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ATC Associates Inc. �.. 1117 Lone Palm Avenue, Suite 201 Modesto, California 95351 209-579-2221 %TC Fax: 209-579-2222 ASSOCIATE S I N C . 8015M; and BTEX, methyl tertiary butyl ether (MTBE), tertiary butyl alcohol (TBA), di-isopropyl ether (DIPE), ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME), 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 Groundwater level measurements collected from monitoring wells MW1 through MW11 on March 24, 2011, ranged from 37.58 to 40.14 feet bgs. Groundwater elevations in the monitoring .r wells ranged from -22.56 to -23.17, representing an average increase in the groundwater table elevation of approximately 2.62 feet since October 2010. The water level data were used to develop the groundwater elevation gradient map provided as Figure 3. The groundwater elevation recorded for MW6 was not used in the development of the groundwater elevation gradient map due to mounding. Shallow groundwater flow beneath the site was toward the northeast with a calculated average hydraulic gradient of approximately 0.0015 feet/foot or 7.76 feet/mile. A summary of groundwater monitoring data is presented in Table 1. ANALYTICAL RESULTS Analytes of interest detected in the groundwater samples collected from the site during the current reporting period include TPHg, BTEX, MTBE, TBA, and 1,2-DCA. None of the analytes of interest were detected in the groundwater sample collected from in MW-11. A summary of the laboratory analytical data is presented in Table 2. A copy of the laboratory analytical report is included in Attachment 2. TPHg were detected in the groundwater samples collected from MW1, MW2, MW3, MW5, MW6, and MW9 at concentrations ranging from 60 to 890 micrograms per liter(Ng/L). Based on the available data, TPHg concentrations in wells MW1, MW2, MW3, MW5, and MW6 have increased since the previous sampling event, while the TPHg concentration in MW9 decreased since the previous sampling event. An isoconcentration map illustrating the distribution of TPHg in groundwater during the March 2011 sampling event is provided as Figure 4. BTEX constituents were detected at relatively low concentrations in the groundwater samples collected from MW2, MW5, and MW6. These detectable BTEX concentrations did not exceed their respective Maximum Contaminant Levels (MCLs) for drinking water standards as established by the State of California Department of Public Health (DPH). w MTBE was detected in the groundwater samples collected from MW1, MW2, MW3, MW4, MW7, and MW8 at concentrations ranging from 0.7 to 41 pg/L. The MTBE concentrations detected in the samples collected from MW3 and MW4 were equal to and/or exceeded the primary MCL for drinking water standards as established by the DPH. An isoconcentration map illustrating the distribution of MTBE in groundwater during the March 2011 sampling event is provided as Figure 5. TBA was detected in the groundwater samples collected from MW1, MW2, MW3, MW5, and MW6 at concentrations ranging from 5.6 to 23 pg/L. The detectable concentrations of TBA in the samples collected from MW2 and MW3 equaled or exceeded the notification level for TBA of 12 pg/L. s:\environmental\22493\Reports\QMR 2011 SA1.doc 4 V r