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4.2.2.3 Soil sample collection <br />Soil samples will be collected for field screening and geologic logging at <br />3 -foot intervals, beginning at a depth of approximately 1 foot, and <br />continuing to a depth of approximately 10 feet. Below this depth, samples <br />will be collected at 5 -foot intervals. After extracting the necessary <br />soil samples, each boring will be backfilled with a cement/bentonite grout. <br />Soil samples will be selected for laboratory analysis based on the following <br />criteria: <br />• The sample just above the depth where gas plant residues are detected <br />(by visual and/or photoionization detection methods). <br />• The sample containing the highest apparent concentration <br />of gas plant residues ("worst case" samples). <br />• The sample just below the depth where gas plant residues are observed. <br />This selection process is in accordance with the "iterative" approach set <br />forth in U.S. EPA "Test Methods for Solid Waste, Physical/Chemical <br />Parameters", Govt. Document no. SW -846, Volumes I and II, November, 1986. <br />Additional soil samples may be selected as necessary to further delineate <br />areas where contamination is extensive. <br />' If no residues are detected in any soil samples taken from a particular <br />boring, a single soil sample collected from a depth where gas plant residues <br />are most commonly encountered at the site will be selected for laboratory <br />analysis. <br />Soil samples selected for laboratory analysis will be analyzed within <br />allowable holding times for selected chemical parameters historically <br />associated with the production of gas. A complete list of the <br />chemical parameters selected for analysis and the soil sample selection <br />rationale is included in Section 4.3.1. Table 1 shows the allowable holding <br />times for each parameter. <br />C <br />1 3542a/BAV102 11 <br />