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groundwater in the wells was measured from the top of the well casing to the.nearest 0.01 foot, using an electronic sounder. The survey data and relative groundwater elevation measurements are presented in Table 1. The well elevation survey map is included in Appendix D, and a graphical interpretation of the groundwater gradient beneath the site is shown in Figure 3. 3.0 SITE GEOLOGY AND HYDROGEOLOGY Soils encountered while drilling during this and previous investigations generally consisted of sandy silt to silty sand to depths of 14 to 18 feet below grade, underlain by a 0.5- to 2-foot- thick silty clay to clayey silt layer. Below the clay and silt, sand with varying silt content was encountered to the total depth of the borings at 20 to 25 feet below grade. -. Hydrogeologic cross sections prepared using boring logs generated during this and previous investigative activities are shown in Figure 4. Lines of hydrogeologic cross sections are shown in Figure 2. Near-saturated soil conditions encountered during drilling and sampling were noted at approximately 10'feet below grade, with the depth to groundwater measured in the ,. monitoring wells at approximately 15 feet below grade. Groundwater elevations in all the wells as measured on September 15, 1993, were used to develop the groundwater potentiometric surface map shown in Figure 3. The groundwater gradient as interpreted from these measurements is approximately 0.0006 foot per foot in a general southeasterly direction across the site. ' 4.0 ANALYTICAL METHODS Pace, Inc., a state-certified analytical laboratory, analyzed the soil and groundwater samples using standard test methods of the U.S. Environmental Protection Agency (EPA) and the California Department of Health Services. The soil and groundwater samples were analyzed for the following: •. Total petroleum hydrocarbons as gasoline (TPH-G) using EPA Methods 5030/8015 • Benzene, toluene, ethylbenzene, and total xylenes (BTEX) using EPA Methods 5030/8020 Additionally, the groundwater.sample collected"from the monitoring well near the used oil tank was analyzed for total petroleum hydrocarbons as diesel (TPH-D) using EPA Methods 3510/8015. Laboratory results for groundwater and soil samples are summarized in Tables 1 and 2, and the official laboratory reports and chain of custody records are included in Appendix F. The results of groundwater analysis are shown in Figure 5. R\0\10-151\551.Rf Tl020494 4 i /�1