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C I FX' L E A kR. ' G R O U P En vi.onnetrrlvf Seru rces 1 3.3 Sorbed-Phase Contamination ' Historical investigation data indicate the presence of one relatively large area of soil contamination beneath the site The most contaminated area is located in the vicimty of MW-5B ' and extends up-gradient to the eastern end the former UST pit (source area) and probably just beyond MW-513 in the down-gradient direction Soli contamination in the area of the former UST pit, as defined by concentrations of TPHg greater than 1 mg/kg, appears to extend from approximately 19 to 29 feet bgs with an areal extent of approximately 10,881 ft2 (Figure 3) and estimated thickness of 7 to 10 ft (Figure 4A) The resulting volume of soil affected in this area is estimated to be 108,810 0 (4,030 cubic yards) (in Iplace) The average concentration of TPHg contamination in this area was calculated to be approximately 264 mg/kg (0 000264 unitless) The mass of residual sorbed-phase gasoline contaminants in this area was calculated to be approximately 2,872 6 lbs (or approximately 463 gallons of gasoline) (Table 4) It should be noted that the sorbed-phase contamination at this site lieappears to reside completely within the saturated zone(Figure 4A) Thus, direct remediation of this area of soil contamination would be difficult Based on the mass calculations presented above, the most impacted soil occurs beneath the former UST pit and in the southeast down-gradient direction This conclusion is corroborated by the resulting distribution of dissolved-phase contamination The core of the dissolved-phase plume is located in the area of well MW-5B, and extends back to the former UST pit Future soil ' remediation efforts at the site would best be directed at this area as it appears to be acting as a significant source of ongoing groundwater contamination VIA ti W �rdti► 04ti'll k 1J � I t � W 3.4 Dissolved-Phase Contamination ti° '4t' elr� Results of cumulative investigation efforts i Zdicate that the dissolved-phase contaminant plume iis generally limited to the dimensions of the subject property, however it is migrating southeast in the direction of groundwater flow The area containing high concentrations of dissolved-phase contaminants is mainly limited to the vicinity of the core of soil contamination Concentrations of dissolved-phase TPHg and benzene in this location (MW-5B) were recently 15,000 gg/L and 1,300 µg/L, respectively (Figure 6 & Table 3) Although some residual sorbed-phase . contamination appears to be present in the southeast corner of the former UST bed, dissolved- phase contaminants are significantly less in this area (MW-1) This indicates that the residual ZB178C CAP 7 November 20,2002