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` Ms Lori Duncan Page 2 of 7 • 2.0 BACKGROUND INFORMATION 2.1 Hydrogeological Setting The location of the property is depicted on Figure 1 The site is situated in the Lodi South quadrangle, Section 8, T2N, R6E, San Joaquin County, California Regionally, the property is located in the San Joaquin Valley physiographic province The valley is a topographic and structural basin bounded on the east by the Sierra Nevada and on the west by the Coast Ranges Locally the topography slopes gently toward the southwest at approximately six feet per mile Significant surface water bodies in proximity to the site are Five Mile Creek, Mosher Slough, and the Calaveras River Mosher Slough and Five Mile Creek, are located approximately 400 feet and 1 mile south of the site, respectively These two waterways flow in a westerly direction The southwest flowing Calaveras River is located approximately 4 miles west southwest of the site and is a tributary of the San Joaquin River The Calaveras River generally exhibits moderate stream flow losses over portions of the year, which contributes to groundwater recharge (USGS Professional Paper 1401-D, 1989) Regional groundwater flow in the site area is generally in an easterly direction toward a regional groundwater depression centered approximately 4 miles east of Stockton (San Joaquin County Flood Control and Water Conservation District, Fall 1998) Drinking water wells in the region are generally completed at depths greater than 100 feet below ground surface (bgs) due to the relatively poor quality of near-surface groundwater Current depth to first groundwater at the site is approximately 32 feet below grade, and is expected to flow in a northeasterly direction (San Joaquin County PHS/EHD Corresp, 9/6/00) Historical data from the San Joaquin County Flood Control and Water Conservation District suggests that water levels are currently at or near a historical high Historical low water levels are expected to have been between 45 and 50 feet bgs At a site immediately south of the subject property (8606 Thornton Road) groundwater flow as measured in shallow monitoring wells is toward the northeast and water levels have ranged between approximately 27 and 33 feet below grade 22 Previous Investigations The site currently is an automotive service center One 550-gallon UST was previously utilized for storage of waste oil The UST was removed under permit from San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) on May 26, 2000 A soil sample collected from beneath the tank contained elevated levels of petroleum hydrocarbons and chlorinated hydrocarbons Analytical results are summarized in Table l On September 11, 2000, five soil borings were advanced at the site to investigate the lateral and vertical extent of soil contamination, as well as the potential impact to groundwater Analytical results of soil samples collected from the borings indicated soil contamination was present at shallow depths within the former tank pit location, however, no analytes of concern were detected in any perimeter borings nor at a depth of 17 feet below grade in the central boring (SB 1) Soil boring locations are shown on Figure 2 Analytical results are summarized in Table 2 dal,ilgrounz.elmiulolreportslwellrt.port dog