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t, n t p � Athotic Rahhdd Comp ink 2 ARCO 595 6100 North E rtw w 99 Stockton CA OLtob,r 2 2004 ASSESSMENT ACTIVITIES AND FINDINGS From June I to June 6, 2000, four groundwater monitoring wells (MW-I through MW-4) and three soil borings (B-1, B-2, and B-3) were completed at the site by West Hazmat Drilling of Ranch Cordova, California Groundwater monitoring well MW-I was set at 75 feet bgs and screened from 40 to 75 feet bgs Groundwater monitoring well MW-2 was set at 65 feet below ground surface (bgs) and screened from 45 to 65 feet bgs Groundwater monitoring well MW-3 was set at 73 feet bgs and screened from 53 to 73 feet bgs Groundwater monitoring well MW-4 was set at 64 feet bgs and screened from 44 to 64 feet bgs Borings B-I to B-3 were drilled to a total depth of 40 feet bgs and backfilled with grout upon completion Boring Logs showing well completion details are included as Attachment B Field procedures are described in Attachment C Subsurface Conditions In each of the borings, primarily silty clay was present from the ground sui face to approximately 48 to 59 bgs Beneath approximately 48 feet to 59 feet bgs, silty sand to sand was encountered First groundwater was encountered at approximately 58 to 62 feet bgs (within the sand layer) Underlying the sand at depthd of 64 to 74 feet was silty clay, which was encountered to the bottom of the deepest boring at 75 feet bgs Groundwater levels stabilized between 56 and 59 feet bgs Soil Sampling and Analysis TPHg was detected in l of 41 samples analyzed at a concentration of 1 88 mg/kg (B- 3@40')40') Benzene was detected in 4 of 41 samples analyzed at a maximum concentration of 0 0645 mg/kg (B-3@40')40') MtBE was detected 2 of 41 samples analyzed at a maximum concentration of 0 308 mg/kg (MW-4@60') TAME, D1PE, E.tBE, TBA, EDB and 1,2-DCA were reported as nondetectable in all samples analyzed Sol] analytical results are presented in Table I Field and laboratory procedures are presented as Attachment C Certified analytical reports and chain-of-custody documentation are presented as Attachment D Groundwater Monitoring Well Development, Sainpling, and Surveying After installation, the groundwater monitoring wells weie developed by rigorously surging over the length of the screen interval and by purging approximately ten casing volumes of water where possible Groundwater samples were collected from the newly installed groundwater monitoring wells on June 16, 2000 Groundwater samples were analyzed for TPHg, BTEX, and MtBE by EPA Method 8015 and fuel oxygenates (MtBE, D1PE, TAME EtBE, TBA, and 1,2-DCA) by EPA Method 8260 TPHg, benzene, and MtBE were reported in groundwatei samples from each well at maximum concentrations of 8,910 ppb, 2,310ppb, and 3,200 ppb, respectively TBA and TAME were reported in well MW-4 at concentrations of 807ppb and 4 48 ppb, respectively Wells MW-2, MW-3, and MW-4 had teported concentrations of 1,2-DCA 077 41941 :.onvLti HIM ill d0