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California Regional Water Quality Control Board I" Central Valley Region + Robert Schneider,Chair Gray Davis Winston H Hickox Secretaryfor Sacramento Main Office Governor Environmental Internet Address http//www swrcb ca gov/rwgcb5 Protection 3443 Routier Road,Suite A,Sacramento,California 95827-3003 Phone(916)255-3000•FAX(916)255-3015 mom+ 27 June 2001 , a �4{ p Mr Joel McRonald 4 California Department of General Services Real Estate Services Division 1812 9th Street Sacramento, CA 95814 OFF-SITE GROUNDWATER INVESTIGATIONREPORT REVIEWAND REQUEST FOR WORKPLAN, FORMER VINTAGE CAR WASH, 601 EAST MINER AVENUE, STOCKTON I reviewed the 16 April 2001 Off-site Groundwater Investigation Report (Investigation Report) submitted on your behalf by IT Corporation(IT) IT completed four cone penetrometer testing (CPT) borings downgradient and cross gradient of the site to determine the lateral and vertical extent of groundwater contamination All four bonngs were completed to 100 feet below ground surface (bgs), and two to three depth-discrete groundwater samples were collected from each boring IT identified shallow (28 to 30 feet), intermediate (57 to 66 feet), and deep (80 to 88 feet) water bearing zones from the four CPT borings MtBE and benzene were identified in the intermediate zone cross gradient of the site, and MtBE, TPHg, and BTEX were Identified In the intermediate and deep zones downgradient of the site Analytical results from depth-discrete groundwater samples show contaminant concentrations decrease from the Intermediate water bearing zone to the deep water bearing zone, however, the vertical extent of contamination was not defined cross gradient or downgradient of the site I IT recommends Installing two Intermediate and deep well pairs with short screen Intervals in the vicinity of the downgradient borings CPT-2 and CPT-3 to verify groundwater contamination Staff believe that IT's recommendations are appropriate and necessary to investigate the off-site groundwater contamination However, staff believes that a groundwater monitoring well is needed In the vicinity of cross gradient boring CPT-1 where MtBE was identified in the intermediate zone By 30 July 2001, please submit a plan of work to complete well installation and sampling The plan of work must Include the following items • A plan to define the vertical extent of groundwater contamination in the vicinity of CPT borings CPT-1, -2, and-3 • An east-west hydrostratigraphic cross-section from MW-7 to CPT-3 showing lithology Identified from monitoring wells and CPT borings Also Include depth-discrete groundwater concentrations of TPHg, benzene, and MtBE from the CPT investigation, and the proposed monitoring well screen intervals California Environmental Protection Agency 0 Recycled Paper The energy challenge facing California is real Every Californian needs to take mmmedtate action to reduce energy consumption For a list of simple ways you can reduce demand and cut your energy costs,see our Web-site at http//www swrcb ca gov/ru gcb5