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ME EE e r n ia:sr.r L AUG 0 7 ?391._ July 29, 1991 ARCO Station No. 760, Lodi, California ENVIRONMENTAL HE Analytical results indicated gasoline hydrocarbons were detected in soil samples from locations 1 and 3 (shown on Plate 3);however, gasoline hydrocarbons were not detected in soil samples from locations 2,4,5 artd 6. Ethylene dibromide and total lead were not detected in the six so+,l samples. These results are presented in Table 1. Because gasoline hydrocarbons were detected in soil sample S-3 PLl but not soil sample S-3-PL5, residual gasoline hydrocarb,ns may not be laterally extensive about We dispenser islands. On the basis of laboratory results of the six soil samples collected on July 5, 1991,and the results of our previous work, Applied GeoSystems recommends that a vapor-extraction system be installed to remove residual gasoline hydrocarbons from the soil. Applied GeoSystems conducted a vapor-extraction test on June 14, 1941. Our iniiial estimates of the effective radius of influence of 22 feet from each vapor-extraction well were made using a vacuum of 30 inches of water column, a flow rate of 50 cubic feet per minute, an initial TPHg concentration of 10,000 milligrams per cubic meter, and the duration of operation of a vapor-extraction system of 12 months. This estimate of the radius of influence can be further defined as the subsurface environmental investigation progresses. The location and screened interval of subsequent vapor-extraction wells will be based on this relined data. Applied GeoSystems concludes that vapor extraction can be a practical and cost effective method of soil remediation. A�11 On the basis of the results of the vaporextraction test and the environmental investigation conducted at the site, a proposed layout of a vapor-extraction system was prepared for ARCO. The proposed location of vapor-extraction wells and evaluated radius of influence are shown on the Proposed Remediation System, Plate 4. Vapor wells will be installed June 13. 1991 Addendum to Work Plan for subsurface using field methods described in our investigation.'Drilting will be terminated at either 5 feet below the last subjective evidence at 55 feet,whichever is deeper. of hydrocarbons or At ARCO's request and with the approval of the attached permit from the SJCFHS-EHD, Applied GeoSystems will install silt additional 4-inch-diameter vaporextraction wells at the apor-extraction system until proposed locations shown on Plate 4. We will not install the v after the appropriate doclsments required for public review have been submitted and approved. We intend to install a thermal or catalytic oxidizer to destroy gasoline hydrocarbons removed from the soil. o7oswh 2 �' 3sws sw