ARCHIVED REPORTS XR0000621 - Laserfiche WebLink

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contamination levels (pollutant mass accumulations) for protection of groundwater at qualified sites benzene (0 ppm), toluene (6 ppm), ethylbenzene (30 ppm), and xylene t (20 ppm) These levels were calculated using Tables 2-4 through 2-7 in the LUFT Manual and the following assumptions average annual precipitation (14 1 inches, _ NOAA, 1_991), depth to groundwater (43 5 feet), distance from sample to surface (25.0 1661), and distance rom mple to groundwater (18 5 feet) The BTEX concentrations b in Sample B-1 are non-detect (benzene, toluene, xylene) and 0 600 ppm (ethylbenzene). Thus, BTEX levels are below acceptable, contamination levels _ s (Appendix E, Preliminary Site Investigation Report, November 1991). Data collected during the SSA has not affected the results of the leaching potential analysis nor the general risk assessment since contamination levels were well below levels obtained during the initial investigation SUMMARY AND CONCLUSIONS ' Field Work Implementation In January 1993, four exploratory boreholes were advanced at the GLI Terminal �p-r ' in Stockton, California These boreholes were successful in defining the— vertical and horizontal extent of subsurface soil contamination Soil samples were collected at five-foot intervals during advancement of they ' boreholes The sample displaying the highest TIV measurement in each borehole was submitted for chemical analyses Soil samples were analyzed for TPHD and BTEX A Photographic Log of the field activities has been included as Appendix C Site Stratigraphy and Hydrogeology ' Subsurface materials consist of clayey silts with moderate to well-sorted, fine sand lenses Shallow groundwater underlying the site occurs under unconfined conditions Groundwater is encountered at depths of 43 to 45 feet. ' Groundwater flows to the south with a hydraulic gradient of 0 003 feet per foot. Soil Chemistry TPHD was not detected at concentrations above the reporting limit of 1 00 mg/Kg in any of the new soil borings installed as part of this investigation Benzene, ethylbenzene and xylenes were not detected at concentrations above the reporting lima of 0 5 µg/Kg in any of the soil samples submitted for analyses Toluene was detected in all four soil samples at concentrations ranging from 0 7 ' (B-5) to 3 4 µg/Kg (B-4) These concentrations are below the detection limit of 0 3 ppm required to evaluate the contamination in the General Risk— Appraisal iskAppraisal Using the leaching potential analysis and the general risk assessment criteria }, outlined in the LUFT Manual, the maximum allowable TPHD that can be left in FJSISY356 0510005 5