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T <br /> Tracy Marine Sales <br /> 2353 Toste Rd, Tracy <br /> Page 2 <br /> • Analytical results of MW-4 , MW-5, and MW-8 all showed <br /> various concentrations of TPH-g, BTEX, and MTBE (dropped <br /> from the two previous sampling events in January 2000 and <br /> December 1999) . <br /> • Groundwater flow gradient is reported to be north- <br /> northwesterly. MW-2 is located west-southwest of MW-7, <br /> while MW-3 is located west of MW-2 . <br /> It is not known at this time if the increase of MTBE and <br /> Benzene concentrations in the MW-2 sample and the decrease <br /> of these contaminant levels in the MW-7 sample indicates a <br /> westerly migration of the MTBE and Benzene plume. PHS/EHD <br /> agreed with the report' s recommendation that installation of <br /> additional groundwater monitoring wells to the north, east <br /> and northwest of the yet to be defined contamination plume <br /> is necessary to delineate the extent of the plume. Sampling <br /> of the wells will provide information on westerly migration. <br /> The deepest soil sample analyzed was collected from MW-6 at <br /> 32 feet below surface grade (bsg) . Analytical results of <br /> this soil sample were non-detect at appropriate detection <br /> limits, but analytical results of the soil sample at 28 feet <br /> bsg were 0 . 065, 0 . 26 , 0 . 07 and 0 . 3 parts per million (ppb) <br /> of BTEX, respectively, 2 . 8 ppm of TPH-g, 170 ppb of MTBE. <br /> PHS/EHD recommends at least two consecutive 5-foot-interval <br /> soil samples of non-detection in analytes near the source of <br /> the release for vertical delineation. Work performed at <br /> nearby Local Oversight Program (LOP) site 2450 Toste Road <br /> reported the presence of various sand strings and gravel <br /> layers as deep as 40 feet bsg. Due to the resilient and <br /> highly mobile nature of MTBE and other oxygenates, PHS/EHD <br /> recommends characterizing the hydrogeological condition at <br /> this site using methods such as continuous core boring with <br /> acetate sleeve or Cone Penetration Testing at the same time <br /> the vertical definition of the contamination is being <br /> defined. <br /> California Department of Health Services Primary Maximum <br /> Contaminant Levels (MCL) of 1, 2-Dichloroethane (1, 2 DCA) and <br /> 1, 2-Dibromoethane (EDB) for drinking water are 0 . 5ppb and <br /> 0 . 02 ppb, respectively. PHS/EHD recommends 1, 2 DCA and EDB <br /> be included in all future work and quarterly reports . <br /> Analysis for 1, 2 DCA and EDB can be included when EPA Method <br />