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ATC Associates Inc .> v 1117 Lane Palm Avenue, Suite B Modesto, California 95351 209-579-2221 fax 209-579-2225 A S S O C I A T E S I N C a site conceptual model that includes analytical data collected during removal of a waste oil tank from the site to September 2003 The requested workplan was submitted by ATC on February 2,2004 SAMPLING ACTIVITIES On December 21, 2005, ATC personnel collected groundwater samples from MWl through MW8 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 Turbidity was visually observed in groundwater purged from the monitoring wells aid recorded Approximately three well casing volumes were purged from each monitoring well prior to sampling The wells were allowed to recover and samples were collected from each well using disposable polyethylene bailers The groundwater samples collected from each well were submitted to State-certified Argon Laboratories Inc Environmental Laboratory Accreditation Program(FLAP)Certification No 2359, m Ceres,California for chemical analyses of total petroleum hydrocarbons as gasohne (TPHg) utilizing Environmental Protection Agency (EPA) Method 8015M, benzene, toluene, ethylbenzene, and xylenes (BTEX) utilizing EPA Method 8021B, and methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE) dr- isopropyl ether (DIPE), tertiary amyl ether (TAME), ternary butyl ether (TBA), 1,2-dnchloroethane (1,2- DCA), and 1,2-lnbromoethane (EDB)Wrong EPA Method 8260B Groundwater well purge and sample logs are contained in Attachment 1 • GROUNDWATER FLOW(DIRECTION Water levels measured in MW I through MW8 on December 21, 2005, ranged from 5 27 to 7 35 fed below the tops of the well casmg elevations, representing an average increase in the shallow water table elevation of approximately 0 40 feet since September 2005 The water level data were used to develop the groundwater elevation contour map (Figure 3) Shallow groundwater flow in the uppermost aquifer beneath the site is tmvards the northamrdeaL The average hydraulic gradient on December 21,2005, was calculated to be 0 0026 feet per foot, or approximately 13 7 feet per mile A summary of groundwater monitoring data is presented in Table 1 ANALYTICAL RESULTS None of the analytes of interest were detected in the groundwater samples collected from MW3 and MW7 TPHg and ethylbenzene were detected in the groundwater sample collected from MW4 at concentrations of 110 micrograms per liter (ug/L) and 0 6 ug/L, respednvely 'MTBE was detested in the groundwater samples collected from MW 1, MW2, MW4, MW5, MW6, and MW8 at concentrations of 4 7 ug/L, 19 ug/L, 51 ug/L,48 ug/L, 61 ug/L,and 290 ug/L, respectively Analytical results of groundwater samples are summarized in Table 2 Laboratory data sheets and chain- of-custody documentation are contained in Attachment 2 An rsoconcentratton map depicting the MTBE concentrations in groundwater samples collected during the fourth quarter 2005 is shown on Figure 4 s\amro mentaNS847M37Vcporb\4W-ZOOS dM 3