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"VV ASSOCIATES I NC develop the groundwater elevation contour map (Figure 6). Assuming horizontal isotropic conditions, the shallow groundwater flow direction beneath the site on November 20, 2003, varied, but was generally toward the southeast. The average hydraulic gradient was calculated to be 0.04 ft/ft or approximately 211 ft/mile. ' 3.0 PREVIOUS ENVIRONMENTAL WORK In March 1997, VHF, Inc., supervised the advancement of one soil boring to 80 feet bgs. Soil and groundwater samples collected from the soil boring contained detectable concentrations of TPHg and BTEX. A water sample was also collected from the on-site drinking water and it ' contained no detectable concentrations of petroleum hydrocarbons. In December 1998, BSK advanced five borings at the site and completed four of the borings as ' groundwater monitoring wells MW 1 through MW4. Soil samples collected from borings B2 and MW2 contained detectable concentrations of TPHg and BTEX. 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 VEI, VE2, and VE3. Groundwater monitoring well MW7 was replaced by vapor extraction well VE3. Soil samples collected from borings B101, B103, B104, VE3, and VEI contained detectable concentrations of TPHg and ' BTEX. 4.0 SUMMARY OF SOIL AND GROUNDWATER CONDITIONS 4.1 Extent of Hydrocarbon-Impacted Vadose Zone Soil TPHg concentrations in soil samples collected from the site vary with depth. The lateral extent of TPHg in soil samples collected from 40 feet bgs to 60 feet bgs is delineated to the east, south, and west by borings B103, MWI, and MW2, respectively. The lateral extent of TPHg in soil samples collected from 60 feet bgs to 75 feet bgs is delineated by boring B101 to the northeast,boring B103 to the east, boring MW 1 to the southeast,boring MW8 to the south,borings MW4 and MW2 to the ' We and boring VE3 to the northwest. The highest concentration of TPHg was detected in the soil sample collected from MW6 at 70 feet bgs. TPHg was detected in soil samples at concentrations ranging from nondetectable to 1,800 milligrams per kilogram (mg/kg). The lateral extent of TPHg ' in vadose zone soil is shown on Figures 7 and 8. Benzene concentrations in soil samples collected from the site vary with depth. The lateral extent of ' benzene in soil samples collected from 40 feet bgs to 60 feet bgs is delineated to the east, south, west,-and northwest by borings B103, MWI, MW2, and VE3, respectively. The lateral extent of benzene in soil samples collected from 60 feet bgs to 75 feet bgs is delineated to the south, west, and northwest by borings MWI, MW41 and VE3, respectively. Low concentrations of benzene were detected in soil samples collected from B101 and B103 located northeast and east of the s:\environmental\25291\reports\irp.doe 3