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S E C 0 R
<br /> _- Groundwater samples from the accessed wells were submitted to Severn Trent
<br /> Laboratories (STL) for analysis of gasoline range organics (GRO), benzene, toluene,
<br /> ethyibenzene, total xylenes (BTEX), and fuel oxygenates (MtBE, TAME, di-isopropyl
<br /> ether [DIPE], ethyl tertiary butyl ether [EtBE], and TBA), 1,2-dichloroethane (1,2-DCA),
<br /> and ethylene dibromide (EDB) by Environmental Protection Agency (EPA) Method
<br /> 82606. Results are discussed below and are summarized in TRC's Quarterly Monitoring
<br /> Report, October through December 2005 dated November 15, 2005, which is included in
<br /> Attachment 1.
<br /> DISCUSSION
<br /> During the fourth quarter 2005, depth to groundwater ranged between 8.16 and 12.69
<br /> feet bgs, which was in range of historical levels (approximately 5.5 feet to 13.5 feet bgs).
<br /> Localized groundwater flow beneath the site was relatively flat; however, the regional
<br /> direction of groundwater flow beneath the properties in the vicinity of the site was
<br /> southwesterly at a gradient of 0.008 foot per foot, which is consistent with groundwater
<br /> flow patterns reported over previous quarters. Over the last two years of groundwater
<br /> sampling, the regional direction of groundwater flow has predominantly been southerly,
<br /> with variations in groundwater flow to the southwest to southeast.
<br /> During the fourth quarter 2005, relatively low levels of GRO and MtBE were detected in
<br /> the site wells. GRO was detected in wells MW-3 and MW-4 at concentrations of 150
<br /> micrograms per liter (pg/L) and 64 pg/L, respectively. MtBE was detected in on-site
<br /> wells (MW-1, MW-3, and MW-6), upgradient well MW-8, and off-site wells located
<br /> downgradient (MW-10, MW-16, MW-18 through MW-20, MW-23, and MW-24) and
<br /> cross-gradient (MW-9 and MW-22) of the site up to a maximum concentration of 47 pg/L.
<br /> The highest MtBE concentrations were detected in on-site wells MW-1 (24 pg/L) and
<br /> MW-3 (22 pg/L), and in off-site downgradient wells MW-16 (47 pg/L) and MW-19 (26
<br /> pg/L). Other fuel oxygenates were not detected in the site wells this quarter, with the
<br /> exception of a concentration of TBA in wells MW-3 (390 pg/L) and MW-20 (14 pg/L).
<br /> Evaluation of historical groundwater data indicates the presence of a large dissolved
<br /> plume, consisting predominantly of relatively low levels of MtBE, extending from beneath
<br /> the site to the south-southwest. However, concentrations of MtBE in the majority of the
<br /> impacted wells have historically decreased over time, with the exception of those within
<br /> MW-14, which have fluctuated within historical levels.
<br /> Review of historical analytical results for other fuel oxygenates indicate that with the
<br /> exception of detections of TAME and TBA, the majority of the wells (MW-1, MW-2, MW-
<br /> 4, MW-5, MW 11 through MW-24) have consistently reported non-detectable
<br /> concentrations of other fuel oxygenates. Wells MW-3, MW-6, MW-8, MW-9, and MW-10
<br /> have reportedly contained TAME and TBA over recent sampling events; however, with
<br /> the exception of TBA in well MW-3 (390 pg/L), these wells did not contain TBA and
<br /> TAME during the fourth quarter 2005. A concentration of TBA was detected in off-site
<br /> well MW-20 at 14 lag/L. The highest concentrations of TBA and TAME were respectively
<br /> detected in wells MW-3 and MW-8 at a historical site maximum concentrations of 640
<br /> pg/L (August 2004) and 71 pg/L (August 2001).
<br /> I:IBP-ARC01111951Reports\QSR&QRPS 200511 1195 QSR& QRPS 4Q05,doc
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