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S <br /> 4.4 ANALYTICAL METHODS - <br /> .' Pace, Inc., a state-certified analytical laboratory, analyzed the soil,and groundwater samples <br /> usizig standard test methods of the U.S. Environmental-Protection,Agency (EPA) and the <br /> California Department of Health Services. <br /> The samples were analyzed for the,following: <br /> • Total petroleum hydrocarbons as gasoline (TPH-G) using <br /> ' EPA Methods 5030/8015 <br /> • Benzene, toluene, ethylbenzen'e, ana total xylenes (BTEX) using <br /> ' EPA Methods 5030/8020 <br /> Laboratory results for groundwater and soil samples are summarized in Tables 1 and 2, and <br /> the official laboratory reports and chain of custody records are included in Appendix F. The <br /> ' results of groundwater analysis are shown in Figure 5. <br /> ' r <br /> 5.0 DISCUSSION OF RESULTS , <br /> 1 The following are the results of field activities and laboratbry'analysis of soil and <br /> 1 <br /> groundwater samples collected during this supplemental site investigation: <br /> • Soils encountered at the site generally consisted of 5 feet of silty clay underlain by <br /> M interbedded sand and silt to the total depth of the borings. ' <br /> • Near-saturated soil conditions were encountered at approximately 18 feet below grade <br /> ' during drilling, with the depth to groundwater measured in the monitoring wells <br /> during sampling at between 17 and 18 feet below grade. <br /> S <br /> • Analysis of soil samples collected from Borings MW-5 through MW-7 at depths of 11 <br /> ` and 16 feet below grade did not detect TPH-G above the reported detection limit. <br /> Benzene at a concentration of 0.13 ppm was detected in the soil sample collected from <br /> ' MW-5 at 16 feet below grade. +. _ <br /> • Adsorbed-phase hydrocarbons detected in the soil appear to be limited to or below _ <br /> the capillary fringe in the vicinity of the underground tasks. <br /> '• Free product or sheen was not observed in any,of the monitoring wells. <br /> Groundwater elevation data as measured on•April 25, 1993 indicate a gradient of <br /> approximately 0:002 foot per foot in a northeasterly direction across the site. <br /> Groundwater.table has increased by approximately 3.4 feet between December 1992 <br /> and April 1994. <br /> E\o\10-136\55LRPr/062294 4 <br /> Rol <br />