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4 } I Quarterly Report - Fourth Quarter 2002 Former CHASE CHEVROLET (MADISON) Facility I 423 North Madison Street, Stockton, California ' 1.0. INTRODUCTION At the request of the City of Stockton,Advanced GeoEnvironmental, Inc (AGE)has prepared this ' quarterly report summarizing field activities performed during the fourth quarter of 2002 at 423 North Madison Street,Stockton, California The scope of work included conducting a quarterly y ground water monitoring event and preparation of this report The site setting is illustrated in Figure 1 Structures and monitoring well locations are illustrated in Figure 2 ' Based on previous investigations,AGE has identified two potential hydrogeologic units informally identified as the Upper and Lower Water Zones, these two zones are separated by approximately 5 ' to 10 feet of clay and salty clay During the previous six years of ground water monitoring, ground water flow direction in,the Upper Water Zone has been consistently toward the north to northeast, r' ground water flow direction in the Lower Water Zone has been toward the west-northwest, southwest and southeast Petroleum hydrocarbon-impacted ground water at the site is limited to the area surrounding the f former UST No 8 location(Figure 2) The northern extent of impacted ground water is defined by minor,intermittent detections of analytes in quarterly ground water samples from wells MW-13 and MW-20B South of the former UST No 8 location,minor concentrations of benzene, toluene,ethyl benzene and total xylenes (BTEX) constituents (less than 5 [.g/1) and steadily declining or non- detectable concentrations of total petroleum hydrocarbons as diesel (TP11-d) in ground water ; samples collected from wells MW-19A and MW-19B indicate that these wells mark the southern margin of impacted-ground water at the site However, the east, west and vertical extent of ' impacted-ground water is not well defined Additional site background information was summarized in Revised Corrective Action Plan - February 1997,Site Investigation Report- USTNo 8,dated 10 February 1998 and Quarterly Report - August 1998, prepared by AGE Data from previous giound water monitoring events is included ' in the tables of this report 2,0. PROCEDURES 'Field activities were performed in accordance with guidelines issuedby the Central Valley Regional Water Quality Control Board (RWQCB) and by the San Joaquin County Environmental Health Department (EHD) for investigation of underground storage tank (UST) sites and sampling of ground water monitoring wells, respectively On 02 December 2002, depth to water was measured,in fourteen of the fifteen ground water monitoring wells at the site(MW-18 was not measured), and ground water samples were collected r Advanced CeoF'nvironmentai,inc r '