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f HORIZON ENVIRONMENTAL INC. Specialists in Site Assessment,Remedial Testing,Design and Operation August 18, 1998 Mr. Robert Sagaser, Environmental Controls Officer Utilities Department City of Tracy 3900 Holly Drive Tracy, California 95376 Subject: Request for Discharge of Groundwater to Sanitary Sewer System Former Discovery Chevrolet 1615 West 11th Street, Tracy, California Mr. Sagaser: At the request of our client, Ms. Michelle Nokes, Horizon Environmental Inc. (Horizon) has I� prepared this second Request for Discharge letter for the above-referenced site (Figure 1). As a part of the ongoing soil excavation operations, Horizon has proposed to extract a volume of groundwater from the excavation prior to backfilling. The groundwater will be extracted with the use of a trash pump, and stored temporarily onsite in a rented aboveground storage tank (AST). Removal of hydrocarbons from the groundwater will then be performed by carbon adsorption. After treatment by the carbon adsorption canister, the_groundwater would then be discharged to the City of Tracy sanitary sewer system. On July 21, Horizon prepared a Request for Discharge letter to discharge groundwater into the sanitary sewer. On August 12, your office issued a letter allowing up to 2,000 gallons of treated groundwater to be discharged from the site into the onsite sanitary sewer. Horizon's earlier estimate of the anticipated volume of water to be pumped was 2,000 gallons; however, the latest onsite estimate is more on the order of 6,000 gallons. The extracted groundwater will be pumped through one 200-pound granular-activated carbon canister, which has the potential to adsorb up to 30 pounds of hydrocarbons before breakthrough. Again, using the highest concentration of 2,400 ppb of TPHg from earlier groundwater analyses, it is estimated that only 1.0 pound of TPHg will need to be removed from the groundwater to produce treated groundwater with nondetectable hydrocarbons. Therefore, one 200-pound granular-activated carbon canister should still be sufficient to process the pumped groundwater prior to discharge into the sanitary sewer system. It is still anticipated that this work will be performed during August 1998. It is our understanding that the discharged groundwater must have nondetectable laboratory results, and that your office must be in receipt of the laboratory results prior to discharge into the sanitary sewer system. 5011 Golden Foothill .Parkway,Suite 7 I Y E Dorado Hills,CA 95762 (916)939-2170 e FAX(916)939-2172 P.O.Box 5283 • Bakersfield,CA 93388 • (805)589-8389 • FAX(805)589-1456