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California Stop September 2013 <br /> 2224 Manthey Road, Stockton <br /> Claim No: 18428 <br /> Downgradient Well <br /> TERT-BUTYL ALCOHOL(TBA)Results for MW6 <br /> 100000 <br /> 90000 <br /> 80000 <br /> _ 70000 <br /> 80000 <br /> 50000 <br /> m 40000 <br /> tY <br /> 30000 <br /> 20000 <br /> 10000 <br /> war.TERT-BUTYLALCOHOL(T8A) Trend j <br /> Evaluation of Current Risk �q <br /> • Estimate of Hydrocarbon Mass in Soil: 6,248 pounds (Advanced GeoEnvironmental, Inc., <br /> 2010). <br /> • Soil/Groundwater tested for MTBE: Yes. <br /> • Oxygen Concentrations in Soil Vapor: None reported. <br /> • Plume Length: <250 feet. <br /> • Plume Stable or Decreasing: Yes. <br /> • Contaminated Zone(s) Used for Drinking Water: No. <br /> • Groundwater Risk from Residual Petroleum Hydrocarbons: The case meets Policy Criterion 1 <br /> by Class 5. This case does not meet Policy Criteria 1 by Class 1 through Class 4 because <br /> irrigation wells are located within 1,000 feet of the Site. However, the MTBE/TBA plume is <br /> stable and decreasing in the directions of those wells and is also limited to the Site boundary. <br /> The monitoring data strongly suggest biodegradation occurring at the Site. The contaminant <br /> plume that exceeds water quality objectives is less than 250 feet in length. There is no free <br /> product. There are no public supply wells regulated by the California Department of Public <br /> Health within 1,000 feet of the defined plume boundary. No surface water body is located <br /> within 1,000 feet of the defined plume boundary. The regulatory agency determines, based on <br /> an analysis of site specific conditions, which under current and reasonably anticipated near- <br /> term future scenarios, the contaminant plume poses a low threat to human health and safety <br /> and to the environment and water quality objectives will be achieved within a reasonable time <br /> frame. <br /> • Indoor Vapor Risk from Residual Petroleum Hydrocarbons: The case meets the Policy <br /> Exclusion for Active Station. Soil vapor evaluation is not required because the Site is an active <br /> commercial petroleum fueling facility. <br /> • Direct Contact Risk from Residual Petroleum Hydrocarbons: The case meets Policy Criterion <br /> 3b. Although no document titled "Risk Assessment' was found in the files reviewed, a <br /> professional assessment of site-specific risk from potential exposure to residual soil <br /> contamination found that maximum concentrations of petroleum constituents remaining in soil <br /> will have no significant risk of adversely affecting human health. Even though maximum <br /> concentrations in soil are higher than those in Policy Table 1 for Commercial/Industrial use, and <br /> the concentration limits for a Utility Worker are exceeded, the impact were limited to the <br /> Pana in of 13 <br />