ARCHIVED REPORTS XR0003361 - Laserfiche WebLink

Home Browse Search

S ECOR i7-Eleven Store#14117 Work Plan for Interim Remediation April 19, 2004 Page 2 On May 13 and 14, 1999, four groundwater monitoring wells (MW-1 through MW-4) were advanced to 51 feet below ground surface (bgs) Benzene, TPHg, and MtBE in sod were reported at maximum concentrations of 2 89 mg/kg (MW-3-15'), 429 mg/kg (MW-3-15'), and 1 95 mg/kg (MW-3-15', Method 8020), respectively (IT Corporation, 1999) (Table 1) On October 30, 2001, three groundwater monitoring wells (MW-5, MW-6, and MW-7)were advanced to 20 feet bgs TPHg, BTEX, and MtBE in soil were not detected above laboratory reporting limits, except for 0 006 mglkg total xylenes (MW-7@20') (Table 2) Selected halocarbons also reported in the soil samples Indicated possible dry cleaner plume contributions (IT Corporation, 1999) An active USA Gasoline (former Exxon) service station is located east of the site On August 14, 2003 SECOR oversaw the Installation of one monitoring well (MW-8) and one soil boring (SB-1) (Figure 2) Sod samples collected from MW-8 Indicated that the vertical limits of TPHg, benzene, and MtBE In soil have been defined south of the pump Islands (Figure 2 and Table 1) The presence of benzene, TPHg, and MtBE in grab groundwater samples collected from MW-8 and SBA Indicate that the vertical limit of dissolved hydrocarbons is not defined onsite south and east of the pump island (Table 2) On February 27, 2004 SECOR submitted the Additional Site Assessment Report and Fate and Transport Model, which Included the results of the August 2003 well installation and the results of Fate and Transport modeling using Flowpath 2 Historical groundwater flow direction data Indicated a time-dependent variability in groundwater flow direction, which appeared to result in a net zero gradient over an extended period of time Four models were run with varying results Results of the first and second modeling runs were very similar and indicate that MtBE will migrate approximately 120 to 180 feet from the source area to the northeast Results of the third and fourth modeling runs represented a near-"flat" hydraulic gradient and indicated that the MtBE contamination would remain In the immediate vicinity of the UST area and concentrations will decrease with time due to dispersion and natural decay Overall, it was determined that it is difficult to accurately model the migration of contaminate plumes at this site because of the relatively flat groundwater table and the highly variable groundwater flow direction in the area INTERIM REMEDIATION As previously discussed with Mr Michael Infurna of the SJCEHD (telephone conversation on January 30, 2004), SECOR proposes periodic groundwater extraction as an Interim remedial measure Groundwater will be extracted from either„MW-1, MW-2, MW-4, or from a conductor casing which was Installed in the UST backfill material for future well installation (Figure 2) Groundwater will be extracted using either a vacuum truck or a dedicated pump Any water not removed immediately from the site will be placed temporarily In an on-Stte storage tank A vacuum truck will be used to remove the water from the site and transport It to an approved disposal facility A grab groundwater sample will be collected from the pumping well prior to commencing each groundwater extraction event The samples will be analyzed for TPHg, BTEX, and the oxygenates, MtBE, ethyl-tert-butyl ether (EtBE), diisopropyl ether (DIPS), tert-amyl-methyl ether (TAME), TBA, and halogenated volatile organic compounds (HVOCs) by EPA Method 82606 The results of the • analyses will be used to calculate the estimated mass removed during each groundwater extraction event I 17-Eievenl7-11 stores1141171Workplans114117 WP for Intenm Remediation doc SECOR International Incorporated