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P %T C V A S S 0 C I A T E S I N C f L- Recent Deposits Recent alluvium consists of sediments deposited on top of the erosional surface that was formed near the end of +L+ the last glacial period. Recent deposits are generally composed of alluvial deposits consisting of unconsolidated gravel, sand, silt, and clays. Subsurface soils encountered during drilling at the site consisted of poorly graded fine to gravelly sands with layers of clay and silt to a depth of approximately 65 feet. Groundwater is II. encountered in these sediments at a depth of approximately 54 feet bgs. * HYDROCARBON-IMPACTED SOIL AND GROUND WATER LN Information obtained from previous soil investigation and ground water monitoring reports indicates that hydrocarbon impacted soil and ground water are present beneath the site. w Soil L' Laboratory analytical data from previous soil investigations indicated petroleum hydrocarbon constituents were detected in soil samples collected from soil borings advanced in the vicinity of the former UST location (borings SB3 and MW1), and in borings MW2 and VEW3 advanced south of the former UST location. The highest concentration of TPHg, 1,900 milligrams per kilogram, was reported in the soil sample collected from SB3 at a depth of 20 feet bgs. Based on the laboratory analytical data, petroleum impacted soil extends from 15 to 45.5 feet bgs in the vicinity of the former UST location and at VEW3. Low concentrations of petroleum +� hydrocarbons were detected in soil samples collected from MW2 at depths of 40.5 and 50.5 feet bgs. The petroleum hydrocarbon concentrations appear to attenuate with depth and do not appear to extend to the water table. Analytical data from soil samples collected at the site are summarized in Table 2. The estimated extent �. of petroleum impacted soil is shown on Figure 3. Ground Water Laboratory analytical results of groundwater samples collected at the site on October 20, 2003, indicated petroleum hydrocarbons were detected in the groundwater samples collected from MW1 and MW2. MTBE was detected in the groundwater sample collected from MWI at a concentration of 7.1 micrograms per liter (p.g/L). TPHg, benzene, toluene, and MTBE were detected in the groundwater sample collected from MW2 at concentrations of 190 pg/L, 1.2 p,g/L, 2.5 pg/L, and 21 p.glL,respectively. Groundwater samples collected from wells MW3, MW4, MWS, MW6, and MW7 did not contain concentrations of TPHg, total petroleum hydrocarbons quantified as diesel fuel (TPHd), total petroleum LM hydrocarbons quantified as kerosene (TPHk), BTEX constituents, or fuel oxygenates at or above the laboratory reporting limits. Analytical data for groundwater samples collected at the site are summarized in Table 3. The estimated extent of petroleum impacted groundwater is shown on Figure 4. Hydrographs showing benzene and MTBE concentrations in MW1 and MW2 are included as Figure 5 and Figure 6. LM L. Diesel Performance January 5,2004 ' ATC Project Number 5462577 Page 3 LM