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BCBrown and Caldwell Consultants . 723 S StreetRECE V D Sacramento Calgomia 95814-7092 (916)444-0123 FEB 2 4 1993 FFAX(916)444 8437 �y r F 1 ENVIRONMENTAL 1194TH PERMIT/SERVICES February 22, 1993 Ms Elizabeth A Thayer Califomia Regional Water Quality Control Board Central Valley Region 3443 Routier Road, Suite A Sacramento, California 95827-3098 017-7220-01/1 Subject National Pollution Discharge Elimination System (NPDES) Permit Application ARCO Station 2093, Tracy, California • Dear Ms Thayer This letter provides supplemental information for an NPDES Permit Applicauon, as requested in your letter of November 9, 1992 The following responses provide information presented in the same order listed in your letter. 1. Treated groundwater will be discharged to the municipal stormwater system. This method of discharge was selected by the City of Tracy (City) Department of Public Works. The City municipal wastewater collection system is hydraulically maximized,and no additional flow is allowed, even during off-peak hours. Since the City has required discharge to the stormwater system, no other land disposal options have been evaluated 2. Groundwater will be extracted from TEX-1 and to a lesser extent from monitoring wells ATR-2, ATR-4, and ATR-5. Well locations are shown on Figure 1. Most of the groundwater will be extracted from TEX-1, which will be equipped with a downhole pump capable of producing 5 to 20 gallons per minute (gpm). The anticipated extraction rate for TEX-1 is 10 to 15 gpm. The purpose of pumping from TEX-1 is to remediate hydrocarbon affected groundwater, which is primarily localized in the immediate vicinity of TEX-1. Wells ATR-2, ATR-4, and ATR-5 will also be plumbed for installation of groundwater • pumps. These wills are expected to be pumped at rates on the order of 2 gpm. The purpose of pumping from these wells are to- 0 sT