 Existing Site Features ...................................................................... ..............................5
1.2.3 Existing Oil Operations ................................................................... ..............................9
1.2.4 Proposed Development ................................................................... ..............................9
1.3 STUDY OBJECTIVES .............................................................. .............................13
1.4 CEQA THRESHOLDS OF SIGNIFICANCE .............................................................
14
2.0 SETTING ............................................................................. .............................15
2.1 WATERSHED ......................................................................... .............................15
2.2 RECEIVING WATER BENEFICIAL USES ..................................... .............................15
2.3 EXISTING WATER QUALITY CONDITIONS .............................. .............................18
2.4 EXISTING DRAINAGE CONDITIONS ...................................... .............................19
2.5 PROPOSED DRAINAGE PLAN ................................................. .............................19
2.5.1 Proposed Storm Drains .................................................................. .............................19
2.5.2 Lowland Area ................................................................................ .............................20
2.5.3 Off -Site Runoff Water Quality/ Detention Basin ............................... .............................20
2.6 FEMA SPECIAL FLOOD HAZARD AREAS .................................. .............................27
3.0 HYDROLOGY ASSESSMENT ................................................ .............................29
3.1 METHODOLOGY .................................................................. .............................29
3.1 .1 Rational Method ........................................................................... .............................29
3.1.2 Small Area Unit Hydrograph Method .............................................. .............................30
3.2 RESULTS & DISCUSSION ........................................................ .............................30
3.2.1 Lowland Area and Salt Marsh Basin ................................................ .............................30
3.2.2 Semeniuk Slough .......................................................................... .............................35
3.2.3 Caltrans Box Culvert at WCH ......................................................... .............................41
3.3 FLOODPLAIN INUNDATION ANALYSIS .................................. .............................45
3.3.1 Methodology ................................................................................ .............................45
3.3.2 Results and Discussion ................................................................... .............................47
3.4 HYDROLOGY /HYDRAULICS IMPACT ASSESSMENT ................. .............................59
4.0 WATER BUDGET ANALYSIS ................................................. .............................63
4.1 SETTING ............................................................................... .............................63
4.1 .1 Arroyo Drainage Characteristics ..................................................... .............................63
4.1.2 Climate ........................................................................................ .............................69
4.2 METHODOLOGY .................................................................. .............................69
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4.2.1 Water Budget Model ..................................................................... .............................69
4.2.2 Surface Inflow ............................................................................... .............................70
4.2.3 Evapotranspiration ........................................................................ .............................71
4.2.4 Loss ............................................................................................. .............................71
4.3 RESULTS & DISCUSSION ........................................................ .............................72
4.3.1 Northern Arroyo ............................................................................ .............................72
4.3.2 Southern Arroyo ............................................................................ .............................73
5.0 WATER QUALITY ASSESSMENT ........................................... .............................77
5.1 REGULATORY FRAMEWORK .................................................. .............................77
5.1 .1 Federal Regulations ....................................................................... .............................77
5.1.2 State and Local Regulations ........................................................... .............................78
5.2 PREDICTED POLLUTANTS AND SOURCES .............................. .............................82
5.3 APPROACH ........................................................................... .............................85
5.3.1 Construction Best Management Practices ........................................ .............................87
5.3.2 Post - Construction Best Management Practices ................................. .............................99
5.3.3 Interior Water Quality Features ....................... ............................... ............................101
5.3.4 Transitional Phase Water Quality Features ....... ............................... ............................103
5.3.5 Regional Natural Treatment Systems & water Quality Basins ............. ............................115
5.4 WATER QUALITY IMPACT ASSESSMENT .. ............................... ............................121
6.0 EXHIBITS ............................................. ............................... ............................127
7.0 TECHNICAL APPENDICES ................... ............................... ............................133
EXHIBITS (INCLUDED IN SECTION 6)
Exhibit 1 Rational Method Hydrology Map For Proposed Condition
Exhibit 2 Rational Method Hydrology Map For Proposed Condition
FIGURES
Figure 1: Project Vicinity Map ............................................................ ..............................3
Figure 2: Existing Site Features .......................................................... ..............................7
Figure 3: Proposed Development ......................................................... ..........................1 1
Figure4: Existing Watershed ............................................................ .............................23
Figure 5: Proposed Drainage Plan .................................................... .............................25
Figure 6: Proposed Sub - Watershed Basins ......................................... .............................33
Figure 7: Semeniuk Slough Drainage ................................................ .............................39
Figure 8: Caltrans Box Culvert .......................................................... .............................43
Figure 9: Northern Arroyo Existing Condition (100 -Year & 2 -Year) Floodplain ...................49
Figure 10: Northern Arroyo Proposed Condition (100 -Year & 2 -Year) Floodplain ..............51
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Figure 11:
Southern Arroyo 100 -Year Floodplain ............................... .............................55
Figure 12:
Southern Arroyo 2 -Year Floodplain ................................... .............................57
Figure 13:
Habitat Drainage, Northern Arroyo ................................... .............................65
Figure 14:
Habitat Drainage, Southern Arroyo ................................... .............................67
Figure 15
GIS Map Method for Determining K and LS Factors ............. .............................89
Figure 16:
Water Quality BMP Plan .................. ............................... ............................107
46
Figure 17:
Typical Green Street Section with Sub- surface Biocell Enhancement ................1
13
Figure 18:
Typical Extended Detention Water Quality Basin ............. ..............................1
19
TABLES
Table 2.1 Beneficial uses for downstream receiving waters .................. .............................16
Table 2.2 Water quality objectives for Santa Ana Region enclosed bays and estuaries . ....... 17
Table 3.1 Existing condition runoff volume summary for Lowland Area and Salt Marsh Basin.
...................................................................................................... .............................31
Table 3.2 Proposed condition runoff volume summary for Lowland Area and Salt Marsh
Basin...............................................................................................
.............................32
Table 3.3
Existing condition hydrology summary for Semeniuk Slough .. .............................36
Table 3.4
Proposed condition hydrology summary for Semeniuk Slough ............................37
Table 3.5
Existing condition hydrology summary for Caltrans Box Culvert at WCH .............41
Table 3.6
Proposed condition hydrology summary for Caltrans Box Culvert at WCH ..........41
Table 3.7
Discharge summary for Northern Arroyo used for HEC -PAS models ...................
46
Table 3.8
Discharge summary for Southern Arroyo used for HEC -PAS models ...................
46
Table 3.9
Existing condition HEC -RAS modeling results for the Northern Arroyo .................47
Table 3.10
Proposed condition HEC -PAS modeling results for the Northern Arroyo . ...........
48
Table 3.11
HEC -RAS modeling results for the Southern Arroyo, 2 -year event .....................
53
Table 3.12
HEC -RAS modeling results for the Southern Arroyo, 100 -year event .................54
Table 4.1
Drainage area summary of the Northern and Southern Arroyos .........................64
Table 4.2
Average monthly temperatures for the project area .............. .............................69
Table 4.3
Average monthly precipitation for the project area ............... .............................69
Table 4.4
Summary of surface runoff inflow factors ............................ .............................70
Table 4.5
Summary of potential evapotranspiration ............................ .............................71
Table 4.6
Water Balance under existing conditions of the Northern Arroyo ........................72
Table 4.7 Water Balance under proposed conditions of the Northern Arroyo .....................73
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Table 4.8 Water Balance under existing conditions of the Southern Arroyo ........................ 74
Table 4.9 Water Balance under proposed conditions of the Southern Arroyo ..................... 74
Table 5.1 Anticipated and potential pollutants of concern for Project land use categories. ..83
Table 5.2 Combined construction site risk level matrix ........................ .............................91
Table 5.3
Preliminary sediment risk factor for Newport Banning Ranch . .............................92
Table 5.4
Combined risk level matrix for Newport Banning Ranch ....... .............................93
Table 5.5
Minimum guidelines for construction storm water management BMPs ................96
Table 5.6
Guidelines for erosion and sediment control practices ......... .............................97
Table 5.7
Summary of landscaping biocell water quality sizing options ............................109
Table 5.8
Summary of BMP sizing for green street features ............... ..............................1
10
Table 5.9 Summary of BMP sizing for water quality basins ................ ..............................1 17
TECHNICAL APPENDICES
APPENDIX A STUDY RELATED DOCUMENTS
Al Salt Marsh Restoration Plan from USACOE
A2 FEMA Map
APPENDIX B HYDROLOGY CALCULATIONS
Bl Existing Condition Rational Method Calculations
B2 Proposed Condition Rational Method Calculations
B3 Existing Condition Small Area Unit Hydrograph Calculations
B4 Proposed Condition Small Area Unit Hydrograph Calculations
APPENDIX C HEC -RAS MODELING
C1 HEC -RAS Modeling Report for Northerly Arroyo Channel
C2 HEC -RAS Modeling Report for Southerly Arroyo Channel under
Existing Condition
C3 HEC -RAS Modeling Report for Southerly Arroyo Channel under
Proposed Condition
APPENDIX D WATER BUDGET ANALYSIS
Dl Northerly Arroyo under Existing Condition
D2 Northerly Arroyo under Proposed Condition
D3 Southerly Arroyo under Existing Condition
D4 Southerly Arroyo under Proposed Condition
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DS ET Reference Material
APPENDIX E BEST MANAGEMENT PRACTICES
E1 Site Design /LID BMPs
E2 Source Control BMPs
E3 LID / Treatment Control BMP Calculations
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ACRONYMS & ABBREVIATIONS
JUNE 30, 2011
AASHTO American Association of State Highway and Transportation Officials
ac -ft acre -feet
AES Advanced Engineering Software
AHIP Affordable Housing Implementation Plan
ATS active treatment system
BAT
best achievable technology
BCT
best conventional technology
BMP
best management practice
Caltrans
California Department of Transportation
CASQA
California Stormwater Quality Association
CDP
Coastal Development Permit
CEQA
California Environmental Quality Act
CFR
Code of Federal Regulation
cfs
cubic feet per second
CWA
Clean Water Act
DSA disturbed soil area
EIR Environmental Impact Report
ET evapotranspiration
EV expected value
FEMA Federal Emergency Management Association
FIRM Flood Insurance Rate Map
ft /s feet per second
GCP General Construction Permit
HC high confidence
HEC -RAS Hydrologic Engineering Centers River Analysis System
HSA Hydrologic Sub -Area
IPM Integrated Pest Management
LDR
low density residential
LID
low impact development
LIP
Local Implementation Plan
LMDR
low- medium density residential
MDR
medium density residential
MEP
maximum extent practicable
MS4
municipal separate storm sewer system
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MSL mean sea level
MU /R mixed use & residential
NAL
numeric action level
NBR
Newport Banning Ranch
NEL
Numeric effluent limitation
NFIP
National Flood Insurance Program
NOI
Notice of Intent
NPDES
National Pollutant Discharge Elimination System
NTU
nephelometric turbidity units
OC DAMP
Orange County Drainage Area Management Plan
PADA
Pre - Annexation Development Agreement
PAH
polycyclic aromatic hydrocarbons
PRD
permit registration documents
QA /QC quality assurance /quality control
RCB
reinforced concrete box
RCP
reinforced concrete pipe
REAP
Rain Event Action Plan
RUSLE
Revised Universal Soil Loss Equation
RWQCB
Regional Water Quality Control Board
SFHA
Special Flood Hazard Area
SIC
standard industrial classification
SQDF
Storm Water Quality Design Flow
SQDV
Storm Water Quality Design Volume
SWPPP
Storm Water Pollution Prevention Plan
SWRCB
State Water Resources Control Board
Tc
time of concentration
TDS
total dissolved solids
TMDL
Total Maximum Daily Load
TPH
total petroleum hydrocarbons
TSS
total suspended solids
USACOE United States Army Corps of Engineers
USDA
United States Department of Agriculture
US EPA
United States Environmental Protection Agency
WCH
West Coast Highway
WDR
Waste Discharge Requirement
WQMP
Water Quality Management Plan
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EXECUTIVE SUMMARY
The purpose of this Watershed Assessment Report is to assess storm water runoff, flood
control, and water quality impacts associated with the proposed Newport Banning Ranch
development project. It also seeks to identify potential project design features and /or
mitigation measures for inclusion into the Project Environmental Impact Report (EIR). The
Report calculations are based on the revised Land Use Plan entitled Exhibit 2 -1, NBR Planned
Community Development Plan by FORMA, dated November 20, 2009.
The Newport Banning Ranch property encompasses approximately 402 acres within
unincorporated County of Orange and portions of the City of Newport Beach, California.
The site has been used as an operating oil field and, today, remnants of old wells and
pipelines coexist with currently operating pump and processing facilities. The proposed
Newport Banning Ranch Project includes the development of roughly 175 acres of the larger
402 -acre project site for residential, commercial, and recreational land uses. Over fifty
percent of the property will be retained as open space, with restored wetland and habitat
areas located throughout the Lowland and Upland Mesa areas.
This report concentrates on sustainable design strategies for the hydrology, flood control, and
water quality issues associated with the proposed Project. Project design features and best
management practices (BMPs) will be implemented to reduce the potential impacts to
hydrology and surface water quality. The effect of the development on groundwater,
geotechnical resources and biology are not included in the scope of this report.
Hydrology Analysis
The objective of this hydrology study is to compute the existing and proposed condition peak
flow discharge rates and runoff volumes for selected recurrence interval storm events and to
use the results to evaluate the hydrologic impacts experienced by the watershed that are
caused by the presence of the Project. The study also seeks to assess impacts to the existing
and proposed drainage facilities in order to determine the level of significance of the impacts
due to the Project. The results apply to three receiving facilities identified as the Salt Marsh
Basin and Lowland Area, the Semeniuk Slough and the Caltrans Reinforced Concrete Box
(RCB) Culvert in West Coast Highway (WCH).
Salt Marsh Basin and Lowland Area: The results of the High Confidence hydrology
analysis reveal that the proposed development will only marginally increase the total
runoff volume in the Salt Marsh Basin and Lowland Area. This is achieved largely by
preservation of open space area in the proposed land use plan to the maximum extent
possible. The predicted volumetric increases are 1.5% for the 10 -year recurrence
interval event, and 1.3% for the 25 -year recurrence interval event. The analysis also
reveals that the Marsh and Lowland storage capacity is sufficient to detain the 25 -year
post- development runoff volume tributary to it. This result indicates that a 25 -year
level of protection is provided in the pre - development, condition and that the 25 -year
level of protection is also maintained in the post - development condition. This is a
favorable result confirming that mitigation for this impact is neither needed nor
warranted to compensate for the presence of the Project.
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• Semeniuk Slough: The results of the Expected Value hydrology analysis reveal that the
proposed development will only marginally increase the peak flow rate and runoff
volume in the Semeniuk Slough. This is achieved by the re- assignment of
approximately 27 acres of tributary area away from the Semeniuk Slough and toward
the Lowland Area. The predicted increase in peak flow rate is 5.6% for the 2 -year
recurrence interval event. The predicted volumetric increase is 3.7 %. The analysis
also reveals that the Semeniuk Slough storage capacity is sufficient to detain the 2-
year post - development runoff volume tributary to it. This result indicates that the 2-
year level of protection is provided in the pre - development condition, and that the 2-
year level of protection is also maintained in the post - development condition. This is
a favorable result confirming that mitigation for this impact is neither needed nor
warranted to compensate for the presence of the Project.
• Caltrans Reinforced Concrete Box (RCB) Culvert in West Coast Highway The results
of the High Confidence hydrology analysis reveal that the proposed development will
significantly decrease the peak flow rate delivered to the lower reach node and the
middle reach node of the RCB. The upper reach node is expected to experience an
increase in peak flow that measures less than 1 %. This result indicates that a 100 -
year level of protection is provided in the pre - development condition and that the
100 -year level of protection is also maintained in the post - development condition.
This is a favorable result confirming that mitigation for this impact is neither needed
nor warranted to compensate for the presence of the Project.
Floodploin Inundation Analysis
The purpose of the channel hydraulics analysis is to establish the flow depths, velocities, water
surface profiles and the resulting flood plain boundaries for a series of design storm events
under the existing and proposed conditions for the Northern and Southern Arroyos. The
Northern Arroyo modeling is to verify the field reconnaissance that this Arroyo is in a stable
channel condition and to quantify the changes between the existing and proposed conditions.
The Southern Arroyo modeling is to quantify the changes between the existing and proposed
conditions and determine long -term stability of the channel.
The results of the hydraulics analysis show that the Northern Arroyo does not generate erosive
velocities, even under the extreme 100 -year condition event. This is consistent with the field
observations that exclude any evidence of erosion in the Arroyo bed and bank. For the
Southern Arroyo, based on the projected hydraulic performance of the channel and the
upstream control basin to reduce the peak flows entering the Southern Arroyo, the channel is
expected to remain stable under the proposed condition. In addition, measures will be taken
to stabilize the eroding tributaries entering the Arroyo thereby controlling the amount of
sediment available for transport to the Semeniuk Slough. Lastly, the diffuser basin at the
downstream end of the Arroyo will also provide an additional measure to control sediment
loading into the Semeniuk Slough.
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Habitat Analysis
The purpose of the hydrologic objectives for habitat is to maintain an appropriate water
budget for all preserved habitat on -site and utilize treated storm water runoff to supplement
areas of enhancement and /or creation of habitat. The water budget analysis estimates the
water demand and supply for the Northern Arroyo and Southern Arroyo habitats and further
determines the ecological condition of the habitat from the water balance perspective.
For the Northern Arroyo, the results of the water budget analysis showed that in general, there
will be no significant change in the habitat - related drainage under the proposed condition.
Specifically for the Northern Arroyo habitat area, the drought season is from May to August
and October, and the remaining months of the year are considered to have sufficient water
budget for the habitat. There is no anticipated water budget impact on the Northern Arroyo
habitat from the proposed development.
In general, under the existing condition, the Southern Arroyo habitat area has a longer
drought period than the Northern Arroyo. The results show a deficit in water balance from
April to October, while the remaining five months exhibit positive balances. However, based
on the field reconnaissance, the existing habitat survives through the year under the existing
water budget condition. For the proposed condition, although the Upland Mesa area will be
converted to the residential area and be therefore removed from its drainage, the water
budget results for the Southern Arroyo do not vary significantly as compared to existing
conditions. The drought period is expected to remain as seven months, and the annual
balance will decrease only by approximately 1 inch.
Overall, there is no significant water budget impact on the Arroyo habitats due to the
proposed development. However, enhancement opportunities exist by diverting treated dry
weather flows and storm event low -flows to the Arroyo from the proposed storm drain system
and incorporated LID features, should this controlled input be necessary.
Water Quality Analysis
The purpose of water quality assurance plan is to define the water quality treatment approach
for the Newport Banning Ranch Project consistent with the details of the current planning level,
and summarize the various water quality systems and concepts being considered within the
development areas. In order to reduce the amount of pollutants in storm water runoff from
the new development plan, best management practices (BMPs) are required to be
implemented in accordance with California Coastal Commission, the City of Newport Beach
and local Regional Board standards.
The holistic approach to water quality treatment for the Newport Banning Ranch Project
includes incorporation of site design /low impact development (LID) strategies and source
control measures throughout the site in a systematic manner that maximizes the use of LID
features to provide treatment of storm water and runoff reduction benefits. In addition,
treatment control BMPs are proposed to treat runoff not treated by LID measures, as well as to
treat off -site runoff from upstream areas that drain towards the Southern Arroyo. Overall, the
Project will provide water quality treatment that exceeds water quality regulations for the long-
term protection against downstream impacts on adjacent habitat areas and downstream
receiving waters.
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One of the primary LID features of importance within the Project is the use of landscaping
biocells within portions of the parkway bioswales of arterial and collector streets. Biocells are
small, vegetated depressions to promote infiltration and filtration of storm water runoff.
Additional LID features that may also be incorporated throughout the Project include
permeable /porous pavement, pocket rain gardens, cisterns and landscaped storm water
planters, among others. The specific details and locations of these measures will occur during
the detailed design phase of each community.
The use of the vegetation biocells and other LID applications will result in a significant
treatment and reduction of runoff at the source of the development areas. Each LID feature
will be designed to accommodate the required treatment volume and additional treatment
where feasible. High flows will be designed to bypass the features for conveyance into the
traditional storm drain system. In those instances where the individual features are not
sufficient to handle treatment requirements independently, water quality calculations will
quantify how much the additional treatment is required by the next downstream LID feature.
The proposed Project will also incorporate the use of water quality basins to provide the final
treatment of runoff for certain portions of the site. One regional water quality facility will be
implemented to accommodate the off -site (City of Costa Mesa) treatment of urban runoff and
first -flush flows from areas tributary to the Southern Arroyo, and will also provide detention
capabilities to reduce peak flow runoff. The water quality basin will have the capacity to
accommodate a minimum of 2.3 ac -ft of treatment. A second basin is also proposed within
the Lowlands of the property, which will also serve as a diffuser basin to control the rate at
which water drains from the top of the Mesa down to the Lowlands. Additional water quality
basins are also provided along the fringes of the development in combination with other LID
features to further provide treatment of runoff.
Clearing, grading, excavation and construction activities associated with the proposed Project
could impact water quality due to sheet erosion of exposed soils and subsequent deposition of
particles and pollutants in drainage ways or introduction of construction - related pollutants.
Under the Statewide General Construction Permit ([GCP], Order 2009- 0009 -DWQ), the
Project proponents will submit a Notice of Intent (NOI) and associated permit registration
documents (PRDs) to the SWRCB prior to commencement of construction activities. In
addition, a Construction Storm Water Pollution Prevention Plan (SWPPP) will be prepared and
implemented at the project site. The SWPPP will describe construction BMPs meeting the
standards required by the GCP and that address pollutant source reduction, and will ensure
that water quality standards are not exceeded in downstream receiving waters due to
construction activities. These include, but are not limited to erosion controls, sediment
controls, tracking controls, non -storm water management, materials & waste management,
and good housekeeping practices. The SWPPP shall be developed in accordance with the
construction plans.
As a result of the construction - related, site design /LID, source control, and additional
treatment control BMPs, water quality exceedances are not anticipated, and pollutants are not
expected in Project runoff that would adversely affect beneficial uses in downstream receiving
waters.
P: \Projects \821 \01 \Wat\Admin \Reports \WAR Update \Report Vol 1 \2011 -0630 \82101 rp_WAR_FINAL_100630_clecn.d=
FUSCOE ENGINEERING, INC. xii
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT .TUNE 30, 2011
[Kim 1M 111 :M PINION I 10M
1.1 PURPOSE OF STUDY
The purpose of this Watershed Assessment Report is to assess storm water runoff, flood
control, and water quality impacts associated with the proposed Newport Banning Ranch
development project (referred to as the "Project "). It also seeks to identify potential project
design features and /or mitigation measures for inclusion into the Project Environmental Impact
Report (EIR). Activities associated with the Project have the potential to alter the existing
drainage courses, modify the impervious surface makeup, and create the possibility for new
potential sources of runoff contamination. The runoff management components for the
Project are described in the following sections:
• Section 1 identifies the framework and objectives for the Watershed Assessment
Report.
• Section 2 provides background regarding the Project watershed and associated
drainage conditions.
• Section 3 identifies the existing versus proposed hydrologic conditions with respect to
the Project watershed along with the associated flood control and drainage impacts.
It also investigates the existing channel hydraulics and stability concerning the
proposed development plan.
• Section 4 provides water budget demands for preserved habitat in the Arroyos to
identify any potential changes to the existing water budgets of the existing Arroyos on-
site and validate that the proposed Project will not significantly alter the existing
hydrologic conditions.
• Section 5 summarizes the existing and proposed water quality features with an
emphasis on the implementation of low impact development (LID) features.
This report concentrates on sustainable design strategies for the hydrologic, hydraulic, and
water quality issues associated with the proposed Project. Project design features will be
implemented to reduce the potential impacts to hydrology and surface water quality. The
effect of the development on groundwater, geotechnical and biology are not included in the
scope of this report; however, their objectives have been considered in the design and water
quality aspects of the Project.
1.2 PROJECT AND SITE DESCRIPTION
1.2.1 LOCATION
The Newport Banning Ranch property encompasses approximately 402 acres within
unincorporated County of Orange and portions of the City of Newport Beach, California.
The property is bounded on the south by the West Coast Highway (WCH), to the west by the
Santa Ana River channel, and by existing residential and commercial developments to the
north and east (see Figure 1, Vicinity Map). The entire property is situated within the Coastal
Zone Jurisdictional Boundary as established by the California Coastal Act, and is therefore
FUSCOE ENGINEERING, INC.
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT
JUNE 30, 2011
also subject to the planning and regulatory jurisdiction of the California Coastal Commission.
The southwestern border of the property is less than one half mile from the Pacific Ocean and
adjoining beaches. The City of Costa Mesa, including Talbert Regional Park, is adjacent to
the northern and a portion of the eastern project boundaries. Wetland areas restored by the
US Army Corp of Engineers (USACOE) extend up the Site's western boundary and separate
the site from the Santa Ana River channel. The City of Huntington Beach is located west of the
Santa Ana River, adjacent to the Site's western boundary. Figure 1 is the Project's Vicinity
Map.
FUSCOE ENGINEERING, INC.
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June 30, 2C
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June 30, 2C
" ' NOT TO SCALE
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT
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FUSCOE ENGINEERING, INC.
JUNE 30, 2011
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT
1.2.2 EXISTING SITE FEATURES
JUNE 30, 2011
Within the project boundary, there are several primary landforms of concern that are
referenced throughout this report:
• Lowland Area: Located in the northeasterly portion of the property. The Lowland Area
currently consists of degraded wetland and ruderal vegetation, as well as roads,
pipelines, and other facilities associated with oil operations. In addition, the Lowland
Area consists of several narrow channels and shallow depressions that occasionally
pond water.
• Upland Mesa: Located in the eastern portion of the properly. Similar to the Lowland
Area, the Upland Mesa currently consists of existing pipelines, roads, buildings, and
other equipment related to oil extraction activities.
• Bluffs: Located adjacent to the Lowland Area and include west and southwest facing
slopes of varying steepness. The bluffs have suffered from erosion in localized areas,
resulting in sloughing and sediment contributions to the Semeniuk Slough.
• Arroyos: There are several existing drainage courses (generally referred to as
"Arroyos") that fall gradually from the eastern project boundary across the Mesa and
Bluffs towards the Semeniuk Slough in the western portion of the site. The two largest
Arroyos, designated as the Northern and Southern Arroyos, are considered significant
drainage features and convey runoff from upstream areas (primarily off -site
contributions) through the project site. The tributaries of these Arroyos, in particular the
Southern Arroyo, have been subject to significant erosion and sloughing of sediment
into the main arroyo channels, and these sediments are delivered downstream during
storm events. The Southern Arroyo conveys the largest amount of flow and sediment
to the downstream receiving water body (Semeniuk Slough) and as part of the
development plan, these eroding tributaries will be stabilized to remove the source of
sediment to the Semeniuk Slough.
Semeniuk Slough (Oxbow Loop): Consists of a meandering drainage course that
flanks the southern portion of the site. The Semeniuk Slough, also known as Oxbow
Loop, receives runoff from both on -site and off -site areas, and drains generally west
and north towards the Lowland Area. However, a small dike separates the Lowland
Area from the Semeniuk Slough channel, and there are several culverts that allow for
tidal exchange between the areas.
Figure 2 highlights these primary landforms and features of the site.
FUSCOE ENGINEERING, INC. 5
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT
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FUSCOE ENGINEERING, INC.
JUNE 30, 2011
P.AProjectA821 A01 AWatAGISWat\MXDAEIR Fig ures &Exhibits\pdfV82101 gh- Fig2_SiteFeatures.pdf
NEWPORT BANNING RANCH FIGURE 2: Existing Site Features
June 30, 2011
NOT TO SCALE
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT
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FUSCOE ENGINEERING, INC.
JUNE 30, 2011
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT .TUNE 30, 2011
1.2.3 EXISTING OIL OPERATIONS
For more than 50 years, the site has been used as an operating oil field and today, remnants
of old wells and pipelines coexist with currently operating pump and processing facilities.
Most of the active oil facilities are located in the central portion of the Upland Mesa and
adjoining Lowland Area. Currently, there are over 460 producing, potentially producing, and
abandoned wells along with related roads, pipelines, and associated facilities located
throughout the Newport Banning Ranch property.
1.2.4 PROPOSED DEVELOPMENT
The proposed Newport Banning Ranch Project includes the development of roughly 149 acres
of the larger 402 -acre project site for residential, commercial, and recreational land uses.
Over fifty percent of the property will be retained as open space, with restored wetland and
habitat areas located throughout the Lowland and Upland Mesa areas. The locations of the
development areas have been selected and will be designed to minimize impacts on adjacent
habitats and open space areas (see Figure 3). Below is a summary of the proposed
development:
• Residential Areas: Approximately 76 acres (or 16 %) of the project site will be devoted
to Residential Land Use. This type of land use is divided into the following districts:
o Low Density Residential (LDR) District: Approximately 13 acres of LDR use
development is planned that may include custom homes or larger individual
lots.
o Low - Medium Density Residential (LMDR) District: Approximately 21 acres of
LMDR land use is planned that may include single - family detached homes,
single - family attached homes as well as multi - family housing.
o Medium Density Residential (MDR) District: Approximately 42 acres of MDR
land use is planned that may include single - family detached homes, single -
family attached homes and multi - family residential projects. This land use will
also include smaller convenience commercial sales sites and service sites to
encourage pedestrian and bicycle use.
o Mixed Use /Residential (MU /R) District: Approximately 21 acres of MU /R land
use is planned along the eastern side of North Bluff Road. It adjoins Costa
Mesa's "MesaWest Bluffs Urban Plan Area" (proposed mixed -use
redevelopment) to the east, which currently is made up of light industrial
developments and mobile home parks. Consistent with Costa Mesa's
MesaWest Bluffs Urban Plan, this will be the most -urban environment within
the Newport Banning Ranch site. The MU /R District will allow 3-, 4 -, and 5-
story attached residential neighborhoods with innovative architecture, creative
parking solutions, and on -site recreation centers with the potential for lofts,
live -work units, and /or commercial development as part of a vertically and /or
horizontally integrated mixed use development. It is anticipated that this
higher density residential area could also accommodate affordable housing
units as defined by the City of Newport Beach and described in an Affordable
FUSCOE ENGINEERING, INC. 9
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT
JUNE 30, 2011
Housing Implementation Plan (AHIP) prepared for the Project, and potentially
in the future Pre - Annexation Development Agreement (PADA) between the
Landowner /Master Developer and the City.
• Visitor- Serving Resort: The Visitor - Serving Resort Overlay District will provide a
maximum of 75 overnight accommodations in an "inn" type setting integrated within
the base Residential District. The design will include on iconic architectural element
for the community and permit a spa and wellness center, restourant(s), and limited
visitor - serving commercial facilities as part of the resort. The residential units
permitted in the base district will be conventionally owned but have opportunities to
use the spa and wellness center, restaurants, and /or other facilities and amenities
provided by the resort.
• Parks and Recreational Areas: Both active and passive public parks will be located
throughout the project site. Multiple trails will be located throughout the site and
adjacent areas to connect to the regional recreational facilities. In addition, smaller
greenways and neighborhood focal points will be placed within the residential areas.
Open Space Areas: various open space uses are proposed throughout the Lowland,
Upland, Bluff, and Arroyo areas, including trails, habitat, wetlands, and arroyos.
Green Streets: Many of the larger streets and arterials throughout the project site will
be designed with "green street" and other low impact development (LID) features.
Green streets are carefully designed roadways that incorporate sustainable design
elements that may include narrower pavement widths, canopy street trees, traffic
calming features, and alternative street lighting systems. In addition, landscaping
along the street edges and within setback areas provide additional opportunities for
treatment of storm water runoff from the streets and adjacent development areas.
Oil Consolidation Sites: Since on -site oil operations are expected to continue, the
Project will include a phased abandonment and consolidation of facilities to specific
areas of the site to continue operations after development. Well abandonment and
remediation processes will be conducted in accordance with all relevant Federal,
State, and local laws and regulations.
FUSCOE ENGINEERING, INC. 10
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NEWPORT BANNING RANCH Figure 3: Proposed Development
, June 30, 2011
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WATERSHED ASSESSMENT REPORT- FINAL DRAFT
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JUNE 30, 2011
FUSCOE ENGINEERING, INC. 12
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT
1.3 STUDY OBJECTIVES
JUNE 30, 2011
This report concentrates on the on -site hydrologic, erosion, and water quality impacts
associated with the proposed Newport Banning Ranch Project, with the following objectives:
• Hydrology Analysis: The objectives of this hydrology study are to evaluate the
expected discharges for a sequence of storm events to evaluate the hydrologic impacts
on the Project watershed for the existing and proposed conditions (including relevant
project design features). The analysis also includes estimating the 100 -year storm
peak discharge rates and volumes before and after the Project using design hydrology
methodologies to assess impacts to the existing and proposed drainage facilities, and
determine the level of significance of the impacts due to the Project. Particular
attention is focused on the potential downstream impacts related to the Semeniuk
Slough and the existing neighborhoods downstream of the project along the Slough.
Mitigation measures will be discussed if necessary to address any identified significant
impacts.
• Floodplain Inundation Analysis: The purpose of the channel hydraulics analysis is to
establish the flow depths, velocities, and water surface profiles (i.e., flood plain
boundaries) for a series of design storm events under the existing and proposed
conditions for the Northern and Southern Arroyos. The analysis utilize agency -
accepted US Army Corps of Engineers (USACOE) models to define the proposed
floodplain boundary of the Arroyos and demonstrate that the proposed flood
protection measures meet the flood protection and drainage guidelines. Relevant
project design features will be included in the assessment, and mitigation measures
will be included to address any identified significant impacts.
• Habitat Analysis: The purpose of the hydrologic objectives for habitat is to maintain
an appropriate water budget for all preserved habitat on -site and utilize treated storm
water runoff to supplement areas of enhancement and /or creation of habitat. The
analysis will focus on smaller scale, more frequent storm events to determine potential
water budget changes to the existing Arroyos on -site and validate that the proposed
Project will not substantially alter the existing hydrologic conditions.
Water Quality Analysis: The Newport Banning Ranch Project offers opportunities for
storm water management that balance Project flood control requirements with
preservation of natural drainage ways for improved water quality. The objective is to
maximize use of low impact development (LID) features and best management
practices (BMPs) to control post - development runoff as well as promote sustoinability
strategies such as water conservation and re -use on -site. The purpose of the water
quality assurance plan is to provide a framework for the implementation of LID BMPs.
The use of LID BMPs will help achieve an appropriate level of treatment for
development runoff while regional water quality facilities will provide ways to improve
the quality of off -site runoff for regional benefit. At the site design level, the primary
LID objective is to minimize the amount of directly connected impervious areas and
promote treatment of runoff through the soil profile. This will be further achieved by
conserving natural drainage features, minimizing the impervious footprint of the
Project and avoiding soil compaction. LID BMPs will be applied primarily to the core
interior development areas and the transitional areas.
FUSCOE ENGINEERING, INC. 13
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT
1.4 CEQA THRESHOLDS OF SIGNIFICANCE
JUNE 30, 2011
California Environmental Quality Act (CEQA) significance criteria are used to evaluate the
degree of impact caused by a development project on environmental resources such as
hydrology and water quality. According to Appendix G of the CEQA Guidelines, a project
would normally have a significant effect on the environment if the project would impact any of
the items listed below.
Would the Project:
A. Violate any water quality standards or waste discharge requirements?
B. Substantially deplete groundwater supplies or interfere substantially with groundwater
recharge such that there would be a net deficit in aquifer volume or a lowering of the
local groundwater table? (e.g., the production rate of pre- existing nearby wells would
drop to a level which would not support existing land uses or planned uses for which
permits have been granted.)
C. Substantially alter the existing drainage pattern of the site or area, including through
the alteration of the course of a stream or river, or in a manner which would result in a
substantial erosion or siltation on- or off -site?
D. Substantially alter the existing drainage pattern of the site or area, including through
the alteration of the course of a stream or river, or substantially increase the rate or
amount of surface runoff in a manner that would result in flooding on- or off -site?
E. Create or contribute runoff water which would exceed the capacity of existing or
planned storm water drainage systems or provide substantial additional sources of
polluted runoff?
F. Otherwise substantially degrade water quality?
G. Place housing within a 100 -year flood hazard area as mapped on a federal Flood
Hazard Boundary or Flood Insurance Rate Map or other flood hazard delineation
map?
H. Place within a 100 -year flood hazard area structures which would impede or redirect
flood flows?
I. Expose people or structures to a significant risk of loss, injury or death involving
flooding, including flooding as a result of the failure of a levee or dam?
J. Be subject to inundation by seiche, tsunami, or mudflow?
FUSCOE ENGINEERING, INC. 14
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT— FINAL DRAFT .TUNE 30, 2011
villl&y:liglzm
2.1 WATERSHED
The Newport Banning Ranch project site lies within the larger Talbert watershed, which covers
21 .4 square miles adjacent to the mouth of the Santa Ana River. It includes portions of the
cities of Costa Mesa, Fountain Valley, Huntington Beach, Newport Beach, and Santa Ana. The
Greenville- Banning Channel, which drains into the Santa Ana River, is one of two main
tributaries that drain this watershed. On the western side of the Santa Ana River, the Talbert
and Huntington Beach Channels drain through the Talbert Marsh before emptying into the
Pacific Ocean. The Greenville - Banning Channel is located north of the project site. It runs
parallel to and ultimately discharges to the Santa Ana River channel.
The Santa Ana River watershed is the largest in Orange County, covering 153.2 square miles.
The river begins almost 75 miles away in the San Bernardino Mountains, crossing central
Orange County before emptying into the Pacific Ocean. The Orange County portion of the
watershed includes portions of the cities of Anaheim, Brea, Huntington Beach, Orange,
Placentia, Santa Ana, Villa Park, and Yorba Linda. The river serves as the main tributary to the
watershed.
Regionally, the project site is located within the Talbert watershed. Storm water runoff from the
site generally ponds in the Semeniuk Slough and Lowland areas, and does not discharge off -
site to the Greenville- Banning Channel. Therefore, the "Project watershed" is hydrologically
independent of the Greenville - Banning Channel. For the purposes of the hydrology analyses
presented in this report, the Project watershed studied includes all upstream areas that drain
onto the project site and into the Lowland Area, but does not include areas further
downstream of the Lowlands.
2.2 RECEIVING WATER BENEFICIAL USES
The Water Quality Control Plan for the Santa Ana River Basin (or "Basin Plan ") developed by
the Santa Ana RWQCB designates beneficial uses and water quality objectives for surface
waters and ground waters within the Santa Ana Region., According to the Basin Plan, the
Newport Banning Ranch project site is located within the Lower Santa Ana River Hydrologic
Area and the East Coast Plain Hydrologic Sub -Area (HSA 801.11), discharging to the Santa
Ana River Tidal Prism and Newport Slough. The beneficial uses of the downstream receiving
water bodies of the Newport Banning Ranch Project, as outlined in the Basin Plan, are
summarized in the following table.
Santa Ana Regional Water Quality Control Board (RWQCB). Water Quality Control Plan for the Santa Ana River Basin
(8). January 24, 1995. Updated February 2008.
FUSCOE ENGINEERING, INC. 15
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT— FINAL DRAFT
JUNE 30, 2011
SURFACE WATER BENEFICIAL USES
Receiving Water
Algae
Waste discharges shall not contribute to excessive algal growth in receiving
o
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In waters designated for REC for fecal coliform: log mean less than 200
Bacteria, Coliform
U
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more than 10% of the samples exceed 400 organisms /100 mL for any 30-
3
Chlorine, Total
O_
Residual
estuaries shall not exceed 0.1 mg/L.
Waste discharges shall not result in coloration of the receiving waters which
Color
causes a nuisance or adversely affects beneficial uses. The natural color of
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Waste discharges shall not contain floating materials, including solids,
Z
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U
Waste discharges shall not result in deposition of oil, grease, wax or other
Oil and Grease
O
U
m
in the water, or which cause a nuisance or adversely affect beneficial uses.
The dissolved oxygen content of enclosed bays and estuaries shall not be
Oxygen, Dissolved
depressed to levels that adversely affect beneficial uses as a result of
W
controllable water quality factors.
L
V
J
N
N
Tidal Prism of
Santa Ana River &+
X
X
X
X
X
X
Newport Slough
X Present or Potential Beneficial Use
+ Excepted from MUN
BIOL — biological significance
RARE
— rare, threatened, or endangered species
COMM — commercial and sport fishing
RECI
— contact water recreation
EST — estuarine habitat
REC2
— non - contact water recreation
MAR — marine habitat
SHEL
— shellfish harvesting
MUN — municipal and domestic supply
SPWN
— spawning, reproduction, and development
NAV — navigation
WILD
— wildlife habitat
Source: Santa Ana Regional Water Quality Control Board (RWQCB). Water Quality Control Plan for the Santa Ana River Basin
(8). January 24, 1995. Updated February 2008.
Table 2.1 Beneficial uses for downstream receiving waters.
Though there are no specific water quality objectives for the Santa Ana River Tidal Prism &
Newport Slough to maintain these beneficial uses, general water quality objectives have been
prescribed in the Basin Plan for all enclosed bays and estuaries in the Santa Ana Region. Brief
summaries of the applicable objectives are provided below.
FUSCOE ENGINEERING, INC. 16
WATER QUALITY OBJECTIVES FOR ENCLOSED BAYS & ESTUARIES
Algae
Waste discharges shall not contribute to excessive algal growth in receiving
waters.
In waters designated for REC for fecal coliform: log mean less than 200
Bacteria, Coliform
organisms /100 mL based on five or more samples /30 day period, and not
more than 10% of the samples exceed 400 organisms /100 mL for any 30-
day eriod.
Chlorine, Total
The chlorine residual in wastewater discharged to enclosed bays and
Residual
estuaries shall not exceed 0.1 mg/L.
Waste discharges shall not result in coloration of the receiving waters which
Color
causes a nuisance or adversely affects beneficial uses. The natural color of
fish, shellfish or other bay and estuarine water resources used for human
consumption shall not be impaired.
Waste discharges shall not contain floating materials, including solids,
Floating Materials
liquids, foam or scum, which cause a nuisance or adversely affect
beneficial uses.
Waste discharges shall not result in deposition of oil, grease, wax or other
Oil and Grease
materials in concentrations which result in a visible film or in coating objects
in the water, or which cause a nuisance or adversely affect beneficial uses.
The dissolved oxygen content of enclosed bays and estuaries shall not be
Oxygen, Dissolved
depressed to levels that adversely affect beneficial uses as a result of
controllable water quality factors.
FUSCOE ENGINEERING, INC. 16
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT— FINAL DRAFT
JUNE 30, 2011
WATER QUALITY OBJECTIVES FOR ENCLOSED BAYS & ESTUARIES
The pH of bay or estuary waters shall not be raised above 8.6 or depressed
pH
below 7.0 as a result of controllable water quality factors; ambient pH levels
shall not be changed more than 0.2 units.
Radioactive materials shall not be present in the bay or estuarine waters of
Radioactivity
the region in concentrations which are deleterious to human, plant or
animal life.
Solids, Suspended and
Enclosed boys and estuaries shall not contain suspended or settleable solids
Settleable
in amounts which cause a nuisance or adversely affect beneficial uses as a
result of controllable water quality factors.
Sulfides
The dissolved sulfide content of enclosed bays and estuaries shall not be
increased as a result of controllable water quality factors.
Waste discharges shall not contain concentrations of surfactants which result
Surfactants
in foam in the course of flow or use of the receiving water; or which
adversely affect a uatic life.
The enclosed bays and estuaries of the region shall not contain, as a result
of controllable water quality factors, taste- or odor - producing substances at
Taste and Odor
concentrations which cause a nuisance or adversely affect beneficial uses.
The natural taste and odor of fish, shellfish or other enclosed bay and
estuarine water resources used for human consumption shall not be
impaired.
The maximum temperature shall not exceed the natural receiving water
temperature by more than 20 °F. Elevated temperature waste discharges
either individually or combined with other discharges shall not create a
Temperature
zone, defined by water temperatures of more than 1 °F above natural
receiving water temperature, which exceeds 25 percent of the cross -
sectional area of a main river channel at any point. No discharge shall
cause a surface water temperature rise greater than 4 °F above the natural
tem erature of the receiving waters at any time or place.
Toxic substances shall not be discharged at levels that will bicaccumulate in
Toxicity
aquatic resources to levels which are harmful to human health. The
concentrations of toxic substances in the water column, sediments or biota
shall not adversely affect beneficial uses.
All enclosed bay and estuaries of the region shall be free of changes in
turbidity which adversely affect beneficial uses. Increases in turbidity shall not
Turbidity
exceed natural levels by more than 20 percent where natural turbidity is
between 0 -50 NTU, and shall not exceed natural levels by more than 10%
where natural turbidity is greater than 100 NTU.
NTU nephelometric turbidity units
Source: Santa Ana Regional Water Quality Control Board (RWQCB). Water Quality Control Plan for the Santa Ana River Basin
8 . January 24, 1995. Updated February 2008.
Table 2.2 Water quality objectives for Santa Ana Region enclosed bays and estuaries.
Geographically, the project site is also located within the Orange County Groundwater
Management Zone as defined in the Basin Plan, which consists primarily of three intra-
connected confined aquifers: the Lower, Middle, and Upper Aquifers.' The main aquifer
s Santa Ana Regional Water Quality Control Board (RWQCB). Water Quality Control Plan for the Santa Ana River Basin
(8). January 24, 1995. Updated February 2008.
FUSCOE ENGINEERING, INC. 17
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT— FINAL DRAFT .TUNE 30, 2011
located within the Middle Aquifer is the primary source of groundwater supply for Orange
County. The elevation of the groundwater table within the vicinity of the Newport Banning
Ranch project site is generally at mean sea level (MSL), and is subject to tidal influences due to
the proximity to the Pacific Ocean. Although the Basin Plan identifies specific water quality
objectives for total dissolved solids (TDS) and nitrate (as N) for the Orange County
Groundwater Management Zone, as previously mentioned in Section 1, the effect of the
development on groundwater and geotechnical resources are not included in the scope of this
report.
Within the vicinity of the project site, three general soil units are present: San Pedro Formation
bedrock, marine terrace deposits, and river alluvium. The San Pedro Formation bedrock
generally consists of gray and dark gray to reddish yellow- stained siltstone and clayey siltstone,
with sandstone interbeds. The marine terrace deposits generally consist of rounded cobbles,
shells, and angular rocks similar to materials found in tidal zones. Both the bedrock and
marine terrace deposits occur beneath the Mesa and elevated portions of the project site.
Soils within the Lowland Area of the site are primarily alluvium, which consist of relatively
young sediments of gravel, sand, and clay deposits. In addition, artificial fill is located
throughout the site, mainly associated with the construction of the on -site oil facilities. 3
2.3 EXISTING WATER QUALITY CONDITIONS
Under Section 303(d) of the Clean Water Act (CWA), States are required to identify water
bodies that do not meet their water quality standards. Once a water body has been listed as
impaired, a Total Maximum Daily Load (TMDL) for the constituent of concern (pollutant) must
be developed for that water body. A TMDL is an estimate of the daily load of pollutants that a
water body may receive from point sources, non -point sources, and natural background
conditions (including an appropriate margin of safety), without exceeding its water quality
standard. Those facilities and activities that are discharging into the water body, collectively,
must not exceed the TMDL.
Storm water runoff from the project site ultimately discharges into the Lowland Area and into
the Tidal Prism of the Santa Ana River, Newport Slough and Semeniuk Slough. These water
bodies are not listed as impaired according to the 2006 303(d) list published by the Santa
Ana RWQCB, and do not have any TMDLs in place .4 However, according to the 2008
California 303(d)/305(b) Integrated Report, the Newport Slough is recommended to be listed
as impaired for enterococcus, fecal coliform, and total coliform.5 Once approved by the
SWRCB and US EPA, the 303(d) List will then be revised to include the new impairments.
a GMU Geotechnical, Inc. Report of Geotechnical Studies. Proposed Newport Banning Ranch Development, City of
Newport Beach /County of Orange. Draft March 2008.
4 Santa Ana Regional Water Quality Control Board (RWQCB). 2006 Clean Water Act Section 303(d) List of Limited Water
Quality Segments. October 25, 2006.
5 Santa Ana Regional Water Quality Control Board (RWQCB). Final 2008 California 303(d)/305(b) Integrated Report
Supporting Information. Approved by RWQCB Order No. RS- 2009 -0032, April 23, 2009.
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2.4 EXISTING DRAINAGE CONDITIONS
In general, the Project's natural drainage flows from the higher elevations in the east toward
lower elevations to the west. Off -site drainage from the existing urban areas of the cities of
Costa Mesa and Newport Beach enter the project site through storm drain culverts at the
upstream ends of the Arroyos. Within the project boundary, the Northern and Southern
Arroyos and Semeniuk Slough convey runoff towards the Salt Marsh Basin and Lowland Area.
There are no major existing storm drain facilities within the project boundary. In the southern-
most portion of the site, an existing underground reinforced concrete box (RCB) storm drain
along West Coast Highway (WCH) also collects runoff from the site, discharging to the
Semeniuk Slough channel. The existing RCB storm drain at WCH is owned and operated by
the California Department of Transportation ( Caltrans). There are several tidal gates and
control pipes that regulate tidal flows between the Santa Ana River and the Semeniuk Slough
and Lowland Area of the project site. The default position of the gates is open to allow tidal
flows to circulate through the Marsh basin. The water surface elevation of the Santa Ana River
controls the gates and determines whether local storm water runoff can be discharged into the
river. Refer to Figure 4 for the Project watershed under existing conditions.
2.5 PROPOSED DRAINAGE PLAN
The objective of the proposed drainage plan is to design the on -site storm drain system and
other drainage features in a manner to neutralize any adverse effects induced by the Project in
storm runoff quantity and quality. In general, no major changes in the drainage patterns are
proposed as compared to the existing conditions of the Project watershed; however, some
minor adjustments in the sub - watershed boundaries are considered necessary for better
overall storm runoff management. In addition, this proposed drainage plan integrates LID
features as well as aesthetic features with traditional local drainage design. The proposed
drainage facilities are described in detail in the following sections. Refer to Figure 5 for the
locations and layout.
2.5.1 PROPOSED STORM DRAINS
The proposed condition contains six primary on -site storm drain systems that will drain Project
flows to downstream receiving water bodies. They are described below as follows:
• Storm Drain A (Drainage Area "A "): Discharges to the existing Caltrans box culvert
under the WCH. Storm Drain A (SD -A)is designed to reduce the tributary drainage
area of this storm drain system as compared to the existing condition to account for
the increase in Project runoff in the proposed condition.
• Storm Drains B and C (Drainage Area "A "): Collect flows from the development areas
adjacent to the Southern Arroyo and delivers these flows to a diffuser basin located
downstream of the Arroyo adjacent to the Semeniuk Slough. The design of Storm
Drains B and C (SD -B, SD -C) serves three primary functions: 1) to minimize the
discharge of storm water flows directly to the Arroyo channel to protect the long -term
channel stability, 2) dissipate erosive energy before flows enter the Semeniuk Slough,
and 3) control sediment contributions to the Semeniuk Slough.
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Storm Drains D and E (Drainage Area "C "): Collect flows from the larger
development areas of the Project and delivers storm flows to the Lowland Area. Under
the existing conditions, a portion of drainage from Storm Drain D (SD -D) is tributary to
the Southern Arroyo and Semeniuk Slough. The proposed drainage re- direction is
specifically designed to maximize the amount of flow to be directed towards the
Lowland Area in order to reduce the flood loading of the Semeniuk Slough. A second
diffuser basin will be installed downstream of Storm Drains D and Storm Drain E (SID-
E) to reduce the momentum of the flows from the pipes and to spread the distribution
of runoff to the Lowland in a manner that will enable future habitat restoration efforts.
Storm Drain F (Drainage Area "B "): Collects flows from the northernmost
development area. The tributary drainage area has been designed to match existing
runoff conditions to the Northern Arroyo. An energy dissipater will be installed at the
outlet to Storm Drain F (SD -F) to transition flows from erosive velocities to mild
velocities, and to deliver non - erosive flows to the natural channel.
Storm Drain G (Drainage Area "D "): Collects flows from the northerly most portion of
the northern development area. Flow in Storm Drain G (SD -G) is delivered to the
Lowland Area via a culvert and a storm drain located in the new Bluff Road roadway
extension to 19" Street.
2.5.2 LOWLAND AREA
While the proposed land use of the Lowland Area is designated as habitat, there could
potentially be an opportunity to increase the flood storage capacity in the area in the future to
accommodate more local runoff during the high tide condition that closes the tidal gates at
the Santa Ana River. The Lowland is located adjacent to the Salt Marsh Basin habitat area.
Currently, the Lowland is not subject to the tidal water circulation because its surface
elevations are higher than the tidal flux elevations. Therefore, if the Lowland Area could be
graded lower in the future, it would create additional sub -tidal channels for tidal circulation
and annexed into the existing Salt Marsh Basin habitat. Thus, flood storage capacity would
also increase. Increasing the storm runoff retention capacity of the Lowland Area during the
high tide condition can effectively lower the flood depth and further reduce the existing
flooding problem in the Semeniuk Slough (further discussed in Section 3.2.2), although it is
not part of the Project proposal at this time. By directing more flow to the Lowland Area, the
Southern Arroyo and Semeniuk Slough will receive less available flows. This will tend to
reduce sediment transport from the eroding Southern Arroyo tributaries and into the Semeniuk
Slough. As part of the proposed drainage plan, these eroding tributaries will be stabilized to
prevent the primary sources of sediment from entering the Arroyos.
2.5.3 OFF -SITE RUNOFF WATER QUALITY / DETENTION BASIN
Under the existing condition, approximately 48 acres of off -site flows from the 16" Street
drainage area of Costa Mesa enter the property (via a 48" RCP) from the east and discharge
into the Southern Arroyo. In general, these flows contain urban runoff pollutants and also
convey sediment from the eroding tributaries of the Arroyo to the downstream end, ultimately
discharging into the Semeniuk Slough during severe storms. Thus, a water quality /detention
basin will be implemented to intercept these off -site flows. As shown in Figure 5, the basin is
proposed within the property boundary at the southeast corner of the proposed 16'h Street
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entrance. The required basin capacity is estimated to be approximately 2.3 acre -feet, which
can treat all dry weather and a portion of first -flush runoff from the off -site tributary as well as
reduce a portion of peak flow discharge (calculations are provided in Appendix E). In
addition to hydrology and water quality benefits, the basin can also alleviate flood loading for
the downstream channel, such as the Semeniuk Slough, when the reduced flood peak
propagates toward downstream from the basin. The reduction in peak discharges combined
with the stabilization of the eroding tributaries of the Arroyo will serve to control the current
sediment loads into the Semeniuk Slough.
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NEWPORT BANNING RANCH FIGURE 4: Existing Watershed
June 30,201
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FIGURE 5: Proposed Drainage Plan
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2.6 FEMA SPECIAL FLOOD HAZARD AREAS
The National Flood Insurance Act of 1968 established the National Flood Insurance Program
(NFIP). The NFIP sets minimal requirements for flood plain management and is designed to
minimize flood damage within Special Flood Hazard Areas (SFHA). The Federal Emergency
Management Agency (FEMA) is the agency that administers the NFIP. Special Flood Hazard
Areas (SFHA) are defined as areas that have a 1% chance of flooding within a given year.
The 1 % chance flood is also known as the 100 -year flood. FEMA developed Flood Insurance
Rate Maps (FIRMS) to identify areas of flood hazards within a community.
The FIRM that applies to the Newport Banning Ranch project site is FIRM Map Number
06059CO26H which was revised on February 18, 2004. A copy of the map is provided in
Appendix A. The northwest portion of the site (the Lowland Area) and the southwest corner of
the site are located within the 0.2% annual chance flood (500 -year flood plain). The balance
of the project site is in the area defined to be outside the 0.2% annual chance (500 -year
floodplain) boundary.
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3.0 HYDROLOGY ASSESSMENT
The purpose of this hydrology analysis is to assess the potential hydrologic impacts in the
Project watershed as a result of the proposed development. In general, the proposed change
in land uses and flow patterns will inherently alter impervious surfaces and runoff potential
within the project site, which in turn, affects the downstream hydrology in the watershed. As a
result of the increase in impervious surfaces as compared to existing conditions, an increase in
peak flow runoff and volume of runoff is expected from the site. The increased peak
discharge rate or volume could potentially cause flood control or environmental issues in the
watershed. Thus, a comprehensive modeling approach is necessary to quantify the difference
in hydrologic response of the Project's watershed in converting from existing to proposed
conditions.
For the purposes of this study, the modeling procedures specified in the Orange County
Hydrology Manual (1986) its Addendum Number 1 were used in the modeling analyses. Two
types of design events defined by Orange County were use for Project watershed analysis: 1)
High- Confidence (HC) events, and 2) Expected -Value (EV) events. As described in the
Manual, HC events are used for flood control facility design and loading assessment, and EV
events are used for mitigation of increased runoff due to development. The following
hydrologic conditions with a range of storm return frequencies were analyzed for each of the
sub - watershed areas within the Project watershed:
• Existing Condition 10 -year, 25 -year, 100 -year HC events;
• Existing Condition 2 -year and 100 -year EV events;
• Proposed Condition 10 -year, 25 -year, 100 -year HC events;
• Proposed Condition 2 -year and 100 -year EV events.
Although the calculations listed above were performed for all Project watershed drainage
areas, the results of the peak flow rate and runoff volume have been presented and
summarized to pertain to the various project features of concern thereby allowing for detailed
understanding of Project impacts on existing features.
3.1 METHODOLOGY
3. 1.1 RATIONAL METHOD
Since the Project's watershed is less than 640 acres, the Rational Method can be used to
model the peak flow rate within the watershed. In accordance with the Orange County
Hydrology Manual, the Rational Method is expressed by the following equation (Equation
3.1):
Q = (C)(1)(A) (3.1)
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Where: Q = peak flow rate in cubic feet per second (cfs)
C = runoff coefficient (unitless)
I = critical rainfall intensity (inches per hour)
A = drainage area (acres)
Data required for the rational method calculations are: 1) rainfall intensity over duration for a
specific design storm; 2) drainage area characteristics of size, shape, slope; and 3) a runoff
coefficient. These data inputs are defined in the Orange County Hydrology Manual or can be
retrieved from the topographic data, both of which have been used in the calculations for this
study. The rational method calculations were executed using Advanced Engineering Software
(AES) Flood Routing and Rational Method computer software (Version 8.0), following the
procedures outlined in the Hydrology Manual.
3.1.2 SMALL AREA UNIT HYDROGRAPH METHOD
In order to model the volume of runoff generated within the Project watershed, the design
storm runoff hydrograph is developed. According the Orange County Hydrology Manual, for
watersheds where the time of concentration (Tc) is less than 25 minutes (such as the proposed
Project watershed), a small area unit hydrograph method can be used to generate the runoff
hydrograph. In this procedure, the unit hydrograph is defined to be a triangle with a base of
2 *Tc, and a peak flow rate at time of Tc, where Tc is acquired from the rational method
modeling. In this study, AES Version 8.0 computer software was also used to perform the
small area unit hydrograph calculation.
3.2 RESULTS & DISCUSSION
The following sections summarize the results of the existing and proposed conditions analyses
for peak flow runoff rates and volumes for each of the larger drainage areas within the
Project's watershed. Potential flood control impacts caused by the Project are also discussed
in terms of the modeling result differences between the existing and proposed conditions.
Figure 6 provides a breakdown of the sub - watershed areas within the Project watershed, and
Rational Method Hydrology Maps for both existing and proposed conditions are provided in
Section 6, Exhibits.
3.2.1 LOWLAND AREA AND SALT MARSH BASIN
As shown in Figure 4, under the existing conditions, storm water runoff within the Project
watershed is generally conveyed through the Semeniuk Slough and Arroyos towards the
Lowland and Salt Marsh Basin areas, adjacent to the east levee of the Santa Ana River. The
Salt Marsh is an engineered- restored habitat. It is located west of the project site near the
Santa Ana River mouth between 100 ft to 4,400 ft upstream of the West Coast Highway
(WCH) bridge. Two tidal gates are installed under the east levee of Santa Ana River, allowing
the circulation of natural tidal flows into and out of the Marsh. The default position of the
gates is open. However, in order to prevent excess storm water of the Santa Ana River from
entering the Marsh, the gates would close if the water level in the Marsh reaches a certain
elevation. Once the gates close, a decrease in water level on the Marsh side (via several
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relief pipes) is be needed to re -open the gates. Thus, while the gates remain closed, storm
water runoff is retained inside and stored within the Salt Marsh Basin and Lowland Area.
According to the design elevations of the tidal gates, they will begin to close when the Marsh
water level reaches 3.0 ft mean sea level' (MSL), and will be completely closed at the water
level of 3.5 ft MSL. The maximum design water level within the Salt Marsh is 6.0 ft MSL. As a
result, the elevation range from 3.5 ft to 6.0 ft MSL can be viewed as the storage capacity in
the Salt Marsh basin for storing local runoff once the gates are closed. The Salt Marsh has a
footprint of approximately 90 acres, and the Lowland Area has a footprint of approximately
126 acres. Examination of the Marsh Basin "As- Built" grading plan and of the Lowland Area
topographic map indicates that the combined flood storage capacity of the two areas is
estimated to be 345 acre -feet.
The results for the existing and proposed runoff volume calculations for HC events are
summarized in Tables 3.1 and 3.2, respectively, for the Lowland and Salt Marsh drainage
areas. Since the Lowland and Salt Marsh drainage areas function as flood control basins
rather than conveyance facilities, peak flow runoff rates were not included in the tables below.
However, detailed calculations for peak flow rates are available under Appendix B. Refer to
Figure 6 for locations of the sub - watershed areas for the Lowland Area and Salt Marsh Basin.
LOWLAND AREA AND SALT MARSH BASIN
EXISTING CONDITION RUNOFF VOLUME SUMMARY (HC EVENTS)
Sub - Watershed
Drainage Area (ac)
10 -year (ac -ft)
25 -Year (ac -ft)
100 -Year (ac -ft)
"A"
349.6
67.3
86.1
131.7
"B"
135.1
30.9
38.9
54.0
"C"
63.6
11.5
15.0
24.0
"D"
14.3
2.8
3.6
5.6
"E"
97.2
22.4
28.1
39.4
"F"
5.8
1.3
1.6
2.1
"G"
1.8
0.4
0.5
0.7
"H"
7
1.5
1.9
2.6
11"
1.1
0.2
0.3
0.4
"J"
11
2.4
3.0
4.0
"K"
6.3
1.4
1.7
2.3
Lowland Area'
126
38.6
47.1
59.1
Salt Marsh Basin'
90
27.6
33.7
42.2
Total
908.8
208.6
261.5
368.1
a For the Lowland & Marsh areas, the runoff volume is estimated by the following: Precipitation (in) x Area (ac) / 12
Table 3.1 Existing condition runoff volume summary for Lowland Area and Solt Marsh Basin.
6 NGVD29 Datum.
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LOWLAND AREA AND SALT MARSH BASIN
PROPOSED CONDITION RUNOFF VOLUME SUMMARY (HC EVENTS)
Sub - Watershed
Drainage Area (ac)
10 -year (ac -ft)
25 -Year (ac -ft)
100 -Year (ac -ft)
"A"
322.0
64.2
81.2
118.3
'B'
120.6
27.5
34.7
48.7
"C"
97.6
19.9
25.5
38.6
'D'
22.4
4.4
5.6
8.8
"E"
97.2
22.4
28.1
39.4
"F"
5.8
1.3
1.6
2.1
"G"
1.8
0.4
0.5
0.7
'H'
7
1.5
1.9
2.6
11"
1.1
0.2
0.3
0.4
"J"
11
2.4
3.0
4.0
'K'
6.3
1.4
1.7
2.3
Lowland Area°
126
38.6
47.1
59.1
Salt Marsh Basin'
90
27.6
33.7
42.2
Total
908.8(+0)
211.8 ( +3.2)
264.9 ( +3.4)
367.2 ( -0.9)
Note: Numbers in parentheses represent change as compared to existing condition.
a Forthe Lowland & Marsh areas the runoff volume is estimated by the following: Precipitation in x Area ac / 12
Table 3.2 Proposed condition runoff volume summary for Lowland Area and Salt Marsh Basin.
As shown in Table 3.1, the existing condition 25 -year runoff volume is 261.5 acre feet (ac -ft).
Since this value is less than the combined flood storage capacity of the Marsh and Lowland
Area value of 345 acre -feet, a 25 -year level of protection is provided in the existing condition.
As shown in Table 3.2, the proposed condition 25 -year runoff volume increases slightly to
264.9 ac -ft. However, the proposed condition 25 -year runoff volume larger value is still less
than the 345 ac -ft storage capacity of the combined Salt Marsh and Lowland Areas.
This comparison demonstrates that a 25 -year level of protection is provided after development
in the proposed condition, and indicates that mitigation is not needed to maintain the pre -
development level of protection.
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3.2.2 SEMENIUK SLOUGH
The Semeniuk Slough is a remnant sub -tidal channel of the former braided river mouth
opening of the Santa Ana River that was present prior to chonnelization of the River. The
Semeniuk Slough begins at the southerly tidal gate and migrates south around an existing
Newport Shores residential neighborhood, ending at the WCH. During high tides, the tidal
prism occupies the channel and leaves limited capacity for storm water conveyance.
According to the field reconnaissance and conversations with the residents along the
Semeniuk Slough, the channel floods when a high tide and ❑ large storm occur
simultaneously.
Storm flows within the Semeniuk Slough are generally stored in the southerly portion of the
Salt Marsh Basin. As shown in Figures 7 and 8, under the existing conditions, the drainage
area of the Semeniuk Slough is composed primarily of Sub - Watershed A and the Newport
Shores residential neighborhood area along the Semeniuk Slough, encompassing
approximately 350 acres. The sub - watershed areas in Newport Shores are labeled as F
through K, and encompass approximately 33 acres. Based on the topographic data, the
elevation of the channel bank on the residential side is approximately at 5 ft MSL. When the
tidal gate is completely closed at 3.5 ft MSL, there is approximately 1.5 ft of depth in the Salt
Marsh Basin available for use to store local runoff between the top of the channel bank and
the closed tidal gate limit. However, due to the presence of several habitat islands
constructed in the Salt Marsh Basin, the basin storage volume is diminished. At present, under
this reduced storage volume condition, the available capacity within the Semeniuk Slough is
estimated to be ±28 ac -ft. This value is approximately equal to the 2 -year event (EV) runoff
volume delivered to the Slough. This situation indicates that the existing condition has a
limited storage capacity in the area the Semeniuk Slough surrounding Newport Shores. This
limited capacity is roughly equivalent to a 2 -year level of protection.
The drainage plan proposed for the Newport Banning Ranch Project is customized to preserve
the 2 -year storage capacity limit in the Semeniuk Slough. The plan was devised to avoid any
significant increase in discharge rate or volume delivered to the Slough that would exceed the
meager 2 -year storage condition. Thus, under proposed conditions, a portion of on -site
development tributary sub -area formerly assigned to the Semeniuk Slough has been re-
assigned away from the Slough and toward the Lowland Area. This is achieved by strategic
site grading and storm drain routing at the interface between Drainage Area "A" and
Drainage Area "C ". In this manner, the proposed condition peak flow rate and volume
directed to the Slough is limited to roughly the existing condition 2 -year values.
Tables 4.3 and 4.4 summarize the modeling results with respect to the existing and proposed
conditions under two expected value (EV) storm frequencies including the 2 -year and 100 -year
events. Since the Semeniuk Slough functions both as a flood conveyance and storage facility,
both runoff volumes and peak flow rates are summarized in the following tables. The time of
concentration (Tc) value has also been provided for the 2 -year evaluation per the
requirements of Section XILD of the fourth -term MS4 Storm Water Permit. Figure 7 illustrates
7 California Regional Water Quality Board, Santa Ana Region (RWQCB). Order R8- 2009 -0030, Amended by Order No.
R8- 2010 -0062, NPDES Permit No. CAS618030 Waste Discharge Requirements (WDR) the County of Orange, Orange
[continues on next page]
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the node locations and basin boundaries in the Semeniuk Slough drainage area. This
evaluation includes contributions from the Caltrans Box Culvert drainage area (see Section
3.2.3). Detailed calculations are provided in Appendix B.
SEMENIUK SLOUGH
EXISTING CONDITION RUNOFF VOLUME (EV EVENTS)
Sub - Watershed
Drainage Area
2 -Year Volume
100 -Year Volume
acres
(ac-ft)ac
-ft
"A"
349.6
17.3
85.2
"F"
5.8
0.5
1.6
'G"
1.8
0.2
0.5
'H'
7
0.6
1.9
11"
1.1
0.1
0.3
17"
11
0.9
3.0
"K"
6.3
0.5
1.7
It Marsh Basin°
54
6.5
20.2
Total
436.6
26.6
114.4
EXISTING CONDITION PEAK
FLOW RATE (EV
EVENTS)
Location
Drainage Area
2 -Year Peak Flow
100 -Year Peak Flow
acres
b
cfs / TO
cfs
Node 19
155.1
80.8/19,24
323.4
(upstream)
Node 23
349.6
121.3 / 37.45
501.2
downstream
cis cubic feet per second
a For the Salt Marsh basin, the runoff volume is estimated by the following: Precipitation (in) x Area (ac) / 12
b Tc = Time of Concentration noted for 2 -year event per Section AI.D of fourth -term MS4 Storm Water
Permit.
Table 3.3 Existing condition hydrology summary for Semeniuk Slough
County Flood Control District and The Incorporated Cities of Orange County within the Santa Ana Region Areawide
Urban Storm Water Runoff, Orange County. May 22, 2009.
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SEMENIUK SLOUGH
PROPOSED CONDITION RUNOFF VOLUME (EV EVENTS)
Sub - Watershed
Drainage Area
2 -Year Volume
100 -Year Volume
acres
(ac-ft)ac
-ft
"A"
322.0
18.3
81.2
"F"
5.8
0.5
1.6
"G"
1.8
0.2
0.5
"H"
7
0.6
1.9
11"
1.1
0.1
0.3
"J"
11
0.9
3.0
"K"
6.3
0.5
1.7
Salt Marsh Basin'
54
6.5
20.2
Total
409.0 ( -27.6)
27.6(+1.0)
110.4 (-4.0)
PROPOSED CONDITION
PEAK FLOW RATE (EV
EVENTS)
Location
Drainage Area
2 -Year Peak Flow
100 -Year Peak Flow
acres
cfs / Tc b
cfs
Node 19
145.8 ( -9.3)
72.7 ( -8.1) /
302.2 ( -21.2)
(upstream)
19.54 ( +0.03
Node 23
322.0 ( -27.6)
128.1 ( +6.8) /
513.9 ( +12.7)
(downstream)
37.51 ( +0.06)
Note: Numbers in parentheses represent change as compared to existing condition.
cfs cubic feet per second
a For the Salt Marsh area, the runoff volume is estimated by the following: Precipitation (in) x Area (ac) / 12
b Tc = Time of Concentration noted for 2 -year event per Section XILD of fourth -term MS4 Storm Water
Permit
Table 3.4 Proposed condition hydrology summary for Semeniuk Slough
As previously described, a portion of the existing Sub - Watershed A drainage area formerly
tributary to the Semeniuk Slough will be reassigned in the proposed condition. The size of
proposed Sub - Watershed A will be reduced by 27.6 acres (349.6 to 322.0 acres) as
compared to the existing condition. While the proposed condition runoff is anticipated to be
slightly higher in the entire Project watershed, the overall results show that the storm runoff of
the proposed condition will be limited to roughly reflect existing conditions. Specifically, in
runoff volume there is a 1.0 ac -ft increase under the 2 -year EV event and a 4.0 ac -ft decrease
under the 100 -year EV event in comparison to existing conditions. Further, the proposed
condition will also have a slight reduction in peak flow rates throughout the channel except at
Node 23, where there is an increase of 10 cfs under the 2 -year frequency and 12.7 cfs
increase under the 100 -year frequency. Overall, the proposed Project is not expected to
measurably increase the flood loading of the Semeniuk Slough beyond the existing 2 -year
return frequency limiting condition.
The fourth -term MS4 Storm Water Permit requires that the 2 -year storm event be analyzed for
pre- and post- condition to determine hydrologic conditions of concern (Order R8 -2009-
0030, Amended by Order No. R8- 2010 -0062, Section XII.D). Based on the requirements of
the Permit, the project would not have a hydrologic condition of concern if the volume and the
time of concentration of storm water runoff for the post - development condition does not
FUSCOE ENGINEERING, INC. 37
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT— FINAL DRAFT
.TUNE 30, 2011
significantly exceed those of the pre - development condition for a 2 -year frequency storm event
(a difference of 5% or less is considered insignificant).' Based on the analysis, the results
demonstrate compliance with these requirements as the proposed volumes and time of
concentration are both within 5% of the existing condition. Therefore, the Project does not
have a hydrologic condition of concern for flows directed to the Semeniuk Slough.
This comparison also demonstrates that a 2 -year level of protection is provided after
development in the proposed condition, and indicates that mitigation is not needed to
maintain the pre - development level of protection.
' Section XII.D.2.a of Order No. R8- 2009 -0030.
FUSCOE ENGINEERING, INC. 38
IV
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Legend
- - - Existing Open Channel /Ditch
Existing Storm Drain Pipe
Proposed Storm Drain
-••- Project Boundary
Marsh /Lowland Boundary
Exisiting Basin Boundary
i Proposed Diffuser Basin
- - - Arroyo
0-0 Hydrologic Node
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NEWPORT BANNING RANCH FIGURE 7: Semeniuk Slough Drainage
June 30, 210
FUSCOL
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FUSCOE ENGINEERING, INC. 40
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT .TUNE 30, 2011
3.2.3 CALTRANS BOX CULVERT AT WCH
Currently, there is an existing underground reinforced concrete box (RCB) culvert under a
portion of WCH along the southern project boundary that is owned and operated by Caltrans.
The existing RCB varies in size, from 8'W x 5'H at the upstream end (Node 16) and increases
to a final size of 14'W x 5'H at the downstream portion (Node 18), where it outlets to a
trapezoidal channel upstream of the Semeniuk Slough. As shown in Figure 8, this Caltrans
RCB receives street flow on WCH. It also receives flows from areas north and south of WCH,
in addition to flows from areas as far north as 15" Street. Its tributary sub -area includes
developed and undeveloped areas, and the undeveloped portion exists primarily within the
project site.
The Project's proposed drainage plan will modify the existing Caltrans RCB in WCH to accept
a new storm drain connection from the development area. Tables 3.5 and 3.6 summarize the
peak flow results for existing and proposed conditions, respectively. Since the existing RCB
provides conveyance of storm flows and does not provide any flood storage, only peak flow
rates are presented. Since this portion of the Project ultimately drains into the Semeniuk
Slough, the 2 -year analysis for hydrologic conditions of concern for this drainage area was
incorporated into the Tables 3.3 and 3.4 under Section 3.2.2. Refer to Figure 8 for locations
of the nodes summarized in the tables. Detailed calculations are provided in Appendix B.
CALTRANS BOX CULVERT AT WCH
EXISTING CONDITION PEAK FLOW RATE (HC EVENTS)
Location
Drainage Area
10 -Year Peak
25 -Year Peak
100 -Year Peak
Location
acres
Flow cfs
Flow cfs
Flow cfs
Node 16
63.3
129.2
156.9
203.4
(upstream)
109.8 ( -8.8)
198.7 ( -14.6)
243.3 ( -18.3)
318.0 ( -23.5)
Node 17
133.4 ( -9.3)
237.9 ( -24.5)
291.6 ( -18.7)
381.4 ( -24.1)
(middle)
118.6
213.3
261.6
341.5
Node 18
(downstream)
142.7
262.4
310.3
405.5
cfs cubic feet per second
Table 3.5 Existing condition hydrology summary for Caltrans Box Culvert at WCH
CALTRANS BOX CULVERT AT WCH
PROPOSED CONDITION PEAK FLOW RATE (HC EVENTS)
Location
Drainage Area
10 -Year Peak
25 -Year Peak
100 -Year Peak
acres
Flow cfs
Flow cfs
Flow cfs
Node 16
(upstream)
63.7 ( +0.4)
130.1 ( +0.9)
158.0 ( +1.1)
204.9 ( +1.5)
Node 17
middle
109.8 ( -8.8)
198.7 ( -14.6)
243.3 ( -18.3)
318.0 ( -23.5)
Node 18
(downstream)
133.4 ( -9.3)
237.9 ( -24.5)
291.6 ( -18.7)
381.4 ( -24.1)
Note: Numbers in parentheses represent change as compared to existing condition,
cis cubic feet per second
Table 3.6 Proposed condition hydrology summary for Caltrans Box Culvert at WCH
FUSCOE ENGINEERING, INC. 41
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT .TUNE 30, 2011
For the three analyzed HC event frequencies summarized in Tables 3.5 and 3.6, the proposed
drainage plan will result in a slight increase in peak flow rate at Node 16 located at the
upstream end of the RCB. The slight discharge increase at this location is due to the inclusion
of new manufactured slope drainage from the project site. The connection of the proposed
on -site storm drain system is located downstream of Node 16. At Nodes 17 and 18 (the
middle and downstream sections of the RCB respectively), the proposed condition peak flow
rates are less than the existing conditions as a result of the reduced size of the sub -area that is
directing flow to the RCB. Overall, the WCH RCB culvert will experience reduced flood
loading as compared to the existing condition. The slight loading increase at Node 16 is not
expected to overload the system because the existing RCB local capacity value at Node 16
exceeds the proposed peak flow value expected to pass through the RCB at that location.
This comparison demonstrates that a 100 -year level of protection is provided after
development in the proposed condition, and indicates that mitigation is not needed to
maintain the pre - development level of protection.
FUSCOE ENGINEERING, INC. 42
P: \Project\ 821 \01 \Wat \GISWat \MXD \EIR Figures& Exhibits \pdf\82101gh- Fig9_CaUrans Box Culvert.pdf
NEWPORT BANNING RANCH FIGURE 8: Caltrans Box Culvert
June 30, 2011
FUSCOF
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FUSCOE ENGINEERING, INC. 44
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT .TUNE 30, 2011
3.3 FLOODPLAIN INUNDATION ANALYSIS
The purpose of the channel floodplain inundation analysis is to assess the potential impacts
on the riverine areas (Arroyos) due to the hydrology changes resulting from the proposed
development. A typical riverine area is usually comprised of a vegetated channel with a soft
bottom and banks providing flood containment and habitat benefits. Adverse influences on
the riverine area may be attributed to changes in the floodplain that cause flooding/ capacity
issues, or by changes in the riparian inundation area that may disrupt diversity and alter
habitat type, or by changes in channel velocity causing channel instability problems. In order
to assess the above potential impacts to the riverine areas of the Project, a comprehensive
hydraulic modeling approach is necessary.
In this analysis, riverine studies are performed on the Northern Arroyo and the Southern
Arroyo. These two arroyos are the main watercourses through the property and reside
adjacent to the proposed development. From the hydrology analysis discussed in the previous
section, the results show that the Southern Arroyo will experience some changes in its tributary
area in association with the proposed development. The Northern Arroyo will be crossed by
the new Bluff Road roadway extension to 19th Street. Thus, to address the expected hydrologic
changes, the following conditions are included in the riverine modeling:
Northern Arroyo:
• Existing condition 2 -year and 100 -year EV events
• Proposed condition 2 -year and 100 -year EV events
Southern Arroyo:
• Existing condition 2 -year and 100 -year EV events
• Proposed condition 2 -year and 100 -year EV events
The Northern Arroyo modeling is to verify the field reconnaissance used to establish that the
Arroyo is operating in a stable manner in the existing condition, and to evaluate the affect of
the new roadway crossing in the proposed condition. The Southern Arroyo modeling is to
quantify the changes between the existing and proposed conditions. In addition to the
modeling efforts, it should be noted that field observations indicate severe erosion and
sloughing of sediment into the Southern Arroyo from the adjacent on -site tributary areas
entering the Arroyo. During large storm events, sediments from the tributaries enters the
Arroyo and are conveyed downstream to the Semeniuk Slough, resulting in large sediment
fans within the channel following these rain events. Historical photos of the site indicate the
erosion and undercutting within the tributaries has been occurring since the 1930's.
3.3.1 METHODOLOGY
HEC -RAS Model
The "Hydrologic Engineering Centers River Analysis System" (HEC -RAS) is a one - dimensional
hydraulics computation application developed by USACOE. It is designed to model irregular
channel cross sections (such as in the natural stream system), and was selected as the
FUSCOE ENGINEERING, INC. 45
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT— FINAL DRAFT .TUNE 30, 2011
modeling tool in this study. In HEC -RAS models, the channel cross sections are taken along
the stream centerline, covering the overbank areas and channel thalwag. The locations of the
cross sections should represent a typical reach in the channel. For this study, six cross sections
were taken for the Northern Arroyo and 12 cross sections were taken to compose the
Southern Arroyo. Figures 10, 11, and 12 illustrate the established HEC -RAS models for the
Arroyos.
For hydraulic parameters, the critical depth condition was used to set the "low tailwater"
condition for the downstream water surface boundary. For the roughness coefficient, the
Manning's n -value of 0.06 was selected to reflect the good vegetation cover existing in both
the Arroyos. In addition, some blocked flow areas (or ineffective flow areas) were set as
necessary to reflect a realistic flow conveyance width.
Hydrology Inputs
As previously mentioned, the discharges of this hydraulics modeling are based on the EV event
hydrology analysis results. The tables below describe the modeled discharges and the
corresponding station locations. Existing and proposed conditions are presented for the
Northern and Southern Arroyos. Refer to Figures 10, 11, and 12 for locations of the stations.
Refer to Appendix C for detailed calculations.
NORTHERN ARROYO DISCHARGE SUMMARY (EV)
2 -Year Peak Flow (cfs)
100 -Year Peak Flow (cfs)
Station No.
Existing
Proposed
Existing
Proposed
8 +55
45
45(+0)
156
156(+0)
4 +00
45
48 ( +3)
156
181 ( +25)
Note: Numbers in parentheses represent change as compared to existing condition.
cfs cubic feet per second
Table 3.7 Discharge summary for Northern Arroyo used for HEC -PAS models.
SOUTHERN ARROYO DISCHARGE SUMMARY (EV)
2 -Year Peak Flow (cfs)
100- Year Peak Flow (cfs)
Station No.'
Existing
Proposed
Existing
Proposed
20 +62
27
28 ( +1)
95
109(+14)
11 +12
34
28 ( -6)
138
114 ( -24)
4 +81
45
28 ( -17)
198
114 ( -84)
Note: Numbers in parentheses represent change as compared to existing condition,
cfs cubic feet per second
a The existing channel starts at 22 +56; no dischar a change from 22 +56 to 20 +62.
Table 3.8 Discharge summary for Southern Arroyo used for HEC -RAS models.
FUSCOE ENGINEERING, INC. 46
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT .TUNE 30, 2011
3.3.2 RESULTS AND DISCUSSION
Northern Arroyo
Tables 3.9 and 3.10 show the modeling summary results for the Northern Arroyo with respect
to the existing and proposed 2 -year and 100 -year conditions. As shown in Table 3. 10, the
majority of flows in the channel are in the sub - critical flow regime ( Froude Number less than
one), which means higher water surface and lower velocity. Accordingly, the depth range is
from 0.9 to 2.4 ft under the 2 -year event, and from 1.9 to 4.8 ft under the 100 -year event.
The 100 -year condition does not exhibit on erosive channel velocity (generally greater than 6
ft /s). Even with the relatively mild discharge velocity, some consideration may be warranted
for the installation of an energy dissipation device at the culvert outlet. The determination to
do so will be deferred to the final design phase, but the device may consist of a conventional
design such as a rip -rap bed lining or similar solution. The modeling results are consistent
with the field reconnaissance. Figures 9 and 10 show the 100 -year floodplain and the 2 -year
riparian inundation areas for the existing and proposed conditions, respectively. Detailed
calculations ore provided in Appendix C.
NORTHERN ARROYO
EXISTING CONDITION HEC -RAS MODELING SUMMARY
Water Depth (ft)
Velocity (ft /s)
Froude No.
Station No.
2 -Year
100 -Year
2 -Year
100 -Year
2 -Year
100 -Year
8 +09
1.7
2.8
2.0
3.2
0.34
0.43
6 +85
0.7
1.3
4.0
5.3
1.01
0.98
5 +19
1.2
2.0
3.8
6.3
0.77
1.01
3 +99
2.0
3.6
2.7
2.9
0.47
0.37
2 +66
2.5
4.1
3.1
5.0
0.41
0.55
1+32
1.6
2.4
4.3
5.9
0.97
1.01
Table 3.9 Existing condition HEC -PAS modeling results for the Northern Arroyo.
FUSCOE ENGINEERING, INC. 47
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT
JUNE 30, 2011
NORTHERN ARROYO
PROPOSED CONDITION HEC -RAS MODELING SUMMARY
Water Depth (ft)
Velocity (N /s)
Froude Number
Station No.
2 -Year
100 -Year
2 -Year
100 -Year
2 -Year
100 -Year
8 +55
2.0
3.3
1.8
2.7
0.28
0.34
6 +95
0.9
1.9
5.2
5.6
1.02
1.01
5 +00
1.1
2.9
4.8
3.4
1.01
0.45
4 +00
2.4
4.8
1.1
1.5
0.15
0.14
1+00
0.9
1.5
1.8
3.0
0.44
0.55
0 +00
0.2
0.5
2.4
3.6
0.33
0.44
Note: A comparison of changes as compared to existing conditions were not provided due to differing station numbers.
{t /s feet per second
Table 3.10 Proposed condition HEC -RAS modeling results for the Northern Arroyo.
FUSCOE ENGINEERING, INC. 48
NEWPORT BANNING RANCH FIGURE 9: Northern Arroyo Existing Condition Floodplain
June 30, 2011
NOT TO SCALE
NEWPORT BANNING RANCH
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JUNE 30, 2011
FUSCOE ENGINEERING, INC. 50
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Drainage Boundary
—... Project Boundary
100yr Floodplain
- ♦; 2yr Floodplain
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NEWPORT BANNING RANCH FIGURE 10: Northern Arroyo Proposed Condition Floodplain
June 30, 2011
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NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT
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FUSCOE ENGINEERING, INC. 52
NEWPORT BANNING RANCH
WATERSHED ASSESSMENT REPORT- FINAL DRAFT .TUNE 30, 2011
Southern Arroyo
Tables 3.11 and 3.12 summarize the modeling results for the Southern Arroyo with respect to
the 2 -year and 100 -year conditions and the existing and proposed development conditions.
In general, the majority of flows in the channel are in the sub - critical flow regime, similar to
the Northern Arroyo. There is no significant hydraulic difference between the existing and
proposed conditions. Specifically, under the 2 -year event, the velocity range is from 1.1 to
3.8 ft /s. The velocity difference between the existing and proposed conditions is from 0 to
0.4 ft /s. Under the 100 -year event, the velocity range is from 1.5 to 5.6 ft /s, and velocity
difference between the existing and proposed conditions is from 0.1 to 0.7 ft /s. The above
velocities are considered to be within a range that is acceptable for stable channel conditions.
In water depth, the proposed condition is similar to existing conditions. The difference is from
0 to 0.2 ft under the 2 -year event, and from 0 to 0.5 ft under the 100 -year event. This range
of differences would only cause a slight change in the floodplains, as shown in Figure 10
(100- yearfloodplain) and Figure 11 (2- year floodpiain).
SOUTHERN ARROYO
HEC -RAS MODELING SUMMARY (2 -YEAR)
Station No.
Water Depth (ft)
Velocity (ft /s)
Froude No.
Existing
Proposed
Existing
Proposed
Existing
Proposed
20 +62
0.8
0.9
3.6
3.6
0.84
0.84
19 +02
0.7
0.7
1.7
1.7
0.39
0.39
16 +57
0.5
0.5
3.7
3.8
1.01
1.01
14 +63
1.5
1.6
1.3
1.3
0.20
0.20
12 +92
0.3
0.4
3.2
3.2
1.00
1.00
11 +12
1.0
1.0
1.2
1.1
0.24
0.23
8 +96
0.4
0.4
3.2
3.0
1.01
1.00
6 +56
0.6
0.6
1.3
1.2
0.30
0.30
4 +81
0.8
0.6
1.2
1.1
0.30
0.31
3 +31
1.4
1.2
2.3
2.0
0.45
0.42
1+25
0.3
0.3
3.0
2.6
1.00
1.00
ft/s feet per second
Table 3.11 HEC -RAS modeling results for the Southern Arroyo, 2 -year event.
FUSCOE ENGINEERING, INC. 53
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WATERSHED ASSESSMENT REPORT- FINAL DRAFT
JUNE 30, 2011
SOUTHERN ARROYO
HEC -RAS MODELING SUMMARY (100 -YEAR)
Station No.
water Depth (ft)
Velocity (ft /s)
Froude No.
Existing
Proposed
Existing
Proposed
Existing
Proposed
20 +62
1.5
1.6
5.3
5.6
0.90
0.92
19 +02
1.4
1.5
2.7
2.8
0.45
0.45
16 +57
1.0
1.1
5.4
5.6
1.00
1.01
14 +63
2.6
2.8
2.2
2.4
0.28
0.29
12 +92
0.7
0.8
4.7
4.8
1.00
1.00
11+12
1.9
1.8
2.1
1.9
0.30
0.29
8 +96
0.9
0.8
4.6
4.4
1.01
1.01
6 +56
1.3
1.1
2.2
2.2
0.37
0.40
4 +81
1.7
1.3
1.7
1.5
0.28
0.27
3 +31
2.5
2.0
3.7
3.1
0.56
0.52
1+25
0.8
0.6
4.6
3.9
1.00
1.01
ft /s feet per second
Table 3.12 HEC -RAS modeling results for the Southern Arroyo, 100 -year event.
Based on the proposed design of tributary areas, the upstream water quality / detention basin
to reduce peak flows entering the Southern Arroyo and the projected hydraulic performance of
the channel the channel is expected to remain stable under the proposed condition. In
addition, measures will be taken to stabilize the eroding tributaries entering the Arroyo thereby
controlling the amount of sediment available for transport to the Semeniuk Slough. These
measures include use of improved grading, soil compaction, drainage improvements to
reduce sheet flow runoff, as well as increased vegetation to further stabilize slopes. Lastly, the
diffuser basin at the downstream end of the Arroyo will also provide an additional measure to
control sediment loading into the Semeniuk Slough.
This portion of the Project ultimately drains into the Semeniuk Slough. The 2 -year analysis for
hydrologic conditions of concern for this drainage area was incorporated into the Tables 3.3
and 3.4 within Section 3.2.2.
FUSCOE ENGINEERING, INC. 54
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_... Project Boundary
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NEWPORT BANNING RANCH FIGURE 11: Southern Arroyo 100 -Yr Floodplain
June 30,2011
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JUNE 30, 2011
FUSCOE ENGINEERING, INC. 56
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t Existing 2 -yr Floodplain
Proposed 2 -yr Floodplain
�... Project Boundary
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FIGURE 12: Southern Arroyo 2 Yr Floodplain
June 30, 2011
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NEWPORT BANNING RANCH
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FUSCOE ENGINEERING, INC. 58
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WATERSHED ASSESSMENT REPORT- FINAL DRAFT .TUNE 30, 2011
3.4 HYDROLOGY /HYDRAULICS IMPACT ASSESSMENT
This hydrology assessment estimated the peak flow runoff potential for a sequence of storm
events to evaluate the hydrologic impacts on the Project watershed for the existing and
proposed conditions. In addition, a channel hydraulics analysis was performed for the
Northern and Southern Arroyos.
The following impact assessments are based on the significance criteria established in Section
1.4 for hydrology. In addition, a long -term sea level rise evaluation has also been provided
following the standard CEQA significance criteria.
Impact B: Would the Project substantially deplete groundwater supplies or interfere
substantially with groundwater recharge such that there would be a net deficit in
aquifer volume or a lowering of the local groundwater table level (e.g. the
production rate of pre- existing nearby wells would drop to a level which would not
support existing land uses or planned uses for which permits have been granted)?
Impact B Analysis: The effect of the development on groundwater resources was not included
within the scope of this report. Therefore, impacts to groundwater systems are not discussed.
Impact C: Would the Project substantially alter the existing drainage pattern of the site or
area, including through the alteration of the course of a stream or river, or in a
manner which would result in a substantial erosion or siltation on- or off -site?
Impact C Analysis: The proposed Project will result in a slight alteration of existing drainage
patterns due to the development areas and increase in impervious surfaces as compared to
existing conditions. In addition, changes in drainage patterns will also occur due to a storm
water management strategy that re- assigns flows to areas that have additional capacity, and
decreases flows to areas with minimal or constrained capacity. The sheet flow runoff under
the existing condition within the project site will be replaced with storm drain systems to convey
flows to the Lowland Area, Semeniuk Slough, and the Caltrans RCB at WCH. Due to the
capacity constraints of the Semeniuk Slough under existing conditions, a portion of the
development area within this drainage area will be re- assigned to the Lowland Area to reduce
proposed runoff in the Semeniuk Slough, creating a proposed condition that roughly matches
the existing limiting conditions. See Tables 3.2 and 3.4 for additional details.
Off -site flows will continue to drain through the Northern and Southern Arroyos as under
existing conditions. The proposed development will not alter the hydraulic behavior of the
Northern Arroyo, and the results of the creek HEC -RAS modeling demonstrates that the Arroyo
topography does not generate erosive channel velocities under peak flow conditions. Field
verifications also support a stable channel designation. For the Southern Arroyo, HEC -RAS
modeling results confirm that there is no significant hydraulic difference between the existing
and proposed conditions that would lead to increased erosion or siltation. The tributaries that
currently contribute to erosion and sedimentation in the Southern Arroyo will be stabilized,
thereby controlling the amount of sediment available for transport to the Semeniuk Slough
under post - development conditions. Because of the proposed grading layout, street layout
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and drainage system, it is evident that on -site and off -site erosion and siltation are considered
to be less than significant. See Tables 3.9, 3.10, 3.11 and 3.12 for additional details.
Impact D: Would the Project substantially alter the existing drainage pattern of the site, or
substantially increase the rate or amount of surface runoff in a manner that would
result in flooding on- or off -site?
Impact D Analysis: As previously mentioned, the increase in impervious surfaces as compared
to existing conditions will result in slight localized increases in peak flow runoff and runoff
volume. However, the proposed runoff management plan will ensure that Project -wide runoff
peak flows and runoff volumes are customized to emulate existing conditions for each major
drainage feature or receiving water. A portion of the development area runoff from the
existing Semeniuk Slough drainage area will be re- assigned to the Lowland Area to maintain
drainage rates that resemble the existing condition in the Slough. The slight marginal increase
in storm runoff volume delivered to the Lowland Area will be absorbed by the storage capacity
of the existing Lowland Area and Salt Marsh Basin. In addition, all on -site curb - and - gutters
and storm drains will be designed per City of Newport Beach Standard Plans and County of
Orange Standard Plans, thereby minimizing potential impacts of on -site development area
flooding. Further, off -site drainage will continue to drain through the Northern and Southern
Arroyos as under existing conditions. Therefore, impacts relating to on -site or downstream
flooding are considered to be less than significant.
Impact E: Would the Project create or contribute runoff water which would exceed the
capacity of existing or planned storm water drainage systems or provide substantial
additional sources of polluted runoff?
Impact E Analysis: Refer to Analyses to Impacts C and D for additional details regarding the
capacity for the downstream receiving waters to accommodate Project flood flows. Impacts to
storm water runoff quality are discussed under Section 5.4.
Impact G: Would the Project place housing within a 100 -year flood hazard area as mapped
on a federal Flood Hazard Boundary or Flood Insurance Rate Map or other flood
hazard delineation map?
Impact G Analysis: The proposed Project will not result in the creation of housing within the
100 -year flood hazard area. The Santa Ana River has been channelized and improved to
protect adjacent areas from the 100 -year storm (1% chance of flooding). Therefore, areas
within the project boundary are included in Zone X, which is defined as areas determined to
be outside the 0.2% annual chance floodplain (500 -year floodplain). Impacts related to flood
zones are considered to be less than significant.
Impact H: Would the Project place within a 100 -year flood hazard area structures which
would impede or redirect flood flows?
Impact H Analysis: As discussed under Analysis to Impact G, the proposed Project will not
result in the creation of housing within the 100 -year flood hazard area. Impacts are
considered to be less than significant.
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Impact I: Would the Project expose people or structures to a significant risk of loss, injury or
death involving flooding, including flooding as a result of the failure of a levee or
dam?
Impact I Analysis: As previously mentioned, the Santa Ana River has been improved and
channelized to protect the adjacent development areas from the 100 -year storm event. The
majority of the development areas are located on the bluffs and at higher elevations than the
River. In addition, the City of Newport Beach has developed and Emergency Management
Plan, which includes procedures and evacuation, plans in the event of dam or levee failures.
Therefore, impacts due to flooding are considered to be less than significant.
Impact J: Would the Project be subject to inundation by seiche, tsunami, or mudflow?
Impact J Analysis: Inundation by seiche or mudflow is not anticipated for the project site. Due
to the Project's proximity to the coast, inundation by tsunami is possible. The proposed
project was evaluated against a recently prepared Tsunami inundation map used for
emergency preparedness (Newport Beach Quadrangle, CA Department of Conservation;
March 15, 2009). The proposed development footprint within the Upper Mesa remains out of
the tsunami inundation area and the project development areas would not be subject to
inundation. The City of Newport Beach has also developed an Emergency Management Plan,
which includes procedures and evacuation plans in the event of tsunamis. Therefore, risks are
considered less than significant.
Long -term Sea Level Rise Impact Assessment
Future sea level rise scenarios are increasingly being incorporated into engineering design
and environmental impact analyses for projects on or near the coast. Due to the Project's
development footprint on the upper Mesa outside of the 500 -year floodploin, sea level rise is
not anticipated to alter the results, recommendations or conclusions derived from the analyses
that were performed to investigate the existing and proposed hydrologic and hydraulic
conditions at the project site. In May 2009, the Pacific Institute published a paper titled "The
Impacts of Sea -level rise on the California Coast" which indicated a worse case scenario sea
level rise of 55 inches or 4.6 feet along the coastline within the year 2100. Similar studies
regarding sea level rise along the California coast have also been prepared, and these
generally all estimate a worst case scenario similar to the sea level rise estimate range provided in
the Pacific Institute report. In order to evaluate the long -term cumulative impacts of sea level
rise over the next 90 years, the Project grading plan was overlayed onto the maximum sea
level rise data provided by the Pacific Institute. The entire development footprint is located
outside both the current coastal base flood (approximate 100 -year flood extent) and the sea
level rise scenario (coastal base flood plus 4.6 ft). In addition, sea level rise will not negatively
impact the ability of the project to drain into the Lowlands or the Semeniuk Slough based on
the hydraulic grade lines of the proposed storm drain system. Localized flooding will occur
along the Semeniuk Slough during periods of high precipitation and storm conditions. In
severe instances, flood flows may back up further into the Lowlands or in the Southern and
Northern Arroyos, and while some limited localized impact would be expected on the
performance of certain low -lying storm drain outlets that may become temporarily submerged,
this will not impact the Project during this temporary condition. Sea level rise will increase the
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potential for flood water depths to increase against the existing slopes leading up to the
development areas within the upland area, but adaptive management strategies can be taken
to ensure the toe of the slopes are stabilized as sea levels rise. For example, geotextile covers
with vegetation enhancement, buried groins with soil /vegetative cover and rip -rap can be
applied to protect specific areas susceptible to sea level rise and erosion. Similarly, adaptive
management strategies can occur with the management of the Santa Ana River levee tidal
gate system administered by the Army Corps of Engineers. Based on this evaluation, the
cumulative impact of sea level rise over the next 90 years is considered less than significant.
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4.0 WATER BUDGET ANALYSIS
Within the project site, there are two existing arroyo habitat areas: the Northern Arroyo and
the Southern Arroyo, located downstream of 18'h Street and downstream of the 16'h Street,
respectively (Figure 6). Unlike the Salt Marsh habitats, the habitats of these two Arroyos rely
on fresh water (storm water) inputs. Thus, the objective in this water budget analysis is to
understand the hydrologic impact on these Arroyos due to the potential change in drainage as
a result of the Project. The water budget analysis estimates the water demand and supply for
habitats and further determines the ecological condition of the habitat from the water balance
perspective. The water budget analysis was performed in this study following the drainage
concept established in the hydrology analysis with respect to the existing and proposed
condition Project watersheds.
4.1 SETTING
4. 1.1 ARROYO DRAINAGE CHARACTERISTICS
In general, both of the Arroyos are found in the Upland Mesa area of the project site, in
association with significant off -site drainage areas. Specifically, the Northern Arroyo is located
around the northeast corner of the project site, receiving the off -site runoff primarily from a
42 -inch storm drain pipe and a "W -ditch along the project boundary. In addition, its
drainage includes the natural land within the project boundary. The Arroyo starts at the
discharge location of the above 42 -inch pipe, runs about 930 ft to the west and discharges to
the Lowland Area. Under the existing condition, there are no engineering improvements to
the Northern Arroyo. The habitat's footprint is approximately 6 acres with mostly good
vegetation cover. Under the proposed condition, the Arroyo will continue to receive storm
water runoff from the existing 42 -inch pipe. Only a small portion of the natural land in its
drainage area will be converted to the residential development. In addition, a proposed
roadway will be added to cross the Arroyo. The flow path of the Arroyo will cross under the
roadway within a new culvert. See Figure 13 for the Northern Arroyo drainage.
The Southern Arroyo is located in the south portion of the project site, and begins at an
existing 48 -inch storm drain pipe discharge point. The Arroyo runs approximately 2,340 ft
through the project site from east to west, and terminates at a dirt road approximately 500 ft
upstream of the Semeniuk Slough. The Southern Arroyo is surrounded by approximately 30
acres of natural habitat area with a heavy vegetation cover. Evidence of undercutting and
erosion of the side tributaries of the Arroyo exist on -site, and these areas will be stabilized
under the proposed condition. Under the existing condition, the Southern Arroyo receives the
runoff from existing off -site developments though a 48 -inch pipe, as well as receives sheet
flow from the surrounding natural area within the project site. Under the proposed Project, a
portion of the Upland Mesa area will be converted to residential and mixed land uses and will
drain towards the Arroyo under proposed conditions. See Figure 14 for the Southern Arroyo
drainage.
Table 4.1 summarizes the drainage areas of the Arroyos with respect to the existing and
proposed conditions. For the water budget analysis, the on -site area used in the table refers
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to the area of riparian habitat associated with the Arroyo. The off -site area refers to the
surface inflow contribution area to the Arroyo habitat areas from both Project and upstream
drainage areas. Refer to Figures 13 and 14 for locations of the drainage areas associated
with the water budget analysis.
Table 4.1 Drainage area summary of the Northern and Southern Arroyos
As shown in the table above, the Northern Arroyo will have similar off -site and on -site
drainage acreages between the existing and proposed conditions. However, the Southern
Arroyo will have its off -site tributary drainage areas reduced by approximately 61 acres and
on -site areas by 2 acres under the proposed condition.
FUSCOE ENGINEERING, INC. 64
ARROYO DRAINAGE AREA SUMMARY
Location°
Off -Site Drainage Area (acres)
On -Site Habitat Area (acres)
Existing
Proposed
Existing
Proposed
Northern Arroyo
129
121 ( -8)
6
5(—l)
Southern Arroyo
115
54( 61)
26
24 ( -2)
Note: Numbers in parentheses represent change as compared to existing condition.
a Refer to Figures 13 and 14 for locations of the on -site and off -site drainage boundaries for the Northern and Southern
Arroyos, respectively.
Table 4.1 Drainage area summary of the Northern and Southern Arroyos
As shown in the table above, the Northern Arroyo will have similar off -site and on -site
drainage acreages between the existing and proposed conditions. However, the Southern
Arroyo will have its off -site tributary drainage areas reduced by approximately 61 acres and
on -site areas by 2 acres under the proposed condition.
FUSCOE ENGINEERING, INC. 64
P: \Project \821 \01 \War \GI SWa! \MHD \EIR Figures &Exh i hits \pdi\82101 gh -Fig 13_N_A rroyo_Droinoge_Mop.pdf
NEWPORT BANNING RANCH FIGURE 13: Proposed Northern Arroyo Drainage
June 30, 2011
NOT TO SCALE
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JUNE 30, 2011
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Legend j
Existing Storm Drain / r�
— Proposed Storm Drain
Arroyo
_... Project Boundary
Existing Drainage Boundary
'114
On -Site Drainage Boundary
z.
C�9
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ilk
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e I
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'--` Drainage Boundary
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NEWPORT BANNING RANCH FIGURE 14: Proposed Southern Arroyo Drainage
June 30, 2011
NOT TO SCALE
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JUNE 30, 2011
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4.1.2 CLIMATE
JUNE 30, 2011
In water budget analysis, climate is an important factor affecting the water demand and supply
for the habitat studied. In general, the project area exhibits a mild Mediterranean -type climate
with warm /dry summers and cold /wet winters. Tables 4.2 and 4.3 below summarize the
monthly temperature range and the average precipitation for the project area, respectively.
AVERAGE TEMPERATURE (°F)
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Maximum
64
64
63
65
66
69
72
73
73
72
67
64
Minimum
47
48
50
52
56
59
62
64
62
58
52
47
Source: Newport Beach Harbor Station (33.36N 117.53W 10 Feet, 11/1/1934-
7/31/1998).
Table 4.2 Average monthly temperatures for the project area.
AVERAGE PRECIPITATION (inches)
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
Rainfall
Depth
2.08
2.05
1.84
0.90
0.17
0.05
0.01
0.09
0.36
0.18
1.55
1.57
10.85
Source: Newport Beach Harbor Station (33.36N I I7.53W 10 Feet, 11/1/1934- 7/31/1998).
Table 4.3 Average monthly precipitation for the project area.
4.2 METHODOLOGY
4.2.1 WATER BUDGET MODEL
The water budget model is a water balance calculation, which accounts for the inflow and
outflow of water to and from the habitat area over a certain period, while at the same,
considering the habitat's water demand. The inflow water usually comes directly from
precipitation or surface water run -on. The outflow water usually results from evaporation, sub-
surface infiltration or surface outflow, thus referring to the amount of the inflow water that
cannot be utilized by the vegetation. Alternatively, the habitat's water demand can be referred
to the plant's evapotranspiration (ET) rate.
However, due to the complexity of the process, the water budget model is usually set up on a
monthly basis to calculate monthly separate results rather than month -to -month continuous
water balance. In addition, for the purposes of this study, all of the water losses are combined
into a single loss term and calculated by using a yearly mean loss ratio in order to simplify the
loss calculation. Therefore, the water budget model is expressed in the following water
balance equation (Equation 4.1):
Water Balance = P + Si — Go — ET (4.1)
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Where: P = precipitation (in inches)
S; = surface inflow (in inches)
Go = loss (in inches)
ET = evapotranspiration (in inches)
JUNE 30, 2011
The monthly precipitation (P) can be directly obtained from Table 4.3. The calculations for the
remaining variables are described in the following sub - sections.
4.2.2 SURFACE INFLOW
The amount of the surface inflow (S;) is determined by the drainage area, land use and
precipitation. The inflow is calculated as total runoff volume first and then converted into the
depth by dividing by the habitat's footprint area. In this water budget model, the runoff
volume (R) is calculated by multiplying a runoff coefficient (RV, defined as the overall average
ratio of runoff to rainfall) to the precipitation (P) and drainage area (A). The runoff coefficient
(RV) is computed by the following equation (Equation 4.2):
RV = (0.007)(IMP) + 0.1
Where: RV = runoff coefficient (unitless)
IMP = percent impervious of the drainage area ( %)
The runoff volume (R) is then determined by the following equation:
R = (P) (A) (RV/ 12)
Where: R = runoff volume (in acre -feet)
P = precipitation (in inches)
A = drainage area (in acres)
RV = runoff coefficient (unitless)
(4.2)
(4.3)
Table 4.4 summarizes the result of the surface runoff inflow factors for the Northern and
Southern Arroyos in terms of drainage area, imperviousness and runoff coefficient. Refer to
Appendix D for detailed calculations.
SURFACE RUNOFF INFLOW FACTORS
Location
Drainage Area (acres)
Average % Impervious
Runoff Coefficient (RV)
Existing
Proposed
Existing
Proposed
Existing
Proposed
Northern
129
121 ( -8)
68%
73%(+5)
0.58
0.61 ( +0.03)
Arroyo
Southern
Arr. .
1 15
54 ( -61)
39 %
79 % ( +40)
0.38
0.65 ( +0.27)
Note: Numbers in parentheses represent change as compared to existing condition.
Table 4.4 Summary of surface runoff inflow factors.
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4.2.3 EVAPOTRANSPIRATION
Evapotranspiration (ET) is a process involving the uptake of water by the plant system in which
excess water is transpired to the atmosphere causing evaporation and transpiration. It thus
can be referred as the water demand factor in the water budget model. The ET amount can
be acquired from monitoring data or estimated from empirical equations. Table 4.5 shows
the monthly potential evapotranspiration amount calculated by the Thornthwaite Method:
ET, _ (0.63)(1 Otc / 1)° (4.4)
Where: ETA = unadjusted potential evapotranspiration (in inches)
tr = temperature ( °F)
I = temperature efficiency index (see Appendix D)
a = 0.000000675(1)3 — 0.0000771(1)2 + 0.01792(l) +
0.49239
Results are summarized in Table 4.5 below. Refer to Appendix D for detailed calculations
regarding the Thornthwaite Method.
POTENTIAL EVAPOTRANSPIRATION (INCHES)
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
ET
1.44
1.60
1.78
2.16
2.66
3.21
3.68
3.77
3.35
2.77
1.91
1.41
29.74
Source: Thornthwaite Method with Correction Factors for Monthly Sunshine Duration (Dunn & Leopold 1978)
Table 4.5 Summary of potential evapotranspiration.
4.2.4 LOSS
For this water budget model, the water losses within the Arroyo habitat areas can be
considered primarily from the infiltration and surface outflow processes. The Arroyo valleys do
not have significant flat -bottom pond areas, and thus the evaporation loss from open water is
considered to be negligible. Since the soils have a slow rate of water transmission (Hydrologic
Soil Group D per the Orange County Hydrology Manual) and the habitats have a good
vegetation cover, the average loss ratio is estimated to be 30 %.
In the original water balance equation discussed at the beginning of this section, the loss term
(Go) is calculated by multiplying 30% to the sum of the precipitation term (P) and the surface
inflow term (Si).
Go = (0.3)(P + S;)
Where: Go = water loss (in inches)
P = precipitation (in inches)
S; = surface inflow (in inches)
(4.5)
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4.3 RESULTS & DISCUSSION
4.3.1 NORTHERN ARROYO
JUNE 30, 2011
Tables 4.6 and 4.7 summarize the monthly water budget results for the Northern Arroyo
habitat area, with respect to the existing and proposed conditions. The red number in
parentheses in the balance row of the tables means a negative balance which indicates a
drought month for the habitat. As shown in the tables, in general, the existing and proposed
conditions exhibit very similar water balance results. Therefore, there will be no significant
change in the habitat - related drainage under the proposed condition.
Table 4.6 Water Balance under existing conditions of the Northern Arroyo.
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NORTHERN ARROYO
MONTHLY WATER BUDGET FOR EXISTING CONDITION
Factor
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
P
2.1
2.1
1.8
0.9
0.2
0.1
0.0
0.1
0.4
0.2
1.6
1.6
10.9
S;
30.0
29.6
26.5
13.0
2.5
.7
0.1
1.3
5.2
2.6
22.3
22.6
156.4
G°
9.6
9.5
8.5
4.2
0.8
0.2
0.0
0.4
1.7
0.8
7.2
7.3
50.2
ET
1.4
1.6
1.8
2.2
2.7
3.2
3.7
3.8
3.4
2.8
1.9
1.4
29.7
Water
210
20.5
18.1
7.6
(0.8)
(2.7)
(3.6)
(2.8)
0.5
(0.8)
14.8
15.5
87.3
Balance°
Note: Red number in parentheses denotes a negative balance.
P Precipitation (inches)
S; Surface Inflow (inches)
Ga Loss (inches)
ET Evapatmnspiration (inches).
a Water balance calculated under Equation 4.1.
Table 4.6 Water Balance under existing conditions of the Northern Arroyo.
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Table 4.7 Water Balance under proposed conditions of the Northern Arroyo.
Specifically for the Northern Arroyo habitat area, the drought season is from May to August
and October. July is the driest month through the year since the precipitation is only 0.01
inch. The remaining seven months of the year are considered to have sufficient water supply
for the habitat. The net annual total of water is around 75 inches. Therefore, there will be no
anticipated water budget impact on the Northern Arroyo habitat from the proposed
development.
4.3.2 SOUTHERN ARROYO
The following tables show the monthly water budget results for the Southern Arroyo habitat
area, with respect to the existing and proposed conditions.
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NORTHERN ARROYO
MONTHLY WATER BUDGET FOR PROPOSED
CONDITION
Factor
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
P
2.1
2.1
1.8
0.9
0.2
0.1
0.0
0.1
0.4
0.2
1.6
1.6
10.9
S;
30.0
29.6
26.5
13.0
2.5
.7
0.1
1.3
5.2
2.6
22.3
22.6
156.4
Go
9.6
9.5
8.5
4.2
0.8
0.2
0.0
0.4
1.7
0.8
7.2
7.3
50.2
ET
1.4
1.6
1.8
2.2
2.7
3.2
3.7
3.8
3.4
2.8
1.9
1.4
29.7
21.0
20.5
18.1
7.6
(0.8)
(2.7)
(3.6)
(2.8)
0.5
(0.8)
14.8
15.5
87.3
B=,,
lance
L
-L
Note: Red number in parentheses denotes a negative balance.
P Precipitation (inches)
S, Surface Inflow (inches)
G. Loss (inches)
ET Evapotranspiration (inches).
a Water balance calculated under Equation 4.1.
Table 4.7 Water Balance under proposed conditions of the Northern Arroyo.
Specifically for the Northern Arroyo habitat area, the drought season is from May to August
and October. July is the driest month through the year since the precipitation is only 0.01
inch. The remaining seven months of the year are considered to have sufficient water supply
for the habitat. The net annual total of water is around 75 inches. Therefore, there will be no
anticipated water budget impact on the Northern Arroyo habitat from the proposed
development.
4.3.2 SOUTHERN ARROYO
The following tables show the monthly water budget results for the Southern Arroyo habitat
area, with respect to the existing and proposed conditions.
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Table 4.8 Water Balance under existing conditions of the Southern Arroyo,
SOUTHERN ARROYO
SOUTHERN ARROYO
MONTHLY WATER BUDGET FOR EXISTING CONDITION
MONTHLY WATER BUDGET FOR PROPOSED
CONDITION
Factor
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
P
2.1
2.1
1.8
0.9
0.2
0.1
0.0
0.1
0.4
0.2
1.6
1.6
10.9
S;
3.5
3.4
3.1
1.5
0.3
0.1
0.0
0.2
0.6
0.3
2.6
2.6
18.2
Go
1.7
1.6
1.5
0.7
0.1
0.0
0.0
0.1
0.3
0.1
1.2
1.3
8.7
ET
1.4
1.6
1.8
2.2
2.7
3.2
3.7
3.8
3.4
2.8
1.9
1.4
29.7
B=,,
lance
2.5
2.2
1.7
L
(0.5)
(2.3)
(3.1)
(3.7)
(3.6)
(2.7)
(2.4)
1.0
1.5
(9.4)
-L
Note: Red number in parentheses denotes a negative balance.
1.3
(10.9)
Balance°
I
L
P Precipitation (inches)
Note: Red number in parentheses denotes a negative balance.
S, Surface Inflow (inches)
P Precipitation (inches)
G. Loss (inches)
S; Surface Inflow (inches)
ET Evapotranspiration (inches).
a Water balance calculated under Equation 4.1.
Table 4.8 Water Balance under existing conditions of the Southern Arroyo,
Table 4.9 Water Balance under proposed conditions of the Southern Arroyo.
In general, under the existing condition the Southern Arroyo habitat area has a longer drought
period than the Northern Arroyo. The results show a deficit in water balance from April to
October. The remaining five months exhibit positive water balances. However, the net water
amount is significantly smaller in comparison to the Northern Arroyo habitat area, putting the
net annual total of water into a deficit. The reason the Southern Arroyo receives less flow
nourishment than the Northern Arroyo is that the Southern Arroyo has a greater habitat
footprint area (about five times larger than the Northern Arroyo). The size of the habitat
footprint attenuates the surface inflow nourishment. Therefore, based on the field
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SOUTHERN ARROYO
MONTHLY WATER BUDGET FOR PROPOSED
CONDITION
Factor
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
P
2.1
2.1
1.8
0.9
0.2
0.1
0.0
0.1
0.4
0.2
1.6
1.6
10.9
S;
3.1
3.1
2.7
1.3
0.3
0.1
0.0
0.1
0.5
0.3
2.3
2.3
16.2
Ga
1.6
1.5
1.4
0.7
0.1
0.0
0.0
0.1
0.3
0.1
1.2
1.2
8.1
ET
1.4
1.6
1.8
2.2
2.7
3.2
3.7
3.8
3.4
2.8
1.9
1.4
29.7
Water
2.2
2.0
1.4
(0.6)
(2.4)
(3.1)
(3.7)
(3.6)
(2.7)
(2.5)
0.8
1.3
(10.9)
Balance°
I
L
Note: Red number in parentheses denotes a negative balance.
P Precipitation (inches)
S; Surface Inflow (inches)
G. Loss (inches)
ET Evapotranspiration (inches).
a Water balance calculated under Equation 4.1.
Table 4.9 Water Balance under proposed conditions of the Southern Arroyo.
In general, under the existing condition the Southern Arroyo habitat area has a longer drought
period than the Northern Arroyo. The results show a deficit in water balance from April to
October. The remaining five months exhibit positive water balances. However, the net water
amount is significantly smaller in comparison to the Northern Arroyo habitat area, putting the
net annual total of water into a deficit. The reason the Southern Arroyo receives less flow
nourishment than the Northern Arroyo is that the Southern Arroyo has a greater habitat
footprint area (about five times larger than the Northern Arroyo). The size of the habitat
footprint attenuates the surface inflow nourishment. Therefore, based on the field
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reconnaissance, the existing habitat survives through the year under the existing water budget
condition.
For the proposed condition, although the Upland Mesa area will be converted to the
residential area and be therefore removed from its drainage, the water budget results for the
Southern Arroyo do not vary significantly as compared to existing conditions. The drought
period will remain as seven months, and the annual balance will decrease only by
approximately 1 inch. The approximately 60 acres of natural land conversion to developed
area leads to only a 10% reduction in surface inflow during the wet season. The reason for
the insignificant influence by the proposed Upland Mesa area conversion is that the primary
supply of the inflow water for this Arroyo is from the off -site development area, and not the
development areas.
It is a commonly accepted observation that urban development, especially residential, has the
potential to create sources of urban runoff during the dry season based on over irrigation, car
washing, cleaning, etc., which can create changes in downstream habitats. Based on the
implementation of the Project LID features and drainage systems designed to deliver initial
flows to landscaped areas, dry season runoff is not expected to be a significant impact and
will be controlled by the on -site water quality features. Refer to Section 5 for further discussion
of the proposed water quality and LID features.
In conclusion, there is no significant water budget impact on the Southern Arroyo habitat due
to the proposed development. However, enhancement opportunities exist by introducing
treated dry weather flows and storm event low -flows to the Southern Arroyo from the proposed
storm drain system and LID features. This creates additional hydrologic inputs to the system
for maximum habitat diversity and also provides additional infiltration and evapotranspiration
opportunities for on -site retention of the design capture volume. The low -flow diversion
alternative will be considered during the resource agency permitting process.
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5.0 WATER QUALITY ASSESSMENT
The purpose of this section is to define the water quality treatment approach for the Newport
Banning Ranch Project consistent with the details of the current planning level, and summarize
the various water quality systems and concepts designed into the development plan. As a
result of the Project's alteration of existing conditions, the proposed development will create
new pollutant sources, and in turn, change the makeup of pollutant constituents generated by
the Site's current operations. In order to reduce the amount of pollutants in storm water runoff
from the new development plan, best management practices (BMPs) are required in
accordance with the City of Newport Beach, California Coastal Commission, and local
Regional Board standards.
5.1 REGULATORY FRAMEWORK
5.1.1 FEDERAL REGULATIONS
Controlling pollution of the nation's receiving water bodies has been a major environmental
concern for more than three decades. Growing public awareness of the impacts of water
pollution in the United States culminated in the establishment of the federal Clean Water Act'
(CWA) in 1972, which provided the regulatory framework for surface water quality protection.
The United States Congress amended the CWA in 1987 to specifically regulate discharges to
waters of the US from public storm drain systems and storm water flows from industrial
facilities, including construction sites, and require such discharges be regulated through
permits under the National Pollutant Discharge Elimination System (NPDES).10 Rather than
setting numeric effluent limitations for storm water and urban runoff, CWA regulation calls for
the implementation of Best Management Practices (BMPs) to reduce or prevent the discharge
of pollutants from these activities to the Maximum Extent Practicable (MEP) for urban runoff,
and meeting the Best Available Technology Economically achievable (BAT) and Best
Conventional Pollutant Control Technology (BCT) standards for construction storm water.
Regulations and permits have been implemented at the federal, state, and local level to form
a comprehensive regulatory framework to serve and protect the quality of the nation's surface
water resources.
In addition to reducing pollution with the regulations described above, the CWA also seeks to
maintain the integrity of clean waters of the United States — in other words, to keep clean
waters clean and to prevent undue degradation of others. As part of the CWA, the Federal
Antidegradation Policy [40 CFR Section 131.12] states that each state "shall develop and
adopt a statewide ontidegradation policy and identify the methods for implementing such
policy..." [40 CFR Section 131.12(a)]. Three levels of protection are defined by the federal
regulations:
a Also referred to as the Federal Water Pollution Control Act of 1972
10 CWA Section 402(p)
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1. Existing uses must be protected in all of the Nation's receiving waters, prohibiting any
degradation that would compromise those existing uses;
2. Where existing uses are better than those needed to support propagation of aquatic
wildlife and water recreation, those uses shall be maintained, unless the state finds that
degradation is "...necessary to accommodate important economic or social development"
[40 CFR Section 131.12(x)(2)]. Degradation, however, is not allowed to fall below the
existing use of the receiving water; and
3. States must prohibit the degradation of Outstanding National Resource Waters, such as
waters of National and State parks, wildlife refuges, and waters of exceptional recreation
or ecological significance.
5.1.2 STATE AND LOCAL REGULATIONS
California Coastal Commission
The California Coastal Commission is responsible for protecting water quality in coastal
environments as defined under Sections 30230 and 30231 of the California Coastal Act.
These water quality provisions provide a broad basis for protecting coastal waters, habitats
and biodiversity associated with new development and redevelopment projects. To meet the
objectives of Sections 30230 and 30231, the Coastal Commission supports a three - pronged
approach to water quality management: site design, source control and treatment control of
BMPs. New development and redevelopment projects that are within the coastal zone are
required to apply for a coastal development permit (CDP) through the Coastal Commission
prior to construction. As part of the CDP process, projects must demonstrate water quality
protection with the implementation of site design, source control, and treatment control BMPs.
State Water Resources Control Board
In the State of California, the State Water Resources Control Board (SWRCB) and local
Regional Water Quality Control Boards (RWQCBs) have assumed the responsibility of
implementing US EPA's NPDES Program and other programs under the CWA, such as the
Impaired Waters Program and the Antidegradation Policy. The primary quality control law in
California is the Porter - Cologne Water Quality Act (Water Code Sections 13000 et seq.).
Under Porter - Cologne, the SWRCB issues joint federal NPDES Storm Water permits and state
Waste Discharge Requirements (WDRs) to operators of municipal separate storm sewer
systems (MS4s), industrial facilities, and construction sites to obtain coverage for the storm
water discharges from these operations.
Basin Plan Requirement
In addition to its permitting programs, the SWRCB, through its nine RWQCBs, developed
Regional Water Quality Control Plans (or Basin Plans) that designate beneficial uses and
water quality objectives for California's surface waters and groundwater basins, as mandated
by both the CWA and the state's Porter - Cologne Water Quality Control Act. Water quality
standards are thus established in these Basin Plans and provide the foundation for the
regulatory programs implemented by the state. The Santa Ana RWQCB's Basin Plan, which
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covers the Newport Banning Ranch project area, specifically (i) designates beneficial uses for
surface waters and ground waters, (ii) sets narrative and numerical objectives that must be met
in order to protect the beneficial uses and conform to the state's antidegradation policy, and
(iii) describes implementation programs to protect all waters in the Region." In other words,
the Santa Ana RWQCB Basin Plan provides all relevant information necessary to carry out
federal mandates for the antidegradation policy, 303(d) listing of impaired waters and related
TMDLs, and provides information relative to NPDES and WDR permit limits.
303(d) List of Water Quality Limited Segments
Under Section 303(d) of the CWA, states are required to identify water bodies that do not
meet their water quality standards. Once a water body has been listed as impaired, a Total
Maximum Daily Load (TMDL) for the constituent of concern (pollutant) must be developed for
that water body. A TMDL is an estimate of the daily load of pollutants that a water body may
receive from point sources, non -point sources, and natural background conditions (including
an appropriate margin of safety), without exceeding its water quality standard. Those facilities
and activities that are discharging into the water body, collectively, must not exceed the TMDL.
Storm water runoff from the project site ultimately discharges into the Lowland Area, Semeniuk
Slough as well as into the Santa Ana River Tidal Prism & Newport Slough. These water bodies
are not listed as impaired according to the 2006 303(d) list published by the Santa Ana
RWQCB (Region 8), and do not have any TMDLs in place. However, according to the 2008
California 303(d)/305(b) Integrated Report, the Newport Slough is recommended to be listed
as impaired for enterococcus, fecal coliform, and total coliform.1z Once approved by the
SWRCB and US EPA, the 303(d) list will then be revised to include the new impairments.
General Construction Permit
The General Construction Permit (GCP), (Order 2009 - 0009 -DWQ), updated by the SWRCB
in September 2009, regulates storm water and non -storm water discharges associated with
construction activities disturbing 1 acre or greater of soil. Construction sites that qualify must
submit a Notice of Intent (NOI) to gain permit coverage or otherwise be in violation of the
CWA and California Water Code.
The GCP requires the development and implementation of a Storm Water Pollution Prevention
Plan (SWPPP) for each individual construction project greater than or equal to 1 acre of
disturbed soil area. The SWPPP must list BMPs that the discharger will use to control sediment
and other pollutants in storm water and non -storm water runoff; the BMPs must meet the BAT
and BCT performance standards. Additionally, the SWPPP must contain a visual monitoring
inspection program; a chemical monitoring program for "non- visible" pollutants; and a
"Regional Water Quality Control Board (RWQCB) Santa Ana Region. Water Quality Control Plan for the Santa Ana
River Basin (8). January 24, 1995. Updated February 2008.
12 Santa Ana Regional Water Quality Control Board (RWQCB). Final 2008 California 303(d)/305(b) Integrated Report
Supporting Information. Approved by RWQCB Order No. R8- 2009 -0032, April 23, 2009.
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sediment monitoring plan. Section XIV of the GCP describes the elements that must be
contained in a SWPPP.i 13
The Project grading limit is greater than 1 acre within the City of Newport Beach, and is
therefore subject to the storm water discharge requirements of the GCP. The Project will
require submittal of an NOI and preparation of a SWPPP prior to the commencement of soil
disturbing activities. In the Santa Ana Region, the SWRCB is the permitting authority, while the
Santa Ana RWQCB provides local oversight and enforcement of the GCP.
Orange County MS4 Permit (Santa Ana Region)
In January 2002, the Santa Ana RWQCB issued the MS4 Storm Water Permit (WDR Order
R8- 2002 -0010, NPDES Permit No. CAS618030) to the County of Orange and the
incorporated cities of Orange County within the Santa Ana Region. Pursuant to this "third -
term" MS4 permit, the County of Orange and incorporated cities were required to develop a
Drainage Area Management Plan (DAMP). The Orange County Drainage Area Management
Plan (OC DAMP) approved by the Santa Ana RWQCB in early 2002, includes a Model Local
Implementation Program (LIP) for municipalities, such as the City of Newport Beach, to
implement in their jurisdiction.
On May 22, 2009 the Santa Ana RWQCB re- issued the MS4 Permit for the Santa Ana Region
of Orange County (Order No. R8- 2009 -0030, Amended by Order No. R8 -2010- 0062). Re-
issuance of this permit will result in future changes to the OC DAMP and City of Newport
Beach LIP and storm water program. This updated fourth -term MS4 Permit includes new
requirements pertaining to hydromodification" and low impact development (LID) features
associated with new developments and redevelopment projects. Within 12 months after the
permit adoption, the County of Orange as the Principal Permittee must finalize a new Model
Water Quality Management Plan (Countywide Mode WQMP) which incorporates feasibility
criteria for LID and hydromodification requirements. Following the approval of the Model
WQMP by the Santa Ana Regional Board, the City of Newport Beach will be required to
update their LIP and storm water programs, and incorporate the new Model WQMP into their
discretionary approval processes for new development and redevelopment projects. The
Model WQMP and accompanying Technical Guidance Document was approved by the Santa
Ana RWQCB on May 19, 2011 with an effective implementation date of 90 days following
the approval.
City of Newport Beach Water Quality Management Plan (WQMP)
One component of the New Development / Significant Redevelopment Section of the City's
LIP Is the provision to prepare a Water Quality Management Plan (WQMP) for specified
categories of development aimed at reducing pollutants in post - development runoff.
Specifically, a project- specific WQMP includes Santa Ana RWQCB approved BMPs, where
applicable, that address post- construction management of storm water runoff water quality.
This includes operation and maintenance requirements for all structural or treatment control
" http: / /www.waterboards.co.gov /water_issues/ programs /storrnwater /construdion.shtml
Hydromodification is generally defined as the alteration of natural flow characteristics.
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BMPs required for specific categories of developments to reduce pollutants in post -
development runoff to the MEP. The categories of development that require preparation of a
project- specific WQMP as defined in the MS4 Permit include:
• All significant redevelopment projects, where significant redevelopment is defined as
the addition of 5,000 or more square feet of impervious surface on an already
developed site;
• New development projects that create 10,000 square feet or more of impervious
surface (collectively over the entire project site) including commercial, industrial,
residential housing subdivisions, mixed -use, and public projects;
• Automotive repair shops (SIC codes 5013, 5014, 5541, 7532 -7534, and 7536-
7539);
• Restaurants where the land area of development is 5,000 square feet or more
including parking area
• All hillside developments on 5,000 square feet or more, which are located on areas
with known erosive soil conditions or where natural slope is twenty -five percent or
more;
• Developments of 2,500 square feet or more of impervious surface or more, adjacent
to (within 200 feet) or discharging directly into environmentally sensitive areas, such as
areas designated in the Ocean Plan as Areas of Special Biological Significance or
water bodies listed on the CWA Section 303(4) list of impaired waters;
• Parking lots 5,000 square feet or more of impervious surface exposed to storm water
runoff;
Streets, roads, highways and freeways of 5,000 square feet or more of paved surface
shall incorporate US EPA guidance, "Managing Wet Weather with Green
Infrastructure: Green Streets" in a manner consistent with the MEP standard;
• Retail gasoline outlets of 5,000 or more square feet with a projected average daily
traffic of 100 or more vehicles per day.
As required by the City of Newport Beach's municipal ordinances on storm water quality
management, the Project WQMP must be submitted to the City for approval prior to the City
issuing any building or grading permits. Since the Newport Banning Ranch Project includes
the development of several of the categories listed above, the Project is therefore subject to
the requirements of the City of Newport Beach WQMP. This includes meeting any new
requirements of the MS4 permit re- issuance, which includes LID features and /or
hydromodification controls once the City's LIP is revised and requirements are implemented
within the City.
General WDR Permit for Groundwater Discharges
Due to the relatively shallow groundwater levels within portions of the region, excess pollutants
in groundwater may pose threats to surface water quality when discharged. Discharges that
may pose a threat to water quality include, but are not limited to, wastes associated with well
installation, development, test pumping, dewatering from subterranean seepage and
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groundwater dewatering wastes from construction sites. The Santa Ana RWQCB requires a
permit for discharges from activities involving groundwater extraction or discharge within the
Santa Ana Region. Under Order No. R8- 2009 -0003 (NPDES No. CAG998001), Permittees
(dischargers) are required to monitor discharges to surface waters that pose an insignificant
(de minimus) threat to water quality. Alternatively, long -term or permanent discharges from
groundwater extraction or dewatering activities may require a separate individual permit
issued by the RWQCB.
Based on the depths to groundwater within the proposed grading areas, construction
dewatering is not anticipated as part of the proposed Project. Should groundwater be
encountered and require dewatering, the Project shall apply for coverage and adhere to the
monitoring and reporting program under Order No. R8- 2009 -0003.
5.2 PREDICTED POLLUTANTS AND SOURCES
The pollutants of concern for water quality are those pollutants that are anticipated (expected)
or potentially could be generated by the Project, based on past and proposed land uses,
along with those pollutants that have been identified by regulatory agencies as potentially
impairing beneficial uses in receiving water bodies. Based on the projected land uses of the
Newport Banning Ranch project site, the pollutants of concern can be divided up into
anticipated pollutants and potential pollutants. 15 Anticipated and potential pollutants for the
Project's general land use categories are summarized in Table 5.1, and pollutants are briefly
described thereafter.
Source: California Stormwater Quality Association. Stormwater Best Management Practices (BMP) Handbooks for New
Development and Redevelopment. January 2003.
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POLLUTANTS OF CONCERN
Priority Project Categories
N
=�
and /or
rn °a
a
E
o
° o
o
rn
cct tur
P
'
O o
o
O
m
°
O
Detached Residential Development
X
X
X
X
X
X
X
Attached Residential Development
P
X
X
X
X
P°
P6
Commercial /Industrial Development
P`
P
P.
P.
Pe
P°
X
P°
X
Restaurants
X
X
X
X
Hillside Development >10,000ft2
X
X
X
X
X
X
X
Parking Lots
P'
X
P.
P°
Xd
P°
X
P°
X
Streets, Highways & Freeways
Pt
X
P°
P°
Xd
X
X
P°
X
X Anticipated
P Potential
Source: County of Orange Flood Control District, 2003. Drainage Area Master Plan, Table 7 -1.3, July 1, 2003.
a A potential pollutant if landscaping or open area exist on -site.
b A potential pollutant if the project includes uncovered parking areas.
c A potential pollutant if land use involves food or animal waste products.
d Including petroleum hydrocarbons.
e Including solvents.
f Analyses of pavement runoff routinely exhibit bacterial indicators.
Table 5.1 Anticipated and potential pollutants of concern for Project land use categories.
• Bacteria /Pathogens. Elevated pathogens are typically caused by the transport of
human or animal fecal wastes from the watershed. Runoff that flows over land such
as urban runoff can mobilize pathogens, including bacteria and viruses. Even runoff
from natural areas can contain pathogens (e.g., from wildlife, plant matter and soils).
Other sources of pathogens in urban areas include pets and leaky sanitary sewer
pipes. The presence of pathogens in runoff can impair receiving waters. Total and
fecal coliform, enterococcus bacteria, and E. coli bacteria are commonly used as
indicators for pathogens due to the difficulty of monitoring pathogens directly.
Trace Metals. The primary sources of trace metals in storm water are metals typically
used in transportation, buildings and infrastructure and also paints, fuels, adhesives
and coatings. Copper, lead, and zinc are the most prevalent metals typically found in
urban runoff. Other trace metals, such as cadmium, chromium, mercury are typically
not detected in urban runoff or are detected at very low levels.16 Trace metals have
the potential to cause toxic effects on aquatic life and are a potential source of
groundwater contamination.
16 Los Angeles County, 2000. Los Angeles County 1994 -2000 Integrated Receiving Water Impacts Report. Los Angeles
County Department of Public Works, Alhambra, CA, September 2000.
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Nutrients. Nutrients are inorganic forms of phosphorous and nitrogen. The main
sources of nutrients in urban areas include fertilizers in lawns, pet wastes, failing septic
systems, and atmospheric deposition from automobiles and industrial operations. The
most common impact of excessive nutrient input is eutrophication of the receiving
water body, resulting in excessive algal production, hypoxio or anoxia, fish kills and
potential releases of toxins from sediment due to changes in water chemistry profiles.
• Pesticides. Pesticides (including herbicides) are chemical compounds commonly used
to control insects, rodents, plant diseases, and weeds. Excessive application of a
pesticide or impractical application of pesticides (i.e., right before rain events) may
result in runoff containing toxic levels to receiving water bodies and the
microorganisms.
Organic Compounds. Organic compounds are carbon - based, and are typically
found in pesticides, solvents, and hydrocarbons. Dirt, grease, and other particulates
can also adsorb organic compounds in rinse water from cleaning objects, and can be
harmful or hazardous to aquatic life either indirectly or directly.
• Sediment. Sheet erosion and the transport and deposition of sediment in surface
waters can be a significant form of pollution that may result in water quality problems.
Increases in runoff velocities and volumes can cause excessive stream erosion and
sediment transport altering the sediment equilibrium of a stream or channel.
Alternatively, unstable tributaries can result in excess sediment loading into the main
channels thereby increasing the amount of sediment moving downstream during storm
events, such as the Southern Arroyo. Excessive fine sediment, such as total suspended
solids, can impair aquatic life through changes to the physical characteristics of the
stream (light reduction, temperature changes, etc.).
• Trash and Debris. Improperly disposed or handled trash such as paper, plastics and
debris including biodegradable organic matter such as leaves, grass cuttings, and
food waste can accumulate on the ground surface where it can be entrained in urban
runoff. Large amounts of trash and debris can have significant negative impacts on
the recreational value of water bodies. Excessive organic matter can create a high
biochemical oxygen demand in a stream and lower its water quality.
Oxygen Demanding Substances. Oxygen- demanding substances include
biodegradable organic material as well as chemicals that react with dissolved oxygen
in water to form other compounds, such as proteins, carbohydrates and fats, as well
as ammonia and hydrogen sulfide. The oxygen demand of a substance can lead to
depletion of dissolved oxygen in a water body and possibly the development of septic
conditions, resulting in the growth of undesirable organisms and the release of
odorous and hazardous compounds.
Petroleum Hydrocarbons /Oil and Grease. The most common sources of oil and
grease in urban runoff stem from spilled fuels and lubricants, discharge of domestic
and industrial wastes, atmospheric deposition and runoff. Runoff can contain
leachate from roads, breakdown of tires /rubber and deposition of automobile
exhaust. Some petroleum hydrocarbons, such as polycyclic aromatic hydrocarbons
(PAHs), can bio- accumulate in aquatic organisms and are toxic at low concentrations.
Hydrocarbons can be measured in a variety of ways including petroleum
hydrocarbons (TPH), oil and grease, or as individual groups such as PAHs.
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Hydrocarbons can persist in sediment for long periods of time in the environment and
can result in adverse impacts on the diversity and abundance of benthic communities.
5.3 APPROACH
The approach to water quality treatment for the Newport Banning Ranch Project includes
incorporation of site design /low impact development (LID) strategies and source control
measures throughout the site in a systematic manner that maximizes the use of LID features to
provide treatment of storm water and reduce runoff. In accordance with the fourth -term MS4
Storm Water Permit, the use of LID features will be consistent with the prescribed hierarchy of
treatment provided in the Permit, including infiltration, evapotranspiration, harvest /re -use and
bio- treatment." Infiltration within the development areas will be limited due to several
constraints but promoted within the Lowlands and Arroyo canyon bottoms. The Project intends
to maximize the use of evapotranspiration on -site to allow for nourishment of habitat areas,
particularly in the Lowland Area. Harvest and water reuse opportunities will be fairly limited
based on several factors, including a reduced irrigation demand due to use of California
native vegetation, existing codes that limit reuse for human health reasons and the limited
areas within the residential development plan that allow for efficient collection, storage and
reuse. More specifically, the use of cisterns or other storage devices are not likely to have
sufficient demand to drain the systems within a timely manner, thereby reducing water quality
protection from rain events that occur within short time frames of one another (i.e., back -to-
back storms). The use of bio- treatment incorporated into the design of the LID features and
treatment control BMPs will be a primary form of treatment prior to discharging these flows
into the Lowland Area and Arroyos for additional infiltration and evapotranspiration
opportunities.
For those areas of the site where LID features are not feasible or do not meet the feasibility
criteria, treatment control BMPs with bio- treatment enhancement design features will be
utilized to provide treatment. Thus, for purposes of CEQA impact assessment, treatment
control BMPs will serve as the primary mechanism to demonstrate the Project's ability to treat
the required design capture volume per the fourth -term MS4 Permit (also referred to as "first -
flush"). Where applicable, LID features will be analyzed to demonstrate their ability to treat
portions of the required design capture volume and reduce the size of downstream regional
treatment control BMPs.
In addition to the use of on -site treatment control BMPs and LID features, it is the intent of the
Project to improve the quality of off -site runoff that passes through the property to the Southern
Arroyo. A regional water quality basin is proposed to provide treatment of runoff from the 16'h
Street drainage area of the City of Costa Mesa. This basin will provide a significant regional
benefit to water quality protection and the basin will also serve to reduce the peak flow rates
entering the Southern Arroyo, thereby reducing scour potential for the long -term stability of the
natural drainage channel (see Section 5.3.5 for further discussion).
Consistent with regulatory requirements and design guidelines for water quality protection, the
following principles are being followed for the Project and will be supported by construction
" Section XII.C.1 of Order No. R8- 2009 -0030.
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level documents in the final Water Quality Management Plans (WQMPS) per each phase of
development and prior to grading permit(s) issuance by the City of Newport Beach:
• Where feasible, LID features will be sized for water quality treatment credit according
to local Regional Board sizing criteria as defined in the fourth -term MS4 Storm Water
Permit for either flow -based or volume -based BMPs. There will be a significant effort
to integrate LID techniques within the internal development areas (site design
objectives), thereby providing treatment of low -flow runoff directly at the source and
runoff reduction of small (i.e., more frequent) storm event runoff (first - flush). In most
instances, LID features will be sized by volume -based analyses to demonstrate
compliance with the required design capture volume for the Project.
• All LID features identified in this report are preliminary in nature but have been sized to
show their relative footprint requirements for technical planning purposes (siting,
treatment volumes, typical profiles, etc.). Detailed drainage calculations, grading, and
confirmation of sizing to occur during the detailed design phase and subsequent
WQMP documentation.
• Where feasible, LID features will be designed to infiltrate and /or reuse treated runoff
on -site in accordance with feasibility criteria as defined in the new Countywide Model
WQMP (approved May 19, 2011). Infiltration within the upper Mesa development
area will be limited based on a number of factors that will influence the amount of
allowable infiltration of the design capture volume, including:
o For development areas residing on the elevated portions of the site (Mesa
area), deep infiltration of storm water runoff into the underlying terrace
deposits and San Pedro Formation within the Mesa should be minimized per
geotech recommendations.t0
o Soil type D is the most predominate soil type within the proposed
development areas of the Mesa, indicating limited infiltration opportunities.19
o The project site is not located in a groundwater recharge zone thereby
eliminating the long -term benefits of groundwater recharge for future aquifer
replenishment.
o The City of Newport Beach limits infiltration on development areas adjacent
to coastal bluff -tops to minimize surface or sub - surface seepage into the
canyons through the bluffs.
For those areas of the project where infiltration is not recommended or acceptable, LID
features will be designed to treat runoff and discharge controlled effluent flows to downstream
habitat areas, or will be collected for on -site re -use such as irrigation. In some circumstances,
treated flows may be discharged off -site in accordance with the new Model WQMP feasibility
criteria for bio- treatment and other approved treatment methods.
's GMU Geotechnical, Inc. Report of Geotechnical Studies Proposed Newport Banning Ranch Development, City of
Newport Beach, County of Orange. Draft March 2008.
19 Williamson and Schmid, Civil Engineers, and Orange County Environmental Management Agency. Orange County
Hydrology Manual. October 1986.
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5.3.1 CONSTRUCTION BEST MANAGEMENT PRACTICES
The updated GCP, Order No. 200- 0009 -DWQ, uses a risk -based approach for controlling
erosion and sediment discharges from construction sites, since the rates of erosion and
sedimentation can vary from site to site depending on factors such as duration of construction
activities, climate, topography, soil condition, and proximity to receiving water bodies. The
updated GCP identifies three levels of risk with differing requirements, designated as Risk
Levels 1, 2 and 3, with Risk Level 1 having the fewest permit requirements and Risk Level 3
having the most - stringent requirements.
The Risk Assessment incorporates two risk factors for a project site: sediment risk (general
amount of sediment potentially discharged from the site) and receiving water risk (the risk
sediment discharges can pose to receiving waters). Sediment risk from a project site is
determined utilizing a derivative of the Revised Universal Soil Loss Equation ( RUSLE), a model
developed by the US Department of Agriculture (USDA) and is utilized by the US EPA for
estimating rates of soil loss at construction sites during rain events. Utilizing RUSLE, the
sediment risk for the project site is thus determined by the following equation:
Where: A
R
K
LS
C
P
A = (R)(K)(LS)(C)(P) (5.1)
rate of sheet and rill erosion, in tons /acre
rainfall - runoff erosivity factor
soil erodibility factor
length -slope factor
cover factor (erosion controls)
management operations & support practices
(sediment controls)
The GCP provides the following procedure for determining the RUSLE equation factors for
construction sites:
R- Factor: Analyses of data indicated that when factors other than rainfall are held
constant, soil loss is directly proportional to a rainfall factor composed of total storm
kinetic energy (E) times the maximum 30 -min intensity (130).20 The numerical value of
R is the average annual sum of E130 for storm events during a rainfall record of at
least 22 years. "Isoerodent" maps were developed based on R- values calculated for
mare than 1,000 locations in the Western U.S. The maps may be utilized to
determine the Standard Risk Assessment, and have been included in Appendix 1 of the
GCP. A hand - calculation may also be utilized to determine the site's R- Factor, either
by utilizing the methodology described in USDA's Agricultural Handbook 703,
Predicting soil erosion by water: A guide to conservation planning with the Revised
20 United States Department of Agriculture (USDA). Predicting Rainfall Erosion Losses A Guide to Conservation Planning.
Agriculture Handbook 537. December 1978.
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Universal Soil Loss Equation (RUSLE), or the EPA's R -value Risk Calculator (available at
htto: / /cfoub.epa. aov/ nodes/ stormwater /LEW /lewCalculator.cfm).
• K- Factor: The soil - erodibility factor K represents: (1) susceptibility of soil or surface
material to erosion, (2) transportability of the sediment, and (3) the amount and rate
of runoff given a particular rainfall input, as measured under a standard condition.
The site - specific K- factor may be determined using the nomograph method as shown
in Appendix 1 of the GCP based on a particle -size analysis (ASTM D -422) performed
for the soils at the project site.
• LS Factor: The effect of topography on erosion is accounted for by the LS factor,
which combines the effects of a hillslope- length factor, L, and a hillslope- gradient
factor, S. Generally speaking, as hillslope length and /or hillslope gradient increase,
soil loss increases. As hillslope length increases, total soil loss and soil loss per unit
area increase due to the progressive accumulation of runoff in the downslope
direction. As the hillslope gradient increases, the velocity and erosivity of runoff
increases. The weighted average LS factor may be determined using the LS Table
located in Appendix 1 of the GCP.
Alternatively, K and LS factors can be derived from Figure 14 on the following page,
provided by the SWRCB. This alternative method is termed the GIS Map Method. The
map is a geographical representation of combined K and LS factors for the State of
California.
C- Factor: Cover factor based on erosion controls. Assumed to equal 1.0 to simulate
bare ground conditions. The implementation of erosion control measures for the
proposed project during construction will reduce the C- Factor to less than 1.0, thereby
reducing the erosion potential.
• P- Factor: Management operations and support practices for sediment controls.
Assumed to equal 1.0 to simulate bare ground conditions. The implementation of
sediment control measures for the proposed project during construction will reduce the
P- factor to less than 1.0, thereby reducing the sediment loss potential.
FUSCOE ENGINEERING, INC. 88
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P: \Projects\ 821 \01 \Wot \GlSwat \MXD \EIR Figures &Exhibits \pdf\Fig 15 GISMapK &LSFactors.pdf
NEWPORT BANNING RANCH Figure 15: GIS Map Method for Determining K and LS Factors
-= FUSCOE
1 1 1 1 1 1 1 1 1 1 1
June 30, 2011
NOT TO SCALE
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With both the C- Factor and P- Factor set at 1.0 to simulate bare ground conditions rather than
utilizing values to simulate conditions where construction is taking place, sediment risk is
condensed to multiplying R, K, and LS factors from RUSLE (Equation 5.1). The resultant risk
of soil loss (A), measured in tons per acre, is then categorized as Low, Medium, or High based
on the following breakdown:
A < 15 tons /acre = Low Sediment Risk
A > 15 and < 75 tons /acre = Medium Sediment Risk
A > 75 tons /acre = High Sediment Risk
The second risk factor in performing a Risk Assessment is Receiving Water Risk. The Receiving
Water Risk is based on whether or not the project site drains to a sediment - sensitive water
body or a water body with spawning, reproduction, and development (SPAWN), cold
freshwater habitat (COLD), and fish migration (MIGRATORY) beneficial uses as designated in
the region's Basin Plan. The GCP identifies a High Receiving Water Risk if the project's
receiving water meets at least one of the above characteristics. If the project does not
discharge to a water body that meets one of the above categories, it is considered a Low
Receiving Water Risk. The receiving water conditions that result in a High Receiving Water
Risk is summarized below:
• The disturbed area discharges (either directly or indirectly) to a 303(d)- listed water
body impaired by sediment.
• The disturbed area discharges to a water body that has a US EPA - approved TMDL
implementation plan for sediment.
• The disturbed area discharges to a water body with designated beneficial uses of
SPAWN, COLD, & MIGRATORY per the region's Basin Plan (see Section 2.2).
The resultant risk levels for Sediment Risk and Receiving Water Risk is then assessed in a matrix
to determine the combined risk level, based on a scale of 1 to 3. The combined risk level
matrix is presented as Table 5.2.
COMBINED RISK LEVEL MATRIX
Sediment Risk
Low
Medium
High
o
Low
Level l
Level
c
High
Level
Level
Table 5.2 Combined construction site risk level matrix
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Based on the Risk Level a project falls under, different sets of regulatory requirements are
applied to the site. The main difference between Risk Levels 1, 2, and 3 are the numeric
effluent standards. In Risk Level 1, there are no numeric effluent standard requirements, as it
is considered a low Sediment Risk and low Receiving Water Risk (see matrix above). Instead,
narrative effluent limits are prescribed. In Risk Level 2, Numeric Action Levels (NALs) of pH
between 6.5 -8.5 and turbidity below 250 NTU are prescribed in addition to the narrative
effluent limitations found in Risk Level 1 requirements. Should the NAL be exceeded during a
storm event, the discharger is required to immediately determine the source associated with
the exceedance and to implement corrective actions if necessary to mitigate the exceedance.
For a Risk Level 3 site, Numeric Effluent Limits (NELs) are applied in addition to the narrative
and numeric effluent standards prescribed for a Risk Level 2 site. Risk Level 3 dischargers are
subject to a pH NEL of 6.0 -9.0 and a turbidity NEL of 500 NTU. Once on NEL is exceeded,
the construction site is considered in violation of the GCP.
GCP Application to Newport Banning Ranch
At this stage in the Newport Banning Ranch Project, a detailed, site- specific Risk Assessment
cannot be performed at this time, since it is unclear how the Project's development will be
phased over ❑ yet to be determined timeline. However, for the purposes of identifying
potential impacts during construction at the CEQA level, a preliminary Risk Assessment of the
Project in its entirety can be performed.
The sediment risk analysis component was evaluated utilizing the Standard Method outlined in
Appendix 1 of the GCP. Based on an assumption of a construction timeline of three21 years to
identify the preliminary sediment risk, an R- Factor value of 120.01 was returned by the US
EPA's R -value Risk Calculator. Utilizing the GIS Map Method (Figure 14), a combined K and
LS Factor of 1.5 was determined. As a result, a preliminary sediment risk value (A) of 180
tons per acre was obtained. The Newport Banning Ranch Project is therefore considered a
High Sediment Risk, since its rate of sheet and rill erosion under bare ground conditions is
anticipated to be greater than 75 tons per acre over the lifetime of the project. This number,
however, is not based on the site - specific conditions nor does it account for the use of any
erosion control, sediment control and scheduling controls when assigning the theoretical
sediment risk value.
NEWPORT BANNING RANCH SEDIMENT RISK FACTOR
R K " LS A Sediment Risk
120.01 1.5 180 tons /acre > 75 tons /acre = High Sediment Risk
Table 5.3 Preliminary sediment risk factor for Newport Banning Ranch
Ultimately, construction may occur in two primary phases over a longer time period (i.e., 5 -7 years). Site - specific
sediment Risk Assessments will be performed prior to construction.
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In terms of Receiving Water Risk, the Newport Banning Ranch Project's receiving water body
according to the Basin Plan (the Tidal Prism of the Santa Ana River & Newport Slough) is not
303(d) listed for sediment and is not subject to a sediment TMDL.22 Furthermore, the receiving
water body does not contain the beneficial uses of SPAWN, COLD, & MIGRATORY. The
Project can therefore be considered a Low Receiving Water Risk.
Based on the assessment above, the Newport Banning Ranch Project is categorized as a Risk
Level 2 site. This is illustrated in the matrix below.
NEWPORT BANNING RANCH
COMBINED RISK LEVEL MATRIX
Sediment Risk
Low
Medium
High
L
a
Low
Level l
Level
3
Y
N
C
High
Level
Level
Table 5.4 Combined risk level matrix for Newport Banning Ranch
Risk Level 2 Requirements
Attachment E of the GCP identifies the following requirements for Risk Level 2 dischargers:
• Implement minimum BMPs as outlined in Attachment D, Sections B through G of the
GCP and briefly described in the preceding section.
• Develop Rain Event Action Plans (REAPS) designed to protect exposed portions of the
site during predicted precipitation events. The REAPs must be developed and
implemented within 48 hours of the predicted rain event (50% chance or greater), and
be developed for all phases of the construction (i.e., grading, vertical construction
phase, landscaping, final stabilization, etc.) for each rain event.
• Implement Visual Monitoring (Inspection) requirements for qualifying rain events23 at
minimum frequencies identified in Attachment D, Section I of the GCP.
• Conduct storm water effluent sampling for pH and turbidity at a minimum of three (3)
samples per day for each qualifying rain event to determine whether any exceedances
of NALs have occurred. In the event that an exceedance of a NAL occurs, the
discharger shall submit an NAL Exceedance Report to the SWRCB no later than 10
days after the conclusion of the rain event.
22 Santa Ana Regional Water Quality Control Board (RWQCB). 2006 Clean Water Act Section 303(d) List of Limited
Water Quality Segments. October 25, 2006.
23 "Qualified Rain Event" is defined by the GCP as "Any event that produces 0.5 inches or more precipitation with a 48
hour or greater period between rain events."
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• Conduct non -storm water discharge sampling where any non -storm water discharges
occurred.
In the event turbidity exceedances are observed during the required storm event monitoring,
the site erosion and sediment controls shall be evaluated to improve effectiveness. If
necessary, Active Treatment Systems (ATS) may be utilized to reduce sediment in storm water
effluent.
Active Treatment System (ATS) Requirements
For sites that implement ATS to reduce sediment and /or turbidity from the site (regardless of
Risk Level), the GCP requires the following to be implemented as described further in
Attachment F of the GCP.
• Prepare and submit an ATS Plan to the SWRCB prior to 14 days of operation that
includes the following:
o ATS Operation and Maintenance Manual for all equipment
o ATS Monitoring, Sampling & Reporting Plan, including associated quality
assurance /quality control (QA/QC) information.
o ATS Health & Safety Plan
o ATS Spill Prevention Plan
• Design the ATS to capture and treat (within a 72 hour period) a volume equivalent to
the runoff from a 10 -year, 24 -hour storm event using a watershed runoff coefficient of
1.0.
Conduct, at a minimum, six site - specific jar treatment tests as well as conduct required
chemical residual and toxicity tests per Attachment F, Section E of the GCP.
• Ensure the ATS meets the turbidity NELs per Attachment F, Section I of the GCP.
• Conduct ATS monitoring requirements in accordance with Attachment F, Section M of
the GCP.
Construction BMP Implementation
Based on a preliminary analysis, the proposed Project falls under the Risk Level 2 category.
Prior to commencement of construction activities, the SWPPP will be prepared in accordance
with the site - specific sediment risk analyses based on the final rough grading plans and
erosion and sediment controls proposed for each phase of construction. The phases of
construction will define the maximum amount of soil disturbed, the appropriate sized sediment
basins and other control measures to accommodate all active soil disturbance areas and the
appropriate monitoring and sampling plans.
Table 5.5 on the following pages is a general guideline for the minimum BMPs required at all
active areas of construction within the Newport Banning Ranch Project. An effective
combination of erosion and sediment controls should be selected based on the specific site
conditions, in particular during major soil disturbing activities. Good housekeeping practices,
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such as waste and materials management, non -storm water management, and tracking
controls should be implemented at all times.
CASQA BMP
ID
EROSION CONTROL
MINIMUM
REQUIREMENT
FC -1
Scheduling
X
EC -2
Preservation of Existing Vegetation
X
EC -3
Hydraulic Mulch
X.
EC -4
Hydroseeding
X.
EC -5
Soil Binders
X.
EC -6
Straw Mulch
X°
EC -7
Geotextiles and Erosion Control Mats
X°
EC -8
Wood Mulching
EC -9
Earth Dikes and Drainage Swales
EC -10
Outlet Protection and Velocity Dissipation Devices
EC -11
Slope Drains
EC -12
Streambank Stabilization
SEDIMENT CONTROL
SE -1
Silt Fence
Xb
SE -2
Sediment /Desalting Basin
SE -3
Sediment Trap
SE -4
Check Dam
SE -5
Fiber Rolls
Xb
SE -6
Gravel Bog Berm
x
SE -7
Street Sweeping and Vacuuming
X b
SE -8
Sandbag Barrier
SE -9
Straw Bale Barrier
SF -10
Storm Drain Inlet Protection
X
WIND EROSION CONTROL
WE -1
Wind Erosion Control
X
TRACKING CONTROL
TR -1
Stabilized Construction Entrance /Exit
X
TR -2
Stabilized Construction Roadway
TR -3
Entrance /Outlet Tire Wash
NON -STORM WATER MANAGEMENT
NS -1
Water Conservation Practices
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CASQA BMP
ID
WRAME
MINIMUM
REQUIREMENT
NS -2
Dewatering Operations
X`
NS -3
Paving and Grinding Operations
NS -4
Temporary Stream Crossing
NS -5
Clear Water Diversion
NS -6
Illicit Connection /Illegal Discharge Detection and Reporting
X
NS -7
Potable Water /Irrigation
NS -8
Vehicle and Equipment Cleaning
X
NS -9
Vehicle and Equipment Fueling
X
NS -10
Vehicle and Equipment Maintenance
X
NS -11
Pile Driving Operations
NS -12
Concrete Curing
NS -13
Concrete Finishing
NS -14
Material and Equipment Use Over Water
NS -15
Demolition Adjacent to Water
NS -16
Temporary Batch Plants
WASTE MANAGEMENT AND MATERIALS POLLUTION CONTROL
skill
WM -1
Material Delivery and Storage
X
WM -2
Material Use
X
WM -3
Stockpile Management
X
WM -4
Spill Prevention and Control
X
WM -5
Solid Waste Management
X
WM -6
Hazardous Waste Management
WM -7
Contaminated Soil Management
WM -8
Concrete Waste Management
WM -9
Sanitary /Septic Waste Management
X
WM -10
Liquid Waste Management
Source: Coltrons Stormwater Quality Handbooks, Construction Site Best Management Practices Manual (March 1, 2003).
California Stormwater Quality Association (CASQA). California Stormwater BMP Handbook for Construction. January, 2003.
a Contractor shall select one of the five measures listed or a combination thereof to achieve and maintain the contract's
rainy season disturbed soil area (DSA) requirements
b Contractor shall select one of the three measures listed or a combination thereof to achieve and maintain the contract's
rainy season disturbed soil area (DSA) requirements
c Required if groundwater is encountered during construction activities. May also require coverage under Order No. RS-
2009 -0009 General Waste Discharge Requirements for Discharges to Surface Waters Which Pose an Insignificant (de
minimus) Threat to Water Quality (Dewaterin Permit).
Table 5.5 Minimum guidelines for construction storm water management BMPs.
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Though site - specific details of how construction activities will be phased for Newport Banning
Ranch is not available at this point in time, it is identified in the GCP that typical tract home
developments can be divided into 4 general phases of construction: (1) mass & rough
grading, (2) utility and road installation, (3) vertical construction, and (4) final stabilization and
landscaping. Therefore, BMP implementation can be evaluated for the Project in this general
context. Further details on individual BMPs will be documented in the project SWPPP based
on the final rough grading plans for the Project.
Mass Grade, Rough Grade & Oil Remediation
During mass and /or rough grading, a substantial amount of soil disturbing activities or
earthwork will occur. As a consequence, soil loss potential will be at its highest risk level to
exceed NALs specified for Risk Level 2 sites. Therefore, an effective combination of erosion
and sediment controls must be implemented during this phase of construction. Table 5.6 is a
guideline for erosion and sediment control applications for this region.
EROSION /SEDIMENT CONTROL APPLICATION GUIDELINES
Season
Construction BMP
Slope (V:H)
:51:20
> 1:20
<_1:4
> 1:4
<1:2
>1:2
INACTIVE
Rainy
Erosion Control
X
X
X
X
Sediment Control
X
X
X
Desilting Basin
DSAs
Non -Rainy
Erosion Control
Sediment Control
X
Desilting Basin
ACTIVE
Rainy
Erosion Control
Sediment Control
X
X
X
Desilting Basin
X
DSAs
Non -Rainy
Erosion Control
Sediment Control
Desilting Basin
Source: Caltmns Stormwater Quality Handbooks, Construction Site Best Management Practices Manual (March 1, 2003).
DSA— Disturbed Soil Area
Table 5.6 Guidelines for erosion and sediment control practices.
This region requires the use of sediment basins to control the amount of sediment discharged
off -site during the rainy season (i.e., October 1 through April 30 each year).
Sediment /desilting basins generally act as primary sediment control facilities at downstream
locations that provide final polish of runoff prior to discharging off -site. Therefore, they are a
major element in a project's erosion and sediment control design. According to the California
Stormwater Quality Association's (CASQA) sediment basin design guidelines, approximately
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3,600 ft' of basin storage volume must be provided per acre of drainage area during this
phase.
Vb.,j� = (3,600 ft'/ac) * (A) (5.2)
Where: Vba,;n = minimum basin storage volume in cubic feet (ft)
A = drainage area (acres)
Over an anticipated disturbance area of 175 acres, this equates to 630,000 ft' of storm
runoff storage capacity. Based on a minimum ponding depth of 3 ft, at least 4.82 acres is
needed for sediment /desilting basin implementation. A maximum of 75 acres of tributary
area is allowed to drain to a sediment basin. Therefore, the project site will require at least
three (3) sediment /desilting basins.
Vb.,;, = (3,600 ft3 /a c) * (175 ac)
Vbo,j� = 630,000 W
It is unlikely that there will be a need for ATS for the Project, since it is not a Risk Level 3 site.
However, should the application of traditional erosion and sediment control BMPs not achieve
compliance with the turbidity NAL of 250 NTU for the Project or prove infeasible, the
discharger may elect to implement ATS to control sediment discharges. Under this alternative,
the ATS must be designed to capture and treat a volume of runoff equivalent to a 10 -year,
24 -hour storm event, using a watershed runoff coefficient of 1.0. According to the Orange
County Hydrology Manual Table B.2., this is equivalent to a rainfall depth of 3.68 inches.
VATS= C * 110,r -24h, * A (5.3)
Where: VATS = ATS minimum treatment volume in cubic feet (ft')
C = runoff coefficient (unitless)
11OYr-24h, = 10 -year, 24 -hour storm event (in inches)
A = drainage area (in acres)
Therefore, a capture and treat volume of 2,338,000 ft' would be needed for ATS. Assuming
a 3 ft ponding depth, approximately 17.9 acres of land area would be needed to
accommodate runoff storage for a 1 75 -acre project area for ATS .24
VATS = (1.0) * (3.68 in.) * (175 ac) * (1 ft /12in.) * (43,560 ft2 /ac)
VATS = 2,338,000 ft3
Utility and Road Installation
In addition to the erosion and sediment control BMP requirements for the rough grading
phase, the utility and road installation phase will introduce materials to the Project that may
cause or contribute to exceedances in the pH NAL for Risk Level 2 sites. Materials include, but
are not limited to hydrated lime, concrete, mortar, Portland cement treated base, and fly ash.
24 Depth of holding ponds can be increased to reduce the land area needed for ATS.
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For this reason, pH levels must be controlled at this stage through non -storm water
management and waste and materials management BMPs. Stockpile management will also
be important due to the trenching activities involved in utility installation. Minimum BMPs are
summarized in Table 5.5. Should NALs be exceeded at any point in time, additional site
management or "good housekeeping" BMPs shall be implemented and the source of
pollution controlled.
Vertical Construction
Once utilities and roads are in place, sediment controls (such as sediment /desilting basins)
found in the rough grade phase may no longer be applicable as previously designed, due to
the installment of curb and gutter, catch basins, and storm drain infrastructure to convey
runoff off -site per the post- construction condition. BMPs at this stage will thus be more
focused on on -lot sediment control BMPs and at discharge points (i.e., catch basin inlet
protection). Erosion control BMPs for manufactured slopes should be in place and require
periodic maintenance to retain their integrity. During vertical construction, a substantial
amount of construction materials will be delivered to the site, and wastes generated from the
site have the potential to negatively impact pH levels. Therefore, non -storm water
management and waste and materials management BMPs will be employed regularly.
Minimum BMPs are summarized in Table 5.5.
Final Stabilization and Landscaping
During final stabilization and landscaping, minimal construction will be taking place and the
majority of the project site will be stabilized. The majority of activities will involve planting and
landscaping lots and common areas. Finished slopes that have not been landscaped will also
be planted. Sediment control at discharge locations and stockpile management will be of
primary concern. Good housekeeping practices will continue in this phase of construction.
Minimum BMPs are summarized in Table 5.5.
5.3.2 POST - CONSTRUCTION BEST MANAGEMENT PRACTICES
Post- construction BMPs are typically divided into three main categories: site design /LID,
source control and treatment control BMPs. The following sections provide a more in depth
discussion of each category.
Site Design / Low Impact Development BMPs
Careful consideration of site design is a critical first step in storm water pollution prevention
from new developments and redevelopments. In general, site design objectives include a
combination of factors that may include: minimization of impervious surfaces including roads
and parking lots; preservation of native vegetation and root systems; minimization of erosion
and sedimentation from susceptible areas such as slopes; incorporation of water quality
wetlands, bio- filtration swales, etc. where such measures are likely to be effective and
technically and economically feasible; and minimization of impacts from storm water and
urban runoff on the biological integrity of natural drainage systems and water bodies.
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Many of the site design BMPs may also be considered low impact development (LID) features.
The goal of using LID features is to mimic the sites existing hydrology by using design
measures that capture, filter, store, evaporate, detain and /or infiltrate runoff, rather than
runoff flowing directly to piped or impervious systems. This includes directing runoff to
vegetated areas, protecting native vegetation, and reducing the amount of impervious
surfaces. Many LID features can also serve as treatment control BMPs when sized properly to
accommodate the design capture volume of runoff from storm events. The incorporation of
site design BMPs and LID features may reduce the need and /or sizing of treatment control
BMPs needed for the site.
Overall, primary site design includes the integration and emphasis of landscaping features to
provide treatment of runoff and control the rate and volume of runoff from impervious
surfaces.
Source Control BMPs
Source control BMPs are operational practices that reduce potential pollutants at the source,
and include both structural and routine non - structural practices. Example source control
measures include street sweeping, low use irrigation systems, catch basin stenciling, and
providing educational materials for homeowners. A list of typical source control measures for
residential and commercial developments is provided in Appendix E.
Treatment Control BMPs
Treatment control BMPs are structural /engineered systems that are similar to LID features in
that they are sized to capture, filter, and /or treat runoff the required runoff volume or flow
prior to discharging into receiving waters. Treatment control BMPs are typically larger scale
than LID features accommodating larger drainage areas, larger treatment volumes, and are
typically located outside of the core development areas. Structural treatment BMPs may be
located on- or off -site, used singly or in combination with other treatment controls, or may be
shared by multiple communities within the project. Selection of treatment control BMPs is
based on the pollutants of concern of the project site, based on the Project's land use
categories (see Section 5.2) and the BMP's ability to effectively mitigate those pollutants, in
consideration of site conditions and constraints. For the proposed Project, water quality basins
will serve as the treatment control BMPs. These basins are typically located at low points
outside the development areas as demonstrated in Figure 15. Due to the proximity to the
coastal bluff -tops, infiltration opportunities will be limited and in some cases, lining of the
basin floors may be required.
In accordance with local Regional Board water quality treatment requirements, the proposed
water quality basins will be designed to treat runoff from a 24 -hour 85" percentile storm
event, as determined from the local historical rainfall record (termed design capture volume,
or "first- flush "). Treated runoff will typically be distributed to the Lowland Area and Arroyo
canyon bottoms for evapotranspiration and infiltration opportunities, and /or collected and
reused for irrigation purposes within the development areas. In some circumstances, treated
flows may be discharged off -site in accordance with the new Countywide Model WQMP
feasibility criteria for bio- treatment and release of design capture volume flows.
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5.3.3 INTERIOR WATER QUALITY FEATURES
Water quality protection will begin within the interior of the Project development areas (i.e.
resort, hotel, condominiums, parks, common areas, etc.). It is the intent of the overall Project
to include a variety of sustainable design measures that address water quality and quantity.
One of the primary sustainable commitments is to incorporate LID techniques into the design
phase to reduce storm water runoff, and to maximize water quality capture and treatment at
the source. Rather than conveying runoff from small, frequent storm events to storm drains
directly, runoff is directed to landscape features and permeable surfaces (as applicable)
located on -site to reduce runoff volume via evapotranspiration and infiltration. These
techniques may include pocket rain gardens within impervious areas such as courtyards and
common areas, porous /permeable paving integration into traditional impermeable paved
areas, landscaped storm water planters, and use of cisterns for capturing rainwater for re -use
from buildings (condominiums, flats, attached units, resorts, etc.). 25 Provided below is a
summary of the various opportunities for implementation of interior LID features within the
major land use categories proposed for the Project:
• Single - Family Residential: For single - family residences, opportunities exist for
incorporating landscaped areas into the drainage design that can also be aesthetically
pleasing due to their small -scale implementation. Roof runoff and driveway runoff can
drain to landscaped gardens or pocket rain gardens. Rain barrels can also be used to
capture and store roof runoff for reuse as irrigation water. In addition, porous
pavements can be used in driveways and patios to reduce runoff.
Multi- Family Residential /Mixed Use — Although multi - family and mixed use
developments usually have lesser amounts of landscaping than single - family
developments, opportunities exist for draining impervious areas to landscaping on -site
as well as for implementing porous pavements within the parking areas, drive aisles
and other low traffic areas. Roof runoff can drain to landscaping or to cisterns for
reuse as irrigation. Runoff from sidewalks, courtyards, and common areas can be
directed to landscaped areas or to pocket rain gardens. Alternatively, sidewalks and
courtyards may be constructed with porous pavement.
• Resort/Commercial Use: Opportunities for LID implementation in resort, hotel and
other commercial land use areas are similar to those for multi - family and mixed use
developments. Landscaping can be incorporated into the drainage design by
diverting runoff from rooftops and other impervious areas (i.e., sidewalks, parking lots)
to landscaping, storm water planters or pocket rain gardens. Cisterns can be used to
capture runoff from rooftops for reuse as irrigation water, and parking stalls can be
constructed of porous pavement to further reduce runoff.
Incorporation of these features within the interior development areas provide pre- treatment of
storm water runoff, removing large sediment and trash and debris, thereby reducing the
amount of pollutants reaching the larger transitional phase water quality features and
improving their overall effectiveness. In addition, by capturing a portion of the first -flush
zs County of San Diego, Department of Planning and Land Use. Low Impact Development Handbook Stormwater
Management Strategies. December 31, 2007.
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runoff, the volume and flow rate of runoff discharged from these features is reduced. Further
details on the examples of interior LID features are discussed below.
• Cisterns and Rain Barrels: Cisterns are storage vessels that are designed to collect
and store storm water runoff for non - potable uses, such as irrigation water. Cisterns
may be placed either above ground or below ground, placed below decks, or may be
decorative in nature to improve aesthetics. Smaller cisterns, ranging from 75 to 150
gallons, are typically referred to as "rain barrels ", and are typically used at single -
family residences and small buildings. Larger cisterns can range in size from 150
gallons to over 10,000 gallons, and are more typically used at high- density multi-
family housing or larger commercial buildings. Cisterns are typically sized based on
the size of the building and irrigation water demand, and typically are not sized to
treat water quality volume requirements unless provided in large quantities.
• Storm Water Planters: Storm water planters are structural, vegetated planters that
receive storm water runoff from roof downspouts and allow pollutants to filter and
settle out prior to discharging off -site. Runoff collected in the planter filters through a
minimum of 18 inches of soil where vegetation will uptake nutrients (e.g., nitrogen
and phosphorous), microbial contaminants, oil and grease, pesticides, and sediments
and fine particulates can settle out. Treated runoff is drained at the bottom of the
planter through a gravel layer and perforated underdrain system, if necessary based
on soil conditions. In general, storm water planters can be sized with a 0.04 sizing
factor (surface area of planter / surface area of tributary impervious area)."
Common Area Porous Pavement: Permeable pavement, such as permeable pavers,
grass pavers, porous concrete, and porous asphalt, provides a surface suitable for
courtyards, common areas, and other light -load applications in which water can drain
through pore spaces to an underlying rock reservoir (approximately 1 -3 ft deep)
underneath. The sub - surface base allows for physical and microbial filtering
processes to take place thereby removing pollutants such as particulates, organics,
hydrocarbons and total suspended sediments, including attached heavy metals.
Porous pavement can be generally sized based on its capacity to store runoff in the
rock reservoir. In general, an approximate ratio of 25% porous pavement to
impervious pavement is sufficient to accommodate treatment requirements for a
reservoir depth of 10 -12 inches.
• Tree Box Filters: Tree box filters are similar to storm water planters, in that they are a
contained planter that receives storm water runoff. Whereas storm water planters are
typically located above ground and receive roof runoff, tree box filters are installed
below grade along a curb line and receive runoff from streets, sidewalks and other
impervious surfaces. Tree box filters consist of a concrete box containing a filter
media designed to capture and filter pollutants. One tree or large shrub is planted
within the media to provide biological processes to provide additional pollutant
removal. A standard curb inlet catch basin is typically placed immediately
26 LFR Inc. and Dan Cloak Environmental Consulting. Contra Costa Clean Water Program Infiltration Site
Characterization Criteria and Guidance Study, Milestone Report #3. April 1, 2005.
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downstream of the tree box filter to capture high flows that bypass the filter. On
average, one tree box filter can treat up to 0.5 -1 acre of impervious surface.27
• Pocket Rain Gardens: Rain gardens are small, vegetated depressions that promote
filtration of storm water runoff. They combine shrubs, grasses, and flowering
perennials in depressions (approximately 6 -8 inches deep) that allow water to pool,
infiltrate or evaporate and /or slowly drain out within 48 -72 hours. Additional design
details include a soil planting depth between 18 inches to 4 ft deep (depending on
plants selected), with a 2 -3 inch mulch layer on top to protect from erosion.
Perforated underdrains may be provided for soils with low infiltration rates and in
areas with high groundwater levels to discharge treated water back into the storm
drain system. Due to the limited ponding area, pocket rain gardens treat small areas
of adjacent impervious runoff from sidewalks and courtyards, but typically are not
suitable for treating large drainage areas.
The specific details and locations of these measures occur during the detailed design phase of
each community, and will be implemented during the design phase and accounted for in the
project -level WQMPs. All LID site design features sized to handle and retain the design
capture volume (also referred to as "first- flush ") on -site will be identified in the WQMPs and
the downstream treatment control basin sizes will be adjusted accordingly.
5.3.4 TRANSITIONAL PHASE WATER QUALITY FEATURES
The transitional phase refers to those primary streets and travelways that lead into and out of
the development areas. Whereas the interior water quality features provide treatment of runoff
at the source and partial reduction of design capture volume runoff quantities, transitional
phase water quality features provide treatment primarily along the major roadways of the
project. Treatment of runoff mainly occurs through integrated bio- retention type "green street"
features which aids in dropping out particulates, sediment and pollutants adsorbed into
sediment. Green streets incorporate slotted curbs and parkway bioswales with enhanced bio-
filtration zones (biocells) within portions of the landscape setback areas for a variety of
different sized streets within the project area. This allows for the treatment of water quality at
the source as well as the reduction of peak storm water runoff volumes and rates. These
streets will provide the necessary water quality treatment of flows generated from the streets
themselves, and provide treatment of adjacent interior core development areas dependent
upon the volumes available within the LID landscaping features. The use of storm water
treatment within the landscape setback areas of the proposed streets is consistent with the
intent of the US EPA guidance on green streets."
The primary features proposed for the transitional phase are referred to as landscaping
biocells, which will be incorporated into select portions of the parkway bioswales identified in
the arterial and collector street cross sections on the Tentative Tract Map No. 17308. These
features function as a soil and plant -based filtration device that removes pollutants through a
variety of physical, biological, and chemical treatment processes. The major treatment of
2' Filters Bioretention Systems, a division of Amencast. Engineering Design Assistance Kit (DAKit) v08 -WZ. 2009.
as Lukes, R., Klass, C., & Low Impact Development Center. Managing Wet Weather with Green Infrastructure Municipal
Handbook, Green Streets. EPA - 833 -F -08 -009. December 2008.
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runoff occurs through the percolation of runoff through several layers of the biocell within the
parkway bioswale prior to either infiltrating into the ground or collected by sub - drains and
returned back to the storm drain system. Landscaping biocells are typically sized based on the
water stored within the cell and the amount of water filtering through the biocell during storm
events.
Biocells function similarly in nature to bioretention cells and rain gardens but tend to have
shallower depths based on a higher reliance on sand -based soil amendments. Biocells
remove storm water pollutants through processes such as adsorption, filtration, plant uptake,
microbial activity, decomposition, sedimentation and volatilization.29 Adsorption is the
process whereby particulate pollutants attach to soil (e.g., clay) or vegetation surfaces.
Filtration occurs as runoff passes through the biocell media, such as the plant cover and
planting soil which aids in dropping out particulates, sediment and pollutants adsorbed onto
sediment (including, for example certain pesticides and pathogens). Pollutants removed by
adsorption include metals, phosphorus, and hydrocarbons.
The following properties of landscaping biocells within the Green Streets were used to
calculate the water quality treatment potential for these features as an example for the Project:
• 8 -16 inch gravel base above the sub -grade with perforated drainage pipes to remove
any excess water that does not infiltrate
• 18 inch of sandy loam with filter fabric to separate from the gravel base.
8 -12 inch of topsoil
• 2 -4 inch of mulch
• 3 -6 inch ponding depth where the bottom occurs at the top of the mulch and the top
occurs at the spill over elevation where water will bypass the biocell and drain towards
the nearest catch basin inlet when at full capacity.
• The volume of treatment for each cell will be demonstrated by adding the minimum
volume of capacity of each layer with the designed drawdown time (infiltration
capacity) of the storage reservoir for a total volume of treatment (see Table 5.7).
Drainage from the roadways and adjacent lot drainage may be directed to the parkway
bioswales with the landscaping biocell features via sheet flow, curb cuts and shallow first -flush
collection pipes for water quality treatment. In some instances, a surface slope (longitudinally)
may be required within the biocell. In these instances, the slope and ponding depth will be
accounted for in the treatment volume calculation. Figure 16 provides a typical section of a
"green street" and a typical cross section of a biocell within the parkway bioswale. The profile
and depths of the biocell will vary in the final design, and all changes will be accounted for in
the treatment volume calculations. In most instances, it will not be necessary to construct the
biocell sub - surface design feature into all portions of the parkway bioswale locations. Based
on the upstream tributary areas and the treatment capacity of the biocells, only a portion of
the parkway bioswale will need to include the biocell sub - surface design feature to meet the
29 US Environmental Protection Agency (US EPA). Storm Water Phase II Proposed Rule Fact Sheet Series, Fad Sheet 3.0.
April 1999.
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volume treatment requirements of the upstream road runoff (approximately 25% ratio of
biocell to parkway bioswole is needed to treat the road runoff). In the event it is feasible to
direct surface runoff from the lots in addition to the road runoff into the parkway bioswales,
the size of biocell component will be increased accordingly.
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K u iilF' �Il
♦ �t r
W
IM t
& `
I
J
LEGEND
Property Boundary
Proposed Storm Drain
Green Street with Parkway Bioswale
Enhanced Landscaping Biocell
Regional Water Quality Basin
Community W.Q. Basin
Diffuser Basin
rya
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i
Figure 16: Water Quality BMP Plan
June 30, 2011
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In order to determine the maximum treatment potential of the proposed subsurface biocells,
the volume capacity was evaluated to determine if the features could accommodate runoff
from the core development areas in addition to the localized street runoff. More specifically,
the landscaping biocell areas within the parkway bioswale were evaluated to determine the
appropriate volume they could treat based on the upstream tributary drainage areas. Results
of the sizing analyses for the biocell sizing options are summarized in Table 5.7 below.
Detailed calculations are provided in Appendix E.
LANDSCAPING BIOCELL SIZING OPTIONS
Symbol
Parameter
Typical Green Street Landscaping Biacell Dimensions (ft)
5' x 10'
10' x 20'
8'x 100'
10' x 100'
AT
Top Area (ft2)
50
200
800
1,000
A,
Bottom Area (ft')
24
108
392
588
P
Average Ponding Depth (ft)
0.25
0.25
0.25
0.5
M
Mulch Depth (ft)
0.16
0.16
016
0.16
rlM
Mulch Porosity ( %)
0.4
0.4
0.4
0.4
G
Gravel Depth (ft)
0.67
0.67
0.67
0.67
%
Gravel Porosity ( %)
0.4
0.4
0.4
0.4
S
Planting Soil Depth (ft)
0.67
0.67
0.67
0.67
ns
Planting Soil Porosity ( %)
0.3
0.3
0.3
0.3
So
Sand Filter Depth (ft)
1.5
1.5
1.5
1.5
rlso
Sand Filter Porosity ( %)
0.3
0.3
0.3
0.3
T
Total Depth Below Surface (ft)
3
3
3
3
W
Soil Water Content ( %)
0.5
0.5
0.5
0.5
Fp
Infiltration Capacity (in /hr)
0.5
0.5
0.5
0.5
SF
Safety Factor for Infiltration
1
1
1
1
V,
Infiltration Velocity (ft /hr)
0.28
0.28
0.28
0.28
T
Time Infiltration Occurs (hr)
18.6
18.6
18.6
18.6
V,
Forcing Volume (ft')
7
39
149
397
Vva,
Volume in Gravel /Sand /Mulch (ft')
4
58
209
313
V,
Volume in Sand Filter (ft')
2
24
88
132
V,
Volume Infiltrated (ft')
39
155
620
775
Vec
Total Volume Treated (ft')
52
275
1,066
1,618
Note: Table represents sizing for typical landscaping biocell designs to determine average sizing ratios. Detailed calculations
are provided in Appendix E.
Table 5.7 Summary of landscaping biocell water quality sizing options.
Based on the analyses summarized in Table 5.7, an average conservative ratio of 1.3 (cubic
feet treated /square foot of landscaping biocell) was determined to satisfy water quality
requirements. For every square foot of biocell landscaping with the sub - surface profile
parameters set forth above, 1.3 cubic feet of treatment is provided. For example, if 1,100 ft'
of biocell is implemented within a parkway bioswale with a top width of 8' (8'W x 1401), a
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treatment capacity of 1,430 ft' would be accommodated within this parkway. This volume is
equivalent to 0.65 acre of drainage from an 80 % impervious tributary area (e.g., high- density
attached condominiums). Based on these ratios, appropriate landscaping areas can be set
for each development area and integrated within the Green Streets or more internally within to
the development areas.
Table 5.8 below provides a summary of the total acreage of roadways proposed with the
parkway bioswale area for both the arterial streets and the collector streets. The minimum
treatment capacity is based on the assumption that approximately 25 % of the total parkway
acreage will include the biocell subsurface feature, which is sufficient to bio -treat the entire
tributary area of the road. In order to minimize maintenance of the landscaping biocells while
maximizing water quality treatment of runoff from the streets, a minimum length of 25 ft of
parkway bioswale will be provided upstream of each landscaping biocell feature to control
sediments and organic particulates from entering the biocells. so
In specific locations, there may be additional capacity within the parkway bioswales to
accommodate additional biocell enhancement beyond the requirements for treating the
design capture volume for the street drainage. In these locations, the biocells may be
expanded to treat additional runoff from adjacent lots, parking surfaces, and other hordscape
areas. These locations and extent of the biocell enhancement will be documented in the final
WQMPs for the associated phases of development.
GREEN STREET TREATMENT POTENTIAL
Green Street
Minimum
Minimum
Primary
with
Landscaping
Area
Design Capture
Treatment
BMP Type
Treatment
Volume
Capacity`
Mechanism
Biocel Is
Arterial Streets
19.42 acres
0.94 ac -ft
—0.94 ac -ft
Green Street
Bio- treatment"
Biocells /Bioswales
Collector Streets
4.14 acres
0.20 ac -ft
—0.2 ac -ft
Green Street
Bio - treatment
Biocells /Bioswales
ac -ft acre feet
a Refer to Exhibit 2 —Proposed Hydrology Map for locations of the drainage boundaries. used for BMP calculations.
b Minimum design capture volume is the required SO DV for the contributing street drainage areas. Detailed calculations are
provided in Appendix E.
c Minimum treatment capacity assumes. approximately. 25% of the proposed parkway bioswoles include the biocell sub-
surface component at the downstream end of the swale, sufficient to treat the design capture volume for associated street
runoff.. In some areas, the biocell sub - surface enhancements may be expanded to bio -treat additional areas beyond the
street drainage where feasible.
d "Bio- treatment" is generally defined as soil and pfor based filtration BMPs, such as bioretention where the runoff volume Is
filtered through vegetation and soil filtration layers. Bio- treatment BMPs that release treated flows off -site are subject to
feasibility criteria per OC DAMP and Countywide Model WQMP. Where feasible, infiltration of treated runoff will be
utilized.
Table 5.8 Summary of BMP sizing for green street features.
30 Clayton, R.A., & Schueler, T.R. (1996, December). Design of Stormwater Filtering Systems. Silver Spring, MD: The Center
for Watershed Protection.
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The use of the landscaping biocells within the parkway bioswales in combination with other
interior LID features will result in significant treatment and reduction of runoff at the source of
the development areas. Each biocell will be designed to accommodate the required treatment
volume, and flow beyond this requirement will be designed to bypass the features for
conveyance into the traditional storm drain system. In those instances where the LID features
are not sufficient to handle treatment requirements independently, water quality calculations
will quantify how much the additional treatment is required by the next downstream LID feature
or water quality basin.
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FUSCOE ENGINEERING, INC. 112
RW RW
1 68' 1
5' 9'
BIOSWALE-7
L — — J
SLOTTED CURB-
20'
20'
9' 1 5'
BIOSWALE
BIOCELL ENHANCEMENT — — J
SLOTTED CURB
TYPICAL GREEN STREET W/ BIOSWALE SECTION
Pcc s
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I
3
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BIOCELL ENHANCEMENT CROSS SECTION
7 Green Street
NEWPORT BANNING RANCH Figure 17: Typical Green Street w/ Biocell Enhancement
iu I:USCOL
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Infiltration and Sub -Drain Systems
LID features will include sub - drains where necessary to ensure flows are treated, collected and
either (1) distributed to the Lowland Area and Arroyo canyon bottom for evapotranspiration
and infiltration benefits; (2) reused on -site for irrigation and other allowable uses; or (3)
discharged back to the backbone storm drain system for delivery off -site in accordance with
bio- treatment feasibility criteria. Although heavy reliance on infiltration within the
development footprint or near coastal bluff -tops is not expected or desired, field percolation
tests will be performed throughout the site to determine if perforated sub - drains may be
allowed within the proposed LID features and landscaping biocell features for minor infiltration
within the shallow soil layers.
Maintenance Considerations
Based on the high level of reliance of the LID features for water quality treatment,
maintenance of the facilities and enforcement of the appropriate measures to control the
loading of sediment- causing clogging from entering these features will be required. For the
landscaping biocells and other LID landscaping features, the key components to ensuring the
long -term functionality of each system include the following:
Minimum pre- treatment lengths of parkway bioswales upstream of bio- treatment
feature such as landscaping biocells to maximize sediment and particulate capture (25
ft recommended).
• Trash and debris removal (typically 1 x /week).
• Weeding, trimming, and landscape maintenance (typically monthly) to ensure the
vegetative height does not prohibit runoff from entering the biocell.
• Visual inspection for health of vegetation, excess ponded water, and excess trapped
sediment and debris (minimum 4x /year).
• Inspect inlet /outlet facilities for signs of damage, and clean out as necessary.
• Integrated pest management (IPM) to reduce reliance on pesticides in accordance with
City standards and guidelines.
5.3.5 REGIONAL NATURAL TREATMENT SYSTEMS & WATER QUALITY BASINS
The proposed Project will also incorporate the use of water quality basins to provide the
backbone treatment system for the majority of the site. The size of the basins will account for
any upstream LID features that treat and retain the design capture volume independently.
Water quality basins are typically designed with a small debris /entrapment area, a spreading
ground, and a deeper pool prior to discharging out the riser tower. Regional water quality
basins are typically planted emergent wetland bottoms with vegetated side slopes that
impound surface runoff and gradually filtrates through the sub -soil. The detained runoff is
filtered through the soil beneath the basin, removing both fine and soluble pollutants.
Removal mechanisms include absorption, filtering, and microbial decomposition in the basin
subsoil. Due to the slow velocity, fine particles will settle in the bottom of the channel and
vegetation will uptake fertilizers and nutrients (e.g., nitrogen and phosphorous), soluble
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metals, microbial contaminants, pesticides and organic matter. The underlying clays in the
native soil below the sub - surface permeable soil will provide absorption sites for heavy metals,
nutrients and other pollutants for further treatment." To increase treatment potential and
storage areas, sub - surface improvements can be made to introduce bioretention
enhancements to the water quality basins. Over - excavating the lower portion of the basin
floor 36 -48 inches and replacing with sand and soil layers to increase storage, treatment
capacity and increased filtration processes serve to improve the effectiveness of the basins.
For the Lowland Area, the introduction of bioretention components serves to increase the
chance of infiltration into the Lowland soils. For those water quality basins along the fringes of
the development adjacent to the coastal bluff -tops, the entire system must be lined with sub -
drains to reduce infiltration into the soils and provide long -term integrity of the soils. Bio-
treated flows will be either discharged off -site or collected and reused on -site in accordance
with the new Countywide Model WQMP feasibility criteria.
Community Water Quality Basins
Similar to the example provided under Section 5.3.4 for landscaping biocells, the Project
analyzed the potential for implementing water quality basins at the perimeter buffer areas to
accommodate the water quality treatment requirements for the tributary residential areas. The
basins within the perimeter trail parkways as well as the multi - family residential areas were
evaluated to determine the appropriate footprints and depths required to treat the required
volume based on the upstream drainage areas. In addition, the potential for utilizing
landscaping biocells within the parkway bioswales in lieu of water quality basins was also
evaluated for several of the drainage areas. The results are summarized in Table 5.9 below,
and detailed calculations are provided in Appendix E. The total design capture volume noted
in the table represents the requirement for the entire development.
California Stormwater Quality Association (CASQA). California Stormwater BMP Handbook for New Development and
Redevelopment. January 2003.
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WATER QUALITY BASINS TREATMENT SUMMARY
Minimum
% of Site
Development Area
Drainage
Runoff
Design
BMP
BMP Type
Treatment
Design
Area'
Coefficient
Capture
Capacity`
Mechanism(s)
Capture
Volume"
Volume
LOWLANDS DRAINAGE AREA
Medium /Medium-
Evapotranspiration,
Low /Low Density
60.54
0.66
2.32 ac -ft
-6.2 ac -ft
Multi -Use Basin
Retention
Residential (SD-D)
44%
Mixed Use
4.57
0.75
0.20 ac -ft
"0.20 ac-
WQ Basin(s) or
Evapotranspiration,
Residential (SD -F)
ft
equivalent BMP
Retention
SOUTHERN ARROYO /SEMENIUK SLOUGH DRAINAGE AREAS
Medium /Medium-
0.79 ac-
WQ Basin(s) or
Evapotranspiration,
Low /Low Density
21.54
0.63
0.79 ac -ft
ft
B
equivalent B
equivaMP
Reuse, Bic-
Residential (SD -C)
treatment'
Low Density/Visitor
Resort Residential
31.48
0.65
1.2 ac-ft
1.2 ac -ft
WQ Basin(s) or
Evapotranspiration,
40%
(SD -B)
equivalent BMP
Reuse, Bio- treatment
Community Parks
22,41
0.26
0.30 ac -ft
-0.3 oc -ft
WQ Basin(s) or
Evapotranspiration,
(SD -A)
e u ivalent BMP
Reuse, Bio - treatment
OTHER
NEW
Community Park
Evapotranspiration,
W/ WQ Basin for
2.39
0.71
0.10 ac -ft
+0.1 oc -ft
WQ Basin
Retention
°
1 /°
Off -site Flows'
Green Streets'
17.52
0.83
0.84
' -"0.84 ac-
Biocells &
Evapotranspiration,
15%
ft
Bioswales
Bio- treatment
Total Design Capture Volume
5.79 ac -ft
9.63 oc -ft
100%
oc -ft acre feet
SD storm drain
WQ water quality
a Refer to Exhibit 2 - Proposed Hydrology Map for locations of the drainage boundaries used for BMP calculations.
b Sizing is approximate based on minimum SQDV for contributing drainage areas of proposed for development. Detailed calculations are provided in
Appendix E.
Z Minimum treatment capacity assumes approximately 25% of the proposed parkway bioswales include the biocell sub- surface component at the
downstream end of the swale, sufficient to treat the design capture volume for associated street runoff.. In some areas, the biocell sub - surface
enhancements may be expanded to do-treat additional areas beyond the street drainage where feasible. "Bic-treatment" is generally defined as soil
and plant -based filtration BMPs, such as bioretention where the runoff volume is filtered through vegetation and soil filtration layers. Biotreatment
BMPs that release treated flows off -site are subject to feasibility criteria per OC DAMP and Countywide Model WQMP. Where feasible, infiltration of
treated runoff will be utilized.
d Acreage and sizing refers to on -site park area only. Water quality basin will be sized for additional upstream, off -site flows, of which are not
included in this table. Refer to Appendix E for additional calculations for off -site tributary area.
e Green streets that are located outside of the above listed drainage areas. For total green street acreages, refer to Table 5.8 and Appendix E.
Table 5.9 Summary of BMP sizing for water quality basins.
Figure 15 provides a typical representation of how the water quality basins may be integrated
within the design of the Project. Similar to the landscaping biocell transitional features, the
use of water quality basins at multiple locations throughout the site, in combination with other
LID and green street features, will result in a significant treatment of runoff from the
development areas.
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Water Quality Basin for Off -Site Runoff
One regional water quality facility will be implemented to accommodate the off -site treatment
of urban runoff from areas tributary to the Southern Arroyo. The off -site drainage area
located within the City of Costa Mesa encompasses approximately 48 acres and is 100%
built -out. The regional facility will be designed to accommodate approximately 2.3- acre -feet
of water quality treatment, which will accommodate all urban runoff (dry weather) and almost
the entire first -flush event in terms of water quality treatment control standards. In addition,
the basin will also provide detention capabilities to reduce peak flow runoff discharging into
the Southern Arroyo. Refer to Figure 15 for location of the proposed basin treating off -site
runoff.
Dual- Purpose Water Quality Basin
A regional basin is also proposed within the Lowland Area of the property (see Figure 15).
This basin will also serve as a diffuser basin to control the rate at which water drains from the
development areas on top of the Mesa down to the Lowlands. The basin will also serve as the
downstream water quality basin for Storm Drain Systems D & E, dependent upon how much
treatment is required after accounting for the upstream LID facilities. The water quality basin
has the capacity to accommodate approximately 6 acre -feet of treatment and without the use
of any upstream LID features, approximately 2.3 acre -feet of treatment is required. Therefore,
the combination of LID features and Lowlands water quality basin will provide sufficient water
quality treatment of the design capture volume for the largest drainage area (Storm Drains D
& E) of the proposed Project. Treated flows from this basin will remain on -site and will be
discharged into the Lowlands for infiltration, evapotranspiration and habitat nourishment
benefits.
Figure 17 provides a typical representation of a water quality extended detention basin for the
proposed Project. Elements of the typical extended detention basin will be incorporated into
the regional and community water quality basins.
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MAXI MUM ELEVATIOFNNl���
OF SAFETY STORM
MAXIMUM ELEVATION -® i. ^•- EMERGENCY
OF ED POOL -- SPILLWAY
VEGETATION RETAINED
RIP -RAP PILOT CHANNEL -. AQUATIC
INFLOW SEDIMENT BENCH
FOREBAY
7� 6- YYS_/Y 11 OUTFACE
SAFETY - �ryy�px MICROPOOL
BENCH
PLAN VIEW
EMBANKMENT
RISER
0100 YEAR LEVEL -\ EMERGENCY
10 YEAR LEVEL SPILLWAY
Illr - Cp, a 2 YEAR LEVEL --- - - - - --
III WO - EDELEVATIOI
STABLE
ZI
INFLgN �OUTFALL
1_.001 1011 -1111 -- -0n-ifni
FOREBAY MICROPOOL BARREL = -
I -
ANTISEEPCOLLARo J
FILTER DIAPHRAGM
PROFILE
Schematic of an Extended Detention Basin (MDE, 2000)
SOURCE: CA STORMWATER BMP HANDBOOK; TC -22 (JANUARY 2003 - ERRATA 5 -06)
PAProjects \821 \01 \Wat \GISWat \MXD \EIR Figures& Exhibits \pdf\Fig18_TypExtendedW OBosin.pdf
NEWPORT BANNING RANCH Figure 18: Typical Extended Detention Water Quality Basin
,I) June 30, 2011
``nil= FUSCOE NOT TO SCALE
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Other Design & Maintenance Considerations
Similar to the LID features discussed previously, for areas with unsuitable soil or slope stability
issues, the water quality basins would include sub - drains to collected treated flows within 48-
72 hours to prevent vector issues. Field percolation tests will be performed to determine
whether infiltration would be feasible or if sub - drains are required for areas throughout the
site. To the maximum extent, all sub - drains will be perforated to promote infiltration into the
sub -grade within the allowable amounts as specified by the geotechnical engineer.
Water quality basins left un- maintained can be a source of sediment containing concentrated
pollutants from the residential areas and also a source for mosquito breeding. These can be
considered an environmental impact if left unmanaged. Operation and maintenance (O &M)
activities for the water quality basins to prohibit these impacts would include the following:
• Conducting frequent site inspections by qualified personnel to observe the integrity of
the facility overtime.
• Removal of any trash and debris removal on regularly scheduled intervals (monthly)
and after all rain events.
Irrigation system inspection and adjustment to ensure proper nourishment of plant
palette without excessive watering.
• Minor vegetation removal /thinning and replanting when necessary.
• Integrated pest management (IPM) to reduce reliance on pesticides in accordance with
City standards and guidelines.
5.4 WATER QUALITY IMPACT ASSESSMENT
Under existing conditions, the Newport Banning Ranch project site consists of former oil
operations and open space areas. No project design features or BMPs for water quality exist
under the current conditions for the site.
Under the proposed conditions, site design and LID features will be integrated throughout the
development areas of the Project to address pollutants of concern from the project site. In
addition, treatment control BMPs are proposed to assist with the treatment of runoff, as well as
treating off -site runoff from upstream areas that drain towards the Southern Arroyo. Overall,
the Project will provide water quality treatment that exceeds water quality regulations for the
long -term protection against downstream impacts on adjacent habitat areas and downstream
receiving waters.
The impact assessments are based on the significance criteria established in Section 1.4 for
water quality. The impact assessments are based on the proposed drainage system inclusive
of project design features and water quality BMPs within the Project areas.
Impact Would the Project violate any water qualify standards or waste discharge
requirements?
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Impact Analysis: Based on the proposed LID features and other source control and treatment
control BMPs, the proposed Project will treat runoff prior to exiting the project site. As a result
of the project design features, LID features, source control and selected treatment control
BMPs, water quality exceedonces are not anticipated, and pollutants are not expected in
Project runoff that would adversely affect beneficial uses in downstream receiving waters.
Individual assessments are provided below:
Sediment: Sediments are typically characterized into two main categories: course
sediment that includes large sand grains, pebbles, etc. and fine particulate sediments
that include total suspended solids (TSS). Of concern to water quality are the fine
particulate sediments that are more typically associated with sheet erosion. Due to the
increase in impervious surfaces (buildings, roads, sidewalks), the proposed Project will
result in a corresponding decrease in sheet erosion potential through less exposed
areas, which is considered beneficial to water quality. However, during the
construction of the proposed Project, sediment has the potential to move off -site due
to the exposed condition of the site. In order to reduce the amount of sediment
discharged off -site due to construction activities, the Project will implement and
effective combination of erosion and sediment control BMPs in conformance with the
General Construction Permit (GCP). During the post - development condition, any
sediment and TSS generated from the development areas will be collected in the
proposed LID features (such as vegetated parkway bioswales with enhanced biocells)
and treatment control BMPs (regional and community water quality basins), all of
which are considered effective for targeting pollutants typically associated with these
impervious surfaces. Further, measures will be taken to stabilize the eroding
tributaries entering the Southern Arroyo thereby controlling the amount of sediment
available for transport to the Semeniuk Slough. Lastly, the diffuser basin at the
downstream end of the Arroyo will also provide an additional measure to control
sediment loading into the Semeniuk Slough. As a result, sediment impacts to water
quality are considered less than significant.
• Trash & Debris: Urban development can generate significant amounts of trash and
debris if not properly managed. The proposed Project is not expected to increase the
amount of potential trash and debris generated on -site. However, the Project will
implement additional measures, such as source control measures and treatment
BMPs, to minimize the adverse impacts of trash and debris. Source control measures
such as periodic sweeping, litter patrol, and storm drain stenciling will be effective in
reducing the amount of trash and debris leaving the site. The proposed LID features
and treatment BMPs also possesses moderate to high removal effectiveness for trash
and debris. Based on these proposed features, impacts from trash and debris for the
proposed Project are less than significant.
• Oil & Grease: The Project can implement several source control measures to reduce
the amount of oil and grease in storm water from the project site. Maintenance
activities, vehicle and equipment fueling and waste handling that have the potential to
introduce oil and grease related compounds will be strictly prohibited in outdoor areas
where they could potentially come into contact with rain. In addition, porous
pavement is effective at removing oil and grease from storm water runoff. Based the
incorporation of source control and treatment control measures, levels of oil and
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grease or other hydrocarbons such as PAHs that could adversely affect beneficial uses
of the Project's receiving waters or exceed water quality standards are not anticipated.
Impacts on water quality, as a result of the proposed Project, are less than significant.
• Bacteria & Pathogens: Based on the existing literature and land use /pollutant
categories, the existing and proposed Project may be a source of pathogens,
especially during storm water runoff conditions. Since natural sources of pathogens
are difficult to control (such as wild animal waste), the focus of the Project source
control measures is on human - related (anthropogenic) and residential sources. In
order to reduce the proposed pathogen contributions from the project site, the
following source control measures are recommended for implementation:
o Landscaping with efficient irrigation design to control runoff and allowing for
maximum infiltration opportunities.
o Proper monitoring and maintenance of landscaped areas to remove accumulated
dead plant material and debris.
o Landscape maintenance activities that include the removal of animal feces.
o Activity restrictions on outdoor mat washing and equipment cleaning related to
restaurant and dining activities, which potentially contribute bacteria entrained in
storm water, as well as waste accumulation and disposal methods.
o LID features (such as vegetated parkway bioswales and enhanced biocells) and
treatment control BMPs (water quality basins) further treat bacteria in storm water
runoff via filtration and infiltration.
• Nutrients: Nutrients, particularly nitrogen and phosphorous found within common
fertilizers, can be of a concern based on the potential for over - application and over
use. Low demand irrigation systems with slow release fertilizers are recommended to
be used on -site to ensure minimal runoff from irrigation that has the potential to
transport nutrients in runoff. Slow- release fertilizers are inorganic fertilizers that slowly
release nutrients at a slower rate and are less susceptible to leaching and loss of
fertilizer in runoff from rain events. In addition, source control measures such as
provisions against applying fertilizers proximate to expected rain events are also
recommended. Through the proper implementation of source control design
measures, there is no expected increase of nutrients in runoff from the project site.
Based on the water quality BMP plan and treatment of the entire design capture
volume, nutrients are not anticipated in Project runoff at levels that could adversely
affect water quality or beneficial uses in downstream receiving waters and potential
nutrient impacts are less than significant.
• Pesticides: Pesticides can be of a concern based on potential uses as well as previous
uses in the past. Under the proposed condition, the localized LID features and
treatment control BMPs throughout the project site will assist in the removal of
pesticides adsorbed to sediment. Low demand irrigation systems consistent with City
standards will be used on -site ensuring minimal runoff from irrigation that has the
potential to transport pesticides in runoff. In addition, source control measures such
as provisions against applying pesticides prior to expected rain events and the use of
properly certified pesticide workers will be required. This will be consistent with City
standards and guidelines for Integrated Pest Management (IPM). As a result, it is
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anticipated that water quality standards will not be exceeded, and potential pesticide
impacts are less than significant.
Metals: Copper, lead and zinc are the most common metals found in urban runoff.
Other trace metals such as chromium, mercury and nickel are not usually detected in
urban runoff or are measured at very low levels. The proposed Project will result in
increases in metals due to the additional streets and parking lot land uses proposed
for the site. The incorporation of the LID features throughout the project site will offset
these increases and provide a means for the settling of metals attached to particulates
as well as vegetative uptake of metals. Additional source control measures, such as
street and parking lot sweeping, will also reduce the potential for metals to reach the
storm drain system. As a result, it is anticipated that water quality standards will not be
exceeded, and potential impacts from metals are less than significant.
Oxygen Demanding Substances: Oxygen- demanding substances include all organic
materials, which consume oxygen as they decompose. Animal droppings, sewage
overflows, fallen leaves, and grass clippings are a few examples of oxygen- demanding
substances. The combination of LID features, source control measures and treatment
control BMPs are aimed at reducing the potential for these types of substances to be
created on -site, and the structural measures including the LID features will provide a
means to remove the potential for these substances to enter the downstream water
bodies. Impacts of oxygen demanding substances are considered less than significant.
• Dry Weather Flow: Although the previous discussions have focused on wet weather
flows, dry weather flows are also important. Dry weather flows due to anthropogenic
sources have the potential to impact local receiving water bodies. Dry weather flows
are typically low in course sediment due to the low -flow rates but pollutants associated
with suspended solids (such as phosphorous, trace metals, pesticides) are typically
found in low concentrations in dry weather flows. The project is not expected to
generate significant amounts of dry weather flows due to the drought tolerant
landscaping and the use of efficient irrigation systems consistent with City standards,
the lack of high intensive water use activities on -site, and the use of integrated storm
water landscaping features to collect, hold and treat these flows and eliminate dry flow
discharges (LID features and treatment control BMPs). Therefore, there are no
significant impacts anticipated with respect to water quality as a result of dry weather
flows.
• Vector Control: The use of integrated storm water landscaping (e.g., parkway
bioswales and enhanced biocells) for storm water treatment increases the potential for
vector issues due to the potential for standing water in these features. The potential
for mosquito breeding is considered a risk when ponding water exists greater than 72
hours. Thus, the estimated depths of ponding within the portions of the parkway
bioswales containing the biocell enhancement features will range from 4 -6 inches and
will be designed to infiltrate and /or discharge from the facility within 24 -36 hours.
Similar vector control precautions will occur with the proposed water quality basin
facilities. The ponding depth for these facilities will be 24 -36 inches and will be
designed to drain within 36 -48 hours. In the event additional vector control is
needed, a number of abatement measures will be used consistent with local
standards, including habitat reduction (reconfiguring of plant palettes), temporary
flooding and drying (draining) of the basins, trapping and killing pests, and
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biochemical pesticides (i.e., the bacteria Bacillus sphaericus [Bs] and Bacillus
thuringiensis israeliensus [Bti]).
Construction- Related Impacts: Clearing, grading, excavation and construction
activities associated with the proposed Project could impact water quality due to sheet
erosion of exposed soils and subsequent deposition of particles and pollutants in
drainage ways or introduction of construction - related pollutants. Based on the
preliminary risk assessment, the proposed Project is considered a Risk Level 2 site. Risk
Level 2 dischargers that pose a medium risk to water quality are subject to technology -
based numeric action levels (NALs) for pH and turbidity. Should the Project exceed a
pH range of 6.5 -8.5 or turbidity of 250 NTU, the discharger is required to
immediately determine the source associated with the exceedance and to implement
corrective actions if necessary to mitigate the exceedance. It is not anticipated that
ATS will be needed for the proposed Project; instead, traditional erosion and sediment
control BMPs will be employed.
Under the Statewide GCP (Order 2009- 0009 -DWQ), the Project proponents will
submit a Notice of Intent (NOI) and associated PRDs to the SWRCB prior to
commencement of construction activities. In addition, a SWPPP will be prepared and
implemented at the project site, and revised as necessary as administrative or physical
conditions change. The SWPPP will describe construction BMPs meeting the BAT /BCT
standards required by the GCP and that addresses pollutant source reduction, and will
ensure that water quality standards are not exceeded in downstream receiving waters
due to construction activities. These include, but are not limited to erosion controls,
sediment controls, tracking controls, non -storm water management, materials & waste
management, and good housekeeping practices. The SWPPP shall be developed in
accordance with the construction plans. The SWPPP shall provide construction BMPs
that are to be maintained for the duration of the construction as well as measures that
are specific to each phase of construction.
Impact F Would the Project otherwise substantially degrade water quality?
Impact Analysis: As a result of the construction - related, site design /LID, source control, and
additional treatment control BMPs, water quality exceedances are not anticipated, and
pollutants are not expected in Project runoff that would adversely affect beneficial uses in
downstream receiving waters. Therefore, impacts to water quality are considered less than
significant. See Impact Analysis to Impact A for additional details.
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6.0 EXHIBITS
EXHIBIT 1 Rational Method Hydrology Map for Proposed Condition
EXHIBIT 2 Rational Method Hydrology Map for Proposed Condition
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NEWPORT BANNING RANCH EXHIBIT 1: Rmionol Method Hydrology Mop for EAsling Condition
�I
0 J..x.3011
FUSCOF
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NEWPORT BANNING RANCH EXHIBIT 2: Rm onal Method Hydrology Map br Proposed CondMon
FUSCOE
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7.0 TECHNICAL APPENDICES
(bound separately)
APPENDIXA STUDY RELATED DOCUMENTS
Al Salt Marsh Restoration Plan from USACOE
A2 FEMA Map
APPENDIX B HYDROLOGY CALCULATIONS
Bl Existing Condition Rational Method Calculations
a) High Confidence Events
i. HC 100 -Year Storm Event
ii. HC 25 -Year Storm Event
iii. HC 10 -Year Storm Event
b) Expected Value (50% Confidence) Events
i. EV 100 -Year Storm Event
H. EV 2 -Year Storm Event
B2 Proposed Condition Rational Method Calculations
a) High Confidence Events
i. HC 100 -Year Storm Event
ii. HC 25 -Year Storm Event
iii. HC 10 -Year Storm Event
b) Expected Value (50% Confidence) Events
i. EV 100 -Year Storm Event
ii. EV 2 -Year Storm Event
.TUNE 30, 2011
B3 Existing Condition Small Area Unit Hydrograph Calculations
a) High Confidence Events
i. Infiltration Analysis
ii. HC 100 -Year Storm Event
iii. HC 25 -Year Storm Event
iv. HC 10 -Year Storm Event
b) Expected Value (50% Confidence) Events
i. Infiltration Analysis
ii. EV 100 -Year Storm Event
iii. EV 2 -Year Storm Event
B4 Proposed Condition Small Area Unit Hydrograph Calculations
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a) High Confidence Events
i. Infiltration Analysis
ii. HC 100 -Year Storm Event
iii. HC 25 -Year Storm Event
iv. HC 10 -Year Storm Event
b) Expected Value (50% Confidence) Events
i. Infiltration Analysis
ii. EV 100 -Year Storm Event
iii. EV 2 -Year Storm Event
JUNE 30, 2011
APPENDIX C HEC -RAS MODELING
C1 HEC -RAS Modeling Report for Northerly Arroyo Channel under
Existing Condition
C2 HEC -RAS Modeling Report for Northerly Arroyo Channel under
Proposed Condition
C2 HEC -RAS Modeling Report for Southerly Arroyo Channel under
Existing Condition
C3 HEC -RAS Modeling Report for Southerly Arroyo Channel under
Proposed Condition
APPENDIX ID WATER BUDGET ANALYSIS
Dl Northerly Arroyo under Existing Condition
D2 Northerly Arroyo under Proposed Condition
D3 Southerly Arroyo under Existing Condition
D4 Southerly Arroyo under Proposed Condition
DS ET Reference Material
APPENDIX E BEST MANAGEMENT PRACTICES
E1 Site Design /LID BMPs
E2 Source Control BMPs
E3 LID / Treatment Control BMP Calculations
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