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kn KLEI NFELDER 5 SUMMARY OF PREVIOUS INVESTIGATIONS AND KLEINFELDER S ASSESSMENT Kleinfelder was retained by Nor-Cal to further assess the vertical extent of contamination at two locations in the backfilled tank excavation. Previous sampling of the tank excavation had indicated that elevated concentrations of petroleum hydrocarbons remained at the bottom of the tank excavation at two locations. The two Kleinfelder soil borings were ' advanced in the vicinity of these two areas. Additionally, Kleinfelder was retained to resample ground water monitoring well MW-1. 5.1 TANK EXCAVATION SOIL SAMPLING AND ASSESSMENT Soil boring B-1 was drilled at a 20 degree angle (from vertical) at the location where elevated TPH concentrations had been previously detected at 21 feet (Plate 3). This boring is located near the western property boundary and was drilled at an angle to evaluate the potential for the vertical migration of petroleum hydrocarbons at the edge of the tank excavation and property. Elevated PID readings (over 100 ppmv above background) were recorded at auger depths of 10 and 15 feet. PID g p readings ranged from ' 36 to 11 ppmv from 20 to 40 feet. The PID is a qualitative screening device and can be affected by soil type, temperature, wind and moisture. Qualitative PID readings cannot be directly correlated to quantitative TPH concentrations in the soil. Petroleum hydrocarbons ' were not detected in the samples analyzed at depths of 20, 25 and 40 feet. The soil sample analyzed at a depth of 20 feet had a PID reading of 36, however, no TPH concentrations were detected. Based on previous sample results and Meinfelder's current assessment, it appears that petroleum hydrocarbons may be present in the soil at the edge of the excavation from 10 to 20 feet below the ground surface. The lack of detected concentrations at 20, 25 and 40 feet indicates that there has not been significant vertical ' migration in the vicinity of boring B-1 and beneath the area with previously detected petroleum hydrocarbons at depths of 11 to 21 feet. ' Boring B-1 was drilled approximately 1 foot away from the fence at the western property boundary at a 200 angle from vertical. The boring was drilled at a slight angle to provide a partial assessment of the lateral migration of petroleum hydrocarbons at the western property boundary. The sample collected at an auger depth of 20 feet was approximately y 6 feet west of the fence; the sample collected at ani auger depth of 25 feet was FR1-92-15 Page 14 of 21 Copyright 1992 Kleinfelder,Inc.