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Californi.- _legional Water Quality Co_ .•ol Board < _� <br /> Central Valley Regionilllll�a�; <br /> Robert Schneider, Chair ``- .r. <br /> Linda S.Adams - Arnold <br /> Secrerar7 far Sacramento blain Office Schwarzenegger <br /> /.n 1'U'onmen to l 11020 Sun Center Drive 4200,Rancho Cordova.California 9567MI la Governor <br /> Prorec•nor Phone(916)464-3291 •FAX(916)464-464? Received <br /> http://w�+'w waterboards.ca.govicentralcalley <br /> 2 August 2006 Ash Creek <br /> Mr. Joe Aldridge, Remediation Manager <br /> Valero, L.P. <br /> 685 W. Third Street <br /> Hanford, CA 93230 <br /> REVIEW OF GROUNDWATER CHARACTERIZATION WORK PLAN, ST SERVICES <br /> STOCKTON TERMINAL, 2940 NAVY DRIVE, STOCKTON, SAN JOAQUIN COUNTY <br /> Staff of the Central Valley Regional Water Quality Control Board (Water Board) has reviewed <br /> the 14 April 2006 Groundwater Characterization Work Plan, ST Services Stockton Terminal <br /> (Work Plan) submitted by Ash Creek Associates, Inc. (Ash Creek) on behalf of ST Services, <br /> L.L.C. (ST Services dba Valero, L.P.) for the ST Services Stockton Terminal located at 2940 <br /> Navy Drive in Stockton (Site). The Work Plan proposes characterization of groundwater <br /> conditions at the southeast boundary of the groundwater petroleum hydrocarbon plume <br /> through the installation, development, and sampling of four monitoring wells. The groundwater <br /> analytical data will be used to assess the stability of the plume through plume boundary <br /> delineation and collection of data to evaluate natural attenuation conditions. <br /> Monitoring wells are proposed near the downgradient east-southeast boundary of the plume <br /> between onsite wells exhibiting high contaminant concentrations (wells PS/MW-15 and <br /> ST/MW-1) and offsite wells with low to non-detectable concentrations (wells PSANC-3S and <br /> PS/MW-17) some 400 to 500 feet away. Two wells are proposed in shallow A-zone <br /> groundwater and two wells are proposed in deeper B-zone groundwater. The need for <br /> secondary casing in the B-zone wells will be based on groundwater concentrations in the <br /> proposed A-zone wells and whether heaving sands are encountered during drilling. <br /> The A-zone wells will be installed during the first phase of work using hollow-stem auger <br /> equipment. Continuous soil samples will be collected during drilling. The wells will be <br /> completed at a depth of approximately 25 feet below ground surface (bgs) and constructed <br /> using 2-inch-diameter Schedule 40 polyvinyl chloride (PVC) casing with 10 to 20 feet of 0.010- <br /> inch-slot well screen placed across the water table. Filter pack sand will be placed to one to <br /> two feet above the top of the screen followed by one foot of hydrated bentonite pellets and a <br /> cement/bentonite mixture to backfill the remaining annulus. The wells will be developed a <br /> minimum of 12 hours after installation using surging, bailing, and/or purging techniques and <br /> will be land surveyed to the same datums as the existing well network. <br /> The wells will be sampled at least 24 hours after installation and will be subsequently <br /> incorporated into existing Monitoring and Reporting Program No. R5-2004-0822. The <br /> groundwater samples will be analyzed for benzene, toluene, ehtylbenzene, and xylenes <br /> (BTEX), and fuel oxygenates of methyl tertiary butyl ether (MTBE), tertiary amyl methyl ether <br /> California Environmental Pi-otectlon Agency <br /> �� Hen clod Paper <br />