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remain the same and are not expected to change because of long-term development limitations in these off-site r drainage watersheds(e.g., agricultural zoning). The College Park project site is divided into three on-site watersheds(Watersheds A,B, and D).The general boundaries of these watersheds,and the locations of the off-site watershed entrance points to the project site are depicted in Figure 4.7-1. Approximately 15%of the project site is currently covered by impervious surfaces (MacKay& Somps 2004). Existing storrawater runoff flowing through and generated on the College Park project site during a 100-year storm event is presented in Table 4.7-1 for each of the three on-site watersheds.As indicated,the Central Parkway,DeAnza Boulevard,and Mountain House Parkway watersheds would generate or pass through 610, 282, and 38 cubic feet per second(cfs),respectively,of runoff during a 100-year storm event,a total of 930 cfs for the site. Approximately 491, 158,and 0 cfs of this the nmoff,respectively, originates from the off-site watersheds located south and southwest of the project site and represents the"pass-through"flows. Table 4.7-1 College Park Stormwater Runoff Quantities' On-site Watershed Existing 100-Year Runoff(Cfs)b Watershed A(Central Parkway System) 6100 Watershed B (DeAnza Boulevard System) 282d ` Watershed D(Mountain House Parkway System) 38` Total 930r Note:Above values include stonnwater drainage originating off-site(i.e.,Watersheds D,E,B,and S139A). The runoff quantities in this table are in cfs and represent the runoff entering or exiting the project site. b These values were calculated by PACE in the Mountain House Drainage Master Drainage Plan Update, May 27,2003. ` Approximately 491 cfs of this is runoff from off-site(pass-through flows). d Approximately 158 cfs of this is runoff from off-site(pass-through flows). s All of these flows originate on-site. r Approximately 649 cfs of this is runoff from off-site(pass-through flows). Source:MacKay&Somps 2004. EXISTING GROUNDWATER CONDITIONS According to the California Department of Water Resources(DWR),the MHMP area is located in the Tracy groundwater subbasin.The subbasin covers an area of approximately 540 square miles and is drained by the San Joaquin River and Corral Hollow Creek. Primary water-bearing formations in the subbasin include semi- consolidated deposits of clay, silt,and gravel of the Tulare Formation, flood basin deposits, and older and younger alluvium. Generally,groundwater flows as a reflection of the surface topography(i.e.,from southwest to north and northeast).Daring subsurface investigations performed in MHMP neighborhoods C,H,I,and J in March 2004, groundwater was detected at depths of 5 and 40 feet below ground surface(bgs) (SJCCDD 2005). Given that these neighborhoods are located further north of the project site where groundwater is closer to the surface,it can be reasonably assumed that groundwater underlying the College Park project site is a minimum of 40 feet bgs. The water quality of the Tracy subbasin is somewhat impaired. Areas of poor water quality existing throughout the subbasin and elevated levels of chloride and nitrate have been detected in the vicinity of the City of Tracy (located approximately 3 miles to the west).According to the Mountain House Master Plan Environmental Impact Report(MHMP EIR),elevated levels of total dissolved solids(TDS),nitrates,and sulfides have been detected in groundwater in the vicinity of the MHMP area.The high levels of TDS may be the result of saltwater intrusion from the Delta.Relatively high levels of nitrates may be the result of poor livestock management in the area and/or releases from household septic systems(SJCCDD 2005). College Park at Mountain House Specific Plan III Draft EIR EDAW San Joaquin County 4.7-3 Drainage