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1 v 1 A S S O C I A T E S I N C Soil samples collected from soil boring B2 contained detectable concentrations of methyl tertiary butyl ether(MTBE) In June and July 2000, WHF supervised the advancement of ten soil borings at the site and completed five of the borings as groundwater monitoring wells MW5, MW6, MW8, MW9, and MW10, and three of the borings as vapor extraction wells VE1, VE2, and VE3 Groundwater monitoring well MW7 was replaced by vapor extraction well VE3 Soil samples collected from borings B101, 13103, B104, VE3, and VE 1 contained detectable concentrations of TPHg and BTEX A summary of the soil sample analytical results are presented in Table I 2.0 SUBSURFACE CONDITIONS 2.11 Geology ' The site has a silt layer from the surface to a depth of approximately 18 feet bgs with an intermittent clay layer present at a depth of approximately 10 feet bgs On the majority of the site, soil from depths between 18 and 47 feet bgs generally consists of sand, although there is a layer of silt from 25 to 38 feet bgs in several borings, and soil from depths between 47 and 90 feet bgs generally consist of silt with several thin layers of sand On the eastern portion of the site, soil from depths between 18 and 80 feet bgs consists of sand, with a silt layer present from 40 to 60 feet bgs Also on the eastern portion of the site, soil from depths between 80 and 86 feet bgs consists of silt, and soil consists of sand from depths between 86 and 100 feet bgs The ' estimated lateral extent of TPHg, benzene, and MTBE are depicted on Figure 3 through Figure 5, Figure 6 through Figure 8, and Figure 9 through Figure 11, respectively 222 Hydrogeology Surface drainage at the site is controlled by the site topography, which slopes to the west The site is located approximately 3,800 feet southeast of Lone Tree Creek, which flows northwest into the French Camp Slough and eventually drains into the San Joaquin River, approximately 25 miles to the northwest of the site A culvert going from north to south on the west side of the property intermittently carries surface runoff ' Water level measurements were collected from wells MW1, MW2, MW3, MW4, MW5, MW6, MW8, and MW9 on September 18, 2003 On September 18, 2003, water levels ranged from 71 93 to 77 02 feet below the tops of the well casing elevations The water level data were used ' to develop the groundwater elevation contour map (Figure 12) Assuming horizontal isotropic conditions, groundwater flow in the uppermost aquifer beneath the site on September 18, 2003 was southeasterly The average hydraulic gradient was calculated to be 0 04 feet per foot (ft/ft) or approximately 233 feet per mile (ft/mile) A summary of groundwater analytical and monitoring data is presented in Table 2 and Table 3, respectively S IEnviromenta1125291Veportslnfs doe 2