Laserfiche WebLink
URS <br /> Ms. Victoria McCartney Page 5 <br /> San Joaquin County Environmental Health Department <br /> ARCO 5450 <br /> December 22, 2005 <br /> URS conducted a visual search for the area within a 500-foot radius of the site for water wells, surface <br /> water bodies, and other sensitive receptors. Additionally, URS conducted a review of the United States <br /> Geological Survey 7.5-minute topographic Stockton West (Photorevised 1987), California quadrangle. <br /> The Port of Stockton Channel is located approximately 300 feet to the south and southwest of the site. <br /> Based upon the visual search and map review, no other sensitive receptors were identified within 500 <br /> feet of ARCO Station 5450. <br /> I <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> The following information fulfills the RWQCB Central Valley Region's outstanding requirements for <br /> site closure. <br /> • Natural attenuation has removed a cumulative mass of 0.01 pounds of xylene and approximately <br /> 0.01 pounds of MtBE from the vadose zone. <br /> • Mass estimates indicate that less than 1 pound of MtBE remains beneath the site. <br /> • Trend analysis of contaminants in site groundwater indicates that MtBE concentrations will <br /> continue to decrease to below detection limits within the next several years. <br /> i <br /> • Based on modeling results using SES011L, the predicted maximum average concentration was <br /> 4.4E-7 mg/L(0.00044µg/L)MtBE in groundwater---essentially,zero predicted impact. <br /> • Existing MtBE concentrations in two of the three site wells are below the method detection <br /> limits. For the remaining well, MtBE concentrations are below the primary maximum contami- <br /> nant level (MCL)of 13 µg/L.but above the secondary MCL of 5 µg/L. <br /> Based on the review of historical soil and groundwater investigations, URS requests that ARCO Station <br /> No. 5450 be considered "low risk" and recommends closure and No Further Action. A checklist of data <br /> required by the RWQCB Central Valley Region for no further action at UST sites is presented as <br /> 1 Attachment G. <br /> This document is based on data, site conditions, and other information that are generally applicable as of <br /> the date of the document. The conclusions and recommendations herein are therefore applicable only to <br /> that timeframe. <br /> I <br /> KAWprocessU5 BP ARCO\054501Soil Closure 05\Draft of 5450 Closure Report.doc <br />