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- K. a , x - �ME -1 11" mm Y Woodward-Clyde Car�st�lfa� i< y 2.0 SCOPE OF WORK To evaluate the extent of subsurface gasoline contamination and prepare a remedial action alternatives analysis, WCC: 1) conducted a soil gas survey of the area surrounding the underground storage tanks, 2) advanced 380 lineal feet of soil borings, and logged and collected soil samples for diemical testing, 3) installed monitoring wells in the borings and developed and sampled these wells for TPH and BTEX, 4) surveyed the well elevations to 0.01 foot and obtained water level elevations for preparation of a groundwater contour map, 5) prepared maps and cross sections showing the limits of contamination, and 6) evaluated treatment strategies to remediate the contamination. WCC's field activities and the results of this investigation are described below. 2.1 Soil Gas &MU WCC subcontracted NET Pacific Laboratories (NET) to conduct a soil gas survey of the underground storage lank area to evaluate the extent of vapor pi-rase contamination. The results of this survey were used to preliminarily locate the hydrocarbon plume, and Position groundwater monitoring wells to map its extent. In June 1988, NET obtained !,.°• 26 soil gas sampias for TPH and BTX analyses by pneumatically advancing a 314-inch galvanized probe into the ground to various depths, vacuum extracting soil gas vapors through the probe into 300-m1 glass sampling vessels (pre-evacuated 10 approximately 0,2 psia), and analyzing the samples with a portable Hewlett-Packard field gas chromatograph using both flame- and photoionization detection. The soil gas sample locations are shown on Figure 3 through 6. NET's analytical results are summarized in Table 1 below. NET's laboratory report is provided in Appendix B. As shown in table 1, NET obtained soil gas samples at points P1-P14 at depths of either 7, 11, 21, 23 27, 32, 33 and/or 40 feel, depending upon the location. TPH and/or BTX were detected In 5011 gas samples obtained from all points except P8. P12 and P14. The highest TPH concentrations observed occur In samples P1 and P2 adjacent to the underground storage tanks at depths of 7 feet, In P11 west of the underground storage tanks at a depth of 33 feet, and in,, P13 southwest of the underground storage tanks at a depth of 32 feet. The location of these sampling points is shown on soil gas isoconenlration maps Figures 4 through 7. These maps show the distribution of subsurface BTEX and TPH in soil gas at the site and were produced by plolting the highest measured soil gas concentration for the 3