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S E C O R
<br /> later found, accessed, and sampled along with well MW-14 on June 6, 2005. Results
<br /> are discussed below and are summarized in TRC's Quarterly Monitoring Report, April
<br /> through June 2005 dated July 1, 2005, which is included in Attachment 1.
<br /> DISCUSSION
<br /> During the second quarter 2005, depth to groundwater ranged between 7.38 and 11.99
<br /> feet bgs, which was in range of historical levels (approximately 5.5 feet to 13.5 feet bgs).
<br /> The direction of groundwater flow in the site vicinity was to the southwest at a hydraulic
<br /> gradient of 0.02 feet per foot (ft/ft), which is also consistent with the groundwater flow
<br /> direction reported over previous quarters. Over the last two years of groundwater
<br /> sampling, the direction of groundwater flow has predominantly been southerly, with
<br /> variations in groundwater flow to the southwest to southeast.
<br /> During the second quarter 2005, petroleum hydrocarbons (specifically GRO), and fuel
<br /> oxygenates MtBE, TAME, and TBA were detected in the site wells. Relatively minor
<br /> concentrations of GRO were detected in wells MW-1, MW-3, MW-11, and MW-12 up to
<br /> 150 micrograms per liter (pg/L). MtBE was detected in the each of the site wells except
<br /> for wells MW-1, MW-11, MW-12, and MW-21, at concentrations up to 1,000 pg/L. The
<br /> highest concentrations of MtBE were detected in upgradient off-site well MW-8 (110 ;
<br /> pg/L), on-site wells MW-3 (160 pg1L) and MW-6 (120 pg/L), and downgradient well MW-
<br /> 14 (1,000 pg/L). TBA was detected for the first time in upgradient well MW-8 (30 pg/L),
<br /> and off-site downgradient wells MW-13 (7.2 pg/L) and MW-14 (100 pg/L); and was 1
<br /> reportedly present in wells MW-3 (410 pg/L), MW-6 (33 pg/L), and MW-10 (7.9 pg/L). :
<br /> Wells MW-3, MW-6, and MW-8 contained relatively minor levels of TAME up to a
<br /> concentration of 0.89 pg/L.
<br /> Evaluation of historical groundwater data indicates the presence of a large dissolved
<br /> plume, consisting predominantly of MtBE and TBA, extending from beneath the site to
<br /> the south-southwest. GRO and/or MtBE concentrations in wells CC-WS, MW-1, MW-2,
<br /> MW-3, MW-4, MW-5, MW-8, MW-10, MW-11, MW-13, MW-15, MW-17, and MW-19
<br /> have decreased over time. Concentrations of GRO and MtBE continue to fluctuate
<br /> within historical levels in wells MW-6, MW-9, MW-14, MW-16, MW-18, and MW-20. The
<br /> dissolved TBA plume as reached off-site downgradient wells MW-13 and MW-14, as
<br /> these wells reported initial detections this quarter.
<br /> CHARACTERIZATION STATUS
<br /> Contamination in soil beneath and downgradient of the site has been adequately
<br /> delineated. The extent of the dissolved plume is delineated by historically non-
<br /> detectable concentrations of petroleum hydrocarbons in well MW-21 to the southwest,
<br /> and by well MW-12 to the west.
<br /> s
<br /> Contamination in groundwater, specifically MtBE, has not been delineated to non-
<br /> detectable concentrations southeast (cross-gradient/downgradient) and south
<br /> (downgradient) of the site. Two additional groundwater monitoring wells (MW-23 and
<br /> MW-24) were installed on May 19, 2005 for the purpose of further delineating the extent
<br /> of the dissolved plume in the aforementioned directions. One additional well (MW-22) is
<br /> .., planned for installation on August 26, 2005 at a revised location southeast of the site.
<br /> t; >J Details of upcoming field work are discussed below.
<br /> I:IConocoPhillipslRetail Sites111195XQSR&QRPS 2005/11195 QSR&QRPS 2Q05.doc
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