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<M"IWA <br /> Working to Restore Nature <br /> } <br /> Between May 1994 and July 1992, RESNA investigated the impact of hydrocarbons to soil <br /> beneath and dust north of the site A total of eighteen soil borings were drilled onsite and <br /> two soil borings were drilled offsite, nine vapor extraction and one offsite vapor extraction <br /> wells were installed at the site Boring locations and well locations are presented in Plate <br /> 2 Residual gasoline and diesel hydrocarbons were detected in soil beneath the site <br /> (RESNA, January 7, 1993, Report 38048-7) <br /> A vapor extraction test was conducted on June 14, 1991, results indicated that vapor <br /> extraction is a feasible method of remediating soil at the site An effective radius of <br /> influence of 22 feet was estimated for the site (RESNA, April 7, 1992, Report 38048-5) <br /> According to SJCPHS-EHD, the depth to groundwater beneath the site is approximately 80 <br /> feet below surface grade (bsg) Because residual hydrocarbons were detected in soil <br /> approximately 15 feet above groundwater, an investigation of groundwater was requested <br /> by SJCPHS-EHD <br /> SUPPLEMENTAL INVESTIGATION <br /> Field Work <br /> On January 24 through 26, 1994, a RESNA field geologist observed Woodward Drilling of <br /> y Rio Vista, Califorma drill three soil borings (B-21, B-22, and B-23) to 75 feet bsg and one <br /> soil boring (B-24) to 41-1/2 feet bsg (Plate 2) Groundwater was encountered at <br /> approximately 63 feet bsg RESNA constructed groundwater monitoring wells MW-1 <br /> through MW-3 in the deeper borings, and a vapor extraction well (VW-11) was constructed <br /> in the shallow boring Our field methods are described in an attachment to this report. <br /> The geologist collected soil samples from the borings at approximately 5-foot intervals for <br /> possible laboratory analyses and to characterize the geology beneath the site Samples were <br /> logged using visual and manual methods and classified according to the Unified Soil <br /> Classification System (Plate 3) Sediments encountered are shown on the Logs of Borings <br />' (Plates 4 through 14) <br /> On January 27, 1994, a technician from RESNA developed wells MW-1 through MW-3 <br /> Water samples collected after well development did not contain floating product or product <br /> sheen On January 31, 1994, at the request of ARCO, purge water was removed from the <br /> site by IWM of Pleasanton, California Tom O Morrow Inc of West Sacramento <br /> California, a licensed land surveyor (California Land Surveyors 3275) surveyed the wells on <br /> January 27, 1994 <br /> i <br /> 0319ccar/3804&11 2 <br /> I <br />