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r ; 1 V . A S S O C I A T E S I N C described to ATC's Summary Report of Additional Subsurface Investigation, Pacific Coast Recreation, 3755 Munford Avenue, Stockton, California, dated July 12, 2004 SAMPLING ACTIVITIES On September 23, 2004, ATC personnel collected groundwater samples from monitoring wells MW I through MW 10 and the domestic well effluent The locations of the wells are shown on Figure 2 Prior to collection of groundwater samples, the depth to water, pH, electrical conductivity, and temperature were measured and turbidity was visually observed in groundwater purged from the monitoring wells and recorded Approximately three well casing volumes were purged from each monitoring well prior to sampling The monitoring wells were allowed to recover and samples were collected from each well using disposable polyethylene bailers The domestic well was sampled utilizing the dedicated domestic well pump system and a sample taken at the well head After the groundwater samples were collected, dissolved oxygen was measured in groundwater purged from each monitoring well The groundwater samples collected from each well were submitted to State-certified Argon Laboratories Inc (Environmental Laboratory Accreditation Program Certification No 2359) in Ceres, California for chemical analyses of TPHg utilizing EPA Method 801513, benzene, toluene, ethylbenzene, xylenes (BTEX) and methyl tertiary butyl ether (MTBE) uttltzing EPA Method 8021B If MTBE was detected by EPA Method 802113, the groundwater sample was subsequently analyzed for MTBE, ethyl tertiary butyl ether (ETBE) di-isopropyl ether (DIPS), tertiary amyl ether (TAME), tertiary butyl ether (TBA), I,2-dtchloroethane (1,2-DCA), and 1,2- dtbromoethane (EDB) utilizing EPA Method 8260B to confirm the results Groundwater well purge and sample logs are contained to Attachment 1 GROUNDWATER FLOW DIRECTION Water level measurements were collected from wells MW I through MW 10 on September 23, 2004 Water levels 1n the shallow aquifer ranged from 71 40 to 73 01 feet below the tops of the well casing elevations, representing an average decrease to the shallow water table elevation of approximately 3 29 feet since June 2004 The water level data were used to develop the groundwater elevation contour map (Ftgure�) Shallow groundwater in the uppermost aquifer beneath the site flowed generally towards the south-southeast The average hydraulic gradient on September 23, 2004 was calculated to be 0 004 ft/ft or approximately 21 ft/mile A summary of groundwater monitoring data is presented in Table 1 ANALYTICAL RESULTS TPHg was detected to MW1, MW2, MW3, MW4, MW6, MW7, and MW8 with the highest TPHg concentration (130,000 micrograms per Mer ug/L) to MW2 BTEX components were . detected 1n MW1, MW2, MW3, MW4, MW6, MW7, and MW8 The highest concentrations of benzene, toluene, and xylenes were detected to MW2 at concentrations respectively of 25,000 S 1163931REPORTS13gr-2004 doc 3