SITE INFORMATION AND CORRESPONDENCE_CASE 1

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M. Scott Mansholt - 2 - 14 December 2005 Chevron Environmental US Can-Welty Road In a 1997 investigation, TCE was not detected in groundwater, but 2.4 µg/L cis-1-2 dichloroethene (a TCE degradation by-product) was detected in one sample. Since TCE, benzene, and gasoline specifically are unrelated to the OVP, after about 1997 analysis for these compounds was not routinely conducted for the pipeline investigations. Elevated TPH concentrations in groundwater generally correspond to and downgradient of the on-site areas having impacted soil and free phase petroleum (sheen) in monitoring wells MW-1 and MW-2. Depth to groundwater is between 32 and 38 feet and the gradient is east/northeast. Consequently, it appears that in addition to the impacts as a result of OVP leaks, the elevated TPHg concentrations and detectable TCE concentrations, suggests that these compounds may be related to the waste/bum pit. Current Investigation and Quarterly Groundwater Monitoring The purpose of the current investigation was to characterize subsurface soils off-site and downgradient of former boring GMX-12 (north of the UPRR tracks) and to delineate impacted groundwater downgradient of the site. The current investigation describes the advancement of four soil borings, installation of MW-5, and collection of soil and groundwater samples for laboratory analysis. During the third quarterly monitoring event (July 2005) groundwater samples were also obtained from three of four on-site wells (MW-1 had a sheen and was not sampled) and two off-site wells (MW-5 and WFSMW-1) as part of the third quarterly monitoring event. Between 1996 and 2003, the onsite wells were sampled three or less quarterly monitoring events, but beginning with the third quarter 2005, and until further notice, sampling will be conducted for several consecutive quarters. A well search, conducted to identify water supply wells within a 2,000 foot radius of the site, noted one crossgradient and two upgradient domestic wells within the search area. Well records for the domestic wells indicate that surface seals are a minimum of 20 feet. Two onsite wells described as "public" wells were observed on-site. Monitoring wells associated with other nearby sites under environmental investigation were also identified. Soil Borings SB-13, 14, and 15 were advanced approximately 100 to 150 feet NE-NW of boring GMX-12 to characterize/delineate the previously identified impact. TPH as crude oil (TPHc) at 15,000 mg/kg in soil was reported at 41.5 feet in GMX-12. The borings were advanced to a target depth of 48 feet to coincide with maximum depths of previous soil borings. According to the results, with the exception of 120 mg/kg TPHc atone foot in SB-14, there was no evidence of petroleum hydrocarbons. Boring SB-15 (converted to MW-5), advanced approximately 100 feet north (downgradient) of boring GMX-10, similarly did not report TPH compounds present in soil. Therefore, it appears borings SB-13 to SB-15 and former borings GMX-6 and GMX-7 define the lateral extent of impacts in soil downgradient, to the north-northwest of the site.