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Phase 11 Site Investigation 7.1.2 Composite Soil Sampling of the analyzed for total petroleum hydrocarbons as Agricultural Chemical Mixing gasoline (TPHg) and total petroleum Areas hydrocarbons as diesel (TPHd)by Environmental �. Protection Agency(EPA) Method 8015M; and To evaluate the potential presence of agricultural also for benzene, toluene, ethylbenzene, and total chemicals in surficial soils in the vicinity of the xylenes(BTEX) with EPA Method 8020. three concrete water boxes one composite sample of the surface soils was collected. This sample In accordance with the approved work plan, was composited from individual composite because none of the samples contained detectable samples collected at each of the three concrete TPHg, soil samples were not analyzed for total water boxes in the following manner. At each of lead or for soluble lead. In addition, in the water boxes, the surfical soil within a one accordance with the approved work plan, square foot area was thoroughly mixed with a because none of the samples contained detectable spade to a depth of 0.5 feet bgs to homogenize the TPHg, soil samples were not analyzed for methyl soils present. After mixing the surficial soil, a tertiary butyl ether(MTBE). MTBE is a gasoline representative sample was collected and placed additive that was first incorporated into gasoline in a clean stainless steel bowl. This process was formulations ten years ago in California and repeated at three additional areas in the within the past few years in the Central Valley immediate vicinity of the concrete water box and (RWQCB, 1996). representative samples from each of the three �.., areas were added to the stainless steel bowl. 7.2.2 Analyses Performed on the Thus, four representative samples were placed in Composite Sample from the stainless steel bowl and then this soil was Agricultural Chemical Mixing mixed again to homogenize the soil from all four Areas locations. A composite sample of the soil representative of that in the vicinity of the water Composite sampling of the agricultural chemical box was thus collected from the stainless steel mixing areas was performed to assess whether bowl and placed in a clean plastic bag. This surficial soils had been impacted. The composite process was repeated at the other two concrete sample was analyzed for organochlorine water boxes and these samples were placed in pesticides with EPA Method 8080, for y plastic bags. These three composite samples, organophosphorus pesticides with EPA Method representative of soil at each water box, were 8140, for chlorinated herbicides with EPA then placed in the stainless steel bowl and Method 8150, for carbamate and urea pesticides thoroughly mixed to homogenize the soil. A with EPA Method 632, and for nitrate with EPA ..� sample, which was a composite sample of soil present at the three concrete water boxes, was Method 300. then collected from the stainless steel bowl. This sample was placed in laboratory-cleaned glass 7.3 Results of Phase 11 Investigation jars, sealed with Teflon-lined covers, and placed in a chilled cooler for transport under chain-of- 7.3.1 Soil Profile custody protocol to a state-certified analytical laboratory. Two generalized cross-sections A-A' and B-B' were constructed from the field logs of six soil 7.2 Analytical Program borings(SB-2 to SB-7) (Plates 4 and 5). As illustrated in the cross-sections, silty gravels with 7.2.1 Analyses Performed on Soil local lenses of clayey silt comprise the upper 22 Samples from Soil Borings to 27 feet of the Site. The gravels are fine- and coarse-grained, with little sand or clay. Cobble- An average of four soil samples were selected and boulder-sized gravels were not encountered. from each boring based on subjective field Beneath these gravels, at depths ranging from 22 criteria (PID readings, soil discoloration, and to 27 feet bgs, are mainly clayey silts, clayey silts hydrocarbon odors) as well as the objectives of with gravel, and occasional lenses of clayey the field investigation. These samples were gravels. The more clay rich lithologies extend to lo the bottom of each of the borings. c:\WRGDH\GH30371Z.151 Harding Lawson Associates 14 r