|
boo In February 1992, IT supervised a hydropunch study, which involved the collection of
<br /> hydropunch groundwater samples from 11 locations (HP-1 through HP-11). Three of the
<br /> sampling locations yielded groundwater for sampling. TPHg (380 parts per billion [ppb] was
<br /> AW detected in a groundwater sample from HP-5, which was located east of the former fuel UST
<br /> complex. Concentrations of BTEX were detected in the groundwater sample from HP-1, which
<br /> was advanced southwest of the former fuel USTs and from boring HP-5 (EMCON, Baseline
<br /> Assessment Report, dated December 27, 1994).
<br /> Between November 16, 2000 and January 2, 2001, eight weekly groundwater extraction events
<br /> were performed. During each event, approximately 2,400 to 3,800 gallons of groundwater were
<br /> removed from well MW-3. In addition, approximately 600 gallons of groundwater were removed
<br /> from well MW-7 on November 16, 2000. A total of approximately 27,200 gallons of groundwater
<br /> were removed from the site. Based on the results of groundwater samples periodically collected
<br /> from well MW-3 prior to and following each of the extraction events, an estimated total of 26.63
<br /> pounds (Ibs) of methyl tertiary-butyl ether (MTBE) were removed from beneath the site. The
<br /> weekly groundwater batch extraction activities were discontinued following the receipt of
<br /> approval from the SJCEHD.
<br /> In April 2001, GRI supervised the drilling of eight Geoprobe soil borings (B-1 through B-8) at
<br /> and in the vicinity of the site, and one cone penetrometer test (CPT) boring on-site (CPT-1).
<br /> Concentrations of petroleum hydrocarbons and fuel oxygenates were not detected in the soil
<br /> from the CPT boring, or in groundwater samples collected from borings B-3 and B-5 through B-
<br /> 8. MTBE was detected in groundwater samples from borings B-1, B-2, B-4, and the 75-foot
<br /> ` groundwater sample from CPT-1 up to a maximum concentration of 120 micrograms per liter
<br /> (pg/L). 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, dated June 2001).
<br /> On August 8 through 10, 2001, GRI supervised the installation of three off-site and one on-site
<br /> groundwater monitoring wells (MW-8 through MW-11). Well MW-11 was constructed in a
<br /> deeper (intermediate) water-bearing zone beneath the site. With the exception of MTBE in the
<br /> 14-foot soil sample from boring MW-11 (1.7 ppm) and MTBE in the groundwater sample from
<br /> well MW-11 (110 ppb), soil and groundwater samples did not contain analytes above laboratory
<br /> r„ method reporting limits (MRL). (GRI, Monitoring Well Installation Report, dated September
<br /> 2001).
<br /> two Between December 3 and 7, 2001, SECOR performed dual-phase extraction (DPE) pilot testing
<br /> at the site. The DPE test was performed on wells MW-3 and MW 7 over a 110-hour period.
<br /> Flow rates during the test varied from 10.90 to 33.41 scfm, and vacuum rates varied from 24 to
<br /> 25 inches of mercury (in Hg). Over the course of the five-day event, a total of zero lbs of TPHg,
<br /> `r 0.01 lbs of benzene, and 6.64 lbs of MTBE were removed from beneath the site. Results of
<br /> DPE testing indicated a vacuum radius of influence between 36 and 60 feet. Approximately
<br /> 20,830 gallons of groundwater were extracted during the DPE event. Based on the low mass
<br /> removal achieved with this test, SECOR concluded that DPE was not an effective remedial
<br /> alternative for this site (SECOR, Dual Phase Extraction Summary Report, dated February
<br /> 2002).
<br /> .r
<br /> On April 23, 2002, the SJCEHD expressed concern with high concentrations of tertiary-butyl
<br /> alcohol (TBA) in wells MW-3 and MW-7. On May 9, 2002, GRI confirmed the presence of high
<br /> r„ concentrations of TBA in the wells (over 200,000 pg/L) and attributed the raised concentrations
<br /> to MTBE metabolism. In correspondence dated July 22, 2002, the SJCEHD required that the
<br /> 3
<br /> rr 76 Service Station No.11192 Cardno ATC Project Number 52.75118.2390
<br /> Stockton,California May 1,2014
<br /> V
<br />
|