Hydrology and Water Quality / Storm Water Quality

DRAFT EIR EASTVIEW SPECIFIC PLAN & ANNEXATION PROJECT JULY 2015

HYDROLOGY AND WATER QUALITY / 4.8 STORM WATER QUALITY

4.8.1 INTRODUCTION

The Hydrology and Water Quality / Storm Water Quality chapter of the EIR describes existing drainage and water resources for the project site, and evaluates potential impacts of the proposed project with respect to flooding, surface water resources, and groundwater resources. Information for this chapter was primarily drawn from the Eastview Specific Plan Drainage Study prepared for the proposed project by Wood Rogers, Inc.1 In addition, the chapter uses information from the Water Supply Assessment for the Eastview Specific Plan,2 the City of Galt Storm Drainage System Master Plan,3 the 2030 Galt General Plan Policy Document4 and associated EIR,5 and the 2030 Galt General Plan Existing Conditions Report.6 It should be noted that impacts associated with water supply and capacity are addressed in Chapter 4.11, Public Services and Utilities / Recreation, of this EIR.

4.8.2 EXISTING ENVIRONMENTAL SETTING

The section below describes the existing hydrological features of the project site and the surrounding region, as well as the water quality of the existing resources in and around the project site.

Regional Drainage

The City of Galt Public Works Department operates the City’s storm drain collection and disposal system, which collects and conveys surface water runoff throughout the City. The City’s storm drainage system consists of curbs and gutters that collect and direct the stormwater into catch basins where the stormwater enters an underground system of pipes. The underground piping system then directs the storm runoff to one of three drainage channels: Dry Creek; Hen Creek; and Deadman Gulch.

Dry Creek is a natural channel that forms the southern boundary of the City and the boundary between Sacramento and San Joaquin County to the south. Dry Creek, flowing in a westerly direction, flows into the Mokelumne River, which then flows to the Delta.

Deadman Gulch flows in the westerly direction generally through the northern sector of the City. East of State Route (SR) 99, Deadman Gulch has been designed and reconstructed to serve as a stormwater detention facility in addition to a stormwater conveyance facility, which occurs as a result of the culvert structure under SR 99 that meters the flow into Deadman Gulch west of the highway. The system allows the stormwater flows from the development occurring east of the highway to better match the channel capacity west of the highway.

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The City owns one detention basin, the Greer Detention Basin, which serves as a joint use facility/City park. Greer Detention Basin is located on the west side of the City, adjacent to Greer Middle School. After being detained in the detention basin, stormwater flows are pumped to Hen Creek for ultimate disposal. The lift station at Greer Detention Basin is one of only two stormwater lift stations in the City. The other is the Wagon Way lift station.

The storm drainage system is comprised of pipelines ranging in size from eight inches to 84 inches in diameter. The larger pipe sizes serve as the outfall structures conveying the storm runoff from the southwest portion of the community to Dry Creek.

Local Drainage

The majority of the project site is currently used for agriculture and is drained via small agricultural ditches. Deadman Gulch courses through the Liberty Ranch site from east to west. Deadman Gulch is a low slope, natural and engineered trapezoidal earth channel that drains the open cropland watershed from upstream of (east of) Marengo Road. Downstream of Marengo Road, an engineered trapezoidal earthen channel with a top-width of approximately 100 feet (built as a part of the Northeast Specific Plan area and Community Facilities District 1988-1), conveys the flow and collects additional runoff from the developed residential and commercial urban watersheds within the City of Galt. The Deadman Gulch watershed at Marengo Road is approximately 2.4 square miles (1,500 acres). According to Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) for the project area, Deadman Gulch is significantly flooded in a 100-year storm event.

As illustrated in Figure 4.8-1, the proposed project site is within watersheds DG4A, DG4B, DG7B, DG7C, and DG6B. Approximately half of watershed DG5 (DG5B) drains north and combines with DG2 to drain ultimately to the upstream end of the Liberty Ranch property. The other half of watershed DG5 (DG5A) drains into the Liberty Ranch property about halfway down the on-site channel. The area along the northern property boundary is not located in the Deadman Gulch watershed and thus does not drain through the project site. Instead, this area drains to the nearby drainages along the existing roadways.

Existing Downstream and Upstream Channel Structures

The Marengo Road channel crossing consists of three seven-by-seven-foot box culverts with an invert of 43.8 feet. An existing drop transition structure constructed of riprap spans across the channel bottom at 10 feet upstream of the Marengo Road crossing. Over time, the creek bed soils upstream of the drop structure have eroded, resulting in a crest at elevation 49.7 feet, which is 2.6 feet higher than the upstream channel invert.

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Figure 4.8-1 Existing Deadman Gulch Watershed

Project Site

Liberty Ranch

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According to the City of Galt, the existing Liberty Ranch High School and Estrellita Continuation High School site on the north bank of Deadman Gulch was built in the floodplain with compensatory storage based on calculations using the FEMA approximate floodplain. The Liberty Ranch High School and Estrellita Continuation High School site drains to off-line retention basins on the north bank of Deadman Gulch, which spill over a weir crest at elevation 56.0 feet into the Deadman Gulch channel. The upstream crossing under Cherokee Lane consists of two 24-inch corrugated metal culverts, which are sized for the bank-full flows, but are undersized for the 100-year flows.

Existing Downstream Channel Conditions

The downstream conditions have not been modeled by the City of Galt or the County of Sacramento to date. The downstream channel as-built plans indicate a 100-year water surface elevation of 51.3 feet downstream of the Marengo Road crossing; however, based on calculations performed as part of the drainage study prepared for the proposed project (which used a surface roughness coefficient assumption of 0.060), the 100-year water surface elevation is expected to be closer to 54.0 feet (2.7 feet higher than the as-built plans indicate). The City is concerned that the actual water surface elevation (and surface roughness coefficient) would be greater due to the channel downstream of Marengo Road currently being unmaintained and densely vegetated. The 100-year storm event would be expected to inundate the existing properties adjacent to Deadman Gulch at an associated roughness coefficient of 0.100. A more refined analysis of the downstream conditions would be required in order to answer the regional question of flooding in Deadman Gulch. Thus, the roughness coefficient remained to be assumed to be 0.060, which was utilized for analysis of both the existing and proposed conditions.

Existing Floodplain

The Effective FEMA Special Flood Hazard Area (SFHA) Zone A (approximate floodplain) boundary, dated August 16, 2012, was refined for the proposed project analysis in order to compare with the proposed conditions. The refined floodplain boundary shown on Figure 4.8-2 reflects the refined analysis using the existing ground surface information that includes fill from the Liberty Ranch High School and Estrellita Continuation High School site, which narrows the existing floodplain from the Effective floodplain.

Ultimately, a Letter of Map Revision (LOMR) based on more accurate data will need to be submitted to FEMA to revise the Effective floodplain boundary on FIRM panel numbers 06067C 0466H and 06067C 0470H. The Deadman Gulch channel must contain the 100-year flow with at least one foot of freeboard and two feet of freeboard at channel crossings per FEMA requirements.

As shown in Figure 4.8-2, consistent with the FEMA FIRM, the capacity of Deadman Gulch is greatly exceeded under existing conditions. The Deadman Gulch channel through Liberty Ranch consists of a constructed agricultural ditch with a bank-full capacity of approximately 50 cfs. Accordingly, the majority, but not all, of the 100-year flow is conveyed in the floodplain. Consequently, under existing conditions, the Deadman Gulch channel does not contain the 100- year or 200-year flow.

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Figure 4.8-2 Existing Floodplain Map

Project Site

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Water Quality

Water is essential to recreation, the viability of agriculture, and the development of housing, commerce, and industry, as well as the maintenance of high-quality fish and wildlife habitats. Land uses and activities that the City must consider in protecting the quality of the City’s water include construction activities, agricultural land uses, and urban runoff.

Construction Activities

Construction grading can impact water quality because it exposes bare soil. Rainfall on bare soil can cause erosion and sedimentation into nearby water bodies. Unstabilized soil can be washed or wind-blown into nearby surface water. Construction activities can also result in petroleum products and other pollutants from construction equipment, entering nearby drainages. In addition, loose trash and debris as well as spilled concrete or paint may result from construction activities.

Agricultural Land Uses

Water running off irrigated agricultural fields may contain fertilizers and pesticides. Improper use and disposal of farm chemicals can contaminate surface and groundwater resources. Agricultural procedures can also result in erosion of unstabilized soil, especially during conversion of vegetation. Aerial spraying could also drift into nearby water bodies.

Urban Runoff

Urban runoff occurs primarily on impervious surfaces such as rooftops, streets, and other pavement areas where various pollutants can occur and be washed into storm drain systems. Urban runoff includes bacteria, nutrients, pesticides, sediments, trash and debris, as well as petroleum products from automobiles and landscaping equipment.

Groundwater and Groundwater Recharge

The groundwater underlying the City is part of the San Joaquin Valley Groundwater Subbasin, which is within the San Joaquin River Hydrologic Region. The City relies solely on groundwater from the Cosumnes Subbasin to provide water to residential, industrial, and commercial users. Surface and recycled water sources are not currently utilized. The Cosumnes Subbasin is an unadjudicated basin that serves both municipal and agricultural uses.

The groundwater basin underlying the City consists of three distinct aquifers: the Younger Alluvium; Older Alluvium; and Miocene/Pliocene Volcanics. The Younger Alluvium (shallow aquifer) is composed of floodplain deposits and extends approximately 100 feet below ground surface. The Older Alluvium (intermediate aquifer) consists of the Laguna/Riverbank Formations and extends from a depth of 100 feet to approximately 1,000 feet below ground surface. The Miocene/Pliocene Volcanics consists of the Mehrten Formation (deep aquifer), which extends from approximately 1,000 feet below ground surface to depths of 2,000 feet or greater. Historically, the shallow and intermediate aquifers have been used for agriculture,

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domestic, and municipal demands. The shallow aquifer is hydraulically separated from the intermediate aquifer by vertically extensive clay layers (aquitards). The City of Galt recently installed a municipal well in the deep aquifer (below 1,000 feet) for municipal supply. The deep aquifer has only recently been identified in the sub-surface underlying the City as a viable groundwater source.

According to Groundwater Elevation Maps published by the County of Sacramento, Municipal Services Agency, Department of Water Resources in the Spring and Fall of 2007, depth to groundwater in the vicinity of the project site ranges from 95 to 110 feet below ground surface. The groundwater beneath the project site generally flows to the southwest; however the site is located within a groundwater “cone of depression”, or area of lowered groundwater elevations, caused by pumping for agricultural purposes. Therefore, local gradients may be reversed.

Groundwater storage capacity of the underlying subbasin is approximately 6,000,000 acre-feet (af). Basin inflows include natural and applied water recharge, totaling approximately 269,518 af, and modeling indicates that the net subsurface outflow is 144,551 af. Other groundwater outflows include an annual urban extraction of 35,063 af and an estimated agricultural extraction of 94,198 af, for a total of 273,812 af.7

On-Site Groundwater

Confirmation well testing of three-onsite agricultural wells (Southeast Well, Northwest Well, and Southwest Well) consisted of one-hour long pumping tests to measure drawdown and capacity. The wells are between approximately 600 to 1,000 feet deep. The well testing data indicated groundwater levels underlying the project are approximately 140 to 160 feet deep. The 24-hour projected pumping water level for the highest producing well (1,191 gallons per minute [gpm]) was 178 feet, with a specific capacity of 82 gallons per minute per foot (gpm/foot) of drawdown.

Drawdown tests for the three on-site wells were completed in order to measure changes in groundwater levels in response to on-site pumping. Two wells (Southwest Well and Northeast Well) were pumped for approximately five days (at a combined flow rate of approximately 2,040 gpm) while groundwater levels were measured continuously in the third well (Northwest Well). Groundwater level measurements in the non-pumping well, located approximately 2,700 feet from the pumping wells, did not indicate a measureable drawdown. Groundwater levels in the observation well increased by approximately one foot during the drawdown test, indicating groundwater recharge after the bulk of the seasonal pumping in the area had declined.

The locations of the three existing wells can be seen in Figure 4.8-3.

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Figure 4.8-3 Agricultural Well Locations

Project Site

Source: Cardno Entrix, 2014.

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Groundwater Quality

Historically, Galt’s municipal groundwater supply wells were drilled to depths between 600 feet and 1,000 feet. At such depths, the groundwater has typically required treatment for iron, manganese, and/or arsenic. The City installed a monitoring well (approximately two miles west of the project site) and did not find detectable arsenic levels (less than two micrograms per liter [μg/L]). As a result, a deep well was drilled at Golden Heights located north of Golden Heights Drive to the west of the project site.

The water quality data from three existing agricultural wells on the project site indicate that treatment for manganese would be needed because manganese exceeds the standard in all wells tested. Manganese was reported between 120 to 220 μg/L, and the Secondary (aesthetic) Maximum Contaminant Level (MCL) for manganese is 50 μg/L. Concentrations of arsenic are acceptable and below the Primary MCL of 10 μg/L, with values ranging from 7.4 to 8.2 μg/L.

4.8.3 REGULATORY CONTEXT

The following is a description of federal, State, and local environmental laws and policies that are relevant to the review of hydrology and water quality under the California Environmental Quality Act (CEQA) process.

Federal Regulations

Federal Emergency Management Agency (FEMA)

The Federal Emergency Management Agency (FEMA) is responsible for determining flood elevations and floodplain boundaries based on U.S. Army Corps of Engineers (USACE) studies. FEMA is also responsible for distributing the Flood Insurance Rate Maps (FIRMS), which are used in the National Flood Insurance Program (NFIP). These maps identify the locations of special flood hazard areas, including the 100-year floodplains.

FEMA allows non-residential development in the floodplain; however, construction activities are restricted within the flood hazard areas, depending upon the potential for flooding within each area. Federal regulations governing development in a floodplain are set forth in Title 44, Part 60 of the Code of Federal Regulations (CFR). These standards are implemented at the State level through construction codes and local ordinances; however, these regulations only apply to residential and non-residential structure improvements. Although roadway construction or modification is not explicitly addressed in the FEMA regulations, the California Department of Transportation (Caltrans) has also adopted criteria and standards for roadway drainage systems and projects situated within designated floodplains. Standards that apply to floodplain issues are based on federal regulations (Title 23, Part 650 of the CFR). At the State level, roadway design must comply with drainage standards included in Chapters 800-890 of the Caltrans Highway Design Manual. CFR Section 60.3(c)(10) restricts cumulative development from increasing the water surface elevation of the base flood by more than one foot within the floodplain.

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Federal Clean Water Act

The National Pollutant Discharge Elimination System (NPDES) permit system was established in the federal Clean Water Act (CWA) to regulate municipal and industrial discharges to surface waters of the U.S. Each NPDES permit contains limits on allowable concentrations and mass emissions of pollutants contained in the discharge. Sections 401 and 402 of the CWA contain general requirements regarding NPDES permits. Section 307 of the CWA describes the factors that EPA must consider in setting effluent limits for priority pollutants.

Nonpoint sources are diffuse and originate over a wide area rather than from a definable point. Nonpoint pollution often enters receiving water in the form of surface runoff, but is not conveyed by way of pipelines or discrete conveyances. As defined in the federal regulations, such nonpoint sources are generally exempt from federal NPDES permit program requirements. However, two types of nonpoint source discharges are controlled by the NPDES program – nonpoint source discharge caused by general construction activities, and the general quality of stormwater in municipal stormwater systems. The 1987 amendments to the CWA directed the federal EPA to implement the stormwater program in two phases. Phase I addressed discharges from large (population 250,000 or above) and medium (population 100,000 to 250,000) municipalities and certain industrial activities. Phase II addresses all other discharges defined by EPA that are not included in Phase I.

Section 402 of the CWA mandates that certain types of construction activities comply with the requirements of the National Pollutant Discharge Elimination System (NPDES) stormwater program. The Phase II Rule, issued in 1999, requires that construction activities that disturb land equal to or greater than one acre require permitting under the NPDES program. In California, permitting occurs under the General Permit for Stormwater Discharges Associated with Construction Activity, issued to the State Water Resources Control Board (SWRCB), implemented and enforced by the nine Regional Water Quality Control Boards (RWQCBs).

As of July 1, 2010, all dischargers with projects that include clearing, grading or stockpiling activities expected to disturb one or more acres of soil are required to obtain compliance under the NPDES Construction General Permit Order 2009-0009-DWQ. This General Permit requires all dischargers, where construction activity disturbs one or more acres, to take the following measures:

1. Develop and implement a Storm Water Pollution Prevention Plan (SWPPP) to include a site map(s) of existing and proposed building and roadway footprints, drainage patterns and storm water collection and discharge points, and pre- and post- project topography; 2. Describe types and placement of Best Management Practices (BMPs) in the SWPPP that will be used to protect storm water quality; 3. Provide a visual and chemical (if non-visible pollutants are expected) monitoring program for implementation upon BMP failure; and 4. Provide a sediment monitoring plan if the area discharges directly to a water body listed on the 303(d) list for sediment.

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To obtain coverage, a SWPPP must be submitted to the RWQCB electronically and a copy of the SWPPP must be submitted to the City of Galt. When project construction is completed, the landowner must file a Notice of Termination (NOT).

Construction Site Runoff Management

In accordance with NPDES regulations, in order to minimize the potential effects of construction runoff on receiving water quality, the State requires that any construction activity affecting one (1) acre or more must obtain a General Construction Activity Stormwater Permit. Permit applicants are required to prepare a Stormwater Pollution Prevention Plan (SWPPP) and implement Best Management Practices (BMPs) to reduce construction effects on receiving water quality by implementing erosion and sediment control measures.

State Regulations

State Water Resources Control Board

The SWRCB and the RWQCBs are responsible for ensuring implementation and compliance with the provisions of the federal CWA and California’s Porter-Cologne Water Quality Control Act. The project site is situated within the jurisdictional boundaries of the Central Valley RWQCB (CVRWQCB) (Region 5). The CVRWQCB has the authority to implement water quality protection standards through the issuance of permits for discharges to waters at locations within their jurisdiction.

The Water Quality Control Plan (Basin Plan) for the California Regional Water Quality Control Board, Central Valley Region, Fourth Edition, outlines the existing and potential beneficial uses, water quality objectives, and an implementation plan for the Sacramento River Basin and the San Joaquin River Basin. The Basin Plan for the Central Valley contains water quality objectives for both groundwater and surface water.8 The surface water quality objectives are presented in the following categories: bacteria; biostimulatory substances; chemical constituents; color; dissolved oxygen; floating material; mercury; methylmercury; oil and grease; pH; pesticides; radioactivity; salinity; sediment; settleable material; suspended material; tastes and odors; temperature; toxicity; and turbidity. The surface water quality objectives apply to all surface waters in the Sacramento and San Joaquin River Basins, including Deadman Gulch, or as noted in the Basin Plan.

Senate Bill 5

In 2012, the State legislature amended the 2007 Senate Bill (SB) 5 requirements related to the urban level of flood protection. Under SB 5, cities and counties in the Sacramento-San Joaquin Valley were required to amend their general plans within 24 months of the Central Valley Flood Protection Board adoption of the 2012 Central Valley Flood Protection Plan (CVFPP). Additionally, cities and counties were required to amend their zoning ordinances within 12 months of amending their general plans. Furthermore, DWR was required to release informational 200-year floodplain maps for urban areas protected by the State Plan of Flood Control (SPFC) by July 2, 2013, which are specifically intended to assist cities and counties

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Local Regulations

The following are the local government environmental goals and policies relevant to the CEQA review process pertaining to the hydrology and water quality aspects of the proposed project.

City of Galt General Plan

The following goals and policies of the Conservation and Open Space Element of the Galt General Plan are applicable to the hydrology and water quality aspects of the proposed project.

Goal COS-1 To protect and enhance the qualities of the area’s rivers, creeks, sloughs, and groundwater.

Policy COS-1.1 Flood Control. The City shall require adequate natural floodway design to assure flood control in areas where stream channels have been modified and to foster stream enhancement, improved water quality, recreational opportunities, and groundwater recharge.

Policy COS-1.2 Flood Protection Ordinance. The City shall continue to implement the City’s flood protection ordinance.

Policy COS-1.3 Inter-Agency Coordination. The City shall cooperate with FEMA, California Department of Water Resources, and other appropriate local, State, and Federal agencies to address local and regional flood issues.

Policy COS-1.4 Storm Flow Impacts. The City will continue to ensure, through the development review process, that future developments do not increase peak storm flows and do not cause flooding of downstream facilities and properties.

Policy COS-1.7 Stormwater Quality Protection. The City shall, through the development review process, ensure compliance with Federal and State stormwater quality standards and regulations.

Policy COS-1.9 Streambed Alteration Watershed Regulations Compliance. The City shall require proposed developments to comply with streambed alteration and watershed protection regulations as administered by the California Department of Fish and Game.

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Policy COS-1.10 Ecological Features Retention. The City shall retain to the extent feasible the ecological features of the creeks, sloughs, and rivers in their natural state.

Policy COS-1.12 Best Management Practices. The City shall require all new development and redevelopment to implement Best Management Practices (BMPs) to reduce pollutants to the maximum extent practicable. Additionally, the City shall require, as part of its Storm Water NPDES Permit and ordinances, to implement the Grading Plan, Erosion Control Plan, and Pollution Prevention Plan (SWPPP) during construction activities of any improvement plans, new development and redevelopment projects for reducing pollutants to the maximum extent practicable.

Policy COS-1.14 Floodplain Dedication. The City should require property owners and developers to dedicate land within 100 year floodplains to the City, or other City-designated entity for biological mitigation credit or similar purpose, when a development project is approved. In addition to the land requirement, the City should require public access adjacent to these areas, but outside the 100 year flood plain, via bicycle and pedestrian trails and related amenities with appropriate signage.

Policy COS-1.17 Floodplain Visual Accessibility. The City shall require visual accessibility to floodplains via direct, single frontage roadways, along the length of any particular stream and associated floodplain section being developed (on both sides).

In addition, the following goals and policies of the Public Facilities and Services Element of the Galt General Plan are applicable to the hydrology and water quality aspects of the proposed project.

Goal PFS-4 To collect and dispose of stormwater in a manner that protects the city’s residents and property from the hazards of flooding, manages stormwater in a manner that is safe and environmentally sensitive, and enhances the environment.

Policy PFS-4.1 Storm Drain Enhancements. The City shall continue to upgrade the storm drainage facilities in the older section of the city, and provide for systems needed in newly developing areas.

Policy PFS-4.2 Conservation/Stormwater. The City shall develop storm water drainage facilities consistent with the policies of the Conservation and Open Space Element.

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Policy PFS-4.3 Stormwater Quality. The City shall ensure compliance with Federal and State clean water standards by continuing to monitor and enforce provisions to control non-point source and point source water pollution contained in the U.S. Environmental Protection Agency NPDES program.

Policy PFS-4.4 Project Design. The City should encourage project designs that minimize drainage concentrations and impervious surfaces.

Policy PFS-4.5 Grading During the Rainy Season. The City shall prohibit grading activities during the rainy season, unless adequately mitigated, to avoid sedimentation of storm drainage facilities.

Policy PFS-4.6 Erosion Control Plan. The City shall require new development projects to prepare an erosion control plan.

Policy PFS-4.7 Mitigating Stormwater Runoff. The City shall require projects that have significant impacts on the quantity and quality of surface water runoff to incorporate mitigation measures for impacts related to urban runoff.

Policy PFS-4.8 Joint Use of Detention Facilities. The City shall encourage stormwater detention facilities to be designed for multiple purposes, including recreational (e.g., parks, ball fields, etc.) stormwater quality improvement, and/or waterfowl habitat.

Policy PFS-4.9 Detention Requirements. The City should require detention storage with measured release to ensure that the capacity of downstream creeks and sloughs will not be exceeded. To ensure downstream capacity is not exceeded, the following measures will be applied:

a. Outflow to creeks and sloughs should be designed and constructed to avoid exceeding downstream channel capacities; and b. Storage facilities should be designed and constructed to prevent problems caused by timing of storage outflows.

Furthermore, the following goals and policies of the Safety and Seismic Element of the Galt General Plan are applicable to the hydrology and water quality aspects of the proposed project.

Goal SS-3 To protect the lives and property of residents and visitors to Galt from flooding hazards and manage floodplains for their open space and natural resource values.

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Policy SS-3.1 Floodplain Mapping. The City shall use the most current FEMA floodplain map to direct development outside of the 100-year floodplain.

Policy SS-3.2 Development in 100-year Floodplain. The City shall prohibit development in the 100-year floodplain of streams to minimize safety hazards, property loss, environmental disruption, and to promote stream enhancement, improved water quality, recreational opportunities, and groundwater recharge.

Policy SS-3.3 Natural Drainageways Enhancements. The City should promote the aesthetic, environmental, and functional improvement of natural drainageways where water courses have been disrupted in such a manner as to balance the protection of abutting uses with the consideration of environmental, recreational, and open space needs.

City of Galt Municipal Separate Storm Sewer System

The cities of Citrus Heights, Elk Grove, Folsom, Galt, Rancho Cordova, Sacramento and the County of Sacramento (also called the Sacramento Stormwater Quality Partnership) submitted a completed Report of Waste Discharge on June 1, 2007 requesting reissuance of waste discharge requirements (WDRs) under the National Pollutant Discharge Elimination System (NPDES) area-wide municipal separate storm sewer system (MS4) to discharge stormwater runoff from storm drains within their jurisdictions. As part of the MS4 permit, a Stormwater Quality Improvement Plan (SQIP) was prepared, which describes the stormwater pollution prevention efforts implemented by each member of the Sacramento Stormwater Quality Partnership. The Partnership together implements the Sacramento Stormwater Management Program, which has been established to satisfy regulatory permit requirements and protect local waterways. A Stormwater Quality Design Manual provides locally-adapted information for design and selection of stormwater quality control measures. As part of the MS4 permit, the City of Galt must review new development projects in order to ensure compliance with the Stormwater Quality Design Manual as well as the mandates of the MS4.

4.8.4 IMPACTS AND MITIGATION MEASURES

This section describes the standards of significance and methodology utilized to analyze and determine the proposed project’s potential impacts related to hydrology and water quality. A discussion of the project’s impacts, as well as mitigation measures where necessary, is also presented.

Standards of Significance

Consistent with Appendix G of the CEQA Guidelines, the City’s General Plan, and professional judgment, a significant impact would occur if the proposed project would result in the following:

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• Substantially alter the existing drainage pattern of the site or area; • Create or contribute runoff water which would exceed the capacity of existing or planned stormwater drainage systems or provide substantial additional sources of polluted runoff; • Violate any water quality standards or waste discharge requirements, or otherwise substantially degrade water quality; • Substantially deplete groundwater supplies or interfere substantially with groundwater recharge; • Place housing within a 100-year flood hazard area as mapped on a federal Flood Hazard Boundary or Flood Insurance Rate Map or flood hazard delineation map, or place within a 100-year floodplain structures which would impede or redirect flood flows; • 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; or • Inundation by seiche, tsunami, or mudflow.

The proposed project’s impacts associated with water supply and capacity are further addressed in Chapter 4.11, Public Services and Utilities / Recreation, of this EIR.

Method of Analysis

Site conditions and impacts analysis for this chapter are based primarily on the drainage study prepared for the proposed project by Wood Rogers, Inc. The drainage study included modeling of the existing and proposed hydraulic conditions on and surrounding the proposed project site using the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) model. In addition, information from the Water Supply Assessment prepared for the proposed project, as well as the City’s Storm Drainage System Master Plan, General Plan and associated EIR, was utilized. Determinations of significance were made based on the existing, or planned, infrastructure’s ability to accommodate the proposed project.

Project-Specific Impacts and Mitigation Measures

The following discussion of impacts is based on the implementation of the proposed project in comparison with the standards of significance identified above. The discussions and mitigation measures presented below apply to Liberty Ranch, “Future Growth Area,” and non-participating properties unless otherwise stated.

4.8-1 Substantially alter the existing drainage pattern of the site or area, or create or contribute runoff water which would exceed the capacity of existing or planned stormwater drainage systems. Based on the analysis below and with implementation of mitigation, the impact is less than significant.

The proposed project, when complete, would result in new impervious surfaces and thus an incremental reduction in the amount of natural soil surfaces available for the infiltration of rainfall and runoff, potentially generating additional runoff during storm events. Additional runoff could contribute to the flood potential of natural stream

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channels or contribute runoff that could exceed the capacity of the City’s stormwater drainage system.

As discussed above, the capacity of Deadman Gulch on the project site is greatly exceeded under existing conditions. However, the proposed project includes improvements to the Deadman Gulch drainage channel that would provide for increased flood protection for not only the current conditions, but to accommodate the increase in stormwater runoff associated with the proposed project as well. Accordingly, the proposed peak flows and flow duration characteristics would be at or below existing conditions in the Deadman Gulch channel. The proposed improvements and associated flow characteristics of the Deadman Gulch channel are presented below.

Proposed Improvements

The proposed project would include improvements to the existing channel structures, installation of an underground stormwater pipe system, and on-site detention basins. The proposed project’s drainage improvements are discussed in further detail below.

Channel Structures

The existing box culverts under Marengo Road would remain; however, the drop structure would be replaced 10 feet upstream of the crossing. The continuation of Walnut Avenue to the east within the proposed project site would require a culvert crossing of two box culverts each seven-by-six feet (see Figure 4.8-4). It should be noted that the aforementioned improvements could cause a tight constriction of the channel flow and could potentially be better designed as a continuous structure under both Walnut Avenue and Marengo Road in order to reduce head losses. A single structure will be considered for the future design phase.

Improvements to Marengo Road to fix an existing spill into the McCaffrey Middle School sports fields west of Marengo Road were requested by the City of Galt. A proposal for how to raise Marengo Road has not been developed at this time; however, for analysis purposes, Marengo Road is assumed to be raised and the weir flow over is assumed to be cut off.

Two additional arterial road crossings are proposed in the upstream half of the channel within the project site in order to connect the north and south neighborhoods of the proposed project. The downstream arterial crossing would consist of two six-by-seven- foot box culverts and the upstream arterial crossing would consist of three seven-by- seven-foot box culverts. The Cherokee Lane crossing would be improved to four twelve- by-four-foot box culverts in order to fit under the existing road elevation and improve the upstream conditions.

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Figure 4.8-4 Proposed Channel Corridor

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Pipe System

The underground pipe system of the proposed project would be sized to convey the Nolte flow (design flow based on the Nolte method – a method the City of Sacramento uses to size pipes) at a minimum velocity of 2.0 feet per second and with 0.5 feet of freeboard from the hydraulic grade line (HGL) and the street gutter elevation. The project would design the pipe conveyances using the 24-hour, 10-year storm, consistent with the 2010 Storm Drainage Master Plan.

The off-site 10-year flow is detained behind the existing railroad embankment and discharges through a 24-inch diameter culvert at both off-site watershed discharge areas (DG6 and DG7A). The off-site watersheds that are cutoff from reaching the proposed Deadman Gulch channel by development of the proposed project would be collected into the underground drainage system and conveyed to the downstream detention basins, basins B and D (see Figure 4.8-5).

Flood Control/Hydromodification/Water Quality Basins

The on-site detention basins would be located at the downstream end of each pipe system, as shown in Figure 4.8-5, and would detain peak 100-year flows to below existing conditions. A stand pipe weir outlet would be designed to discharge flows below existing conditions. An orifice in the standpipe would be designed to control annual flows to meet the hydromodification requirements of the Regional Water Quality Control Board (RWQCB). Hydromodication analysis would be conducted at two points in the channel, which would be located in the proposed Deadman Gulch channel downstream of Basin C-1 outfall and downstream of the Marengo Road crossing, in order to compare pre- and post-development flows.

The water quality portion of the basins would be designed as wet basins per the Stormwater Quality Design Manual. Wet basins are shallow basins that maintain a permanent pool of water by using an elevated outlet control structure. The outlet control structure is elevated to allow pollutant-laden solids to settle to the bottom and cleaner surface water to exit. Wet detention basins treat stormwater through sedimentation and biological uptake of pollutants by plants, algae, and bacteria. Vegetation growing around the perimeter of the basin provides for biological uptake of nutrients. Stormwater runoff in excess of the permanent pool is slowly released from the basin to prevent downstream erosion. The basins would be designed in accordance with all City guidelines.

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Figure 4.8-5 Proposed On-Site Drainage System

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Floodplain Conditions with Proposed Project

As shown in the figure, the proposed drainage system improvements, as well as the raising of Marengo Road, would reduce the size of the floodplain associated with Deadman Gulch. The raising of Marengo Road would eliminate the existing spillover at Marengo Road into the McCaffrey Middle School sports fields west of Marengo Road. By eliminating the spillover at Marengo Road, an increase in peak elevation of 0.2 feet is expected upstream of the Marengo Road crossing compared to the existing conditions. The on-site detention basins located downstream from the proposed on-site channel crossings would accommodate the increase in peak flow elevation of 0.2 feet resulting from the raising of Marengo Road. In addition, the proposed conditions in comparison to the existing conditions, based on floodplain modeling, are presented in Table 4.8-1. The results indicate that the proposed improvements would ensure that the Deadman Gulch channel would be capable of handling 100-year peak flows due to the project development.

Table 4.8-1 Existing vs. Proposed Modeling Results Existing Conditions Proposed Conditions Peak Water Peak Water Surface Surface Peak Flow Elevation Peak Flow Elevation Location (cfs) (feet) (cfs) (feet) Marengo Road (Downstream) 750 54.0 717 54.0 High School Retention Basin 724 56.2 640 55.0 Outlet Weir Cherokee Lane (Upstream) 450 63.8 469* 63.4 Note: * The upstream off-site flow is potentially increased in the dynamic model due to the increased conveyance through the proposed culvert.

Source: Wood Rodgers, Inc., 2014.

As discussed above, per FEMA requirements, the Deadman Gulch channel must contain the 100-year flow with at least one foot of freeboard and two feet of freeboard at channel crossings. In addition, per SB 5 requirements, flood protection up to the 200-year water surface elevation shall be provided. Neither of the aforementioned conditions is currently met. However, with the increased conveyance in the Deadman Gulch channel due to the proposed improvements, the channel would be capable of containing the 100-year water surface elevation on the project site. In addition, according to the drainage study prepared for the proposed project, the conservatism in the channel freeboard provided, as well as the raised house pad grades of the proposed project, would provide protection from the 200-year water surface elevation.

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Conclusion

The proposed project would alter the existing drainage pattern of the site and surrounding area and would increase impervious surfaces on the site, which would result in an increase in runoff associated with the site. However, the proposed project would include improvements to the existing drainage channel on the site and surrounding area to not only fix the currently inefficient channel conditions, but to accommodate the increase in stormwater runoff that would be created by development of the proposed project. Because the proposed peak flows and flow duration characteristics of the existing drainage channel on the site and surrounding area would be at or below existing conditions in the Deadman Gulch channel, the capacity of the stormwater drainage system would not be exceeded. Therefore, assuming Marengo Road is raised above the 100-year spill elevation and the improvements to Deadman Gulch are completed, stormwater drainage system for the project site would sufficiently handle runoff from the project while not exceeding the capacity of the City’s downstream stormwater facilities or the on-site flood potential. Without mitigation to ensure Marengo Road is raised to an elevation of 55 feet and Deadman Gulch is improved, a potentially significant impact would result. Water quality associated with runoff from the project site is discussed in further detail below.

Mitigation Measure(s) Implementation of the following mitigation measures would reduce the above impact to a less-than-significant level.

Liberty Ranch

4.8-1(a) Prior to the approval of improvement plans, the raising of Marengo Road above the 100-year spill elevation shall be shown on the improvement plans. The raising of Marengo Road shall be completed in accordance with the Wood Rodgers Drainage Study dated April 23, 2015, which assumes a minimum raise to an elevation of 55 feet. Raising the road would be required in order to avoid inundation of the McCaffrey Middle School sports fields west of Marengo Road. When grading plans are available, the height of the roadway may be adjusted to the satisfaction of the City Engineer.

4.8-1(b) Prior to the approval of improvement plans, the improvements to Deadman Gulch in order to contain the 100-year flow with at least one foot of freeboard shall be shown on the improvement plans. In addition, the improvement plans shall show that storm detention would be constructed along Deadman Gulch to mitigate peak 100-year flows into the channel. Furthermore, the design of the proposed Deadman Gulch channel shall be required to have an operations and maintenance plan which should keep vegetation to a controllable level. The final design of the Deadman Gulch channel and storm detention improvements shall be

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constructed to the satisfaction of the City Engineer. The operations and maintenance plan shall be reviewed and approved by the City Engineer.

4.8-2 Violate any water quality standards or waste discharge requirements, provide substantial additional sources of polluted runoff, or otherwise substantially degrade water quality during construction. Based on the analysis below and with implementation of mitigation, the impact is less than significant.

The potential impacts to water quality related to construction activities are discussed in further detail below separately for the non-participating properties and Liberty Ranch (including “Future Growth Area”) portions of the project site.

Non-Participating Properties

The non-participating properties would retain the currently adopted General Plan land use designations and development of the non-participating properties is not proposed as part of the proposed project. As such, construction activities would not occur on the non- participating properties with implementation of the proposed project. Therefore, impacts related to a violation of water quality standards or waste discharge requirements, additional sources of polluted runoff, or degradation of water quality would not occur associated with the non-participating properties.

Future Growth Area

The proposed project does not include development of the “Future Growth Area.” As such, construction activities would not occur on the “Future Growth Area” with implementation of the proposed project. Therefore, impacts related to a violation of water quality standards or waste discharge requirements, additional sources of polluted runoff, or degradation of water quality would not occur associated with the “Future Growth Area.”

Liberty Ranch

Construction would require grading, excavation, and other construction-related activities that could cause soil erosion at an accelerated rate during storm events. In addition, spilled concrete or paints or loose trash and debris may result from construction. All of these activities have the potential to affect water quality and contribute to localized violations of water quality standards if stormwater runoff from construction activities enters receiving waters.

Construction activities such as grading, excavation, and trenching for site improvements would result in the disturbance of on-site soils. The exposed soils have the potential to affect water quality in two ways: 1) suspended soil particles and sediments transported through runoff; or 2) sediments transported as dust that eventually reach local water bodies. Spills or leaks from heavy equipment and machinery, staging areas, or building sites also have the potential to enter runoff. Typical pollutants include, but are not limited

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to, petroleum and heavy metals from equipment and products such as paints, solvents, and cleaning agents, which could contain hazardous constituents. Sediment from erosion of graded or excavated surface materials, leaks or spills from equipment, or inadvertent releases of building products could result in water quality degradation if runoff containing the sediment or contaminants should enter receiving waters in sufficient quantities. Impacts from construction-related activities would generally be short-term and of limited duration.

Because the proposed project would require construction activities that would result in a land disturbance greater than one acre, the applicant would be required by the State to obtain a General Permit for Discharges of Storm Water Associated with Construction Activity (Construction General Permit), which pertains to pollution from grading and project construction. Compliance with the Permit requires the project applicant to file a Notice of Intent (NOI) with the SWRCB and prepare a SWPPP prior to construction. The SWPPP would incorporate BMPs in order to prevent, or reduce to the greatest feasible extent, adverse impacts to water quality from erosion and sedimentation. In addition, treatment of stormwater runoff would be addressed via the proposed on-site detention basins. The basins would be designed as wet basins per the Stormwater Quality Design Manual and in accordance with all City guidelines. The project’s required compliance with the SWRCB standards, MS4 permit, and SQIP would ensure that construction activities would not result in degradation of downstream water quality.

It should be noted that the Sewer Study prepared for the proposed project noted the potential for groundwater in the area of the project site to be high. Should groundwater be present during construction and dewatering activities are deemed necessary, mitigation would be required to ensure impacts related to dewatering discharge do not occur.

Conclusion

Impacts to water quality would not occur associated with the non-participating properties. In addition, compliance with regulations would ensure that construction activities would not result in degradation of downstream water quality. Overall, without mitigation to ensure potential dewatering activities do not result in impacts to groundwater quality, the proposed project would result in a potentially significant impact related to a violation of water quality standards or waste discharge requirements, additional sources of polluted runoff, or degradation of water quality during the construction phases.

Mitigation Measure(s) Implementation of the following mitigation measure would reduce the above impact to a less-than-significant level.

Liberty Ranch

4.8-2 If the site-specific geotechnical report identifies a high groundwater table, the project applicant shall obtain the appropriate NPDES dewatering general permit prior to commencement of dewatering activities.

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4.8-3 Violate any water quality standards or waste discharge requirements, provide substantial additional sources of polluted runoff, or otherwise substantially degrade water quality during operations. Based on the analysis below, the impact is less than significant.

Non-Participating Properties

The non-participating properties would retain the currently adopted General Plan land use designations and development of the non-participating properties is not proposed as part of the proposed project. As such, an increase in impervious surfaces would not occur on the non-participating properties with implementation of the proposed project. Therefore, impacts related to a violation of water quality standards or waste discharge requirements, additional sources of polluted runoff, or degradation of water quality would not occur associated with the non-participating properties.

Future Growth Area

Liberty Ranch

Urban runoff is typically associated with impervious surfaces, such as rooftops, streets, and other paved areas, where various types of pollutants may build up and eventually be washed into the storm drain system after storm events. The project facilities (e.g., homes, paved driveways, and roads) would involve a substantial amount of new impervious surface, which could increase the amount of surface runoff as well as convey non-point- source contaminants to surface waters during storm events. Additional runoff could contribute to the flood potential of natural stream channels, accelerate soil erosion and stream channel scour, and provide a more lucrative means of transport for pollutants to enter the waterways. Contaminated runoff waters could flow into Deadman Gulch and degrade the water quality.

During the dry season, vehicles and other urban activities release contaminants onto the impervious surfaces, where they would accumulate until the first storm event. During this initial storm event, or first flush, the concentrated pollutants would be transported via runoff to stormwater drainage systems. Anticipated runoff contaminants associated with the proposed project include sediment, pesticides, oil and grease, nutrients, metals,

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bacteria, and trash. It should be noted that some of these contaminants may be expected in the existing agricultural runoff from the project site.

As discussed above, the proposed project includes on-site wet detention basins, which would detain stormwater during major storm events, as well as remove pollutants from stormwater runoff. The wet detention basins would treat stormwater through sedimentation and biological uptake of pollutants by surrounding vegetation, algae, and bacteria. While pollutants settle out within the basins, only the clean surface water within the basins would be allowed to exit into the Deadman Gulch drainage channel via outlet control structures. The basins would be designed in accordance with all County and City guidelines. In addition, the proposed project would implement the requirements of the SWRCB, the MS4 permit, the SQIP, the Sacramento Stormwater Management Program, and the Stormwater Quality Design Manual. Thus, the on-site detention basins and improvements to the Deadman Gulch channel would be sufficient to ensure that water quality standards or waste discharge requirements are not violated and water quality is not degraded as a result of the proposed project operations.

Conclusion

For the aforementioned reasons, urban pollutants entering and potentially polluting the local water system would not be expected to occur as a result of the proposed project. Therefore, the proposed project would not violate any water quality standards or waste discharge requirements, provide substantial additional sources of polluted runoff, or otherwise substantially degrade water quality during operations, and impacts would be less than significant.

Mitigation Measure(s) None required.

4.8-4 Substantially deplete groundwater supplies or interfere substantially with groundwater recharge. Based on the analysis below, the impact is less than significant.

The City relies solely on groundwater from the Cosumnes Subbasin to provide water to residential, industrial, and commercial users. Surface and recycled water sources are not currently utilized. The proposed project’s impacts on groundwater supplies are discussed in detail in Chapter 4.11, Public Services and Utilities / Recreation, of this EIR. The discussion below relates to impacts associated with interference with groundwater recharge only. As discussed in Chapter 4.11, groundwater levels in the vicinity of the project site are relatively stable with respect to yearly variations during the past five years, with seasonal variations of approximately 10 to 20 feet. During the current drought, groundwater levels are expected to be slightly deeper than previous measurements. Groundwater levels in the groundwater basin have historically recovered following past droughts.

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The groundwater underlying the City is part of the San Joaquin Valley Groundwater Subbasin. Basin inflow consists of natural and applied water recharge, where rainfall and surface water or other applied waters are allowed to percolate through the soil into the underlying aquifer. Groundwater recharge zones are areas in which surface water is able to percolate downward to sub-surface water bearing formations. Within the City of Galt, areas adjacent to local watercourses provide moderate to high recharge capability.9 Therefore, within the proposed project site, Deadman Gulch would provide moderate to high recharge capability. Groundwater in the Galt General Plan study area is recharged by local precipitation and through percolation from the surrounding surface waters.

The City plans to accommodate new water demands by increasing groundwater pumping. As stated in the 2010 UWMP, if warranted by demand, the City would construct new wells and supply facilities; a new well would be constructed to serve the proposed development at the Eastview Specific Plan site that has the ability to provide water to the project site.

The Mehrten Formation aquifer underlying the City is hydraulically separated, meaning the aquifer is vertically separated from other underlying aquifers by geologic formations that permit little or no water to flow in or out.10 For the proposed project, the City well would go down to the lower Mehrten Formation aquifer, which is a hydraulically separated; therefore, installation of a well on-site would not impact existing wells in the upper aquifers.

The proposed project would involve an increase in impervious surfaces (e.g., roads, driveways, and homes) on the project site, which would reduce the amount of natural soil surfaces available for the infiltration of rainfall and runoff to the underlying aquifer. However, the proposed project would improve the existing Deadman Gulch drainage channel on the project site. Runoff from the developed portions of the project area would drain to the on-site detention basins and ultimately to the drainage channel. The channel area would contribute towards the recharge of the underlying groundwater aquifer. Therefore, the proposed project would not interfere with groundwater recharge, and related impacts would be less than significant.

Mitigation Measure(s) None required.

4.8-5 Place housing within a 100-year flood hazard area as mapped on a federal Flood Hazard Boundary or Flood Insurance Rate Map or flood hazard delineation map, or place within a 100-year floodplain structures which would impede or redirect flood flows. Based on the analysis below, the impact is less than significant.

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Non-Participating Properties

Currently the Liberty Ranch High School and Estrellita Continuation High School site is almost entirely in the 100-year floodplain. According to the City of Galt, the existing Liberty Ranch High School and Estrellita Continuation High School were built in the floodplain with compensatory storage based on calculations using the FEMA approximate floodplain. The high school site currently drains to offline retention basins on the north bank of Deadman Gulch. The proposed Deadman Gulch drainage system improvements would benefit the existing high schools by reducing the floodplain affecting the site.

The remainder of the non-participating properties is predominantly not within the 100- year floodplain. In addition, the non-participating properties would retain the currently adopted General Plan land use designations and development of the non-participating properties is not proposed as part of the proposed project. As such, new housing or structures would not be placed on the non-participating properties. Thus, impacts related to placing housing or structures within a 100-year flood hazard area would not occur associated with the non-participating properties.

Future Growth Area

The “Future Growth Area” is not within the 100-year floodplain. The proposed project does not include development of the “Future Growth Area.” As such, construction activities would not occur on the “Future Growth Area” with implementation of the proposed project. As such, new housing or structures would not be placed on the “Future Growth Area.” Thus, impacts related to placing housing or structures within a 100-year flood hazard area would not occur associated with the “Future Growth Area.”

Liberty Ranch

Deadman Gulch courses through the Liberty Ranch site from east to west. The Effective FEMA SFHA Zone A (approximate floodplain) boundary on the project site could be seen in Figure 4.8-2. As discussed above, under current conditions, the capacity of Deadman Gulch is greatly exceeded under existing conditions and the site is inundated in the floodplain during the 100-year flood event consistent with the FEMA FIRM. It should be noted that the Effective FEMA SFHA Zone A boundary was refined for the proposed project analysis in order to compare with the proposed conditions. The refined floodplain boundary, which reflects the refined analysis using the existing ground surface information that includes fill from the Liberty Ranch High School and Estrellita Continuation High School site, is also shown on Figure 4.8-2. It should be noted that a LOMR based on more accurate data will need to be submitted to FEMA to revise the Effective floodplain boundary on FIRM panel numbers 06067C 0466H and 06067C 0470H. As shown in Figure 4.8-2, the refined floodplain boundary narrows the existing floodplain from the Effective floodplain.

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The proposed project would conserve and improve the on-site Deadman Gulch drainage channel. Improvements to the existing drainage channel on the site and surrounding area would increase conveyance in the Deadman Gulch channel sufficient to adequately contain the 100-year water surface elevation on the project site. In addition, according to the drainage study prepared for the proposed project, the conservatism in the channel freeboard provided, as well as the raised house pad grades of the proposed project, would provide protection from the 200-year water surface elevation as well. Furthermore, as shown in Figure 4.8-4, new housing or structures are not proposed within the 100-year floodplain. Therefore, the proposed project would not place housing within a 100-year flood hazard area, place within a 100-year floodplain structures that would impede or redirect flood flows, or expose people or structures to a significant risk of loss, injury or death involving flooding.

Conclusion

Based on the above discussions, the proposed project would not place housing within a 100-year flood hazard area as mapped on a federal Flood Hazard Boundary or Flood Insurance Rate Map or flood hazard delineation map, or place within a 100-year floodplain structures which would impede or redirect flood flows. It should be noted that a LOMR must be approved and submitted to FEMA prior to any development on the project site. Overall, impacts associated with the 100-year floodplain would be less than significant.

Mitigation Measure(s) None required.

4.8-6 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. Based on the analysis below, the impact is less than significant.

As discussed above, implementation of the proposed project would not expose people or structures to a significant risk of loss, injury or death involving flooding associated with the project site. According to the City’s General Plan EIR, flood hazards associated with inundation resulting from levee or dam failure are considered a low threat in the City of Galt. A system of levees and dikes for the streams and creeks draining to the Cosumnes River are generally found in the northwestern portion of the General Plan study area, outside of the General Plan boundary and to the north of the study area. Laguna Creek may be subject to dam failure inundation in the event of a major dam failure at Rancho Seco Dam, which is located almost 10 miles northeast of the City of Galt; however, the dam inundation area along Laguna Creek and near the City of Galt is located along the northern boundary of the General Plan study area where development is not proposed as part of the General Plan, as such areas are outside of the City’s Sphere of Influence boundary. Therefore, the proposed project would not expose people or structures to a significant risk of loss, injury or death involving flooding as a result of the failure of a levee or dam, and impacts would be less than significant.

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Mitigation Measure(s) None required.

4.8-7 Inundation by seiche, tsunami, or mudflow. Based on the analysis below, the project would have no impact. Based on the analysis below, the project would have no impact.

The project area is not located near any large bodies of water that would pose a seiche or tsunami hazard. In addition, the project site is relatively flat and is not located near any physical or geologic features that would produce a mudflow hazard. Therefore, no impact would occur related to inundation by seiche, tsunami, or mudflow.

Mitigation Measure(s) None required.

Cumulative Impacts and Mitigation Measures

The following discussion of impacts is based on the implementation of the proposed project in combination with other proposed and pending projects in the region. Other proposed and pending projects in the region under the cumulative context would include buildout of the City’s General Plan, as well as development of the most recent planned land uses within the vicinity of the project area.

4.8-8 Cumulative impacts to hydrology and water quality within the City of Galt. Based on the analysis below, the impact is less than significant.

While continued development within the City of Galt would result in additional stormwater runoff and entry of pollutants into receiving waters via construction and operation of future projects, each project is required to comply with the City’s regulatory stormwater documents, standards, and requirements (including the MS4 permit, SQIP, Sacramento Stormwater Management Program, and Stormwater Quality Design Manual). Compliance with such would ensure that each project provides adequate storage capacity for the additional stormwater runoff generated, as well as incorporates sufficient BMPs to successfully remove pollutants from site runoff during the construction and operational phases.

As discussed previously, the proposed drainage system improvements, as well as the raising of Marengo Road, would reduce the size of the floodplain associated with Deadman Gulch. The raising of Marengo Road would eliminate the existing spillover at Marengo Road into the McCaffrey Middle School sports fields west of Marengo Road. The on-site detention basin locations downstream from the proposed on-site channel crossings would accommodate the peak water surface elevation, and the proposed improvements would ensure that the Deadman Gulch channel would be capable of handling 100-year peak flows.

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As demonstrated above, the project’s contribution to cumulative hydrology and water quality impacts would be considered less than significant.

Mitigation Measure(s) None required.

Endnotes

1 Wood Rodgers. Eastview Specific Plan Drainage Study. December 9, 2014. 2 Cardno ENTRIX. Water Supply Assessment for the Eastview Specific Plan. October 16, 2014. 3 Carollo Engineers, Inc. City of Galt Storm Drainage System Master Plan. May 2010. 4 City of Galt. 2030 Galt General Plan Policy Document. April 2009. 5 City of Galt. Final Environmental Impact Report for the 2030 Galt General Plan. March 2009. 6 City of Galt. 2030 Galt General Plan Existing Conditions Report. November 2005. 7 Cardno ENTRIX. Water Supply Assessment for the Eastview Specific Plan [pg. 4-1]. October 16, 2014. 8 California Regional Water Quality Control Board, Central Valley Region. The Water Quality Control Plan (Basin Plan) for the California Regional Water Quality Control Board, Central Valley Region, Fourth Edition. Revised October 2011 (with approved amendments). 9 City of Galt. 2030 Galt General Plan Existing Conditions Report [pg. 8-5]. November 2005. 10 University of California, Davis – Division of Agriculture and Natural Resources. Reference: Basic Concepts of Groundwater Hydrology. 2003. Available at: http://groundwater.ucdavis.edu/files/156562.pdf.

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