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ATC Associates Inc. 1117 Lone Palm Avenue, Suite B %TC 0 Modesto, California 95351 209-579-2221 IV A S S O C i a r E S I n C. fax:209-579-2225 i M 7 In September 23 and 24, 2003, H2OGEOL collected groundwater samples from MW1 and MW4 through MW8. Petroleum hydrocarbons were detected in groundwater samples collected from these wells' The reported groundwater flow direction was to the north. Refer to H2OGEOL's Third Quarter, 2003+Groundwater Monitoring Report, dated October 31, 2003, for more information. In a letter dated November 14, 2003, the EM indicated that the proposed scope in the H20GEOL workNan was not adequate or necessary. The EHD requested that a workplan be prepared in the context of a site conceptual model that includes analytical data collected during removal of a waste oil tank from the site in September 2003. The requested workplan was submitted by ATC on February 2, 2004.' SAMPLING ACTIVITIES On September 30, 2005, ATC personnel collected groundwater samples from MWl and MW4 through MW8. The locations of the wells are shown on Figure 2. Prior to collection of groundwater f samples, the depth to water, pH, electrical conductivity, and temperature were measured 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 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) Cert. No. 2359, in Ceres, California far chemical analysis of total petroleum hydrocarbons as gasoline (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) di-isopropyl ether (DIPE), tertiary amyl ether(TAME), tertiary butyl ether (TBA), 1,2- dichloroethane (1,2-DCA), and 1,2-dibromoethane (EDB) utilizing EPA Method 8260B. Groundwater well purge and sample logs are contained in Attachment 1. GROUNDWATER FLOW DIRECTION Water levels were measured in MW1 through MW8 on September 30, 2005. Depth to water in the shallow aquifer ranged from 5.68 to 7.71 feet below the tops of the well casing elevations, representing an average decrease in the shallow water table elevation of approximately 0.17 feet since June 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 towards the north-northeast. The average hydraulic gradient on September 30, 2005, was calculated to be 0.0035 feet per foot,or approximately 18.5 feet per mile. A summary of groundwater monitoring data is presented in Table 1. i ANALYTICAL RESULTS I Groundwater samples collected from MWl, MW4, MW5, MW6, MW7, and MW8 contained no detectable concentrations of TPHg or BTEX constituents. s:lenviromema112584'AO037Teportsl3gr-2005.doc 3 7