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19 May 1997 AGE-NC Project No. 96-0266 Page 4 of 8 4.0. REGIONAL GROUND WATER ELEVATION it The estimated depth to ground water at this property is approximately 10 to 15 feet below surface grade(bsg), based on information from Lines of Equal Depth of Water Wells, Fall 1995 published by the San Joaquin County Flood Control District and Water Conservation District. However, the PHS-EHD records indicted that the highest ground water elevation was observed in 1986 at 10 feet bsg. The prevailing ground water flow in western Stockton flows generally to the west, while localized ground water flow may vary during winter/summer cycles. Ground water was observed at twelve feet bsg during the limited subsurface investigation. .5.0. SCOPE OF WORK According to Mr. Harlin Knoll of the San Joaquin County PHS-EHD,the investigation of the former UST in San Jose Street will require additional investigation to verify the lateral and vertical extent of gasoline-impacted ground water. At a minimum, four ground water monitoring wells should be installed in this area, including at least one well in the assumed up-gradient location, near the western property line to confirm the source and migration of the diesel onto the site. In order for the CV RWQCB to grant certified closure for the suspected release of the metals on the site, an additional investigation of the plating shop area would be required to evaluate the potential source of the elevated metal concentrations in ground water and to delineate the extent of the metals- impacted ground water. For this.purpose, a minimum of one ground water monitoring well will be required in this area. However, if data obtained from a single well is inconclusive, additional wells may be required. In addition, ground water samples should be collected from proposed wells near the UST area; other surrounding properties; and analyzed for metals to establish "background" metals concentrations against the ground water at the site. 5.1. DRILLING AND SAMPLING The scope of work will include the advancement of five borings to a total depth of approximately. 20 feet below surface grade(bsg),collection of soil samples,and the installation of a 2-inch diameter ground water monitoring well. Proposed boring locations are depicted on Figure'2. Soil borings will be advanced utilizing a truck-mounted, drill rig equipped with 8.25-inch hollow- stem augers. Soil samples will be collected at five-foot intervals beginning at a depth of 5 feet bsg, preserved and placed in a chilled container for transportation to a State-certified laboratory. Soils