Olson Residential Community Project – City of San Gabriel Draft Environmental Impact Report 4.9 HYDROLOGY AND WATER QUALITY This section describes the hydrologic conditions on and adjacent to the project site and evaluates potential impacts to surface and groundwater resources associated with the proposed project. The analysis contained in this section is based on the following technical studies prepared for the proposed project which are in Appendix J of this EIR: Preliminary Hydrology and Hydraulics Study, TTM 72626, C&V Consulting, Inc. January 2014. Standard Urban Stormwater Management Plan (SUSMP), TTM 72626, C&V Consulting, Inc. February 2014. In addition to these project-specific technical studies, the analysis contained in this section is also based on the following reference documents: County of Los Angeles Hydrology Manual, 2006. Los Angeles Basin Water Quality Management Plan. Regional Water Quality Control Board, LA Region. 2010. 2009 Construction Best Management Practices (BMP) Handbook, California Stormwater Quality Association (CASQA), July 1, 2010. Draft Final Urban Water Management Plan (UWMP), San Gabriel County Water District, Stetson Engineering, April 2011. 4.9.1 Existing Setting 4.9.1.1 Drainage The project site is part of the West San Gabriel Valley which drains from the San Gabriel Mountains south toward and into the Rio Hondo River, then the San Gabriel River, and finally into the Pacific Ocean. The Rubio Wash, a large fully improved flood control channel runs along the eastern boundary of the residential portion of the project (i.e., divides the overall property) and is maintained by the Los Angeles County Flood Control District (LAFCD). The site has several small catch basins along the east side of the site that outlet directly to the Rubio Wash (C&VC 2014, page 1). There is a publically maintained 30-inch reinforced concrete pipe (RCP) storm drain main line that runs in Santa Fe Avenue and runs beneath the project site and empties into the Rubio Wash. This line is currently being reconstructed to include several water quality basins as part of the regional Alameda Corridor East (ACE) project to lower the railroad lines through a portion of the City of San Gabriel. There is also a publically maintained 45-inch RCP storm drain line in El Monte Street that conveys runoff from the west to the Rubio Wash to the east (C&VC 2014, Appendix “As Built Plans”). The project hydrology study divides the site into seven drainage sub-basins (P1-P7). Existing runoff from the site was calculated in the project hydrology and hydraulics study and is shown in Table 4.9.A. At present, the site currently has a 24-hour volume of 6.6 acre-feet (2.15 million gallons)1 and 15.1 cubic feet per second (cfs)(C&VC 2014, Proposed and Existing Flows). Figure 4.9.1 shows the existing drainage subarea. 1 1 acre-foot equals approximately 326,000 gallons of water Section 4.9 Hydrology and Water Quality 4.9-1 Olson Residential Community Project – City of San Gabriel Draft Environmental Impact Report Table 4.9.A: Existing Onsite Runoff Characteristics Drainage Sub-Areas Runoff Characteristics P1 P2 P3 P4 P5 P6 P7 Total Area (acres) 0.31 1.04 1.64 0.64 0.88 1.07 0.38 5.96 24-Hour Runoff Volume 0.15 0.42 0.66 0.26 0.35 3.52 1.25 6.61 (acre-feet) Peak Flow Rate 1.22 3.42 4.88 2.10 2.89 0.43 0.15 15.09 (cubic feet/second or cfs) Source: Preliminary Hydrology and Hydraulics Study, TTM 72626, C&V Consulting, Inc. January 2014. Proposed and Existing Flows” Appendix. 4.9.1.2 Water Quality The project area is within the Los Angeles Region of the State Regional Water Quality Control Board (RWQCB), which encompasses the coastal watersheds of Los Angeles and Ventura Counties. The Los Angeles Regional Board's Basin Plan1 (Basin Plan) is designed to preserve and enhance water quality and protect the beneficial uses of all regional waters. Specifically, the Basin Plan: (a) designates beneficial uses for surface and ground waters; (b) sets narrative and numerical objectives that must be attained or maintained to protect the designated beneficial uses and conform to the state's anti-degradation policy; and (c) describes implementation programs to protect all waters in the Region. In addition, the Basin Plan incorporates (by reference) all applicable State and Regional Board plans and policies and other pertinent water quality policies and regulations. Those of other agencies are referenced in appropriate sections throughout the Basin Plan. The Basin Plan is a resource for the Los Angeles Regional Board and others who use water and/or discharge wastewater in the Los Angeles Region. Other agencies and organizations involved in environmental permitting and resource management activities also use the Basin Plan. Finally the Basin Plan provides valuable information to the public about local water quality issues. The Basin Plan is reviewed and updated as necessary. Following adoption by the Regional Board, the Basin Plan and subsequent amendments are subject to approval by the State Board, the State Office of Administrative Law (OAL), and the United States Environmental Protection Agency (USEPA). According to the Los Angeles Region Basin Plan, water quality in the project area is affected by a number of factors including but not limited to consumptive use, importation of water high in dissolved solids, runoff from urban and agricultural areas, and the recycling of water within the basin. In general, water quality in the Los Angeles Region becomes progressively poorer as water moves along hydraulic flow-paths. The highest quality water is typically associated with tributaries flowing from surrounding mountains and groundwater recharged by these streams. As indicated in the Basin Plan, there is one receiving water downstream of the project site as identified in the most recent Federal Clean Water Act (CWA) Section 303(d) list of impaired water bodies – San Gabriel River Reach 3 for toxicity (SUSMP, C&V Consulting 2014, Impaired Waters Appendix). This proposed development is subject to the Los Angeles County Department of Public Works (LACDPW) Standard Urban Stormwater Mitigation Plan (SUSMP) requirements under the "Redevelopment" category. According to the LACDPW, "redevelopment" means land-disturbing activity that result in the creation, addition, or replacement of 5,000 square-feet or more of impervious surface area on an already developed site. In this case, the entire project site is proposed to be 1 “Basin Plan for the Coastal Watersheds of Los Angeles and Ventura Counties” available at http://www.waterboards.ca.gov/rwqcb4/water_issues/programs/basin_plan/basin_plan_documentation.shtml 4.9-2 Hydrology and Water Quality Section 4.9 FIGURE 4.9.1 !!SN Olson San Gabriel Residential Community Project Environmental Impact Report 0 60 120 Feet Source: C&V Consulting, Inc., 2014. Onsite Drainage Areas I:\OLC1305\Reports\EIR\fig4-9-1_OnsiteDrainage.mxd (3/19/2014) Olson Residential Community Project – City of San Gabriel Draft Environmental Impact Report THIS PAGE INTENTIONALLY LEFT BLANK 4.9-4 Hydrology and Water Quality Section 4.9 Olson Residential Community Project – City of San Gabriel Draft Environmental Impact Report developed, although the amount of impervious surfaces on the site are anticipated to go from 84 to 76 percent since the site is currently covered with a warehouse building and parking, and will be replaced by residential development with extensive landscaped areas (C&VC 2014, SUSMP Calculations Appendix). As indicated in Tables 4.9.B and 4.9.C, each of the receiving waters has multiple designated beneficial uses. These designations provide a description of how the water is used and what beneficial purposes it serves. Table 4.9.B provides a description of each of these beneficial water uses, while Table 4.9.C shows the specific locations of the various beneficial use designations. Note that in addition to the beneficial uses shown in Table 4.9.B, both the Rubio Wash and Reach 3 of the Rio Hondo River are also generally indicated as possible wetland habitat (WET) but Table 2-1 of the Basin Plan also indicates that classification may only apply to portions of those channels and only where native vegetation and biological habitat is available. Adjacent to the project site, the Rubio Wash is fully improved, and the Rio Hondo River is four miles downstream of the project site, so no direct effects related to wetland habitat are expected related to this project. Table 4.9.B: Descriptions of Beneficial Uses Designated Beneficial Use Description of Beneficial Use Municipal and Domestic Waters used for community, military, or individual water supply systems including, Supply (MUN) but not limited to, drinking water supply. Groundwater Recharge Waters used for natural or artificial recharge of groundwater proposed for future (GWR) extraction, maintenance of water quality, or halting of saltwater intrusion into freshwater aquifers. Warm Freshwater Habitat Waters that support warm water ecosystems including, but not limited to, (WARM) preservation and enhancement of aquatic habitats, vegetation, fish, and wildlife, including invertebrates. Wildlife Habitat (WILD) Water that support wildlife habitats including, but not limited to, the preservation and enhancement of vegetation and prey species used by wildlife, such as waterfowl. Rare and Endangered Waters support habitats necessary for the survival and successful maintenance Species Habitat (RARE) of plant or animal species designated under State or Federal law as rare, threatened, or endangered.