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During purging, temperature, conductivity, and pH were measured to confirm entrance of <br /> formation water into the monitoring wells (Appendix F). <br /> 3.0 ANALYTICAL METHODS <br /> Soil andground water samples were analyzed in the laboratory using the following <br /> procedures: <br /> 0 TPH quantified as gasoline (T PH-G) using Environmental Protection Agency (EPA) <br /> Method 5030/8015 <br /> • TPH quantified as diesel (TPH-D) using EPA Method 3550/8015 for soil and <br /> 3510/8015 for water <br /> • BTEX using EPA Method 5030/8020 <br /> Analytical results of soil sampling are presented in Table 2 and ground water sampling in <br /> Table 1. Figure 4 shows the results of the sampling event performed on April 24. Analytical <br /> methods, chain of custody records, and official laboratory reports are presented in <br /> Appendix G. <br /> 4.0 SITE GEOLOGY AND HYDROGEOLOGY <br /> A review of the boring logs from this and previous studies shows that, with the exception of <br /> the backfilled area, the predominant soil type at the site is sandy silt to silt from ground <br /> surface to between approximately 11 and 15 fbg. In the vicinity of AW-2 and AW-4, a stiff <br /> to hard silty clay unit underlies the sandy silt to silt unit, persisting to the total depth of the <br /> borings. To the north and northwest, the sandy silt to silt unit is underlain by gravelly sand <br /> to sand; first observed in AW-3 from approximately 14 to 19 fbg, this unit thickens toward <br /> AW-6, occurring from 10 to 25 fbg, and thins towards AW-8, occurring from 14 to 19 fbg. <br /> The gravelly sand unit is underlain by the hard silty clay unit. <br /> Ground water elevations from Monitoring Wells AW-1 through AW-9, as measured on <br /> April 24, 1992, were used to develop the ground water elevation contour map shown in <br /> Figure 3. The average depth to water is approximately 10.9 fbg (20.6 feet msl). The average <br /> ground water gradient direction is to the northeast, with a magnitude of approximately 0.01 <br /> foot per foot across the area of study. Ground water elevation and gradient direction and <br /> magnitude have remained relatively consistent since monitoring was initiated in 1990. <br /> 4 <br />