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r <br /> lir <br /> the northeast) . Additional investigations were conducted by <br /> Exceltech and presented in a March, 1988 report entitled "Report <br /> of Monitoring Well Installation, Sampling and Analysis for <br /> Tri/Valley Growers". The report indicated the following results: <br /> 1. Laboratory testing of a groundwater sampling from the newly <br /> installed (down gradient) monitoring well iMW4) detected <br /> concentrations of benzene and toluene above Department of Health <br /> Services (DHS) action levels. [LKd TI'14_44-a1q-5,t,:,e <br /> 2. No hydrocarbon cincamination of soil (composite sample) was <br /> detected in samples from MW4. <br /> 3. Testing of a domestic well located on property adjacent to <br /> the Tri/Valley Growers did not record dissolved hydrocarbons <br /> above method detection limits. <br /> 4. Sampling of the soils excavated form the tank pit did not <br /> record hydrocarbons above detection limits thus indicating these <br /> soils may be used to fill in the exca,ration pats which remains <br /> open. <br /> The purpose of WaterWork's investigation is twofold; first, to <br /> sample the open tank pit excavation to determine the degree of <br /> hydrocarbon contamination; if present, in order to assess the <br /> potential for backfilling, and secondly, define the vertical and <br /> lateral extent of dissolved hydrocarbon contamination, down <br /> groundwater gradient from the tank pit and the documented <br /> contamination in MW4. To confirm . the reported northeasterly <br /> groundwater gradient, WaterWork monitored and surveyed the four <br /> existing wells on May 26, 1988. The calculated flow is similar <br /> to the . September 19, 1938 flow direction reported by Exeltech <br /> (Figures 3, 4) . A workplan to conduct the a:dJitional <br /> investigations is prejented below. <br /> WORKPLAN <br /> A. Tank Pit Excavation <br /> 1. Examine the soils in and around the former tank pit for <br /> evidence of hydrocarbon contamination. <br /> 2. 2f no contamination is detected by field inspection, a <br /> total of six soil samples, one from each side and two from the <br /> pit bottom will be collected. These six samples will be <br /> collected by driving two inch diameter by six inch long brass <br /> tubes directly into the pit walls and bottom after removal of six <br /> inches of soil. The brass sampler_ container will be sealed with .. <br /> _.... <br /> foil, a plastic cap and tape. The labeled sample will be place <br /> in a refrigerated container and transported under chain of <br /> custody protocol to a state certified laboratory. <br />