ARCHIVED REPORTS_XR0005758 CASE 2

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IAtlantic Richfield Company 2 ARCO 6020 1711 Yosemite Avenue Manteca CA A n] 12,2001 are labeled T-1, T-2, and T-3 on Figure 2 Sampling activities associated with removal of the USTs and product lines at the site revealed the presence of petroleum hydrocarbon impacted soil and groundwater in the vicinity of the USTs TPHg and MtBE were reported at maximum concentrations of 1,430 mg/kg and 20 8 mg/kg, respectively, in soil samples collected after over-excavation was performed Additionally, three groundwater"grab" samples collected from the within the UST cavity were reported to contain MtBE at concentrations ranging from 180 micrograms per liter (gg/L)to 310 µg/L The IT Corporation installed two new gasoline USTs in August of 2000, as shown on Figure 2 ASSESSMENT ACTICITIES AND FINDINGS From January 30 to 31 2001 6 four-inch groundwater monitoring wells MW-5 MW-6 ' MW-7, MW-8, MW-9, and MW-10) were completed by West Hazmat Drilling of Rancho Cordova, California under the direction of SECOR Monitoring wells were set at approximately 35 feet bgs, and screened from approximately 10 feet to 35 feet bgs I Boring logs showing well completion details are included as Attachment B The findings of this assessment are discussed below ' Subsurface Conditions. i The subsurface materials encountered consisted primarily of silty to gravelly sand, with silt and clay strata encountered at varying depths between fifteen and thirty five feet below ground surface Groundwater was encountered between 21 feet bgs and 25 feet bgs,dust after construction and stabilized between 19 5 feet bgs and 23 feet bgs in the ' monitoring wells The groundwater was encountered in silty sand to silt Boring Logs are presented as Attachment B ' Soil Sampling and Analysis Soil samples were collected at 5-foot intervals using a split spoon sampler Selected samples were analyzed for TPHg by EPA Method 8015, benzene, toluene, ethylbenzene, ' and xylenes (BTEX), and fuel oxygenates including methyl tertiary butyl ether (MtBE), tertiary amyl methyl ether(TAME), di isopropyl ether (D1PE), ethyl tertiary butyl ether ' (EtBE), tertiary butyl alcohol (TBA), ethylene dibromide (EDB), and 1,2-dichloroethane (1,2 DCA) by EPA Method 8260 MtBE was reported in three soil samples (MW-6 @ 25', MW-6C&30', and MW-7q35') at ' concentrations of 0 657 mg/kg, 0 533 mg/kg, and 0 109 mg/kg, respectively Benzene was reported in one soil sample (MW-9@30') at a concentration of 0 00978 mg/kg All ' other analytes were reported below laboratory detection limits Soil analytical results are presented in Table 1 Field and laboratory procedures are presented as Attachment C Certified analytical reports and chain-of-custody documentation are presented as Attachment D 6,1 ' 077 42070 330[Well Install report-6020 doc