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<br /> • sampling locations yielded groundwater for sampling TPHg (380 parts per billion [ppb]
<br /> was detected in a groundwater sample from HP-5, which was located east of the former
<br /> fuel UST complex Concentrations of BTEX were detected in the groundwater sample
<br /> from HP-1, which was advanced southwest of the former fuel USTs and from boring HP-
<br /> 5 (EMCON, Baseline Assessment Report, December 27, 1994) ;
<br /> Between November 16, 2000 and January 2, 2001, eight weekly groundwater extraction
<br /> events were performed During each event, approximately 2,400 to 3,800 gallons of
<br /> groundwater were removed from well MW-3 In addition, approximately 600 gallons of
<br /> groundwater were removed from well MW-7 on November 16, 2000 A total of
<br /> approximately 27,200 gallons of groundwater were removed from the site Based on the
<br /> results of groundwater samples periodically collected from well MW-3 prior to and
<br /> following each of the extraction events, an estimated total of 26 63 pounds of methyl
<br /> tertiary butyl ether (MtBE) were removed from beneath the site The weekly groundwater
<br /> batch extraction activities were discontinued following the receipt of approval from the
<br /> SJCEHD
<br /> In April 2001, Gettler-Ryan, Inc (GRI) supervised the drilling of eight Geoprobe soil
<br /> borings (B-1 through B-8) at and in the vicinity of the site, and one cone penetrometer
<br /> test (CPT) boring on-site (CPT-1) Concentrations of petroleum hydrocarbons and fuel
<br /> oxygenates were not detected in the soil from the CPT boring, and in groundwater
<br /> samples collected from borings B-3, B-5, B-6, B-7, and B-8 MtBE was detected in
<br /> groundwater samples from borings B-1, B-2, B-4, and the 75-foot groundwater sample
<br /> from CPT-1 up to a maximum concentration of 120 micrograms per liter (pg1L)
<br /> Concentrations of di-isopropyl ether (DIPE) and 1,2-dichloroethane (1,2-DCA) were also
<br /> detected in groundwater from borings B-1 and CPT-1, respectively (GRI, Subsurface
<br /> Investigation Report, June 2001)
<br /> On August 8 through 10, 2001, GRI supervised the installation of three off-site and one
<br /> on-site groundwater monitoring wells (MW-8 through MW-11) Well MW-11 was
<br /> constructed in a deeper (intermediate) water-bearing zone beneath the site With the
<br /> exception of MtBE in the 14-foot soil sample from boring MW-11 (1 7 ppm) and MtBE in
<br /> the groundwater sample from well MW-11 (110 ppb), soil and groundwater samples did
<br /> not contain analytes above laboratory method reporting limits (MRL) (GRI, Monitonng
<br /> Well Installation Report, September 200 1)
<br /> Between December 3 and 7, 2001, SECOR performed dual-phase extraction (DPE) pilot
<br /> testing at the site The DPE test was performed on wells MW-3 and MW-7 over a 110-
<br /> hour period Flow rates during the test varied from 10 90 to 33 41 scfm, and vacuum
<br /> rates varied from 24 to 25 inches of mercury (in Hg) Over the course of the five-day
<br /> event, a total of 0 pounds (lbs) of TPHg, 0 01 lbs of benzene, and 6 64 lbs of MtBE were
<br /> removed from beneath the site Results of DPE testing indicated a vacuum radius of
<br /> influence between 36 and 60 feet Approximately 20,830 gallons of groundwater were
<br /> extracted during the DPE event Based on the low mass removal achieved with this test,
<br /> SECOR concluded that DPE was not an effective remedial alternative for this site
<br /> (SECOR, Dual Phase Extraction Summary Report, February 2002)
<br /> On April 23, 2002, the SJCEHD expressed concern with high concentrations of tertiary
<br /> butyl alcohol (TBA) in wells MW-3 and MW-7 On May 9, 2002, GRI confirmed the
<br /> • presence of high concentrations of TBA in the wells (over 200,000 Ng/L), and attributed
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