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! r(VVIF8 A S S O C I A T E S I N C 5.2 Groundwater Conditions 5.2.1 Site Hydrogeology From January 1999 to June 2002, static water levels have fluctuated from approximately 19 to 24 feet bgs, variations in depth to water between the wells during each monitoring event are ' consistent with seasonal fluctuations ATC performed quarterly monitoring of wells MW1 through MW5 in December 2000, Marchand October 2001, and April 2002 During this period, groundwater was measured at depths ranging from 21 43 to 24 91 feet bgs The groundwater flow direction was consistently southwest at a gradient of 0 0005 to 0 0006 ft/ft Groundwater contour maps are included in Appendix D and groundwater elevation measurements are presented in Table 3 5.2.2 Petroleum Hydrocarbons in Groundwater ' Petroleum hydrocarbons have historically been detected only in well MW2, although detectable concentrations of TPHd were detected in wells MW4 and MW5 until September 2000 The concentrations of petroleum hydrocarbons in well MW2 have generally decreased over the monitoring period No petroleum hydrocarbons were detected in any of the groundwater samples collected from wells MW1, MW3 and no petroleum hydrocarbons have been detected in wells MW4, and MW5 since September 2000 None of the wells have ever contained detectable ' concentrations of fuel oxygenates ATC estimated the lateral extent of TPHd impacted groundwater as depicted on Figure 9 and TPHg impacted groundwater as depicted on Figure 10 5.2.3 Mass Balance Calculations - Groundwater Using groundwater analytical results presented in Table 2, the most recent data available, ATC estimated the lateral extent of dissolved TPHd and TPHg concentrations beneath the site as depicted on Figures 9 and 10, respectively The total mass of TPHd remaining in the groundwater was not calculated because TPHd was not detected in groundwater samples collected during the most recent sampling event The isoconcentration shown on Figure 10 was used by ATC to perform mass balance calculations to estimate the mass of TPHg impacted groundwater The total mass of TPHg remaining in the groundwater is estimated to be approximately 0 7 pounds of 0 3 kilograms Mass balance calculations are included in Appendix F 6.0 GROUNDWATER RECEPTOR SURVEY ' ATC performed a well survey for the site at the request of SJCEHD ATC reviewed SJCEHD groundwater well construction logs, Department of Water Resources (DWR) groundwater well construction logs, conducted a site walk in the vicinity of the site, and contacted the City of Ripon Public Works Department to identify any groundwater wells located within a 2,000 -foot w 113099\reportslclosure doe 7