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r. <br /> ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> o._�f.coG Unit Supervisors <br /> Donna K.Heran,R.E.H.S. Carl Borgman,R.E.H.S. <br /> 304 East Weber Avenue, Third Floor <br /> w :{ Director Mike Huggins,R.E.H.S.,R.D.I. <br /> Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. <br /> �. Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> 4I:i I.I Laurie A.Cotulla,R.E.H.S. Robert McClellon,R.E.H.S. <br /> Program Manager Fax: (209) 464-0138 Mark Barcellos,R.E.H.S. <br /> DAVID A ROSSO NOV Q 8 2004 <br /> STOCKTON CENTER SITE AUTHORITY <br /> 401 GOLDEN SHORE, SECOND FLOOR <br /> LONG BEACH CA 90802 4210 <br /> RE: California State University Stanislaus RO 0700 <br /> 1252 N. Stanislaus Street <br /> Stockton, CA 95205 <br /> San Joaquin County Environmental Health Department (EHD) has received and <br /> reviewed Soil Vapor Extraction and Air Sparge Feasibility Evaluation Work Plan <br /> (WP) dated 15 September 2004 and Third Quarter Groundwater Monitoring <br /> Report (August 2004), dated 10 September 2004, both prepared by Condor <br /> Earth Technologies, Inc. (Condor) and both received by EHD on 15 October <br /> 2004. In the WP Condor relates that changing site priorities rendered the <br /> previously approved excavation work plan unnecessary and proposed to install <br /> three soil vapor extraction (SVE) wells and an air sparge (AS) well to conduct <br /> feasibility testing to evaluate SVE and AS as more cost-effective remedial <br /> alternatives to excavation. <br /> Condor proposes to set the SVE wells at 45 feet below surface grade (bsg) with <br /> screen intervals between 25 and 45 feet bsg. The proposed AS well is to be <br /> screened from 50 to 55 feet bsg. During the last groundwater monitoring event, <br /> the depth to water on the site was approximately 41 feet bsg. Following <br /> installation of the wells, Condor proposes to test SVE through a step test and a <br /> 24-hour constant rate test and to test AS utilizing a helium tracer. <br /> EHD is in favor of evaluating potentially more cost-effective remedial alternatives <br /> to address subsurface contamination, but has the following concerns: <br /> • The subsurface soil type between 25 and 45 feet bsg is predominantly silt <br /> and clay, which may have much less than the anticipated 30-foot radius of <br /> influence (ROI) for SVE. Local occurrences of sand in the interval are <br /> suggestive of small channel sand units that may quickly clean up and <br /> reduce the SVE effect on the remaining impacted fine-grained soil. <br /> • The proposed AS screen interval between 50 and 55 feet bsg in the <br /> former underground storage tank (UST) area apparently is in a clayey <br /> sand unit overlain by fine-grained soil (see the GP-6 and GP-8 boring <br />