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ENVIROA4ENTAL HEALTHq)EPARTMENT <br /> SAN JOAQUIN COUNTY <br /> e y Donna K. Heran, R.E.H.S. Unit Supervisors <br /> ti Director 304 East Weber Avenue,Third Floor cad Borgman,R E H.S. <br /> Laurie A. Cotulla, R.E.H.S. Stockton,California 95202-2708 Mike Huggins, R.E.H.S., R.D.I. <br /> Manager Program MDouglas W. Wilson, R.E.H.S. <br /> o"<lkoR�'•� K g Telephone: (209)468-3420 Margaret Lagorio,R.E.H.S. <br /> Fax: (209) 464-0138 Robert McClellon, R.E.H.S. <br /> Website:www.sjgov.org/ehd/ Jeff Carruesco, R.E.H.S. <br /> KEN ENRICH APR 2 8 2006 <br /> 1770 GILLIS RD <br /> STOCKTON CA 95215 <br /> RE: Former Top Filling Station <br /> 101 S. Wilson Way Site Code 1294 <br /> Stockton, California <br /> San Joaquin County Environmental Health Department (EHD) has received and <br /> reviewed Additional Site Assessment Work Plan (AWP) dated 15 November <br /> 2005, prepared by Advanced GeoEnvironmental, Inc. (AGE) on your behalf. The <br /> AWP was prepared in response to EHD directives issued by letters dated <br /> 29 June 2005 and 31 August 2005 to complete the lateral characterization and <br /> delineation of the dissolved contaminant plume. <br /> The AWP contains a proposal for four cone penetration test (CPT) borings to <br /> target depths of 125 feet below surface grade (bsg) in the left, northbound lane of <br /> Wilson Way to identify permeable strata and collect discreet groundwater <br /> samples for laboratory analysis to continue the lateral assessment of impacted <br /> groundwater in potential migration pathways at various depths. The proposed <br /> locations for the four CPT borings were selected to evaluate the likelihood of <br /> impacted groundwater from your site migrating and impacting the 102 and/or 130 <br /> South Wilson Way sites. <br /> EHD is concerned with the safety issue inherent with putting borings in a traffic <br /> lane on Wilson Way. The site map does not appear to be accurate for the street <br /> by not showing the turning lane or painted stripped island in the center of the <br /> street, but shows the proposed borings to be located in the left, northbound traffic <br /> lane. Although the investigation design would be compromised to some degree, <br /> you may want to consider moving the proposed CPT locations either into the <br /> turning lane (paint-stripped island area) or approximately 25 feet toward the east <br /> and advancing the borings in or near the sidewalk. <br /> EHD recommends that an initial CPT also be advanced on site in the primary <br /> suspected source area to at least 160 feet bsg to assess the vertical extent of <br /> impacted groundwater on site and adjust the target depths of the off-site CPT <br /> borings to include deeper permeable intervals if appropriate. Note that wells <br /> MW-6E (screened 137 to 142 feet bsg) and MW-7E (screened 125 to 135 feet <br /> bsg) monitor impacted groundwater. EHD also recommends that one CPT boring <br /> be located in the predominant down-gradient direction from your most intensely <br /> impacted area. <br />