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Former Thrifty Co.Station No.172
<br /> Workplan for Additional Soil and Groundwater Assessment
<br /> May 8,2017
<br /> hour groundwater extraction test was also performed on monitoring well MW-11 at a maximum
<br /> sustainable flow rate of four gallons per minute (gpm).
<br /> In April 2004, Terra Vac observed the advancement of six soil borings (131 through B3 and B5
<br /> through 67) in the vicinity of the USTs and dispenser islands. Terra Vac performed this work
<br /> during due diligence site assessment. Borings were advanced to depths of 10 to 25 ft bgs, and
<br /> groundwater was not encountered. Soil samples were collected from borings B2, B3, and B5
<br /> for laboratory analyses. Petroleum hydrocarbon concentrations were not detected in the soil
<br /> samples.
<br /> On June 8, 2006, Terra Vac performed a baseline soil assessment prior to temporary closure of
<br /> the USTs and lease termination. Three soil borings (131-06, 132-06, and 133-06) were advanced
<br /> to 45 ft bgs. Results of the soil sampling indicated concentrations of up to 452 mg/kg TPH, 1.97
<br /> mg/kg benzene, and 0.128 mg/kg MTBE. Based on the decreasing trend of petroleum
<br /> hydrocarbon constituents observed in soil, Terra Vac concluded that a new release of gasoline
<br /> had not occurred.
<br /> In December 2007, GeoHydrologic Consultants, Inc. (GHC) performed oversight of the UST
<br /> removal, well and piping removal, and soil sampling activities conducted at the site. Three
<br /> 12,000-gallon USTs, associated fuel lines, and three dispenser islands were removed from the
<br /> site. Soil sample results for the samples collected from beneath the gasoline LISTS, fuel lines,
<br /> and dispensers did not indicate detectable concentrations of petroleum hydrocarbons. The
<br /> related conveyance piping from MW-3, VW-4, and MW-10/VW-1 in the proximity of the
<br /> excavation areas was disconnected, severed, and removed. The existing lines inside of the
<br /> proposed excavation areas were cut back and capped to prevent damage and plugging of the
<br /> conveyance lines. Groundwater monitoring well MW-12 and dual nested wells MW-11/VW-3
<br /> and VW-2 were properly destroyed by over-drilling the depth of the wells. Following the tank
<br /> removal and well destruction activities, GHC supervised the installation of replacement wells for
<br /> MW-11/VW-3 and MW-12 in January 2008. At the direction of the SJCEHD, VW-3 was
<br /> reportedly installed in a separate borehole approximately three feet southwest of well MW-11 R.
<br /> Replacement wells MW-11 R, MW-12R, and VW-3 were installed in the UST area. After UST
<br /> removal activities, soil samples were collected from beneath the USTs (UST1 N-20.5, UST1 M-
<br /> 21.5, UST1 S-21, UST2N-20, UST2M-21.5, UST2S-21, UST3N-20, UST3S-20, UST3M-22, and
<br /> UST3M-N-21), piping (P-1-15, P-1-35, P-1-55, and P-1-75), and dispensers (D1-10, D2-10, D3-
<br /> 10) using direct-push or hollow-stem auger methods.
<br /> Complete references for activities performed prior to 2009 can be found in Stantec's Site
<br /> Conceptual Model dated October 23, 2009.
<br /> In preparation for pending site redevelopment activities, in October 2010, Stantec destroyed
<br /> wells MW-4, MW-10, MW-11R, VW-1, VW-3, VW-4 (A,B,C), VW-5 (A,B,C), and VW-6 (A,B,C)
<br /> and protected wells MW-3, MW-7, and MW-12R in accordance with Stantec's Addendum to July
<br /> 8, 2010 Work Plan for Monitoring Well Destruction and Replacement, and Additional Path
<br /> Forward, dated September 23, 2010. Well destruction and protection activities are documented
<br /> in Stantec's Well Destruction and Well Protection Report, dated March 15, 2011.
<br /> In May 2011, ATC Associates Inc. supervised the recovery of previously protected wells MW-3,
<br /> MW-7, and MW-12R, and the installation of monitoring wells MW-4R and MW-13 through MW-
<br /> 16. Results of the well installation activities are documented in ATC's Monitoring Well
<br /> Installation Report, dated July 22, 2011.
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