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19 June 2000
<br /> AGE-NC Project No 96-0232
<br /> Page 14 of 35
<br /> Figures 9, 10 and 41 depict selected soil sample locations and the estimated extent of MTBE
<br /> concentrations adsorbed in soil in cross sectional and plan views Based on Figures 9, 10 and 41,soil
<br /> borings P 1, P6, P12, P14, P19, P22, P23, P24, P31 and P32 are all located within the adsorbed
<br /> MTBE-impacted soil plume Based on Figures 9, 10 and 41, an average short diameter of 40 feet,
<br /> an average long diameter of 202 feet and a height of 30 feet were used to estimate a coned elliptical
<br /> volume of impacted soil When the data collected at the site is plotted in both plan view and cross
<br /> sectional views, the apparent volume of MTBE impacted soil is approximately 3,337 cubic yards
<br /> Volume calculations are included in Appendix H
<br /> 7.0. ASSESSMENT OF HYDROCARBON-IMPACTED GROUND WATER
<br /> Between August 1997 and May 2000, grab ground water samples were collected from twenty-six
<br /> soil borings(P 1 through P5,P 13 through P32,P34 and P3 5) Laboratory analysis of the grab ground
<br /> water samples site indicated that ground water at the site has been impacted by MTBE, TPH-d and
<br /> TPH-g, laboratory analysis of the grab samples also detected low concentrations of dissolved
<br /> 1,2-DCA, TBA, ethanol and methanol during investigation at the site (Table 6)
<br /> The highest concentration of dissolved MTBE in shallow ground water was detected in the sample
<br /> from soil boring P32 near the southwest fuel dispenser, at a concentration of 11,000 pg/l, moderate
<br /> to high concentrations of dissolved MTBE were detected in samples from P19, P22 , P30, P31 and
<br /> P34 at concentrations ranging from 1,000 µg/1 to 4,300 pg/1 (See Figure 27)
<br /> The highest concentration of dissolved TPH-g detected was from the grab sample from soil boring
<br /> P30 near the middle-west fuel dispenser, at a concentration of 11,000 pg/l, low concentrations of
<br /> dissolved TPH-g were detected in samples P22,P24,P31 and P34 at concentrations ranging between
<br /> 110 pg/1 and 210 pgd (See Figure 26) These results suggest that the dispenser area and possibly the
<br /> southwest corner of the UST pit and the storm water drain line area the source area(s) for the MTBE
<br /> and TPH-g
<br /> The highest concentration of dissolved TPH-d detected was also in the sample from soil boring P30,
<br /> at a concentration of 1,900 pg/l, moderate to low concentrations of dissolved TPH-d were detected
<br /> in samples from P18, P19, P20, P23,P24, P25, P27, P28, P31, P32, P34 and P35 at concentrations
<br /> ranging from 60 µg11 to 250 pg/1 (See Figure 25)
<br /> Between 19 July 1996 and 26 May 2000, approximately two to twelve ground water monitoring
<br /> events (depending on well installation date) were conducted on Flag City Chevron wells MW-1,
<br /> MW-2,MW-4,MW-5,MW-6(A and B),MW-7,MW-8 (A,B and C),MW-9(A,B and C),MW-10
<br /> (A, B, C, D and E), MW-I I (A, B, C and D), MW-12 (A, B, C and D and MW-13 (A, B, C and D)
<br /> to monitor shallow and deeper dissolved fuel component concentrations and to characterize ground
<br /> Advanced CeoEmironmentel,Inc
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