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<br /> In 1991, three 10,000-gallon USTs and four 2,000-gallon USTs were removed The
<br /> USTs were replaced with those that currently exist at the site (three 10,000-gallon
<br /> gasoline USTs) Well MW-2 was destroyed during UST removal activities (GRI,
<br /> Groundwater Monitoring Well, CPT, and Ozone Microsparge System Installation Report,
<br /> May 9, 2003) ,
<br /> In 1992, a hydropunch study and a soil vapor extraction (SVE) test were conducted
<br /> The SVE test was conducted over a six-hour period on January 21, 1992 Results of the
<br /> SVE test indicated that a 100-standard cubic feet per minute (scfm) air flow rate was
<br /> sufficient to achieve an 85 foot radius of influence (IT, Soil Extraction Pilot Test, March,
<br /> 1992)
<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 /> San Joaquin County Environmental Health Division (SJCEHD)
<br /> • In April 2001, GRI supervised the drilling of eight Geoprobe soil borings (B-1 through B-
<br /> 8) at and in the vicinity of the site, and one cone penetrometer test (CPT) boring on-site
<br /> (CPT-1) Concentrations of petroleum hydrocarbons and fuel oxygenates were not ,
<br /> detected in the soil from the CPT boring, and in groundwater samples collected from
<br /> borings B-3, B-5, B-6, B-7, and B-8 MtBE was detected in groundwater samples from
<br /> borings B-1, B-2, B-4, and the 75-foot groundwater sample from GPT-1 up to a
<br /> maximum concentration of 120 pg/L Concentrations of di-isopropyl ether (DIPS) and
<br /> 1,2-dichloroethane (1,2-DCA) were also detected In groundwater from borings B-1 and
<br /> CPT-1, respectively (GRI, Subsurface Investigation Report, June, 2001)
<br /> On August 8, 9 and 10, 2001, GRI supervised the installation of three off-site and one
<br /> on-site groundwater monitoring well (MW-8 through MW-11) With the exception of a
<br /> concentration of MtBE in a 14-foot soil sample from boring MW-11 (1 7 ppm) and a
<br /> concentration of MtBE In the groundwater sample from well MW-11 (110 parts per billion
<br /> [ppb]), soil and groundwater samples did not contain detectable concentrations of
<br /> contaminants (GRI, Monitoring Well Installation Report, September, 2001)
<br /> Between December 3 and 7, 2001, SECOR International Incorporated (SECOR) �
<br /> performed dual-phase extraction (DPE) testing at the site The DPE test was performed
<br /> on wells MW-3 and MW-7 over a 110-hour period Flow rates during the test varied from
<br /> 10 90 to 33 41 scfm, and vacuum rates varied from 24 to 25 inches of mercury (in Hg)
<br /> Over the course of the five-day event, SECOR reportedly removed a total of 0 pounds
<br /> (lbs) of TPHg, 0 01 lbs of benzene, and 6 64 lbs of MtBE SECOR determined that the
<br /> vacuum radius of influence was between 36 and 60 feet Approximately 20,830 gallons ,
<br /> iof groundwater were extracted during the DPE event Based on the low mass removal _14r
<br /> achieved with this test, SECOR concluded that DPE was not an effective remedial
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