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4.8 WATER QUALITY This section evaluates the potential water quality impacts associated with construction of College Park features and long-term changes in land uses that would occur under development of the College Park at Mountain House Specific Plan D1.This section is complementary to Section 4.7,"Drainage,"in that the effects of College Park development on the water quality of surface waters that receive runoff from the project site would be closely linked to the design and functioning of the stormwater drainage facilities that are addressed in Section 4.7. Documents used to prepare this section include the 1994 Mountain House Master Plan EIR(MHMP EIR),Final Environmental Impact Report for Mountain House Master Plan and Specific Plan I(San Joaquin County 1994), Mountain House Speck Plan III(Neighborhoods A, B, and the Easterly Portion of D),Initial Study(San Joaquin County 2003),Mountain House New Community Specific Plan III College Park(EDAW 2004),Mountain House Storm Water Master Plan Update(Mountain House Community Services District [MHCSD]2003),and Specific Plan III Amendment to the Stormwater Master Plan Update(MacKay& Somps 2004). 4.8.1 PHYSICAL SETTING SACRAMENTO-SAN JOAQUIN DELTA AND OLD RIVER Drainage from the project site flows to Old River, a historical channel of the San Joaquin River within the Sacramento-San Joaquin River Delta(Delta)that forms the northern boundary of the entire Mountain House Community area(refer to Figure 3-2 in Section 3,"Project Description").The Delta covers approximately 1,500 square miles and is interlaced with hundreds of miles of waterways.Delta channels are generally less than 20 feet deep unless dredged,and vary in width from less than 100 feet to more than 1 mile.The Delta is a tidally influenced estuary with complex hydraulics.Freshwater inflows to the Delta vary greatly depending on precipitation,snowmelt, Delta export operations at the Central Valley Project(CVP),and State Water Project(SWP)pumping stations in the south Delta.During summer,most of the inflow to the Delta comes from regulated releases from SWP and CVP reservoirs. The CVP and SWP pumping plants are key water supply facilities in California and withdraw millions of acre- feet of water from the Delta each year for agricultural uses in the San Joaquin Valley, and urban uses in Southern California and the San Francisco Bay Area,respectively.During much of the late summer and fall of most years, the withdrawal rates at the CVP and SWT pumps are large enough that the flow is in a reverse direction in the section of Old River located north(i.e.,downstream)of the pumps. PROJECT AREA CLIMATE AND DRAINAGE Average annual rainfall in the project vicinity is 10-12 inches,with most rainfall occurring from November to April. Drainage from the project site flows to Old River via Mountain House Creek.Mountain House Creek is north of the project area(refer to Figure 3-11)and flows from the southwest to the northeast and joins Old River via a restored section of the stream and Dredger Cut(a feature of Old River that was formerly isolated by levees).Drainage in the project site itself is generally in a northeasterly direction via small surface drainage swales and overland flow. Section 4.7,"Drainage,"provides a detailed description of drainage conditions from the project site. WATER QUALITY CONDITIONS The 2002 version of the Section 303(d)list for California issued by the State Water Resources Control Board (SWRCB)(discussed below in Section 4.8.2,"Regulatory Setting")identifies all channels in the eastern Delta, including Old River,as impaired for a number of contaminants.The Delta is on the Section 303(d) list for impairment from chlorpyrifos and diazinon(i.e.,organophosphate pesticides), electrical conductivity,unknown toxicity,Group A pesticides specifically including DDT(i.e.,a group of specific organochlorine pesticides that College Park at Mountain House Specific Plan III Draft EIR EDAW San Joaquin County 4.8-1 Water Quality