ARCHIVED REPORTS_XR0002089 - Laserfiche WebLink

Home Browse Search

Mr. Harlin Knoll August 25, 1998 Page 5 • Gasoline constituents detected in groundwater samples collected from DB-1 a, DB-2, and DB- 3 were consistent with levels historically detected in groundwater monitoring well MW-5 CONCLUSIONS Soil and groundwater beneath the site have been impacted by gasoline hydrocarbons as a result of the USTs formerly located at the site Gasoline contamination in soil attenuated with depth and the vertical limits have been essentially defined The apparent vertical limit of soil contamination is approxinately 100 feet in the vicinity of the former USTs and approximately 70 feet near borings DB-2 and DB-3 Soil contamination at depth may be attributable to the relatively lugh concentrations in groundwater The gasoline hydrocarbon concentrations detected in the groundwater grab samples were consistent with levels historically detected in nearby well MW5 No dissolved petroleum hydrocarbons are present in wells MW2, MW3, MW4, MW6, MW7, or MW8 The most recent sample collected from well MW1 (8/6/98)contained TPHG and benzene at 1,200 ppb and 52 ppb, respectively The lateral extent of groundwater contamination has been essentially defined except to the north and northeast, which are hydraulically upgradient and crossgradnent, respectively, from the farmer USTs RECOMMENDATIONS Ground Zero recommends conducting a receptor survey to determine of there are any surface waters or domestic/production wells that may be affected by dissolved contamination originating from the site The survey will involve reviewing well construction details provided by the Department of Water Resources (DWR) and PHS/EHD for any known domestic/production wells within 2,000 feet of the site The receptor survey may be included in a Risk Based Corrective Action (RBCA) evaluation The RBCA evaluation would include all the elements per ASTM designation E-1739-95 and will compare the magrutude of contamination with Risk Based Screening Levels (RBSLs) developed using the computer program "Tier 2 RBCA." Based on the results of the RBCA evaluation, Ground Zero would pursue closure as a low-risk case, identify any data deficiencies, or recommend an appropriate corrective action CERTIFICATION This investigation was performed under the direct supervision of John P Lane, RG 6795, and Gregory P Stahl,R G 5023, C H G 264, who have reviewed and approved tlus report The methods and procedures employed in the development of this report conform to industry standards Limitations This report has been prepared for the exclusive use of Mr Carl Knowles, as it applies to the contiguous property at 1140 West Hammer Lane, Stockton, California The conclusions and • recommendations rendered herein are opinions, based on readily available information obtained to date, within the scope of work authorized by the client Work has been performed in accordance 1cs n=om\mmTL ac