ARCHIVED REPORTS XR0003311 - Laserfiche WebLink

Home Browse Search

S E C 0, R 7-Eleven Store#20632 . Offsite Assessment Report May 18, 2005 Page 2 three 10,000 gallon USTs prior to tank lining permit approval Grab groundwater samples were collected from borings GP-1, GP-5, and GP-7 through GP-10 Maximum benzene, methyl tert butyl ether (MtBE), and total petroleum hydrocarbons as gasoline (TPHg) concentrations in soil samples collected were in GP-3-5' at 0 44 milligrams per kilogram (mg/kg), 12 mg/kg and 150 mg/kg, respectively Maximum benzene, MtBE and TPHg concentrations in groundwater were in GP-1 at 390 micrograms per liter (fag/L), 16,000 pg/L and 16,000 Pg/L, respectively Historical soil and groundwater analytical results are in Tables 2 and 3 The assessment concluded that soil impacted with gasoline appeared restricted to an area surrounding the UST pit and underlying the fuel dispensers On September 21 and 22, 1997, Flour Daniel GTI supervised the installation of groundwater monitoring wells MW-1 through MW-4 to depths ranging from 16 5 to 21 5 feet bgs (Figure 3 and Table 1) On October 21, 1998, three 10,000 gallon USTs and associated piping were removed from the site Eight soil samples were collected from the side walls of the UST excavation, six soil samples were collected from the beneath the former product lines and dispensers, and two soil samples were collected from beneath the former vent piping (Figure 3) Approximately 1,130 cubic yards of soil was generated during the UST removal and over-excavation to • accommodate new USTs Due to shallow groundwater at the site, approximately 92,000 gallons of water was generated during the UST replacement and transported from the site for proper treatment and disposal Groundwater monitoring well MW-4 was destroyed during the excavation activities Groundwater monitoring well MW-5 was installed in December 1998 to provide a monitoring point near the dispenser island Additional lateral and vertical assessment of dissolved MtBE and hydrocarbons was conducted through 2002 In April 2002, three onsite monitoring wells (MW-4R, MW-6, and MW-7), two dual-nested sparge/vent wells (SPV-1 and SPV-2) and a vertical delineation soil boring (SB-1) were installed at the site site (Figure 3 and Table 1) There are currently seven onsite monitoring wells On April 22, 2002, a soil vapor extraction (SVE) test was conducted at the site Vapor was extracted from MW-41R, MW-7, SPV-1, and SPV-2 Low influent vapor concentrations and poor vacuum response in observation wells were documented during the test An air sparge test in SPV-1 increased the groundwater dissolved oxygen concentration from 0 5 to 2 4 milligrams per liter (mg/L) in SPV-1 In April 2003, 7-Eleven, Inc upgraded the product lines at the site Benzene, TPHg, and MtBE were reported at maximum concentrations of 0 019 mg/kg, 4 7 mg/kg, and 0 60 mg/kg, respectively, in soil samples collected beneath the product lines and fuel dispensers I W-Elevenl7-11 Stores1206321Reports120632 Assessment Report 05-8-05 doe