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IMM — ENWRONMENTAL PROTL . ,uN AGENCY 0 CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— CENTRAL VALLEY REGION 3443 ROUTIER ROAD, SUITE A SACRAMENTO, CA 95827-3098 PHONE: (916) 255-3000 FAX: (916) 255-3015 30 August 1994 Mr. James B. Giottonini Department of Public Works City of Stockton 425 N. El Dorado Street Stockton, CA 95202-1997 a ! q PV eq W4Vt+gyp' r I r, A UG' 3 1 1994 ENVil?ONMENTAL ,'ERMITISERVICE LTA{ CITY OF STOCKTON AUSTIN ROAD LANDFILL, SAN JOAQUIN COUNTY (Case No. 2148) Thank you for your 19 August letter regarding ground water contamination at the Austin Road Landfill and the 10 August 1994 letter from the State Office of Real Estate and Design Services (OREDS). You are correct that no volatile organic compounds (VOCs) were confirmed in domestic supply wells at the Northern California Youth Center. VOCs were detected by the City's consultant in two of four domestic supply wells at NCYC, but not confirmed in subsequent samples. VOCs were also detected in a residential well at 8106 Austin Road, near the NCYC irrigation well sampled by OREDS (Attachment 1). The landfill's 19 June 1989 SWAT report states this residential well was resampled and VOCs were confirmed (sampled 23 February 1989 and resampled 11 April 1989) but the source of the VOCs was not determined. As noted in your letter, the City's consultant conducted a verification monitoring program in 1991. This work consisted of a one-time sampling of ground water using HydroPunchTM technology on a grid pattern north of the landfill. The City's consultant concluded the contaminant plume extended about 1000 feet north of the landfill as shown by the dashed line on Attachment 1, far short of the distance to the NCYC or residential supply wells. When I spoke with OREDS staff regarding their sample results, I recalled only the original identifica- tion of VOCs in the two NCYC wells and one residential supply well and my impression of the extent of the contaminant plume based on the original sampling, but not the follow up work done by the City that limited the plume's northern extent. In our letter of 17 August 1994 to Stephen Chen, we requested that the City sample the irrigation well tested by OREDS, plus two nearby supply wells including 8106 Austin Road. Our request to sample these three wells was prompted by the following circumstances. First, the contaminants found by OREDS, PCE and TCE, are also in contaminated ground water at the landfill. Second, the same VOCs were confirmed in 1989 in the well at 8106 Austin Road. Third, the City's ground water monitoring data indicate the three supply wells are downgradient, as shown on Attachment 2, of the most contaminated portion of the landfill, i.e., the area near monitoring wells MW -10 and 11 where PCE is found at levels up to 70 µg/1. Although monitoring wells MW -12 and MW -13 are