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Mr. Dave Deaner
<br /> February 16, 1998
<br /> Page 2
<br /> On October 9, 1989, the 500- gallon UST was removed from the Lopez property. One soil sample was
<br /> collected from the base of the excavation. The soil sample contained total petroleum hydrocarbons
<br /> identified as gasoline (TPHg) at 3.9 milligrams per kilogram (mg/Kg). Benzene, toluene, ethylbenzene,
<br /> and total xylenes (BTEX) were not detected at or above the reporting limit. Refer to the WaterWork
<br /> report dated October 27, 1989.
<br /> In November 1994, three soil borings (SBA, SB3, and S134) were advanced and sampled at the subject
<br /> site by RAH Environmental, Inc. (Figure 2). Analytical laboratory results detected concentrations of
<br /> TPH-g at 1,000 mg/Kg and benzene at 6.8 mg/kg in a soil sample collected from soil boring SBA at a
<br /> depth of 20 feet below grade surface (bgs). Ground water samples were collected through the hollow-
<br /> stem augers at the location of the soil borings and analyzed for the presence of TPH-g and BTEX. The
<br /> analytical results indicated the greatest concentrations were detected at the location of SBA. On the
<br /> basis of these results, RAH Environmental, Inc. concluded that the source of the petroleum
<br /> hydrocarbons identified at the location of drill hole SBA most probably resulted from the former UST on
<br /> the Lopez property. Refer to the RAH report dated January 18, 1995,
<br /> In February 1996, Fugro West, Inc., witnessed the advancement of five drill holes (MW-1, MW-2, MW-
<br /> 3,
<br /> W3, SB-A1, and SB-A2) at the locations illustrated on Figure 2. The drill holes were advanced to
<br /> approximate depths ranging from 20.5 to 35.5 feet. Drill holes MW-1, MW-2, and MW-3 were
<br /> completed as 2-inch diameter ground water monitoring wells. TPH-g was detected at 5,500 mg/Kg
<br /> and benzene at 22 mg/Kg in a soil sample collected from drill hole SB-A2 at a depth of 16 feet bgs.
<br /> Refer to the Fugro report-dated March 1996.
<br /> Ground water monitoring activities were conducted from February 13, 1996 through July 22, 1997.
<br /> Low levels of TPH-g (between 51 ug/Kg and 110 ug/Kg) have been detected intermittently in ground
<br /> water monitoring wells MW-1, MW-2 and MW-3. Concentrations of BTEX have only been detected in
<br /> ground water samples collected during the first sampling event on February 13, 1996. On July 22,
<br /> 1997, depth to ground water was approximately 12 feet bgs, and was estimated to flow to the
<br /> southeast at an average hydrogeologic gradient of 0.006 feet per foot (ft/ft). Refer to ENSR's Second
<br /> Quarter 1997 Ground Water Monitoring Report, dated September 23, 1997ground water monitoring
<br /> reports.
<br /> Site Conditions
<br /> The site is a residential property consisting of one building, a paved driveway and surrounding grass
<br /> area. The site is located at an approximate elevation of 10 feet above mean sea level. Near surface
<br /> soils beneath the site are classified as Sailboat silt loam. This very deep, somewhat poorly drained
<br /> nearly level soil is on flood plains. Sailboat silt loam formed in alluvium derived from mixed rock
<br /> sources. Typically, the surface layer is brown silt loam about 8 inches thick. The underlying material
<br /> consists of intermittent layers of brown silty clay and silty sand to depths of 20 feet below grade surface.
<br /> Water for agriculture, domestic, and industrial uses in San Joaquin County is obtained from wells, rivers,
<br /> creeks, canals, and sloughs. The water flows to the county mainly through the Mokelumne, Calaveras,
<br /> Stanislaus, and San Joaquin Rivers. The water in the northern and eastern parts of the county is of
<br /> relatively good quality. The natural source of this water is runoff from the accumulation of rainfall and
<br /> snowfall in the Sierra Nevada (United States Department of Agriculture, Soil Survey of San Joaquin
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<br /> 8716002.0 Ls
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