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Global Presence Personal Attention HERST & ASSOCIATES, INC.` UIlLS FD Mr. Steve Rosenbaum Senior Engineering Geologist 0-AN 1 6 2009 California Regional Water Quality Control Board EN Central Valley RegioENVIRONMENTHEALTH 11020 Sun Center Drive#200 PERMl i/SERVICES Rancho Cordova, California 95670-6114 January 15, 2009 Dear Mr. Rosenbaum: Downgradient Water Well Sampling Plan, Forward Inc.,Austin Road Landfill, San Joaquin County A December 8, 2008 Cleanup and Abatement Order(CAO) R5-2008-0714, page 9, requested a plan (Plan)to sample all downgradient water wells (i.e. drinking water wells)that are within 4,000-feet of the point of compliance of the Austin Road Landfill. As described in the CAO, the purpose of the sampling effort is to identify any drinking water wells that may be impacted by volatile organic compounds(VOCs)in groundwater,and if impacted,Forward,Inc. is to provide replacement drinking water at no cost to the landowner,unless the City of Stockton is already providing such a supply. • In order to develop a Plan that complies with the CAO requirements, it is necessary to develop an understanding of the following: ➢ Point of Compliance ➢ Groundwater Flow Directions ➢ Location of Downgradient Water Wells Within 4,000 Feet of the Point of Compliance The Point of Compliance for the Austin Road Landfill is established by Waste Discharge Requirements. Order No. R5-2003-0049 specifies that the groundwater Point of Compliance a vertical surface established at the hydraulically downgradient limit of the facility that extends through the uppermost aquifer underlying the facility. The WDR specifies that for the Austin Road Landfill, the point of compliance is the downgradient margin of the landfill. Groundwater flow directions can be determined by referencing groundwater potentiometric surface maps. There are two primary zones of interest at and near the Austin Road Landfill — a water table zone present at depths of approximately 80 feet below ground surface and a deeper zone that immediately overlies a thick clay sequence,at a depth of approximately 170 feet below ground surface. The shallow water table zone has been monitored on a routine basis for many years,with data regularly provided to RWQCB as part of routine reporting. Data for the deeper zone recently became available as part of deep zone monitoring well installations performed in November and December of 2008, as previously reviewed and approved by RWQCB in November 3, 2008 email correspondence from Howard Hold of RWQCB(Attachment 1). The direction of groundwater flow in the shallow zone is consistently toward the northeast. Numerous 40 reports previously submitted to RWQCB confirm the consistency of groundwater flow direction in the 4630 South Highway 94—North Outer Road Telephone(636)939-9111 St.Charles,Missouri 63304 Fax(636)939-9757