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SECOR
<br /> Ms. Vicky McCartney
<br /> September 15, 2003
<br /> Page 4
<br /> Vlir
<br /> benzene at 84 pglL (VW-1), MtBE at 250,000 jig/L , and Tert-butyl Alcohol (TBA) at 17,000,,E 9/L /z -o
<br /> (MW-2R) (Cambria, 2000).
<br /> In August 2000, GR implemented an interim migration control plan at the site to reduce the amount of
<br /> petroleum hydrocarbons and MtBE beneath the site, and to prevent further off-site migration of the
<br /> dissolved plume (GR, 2000). The plan consisted of the periodic extraction of approximately 5,000
<br /> gallons of impacted groundwater from wells historically containing the highest concentrations of
<br /> petroleum hydrocarbons and MtBE (MW-1 R, MW-219, and VW-1). This interim remediation
<br /> technique continues to be performed at the site on a weekly basis by Onyx Industrial Services
<br /> (Onyx).
<br /> In November 2001, SECOR conducted a five-daydual-pphase extractipn=(DPE) test to reduce the
<br /> amount of petroleum hydrocarbons in soil and groundwater beneath the site, and to determine the
<br /> feasibility of DPE as an applicable technology for remediation at the site. DPE tests were performed
<br /> on well MW-1 R for 3 hours,_ oursMW-2R for 3 hours, VW-1 for 2 hours, and simultaneously on wells MW-
<br /> 1 R,..MW-2W
<br /> R, and V -1 for 92 h . E w
<br /> DPas conducted es ran
<br /> at vapor extraction flow ratging
<br /> beteee 10:94 scfm�(standard cu'is feet per minute) to 42.86 scfm, at vacuums ranging from 14 to
<br /> 25 inches of mercury, and at groundwater extraction flow rates ranging from 0.01 gallons per minute
<br /> (gpm) to 6.2 gpm. During DPE testing, an estimated 8.11 pounds of TPHg, 0.17 pounds of benzene,
<br /> and 5.26 pounds of MtBE were removed from beneath the site, and approximately 26,210 gallons of
<br /> impacted groundwater were extracted and transported off-site for disposal. Based on the results of
<br /> DPE testing, this technology was determined to be.ineffective based on the low soil vapor extraction
<br /> radius of influence calculated for simultaneous applica on of DPE (24 feet), the large quantity of
<br /> extracted groundwater', and low estimated mass removal quantities (SECOR, 2002).
<br /> SUMMARY OF CURRENT INTERIM REMEDIAL ACTION
<br /> Interim remediation via groundwater batch extraction has been performed on a weekly basis from
<br /> wells MW-1 R, MW-2R, and VW-1 since August 2000. Between August 2000 and July 21, 2003, a1,}51w
<br /> total of 790,900 gallons of impacted groundwater has been removed from the site. Since January 2, ����1w
<br /> 2002, batch extraction has occurred from well MW-1R. A historical account of interim batch ion
<br /> extraction removal activities is included in Table 1.
<br /> Interim groundwater batch extraction performed from August 2000 through May 2003 has resulted in
<br /> the reduction of MtBE within the source area, which is evidenced by decreasing MtBE trends in wells
<br /> MW-1 R, MW-2R, and VW-1 (Figures 3 through 5)._IDuring this time period, concentrations of MtBE
<br /> in downgradient well MW-6 steadily increased since the initiation of interim remedial activities until
<br /> August 2002 (Figure 6), which suggests that this interim remedial alternative is limited in its
<br /> effectiveness in controlling the migration of residual MtBE beneath the site. However, since August
<br /> 2002, concentrations of MtBE have declined, which may suggest that interim groundwater batch
<br /> extraction has resulted in reduced concentrations within the source area, and subsequent reductions
<br /> in concentrations of MtBE that have potentially migrated off-site. Given the relatively flat east to
<br /> northeast hydraulic gradient historically reported beneath the site (Table 2), decreased
<br /> concentrations of MtBE in the source area, interim groundwater batch extraction activities appear to
<br /> have significantly influenced the extent and magnitude of the dissolved plume beneath and
<br /> downgradient of the site. Historical concentrations of petroleum hydrocarbons and fuel oxygenates
<br /> are included in Tables 3 and 4.
<br /> 1AGonocoPhi11ips\Tosco Marketing1111MReportslRevised IRAP&WP.doc
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