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8-13-1998 10:3GAM FROM HORIZON/ELDORADO 91G 939 21 /2 <br /> HORIZON ENVIRONMENTAL INC. <br /> ... ver Specialists in Site Assessment,Remedial^7est p,Design and Operation <br /> July 21, 1998 <br /> Mr. Robert Sagaser, Environmental Controls Officer <br /> Utilities Department <br /> City of Tracy <br /> 3900 Holly Drive <br /> Tracy, California 95376 <br /> Subject: Request for Discharge of Groundwater to Sanitary Sewer System <br /> former Discovery Chevrolet <br /> 1615 West 11th Street, Tracy,California <br /> Mr. Sagaser: <br /> At the request of our client, Ms. Michelle Nokes, Horizon Environmental Inc- (Horizon) has <br /> prepared this Request for Discharge letter for the above-referenced site (Figure 1). In earlier <br /> conversations, you stated that your office requires a Request for Discharge letter prior to <br /> issuing a Wastewater Discharge Permit. It is our understanding that the disebarged <br /> groundwater must have nondetectable laboratory results prior to discharge into the sanitary <br /> Sewer system_ <br /> A Corrective Action Plan (CAP) was prepared by horizon for the site (Horizon, June S, 1998) <br /> and approved by the San Joaquin County .Public Health Services - Environmental Health <br /> Division (SJCPHS-EHD). As proposed in the CAP, the selected remedial alternative for the <br /> site remediation will involve excavation and disposal of hydrocarbon-impacted soil present <br /> beneath the former underground storage tank(UST)pit at the site. <br /> As a part of the soil excavation operations, Horizon has proposed that it would be a relatively <br /> quick and prudent measure to extract a volume of groundwater from the excavation prior to <br /> backfilling. The groundwater could be easily extracted with the use of a trash pump, and <br /> stored temporarily onsite in a rented aboveground storage tank- (AST)_ Removal of <br /> hydrocarbons from the groundwater would most easily and quickly be performed by carbon <br /> adsorption. After treatment by the carbon adsorption canister, the groundwater could then be <br /> discharged to the City of Tracy sanitary sewer system, depending on the local discharge <br /> regulations. <br /> Monitoring of the groundwater from wells MW-I and MW-2 Since 1994 has revealed <br /> declining concentrations of total petroleum hydrocarbons as gasoline (fPHg) and the volatile <br /> aromatics benzene, toluene, ethylbenzene, and xylenes (BTEX). The latest groundwater <br /> sampling event performed on June 5, 1998 indicated concentrations of I'PHg at So parts per <br /> billion (ppb) in both wells, benzene between 10 ppb and 12 ppb, toluene between 1,0 ppb and <br /> 1.9 ppb, ethylbenzene between 4.4 ppb and 4.9 ppb, and total xylenes between 12 ppb and 14 <br /> ppb. During the past year, the average concentration of TPHg in the groundwater has been <br /> 6011 Golden Foothill Parkway,Suite 7 . EI Dorado Hills,CA 95762 • (916)939.217(] • FAX(916)439.2172 <br />