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.I— <br /> ENVIRONMENTALv <br /> HEALTH DEPARTMENT <br /> AQ N SAN JOAQUIN COUNTY <br /> Donna K.Heran,R.E.H.S. Unit Supervisors <br /> Director 304 East Weber Avenue, Third Floor Carl Borgman,R.E.H.S. <br /> Al Olsen,R.E.H.S. Stockton, California 95202-2708 Mike Huggins,R.E.H.S.,R.D.I. <br /> • �4 .. o ,a�P • Program ManagerTele hone: 209 468-3420 Douglas W.Wilson,R.E.H.S. <br /> �rF Laurie A.Cotulla,R.E.H.S. ( ) Margaret Lagorio,R.E.H.S. <br /> Fax: (209) 464-0138 Robert McClellon,R.E.H.S. <br /> Program Manager Mark Barcellos,R.E.H.S. <br /> SAIYED ALI MAY 1 6 20OZ <br /> CALTRANS DISTRICT 10 <br /> P O BOX 2048 <br /> STOCKTON CA 95201 <br /> RE: Caltrans Shop 10 SITE CODE: 1018 <br /> 1603 South B Street <br /> Stockton CA 95215 <br /> San Joaquin County Environmental Health Department(SJC/EHD) has reviewed the"Remedial <br /> Action Pian, Shop 10 Maintenance Station"dated March 19, 2002 that was prepared on your <br /> behalf by IT Corporation and has the following comments. <br /> In preparing this Remedial Action Plan (RAP), IT Corp. completed a review of historical data from <br /> this site, including all site investigations, feasibility studies and reports of findings. The soil <br /> contaminant mass remaining at the site has been estimated at 3,300 pounds of total petroleum <br /> hydrocarbons as gas and 22 pounds of benzene. The majority of this mass extends to a depth of <br /> 50-feet below surface grade (bsg), and laterally to a radius of approximately 65-feet from the <br /> former tank pit(source area). Analytical results of water samples collected from a cone <br /> penetrometer test boring advanced near the source area indicate that the bulk of the groundwater <br /> contaminant plume extends to above 60-feet bsg. Laterally the plume is concentrated near the <br /> source area, extending to less than 65-feet down gradient. <br /> Two vapor extraction pilot tests have been conducted at this site. Based on the results of these <br /> tests, IT Corp proposes to remediate the remaining contamination with a combination of air <br /> sparging of the groundwater and soil vapor extraction. The RAP proposes the installation of two <br /> soil vapor extraction wells (VEW)and four air sparge(AS)wells, to cover the affected area. The <br /> VEW's will be built to total depth of 46-feet bsg, with a screened interval from 15-46 feet bsg. The <br /> AS wells will be built to total depth of 93-feet bsg with a screened interval from 88-93 feet bsg. <br /> Current depth to water at the site is approximately 50-feet bsg. The estimated radius of influence <br /> (ROI)of the VEW wells is 80-feet, and that of the AS wells is 25-feet. Extracted vapors will be <br /> treated, under permit with the San Joaquin County Air Pollution Control District, with a thermal <br /> oxidizer prior to release to the atmosphere. <br /> SJCIEHD approves the proposed RAP. In conversation with Cal Trans personnel SJCIEHD was <br /> informed that implementation of the RAP should occur by September 2002, <br /> Donna Heran, REHS, Director <br /> Environmental Health Department <br /> Lori Duncan, Senior REHS Margaret�Lago6o, Supervising REHS <br /> LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit IV <br /> cc: Marty Hartzell, CVRWQCB <br /> Sue Kraemer, IT Corporation <br />