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<br /> confirmed petroleum impact beneath one of the two USTs. There is no known documentation to suggest
<br /> that over-excavation occurred at that time, thus the soil from the two former UST basins was assumed to
<br /> 'W be left in-place and backfilled with imported fill to surface grade. Based on soil analytical results from
<br /> soil borings completed on and off site, the shallow (0 — 15 feet bgs) residual soil contaminant mass is
<br /> primarily limited to an area within and immediately surrounding the two former UST basins with deeper
<br /> (20—40 feet bgs)hydrocarbon impact observed up to 75 feet from the former USTs. Refer to Table 2 for
<br /> a summary of the soil analytical data and Figures 5 and 6, which depict the vertical profile of soil with
<br /> TPHg and BTEX concentrations in cross sectional view.
<br /> 5.2 Contaminant Mass Distribution in Water
<br /> Site contaminant impact to groundwater beneath and beyond site boundaries consists of TEX, MTBE,
<br /> TBA, 1,2 DCA, and TPHg,. TPHg accounts for the majority of the contaminant mass compared to the
<br /> remaining compounds. The monitoring well network, consisting of 11 wells, provides a sufficient array
<br /> to evaluate the dissolved phase contaminant mass distribution. Those compounds with a higher molar
<br /> mass generally displayed a greater lateral distribution and migration distance from the source area.
<br /> Figure 10 and Figure 11 provide a vertical profile of the dissolved TPHg and MTBE concentrations in
<br /> cross sectional view.
<br /> 5.3 Mass Calculations for Site Specific Compounds
<br /> Contaminant mass calculations (refer to Appendix C for the detailed mass calculations) have been
<br /> completed for TPHd, TPHg, and BTEX in soil and, TPHg, TEX, MTBE, TBA, and 1,2 DCA in
<br /> groundwater. A summary of the quantified mass values are presented in the following table:
<br /> # Mass in € Volume of
<br /> Groundwater Groundwater_' Mass in Soil 1 Volume of Soil
<br /> Pounds Cubic Feet Pounds ? Cubic feet
<br /> y
<br /> TPHg 1.96 1341,165 2,850.55 95 510.00
<br /> TPHd Not applicable Not applicable 246.19 2,093.42
<br /> Benzene_ i Not applicable i Not applicable v1 0.85_ ! 3,510.02
<br /> Toluene i 0.00 j 82,635_ 36.81 l 96 533.42
<br /> Eth lbenzene j 0.052 !181,797 1 26.54 96,533.42
<br /> Total Xylenes 0.025 ! 82,635 1 150.68 96 533.42
<br /> MTBE 0.091 755 520 _Not applicable Not applicable
<br /> 1,2 DCA ! 0.39 1,784,916 Not applicable q Notapplicable
<br /> TBA 0.205 552,474 Not applicable Not applicable
<br /> Total Mass in TPHg 1.96 -- 2,850.55 --
<br /> 5.4 Mass Calculation Assumptions for Soil and Groundwater
<br /> BTEX constituents were detected in soil samples collected from borings SBI, SB4, SB7, MW1, MW2,
<br /> MWS, MW6, and MW 11. TPHg was detected in soil samples collected from borings SB 1, SB4, SB7,
<br /> SB9, MW2, MW3, MWS, MW6, OS2, and OS4. Based on results of selected soil samples collected and
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