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GEOMATRIX WORK PLAN FOR ASSESSING LATERAL AND VERTICAL EXTENT r OF PETROLEUM HYDROCARBONS IN SOIL AND GROUNDWATER Site No 3 (Site Code 1282-124) — Port of Stockton Stockton, California r r1.0 INTRODUCTION This work plan has been prepared by Geomatnx Consultants, Inc (Geomatnx) on behalf of the Port of Stockton (Port) to respond to the June 14, 2001 letter from the San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) In that letter, the ' PHS/EHD indicated that they have reviewed the quarterly reports submitted by the Port, which document the groundwater monitoring conducted at Site No 3 Based on the PHS/EHD's review, it has been determined that soil contarrunation has been defined vertically at the site, but not laterally, and that groundwater contamination has not been defined laterally or vertically The PHS/EHD concluded that further site investigation is required and requested that the Port submit a work plan to investigate the extent of contamination in the soils and groundwater in the vicinity of the site On July 25, 2001, the Port met with representatives from PHS/EHD and the Regional Water Quality Control Board, Central Valley Region (CVRWQCB) to discuss an appropriate scope of work for the investigation The discussion included a summary of the findings to date, which highlighted the variability in groundwater gradient direction, the relative stability in petroleum Ihydrocarbon compounds in the monitoring wells, and the lack of methyl tertiary butyl ether (MTBE) in the groundwater samples Thas work plan reflects the discussions at that meeting iincluding the need to assess the extent of groundwater contamination in multiple directions, the need to assess the lateral and vertical extent of groundwater contamination using monitoring wells, and the logistical constraints dictated by the industrial environment surrounding the former source area (underground storage tanks) 1.1 SITE SETTING The property is located in the central portion of the Port in the City of Stockton, San Joaquin County, California (Figure 1) This site, along with Site 2, has been identified by PHS/EHD as "Site Code 1282-124 " Site 2 was determined to require no further investigations by PHS/EHD Site 3 is approximately 50 feet north of Port Road G and about 300 feet west of Port Road 14 (Figure 1) I 1PRojECi16437 000/6437 Wk PIn Sue 3 doe l I