|
. r,
<br /> • 15 October 2000
<br /> AGE-NC Project No 96-0232
<br /> Page 6 of 11
<br /> Twelve ground water monitoring events have been conducted to monitor shallow and deeper
<br /> dissolved fuel component concentrations and to characterize ground water flow direction and
<br /> gradient on the site Currently, the ground water monitoring well network includes wells MW-1,
<br /> MW-2,MW-4,MW-5, MW-6(A and B), MW-7, MW-8 (A, B and C), N4W-9 (A, B and C), MW-10
<br /> (A, B, C, D and E), MW-I 1 (A, B, C and D), MW-12 (A, B, C and D and MW-13 (A, B, C and D)
<br /> Laboratory analysis of ground water samples indicated ground water at the site has locally been
<br /> significantly impacted by MTBE Laboratory analysts of the grab samples detected less significant
<br /> concentrations of dissolved TPH-g, TPH-d, BTEX compounds, TA11ME, ETBE, TBA, methanol,
<br /> ethanol and 1,2-DCA during the site investigation Substantial concentrations of ethanol were
<br /> detected in the initial ground water samples collected from multi-level monitoring wells MW-8,
<br /> MW-9, MW-10, MW�-11, MW-12 and MW-13 However, AGE believes the substantial ethanol
<br /> f . .
<br /> concentrations detected were a result of ethanol and ethanol acetate in the time-release coating on
<br /> the bentonite pellets that dissolved in ground water
<br /> The highest dissolved MTBE concentration detected (5,500 µg/1) in the ground water monitoring
<br /> well samples was collected from monitoring well MW-1, low concentrations of dissolved MTBE
<br /> have been detected in shallow ground water samples from monitoring wells MW-2, MW-4, MW-5,
<br /> MW-6A, MW-7, MW-12A and MW-13A, low concentrations of dissolved MTBE have been
<br /> detected in samples from deeper ground water monitoring wells MW-6B (43 to 48 feet), MW-9A
<br /> (40 to 50 feet), MW-I IB (65 to 75 feet), MWA ID (130 to 150 feet) and MWA 3B (50 to 60 feet)
<br /> At depths deeper than 75 feet, dissolved MTBE has been detected in MW 11 D (130 feet and 150 feet
<br /> bsg) at concentrations as high as I 0 ug/1
<br /> Based on geologic model depicted in the cross sections and on the results of laboratory analysis of
<br /> ground water samples (see Problem Assessment Report), the vertical extent of impacted•ground
<br /> water on-site appears to tic between 10 feet bsg(estimated depth to ground water) and 50 to 60 feet
<br /> bsg in the arca of P I, P 14, MW-I and MW-9 Impacted ground water in the area at 40 to 50 feet bsg
<br /> in MW-9 is underlain by two thin fine-grained units that appear to have retarded the downward
<br /> migration of the MTBE as evidenced by the non-detectable concentrations in samples from P14 at
<br /> 59 to 62 feet bsg Two thicker fine-grained units, each more than 10 feet thick, occur below 60 feet
<br /> bsg The latter two fine-grained units definitely appear to effectively retard the downward migration
<br /> of MTBE as evidenced by the non-detectable concentrations in samples from P14 at 73 to 76 feet
<br /> bsg and 85 to 88 feet bsg and at 100 feet bsg in MW-9 bsg in the area
<br /> Going off-site toward the west, the plume may extend to as mucin as 70 feet bsg approaching the area
<br /> of P16 and MW-11, near Rocky's Restaurant domestic well (RDW-1) as the underlying fine-grained
<br /> sedimentary units thin and pinch out In the immediate area of P16, MW-I 1 and RDW-1, the plume
<br /> of impacted ground water extends vertically from approximately 10 feet bsg to as much as 150 feet
<br /> bsg, as evidenced by detectable concentrations ofMTBE in MW-7 and MWA ID Vertical migration
<br /> .Advanced CeoEnwronmental,Inc
<br /> • t
<br /> . t
<br />
|