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.. Ms. Victoria McCartney May 27, 2008 rr CONESTOMA-ROVERS &ASSOCIATES soil. The grab-groundwater sample collected from boring GP-1 at 36 fbg contained 79 micrograms per liter(pg/L) MTBE and 6.3 pg/L tertiary-amyl methyl ether(TAME). The grab-groundwater sample collected from GP-2 at 37 fbg contained 0.85 pg/L benzene, 0.51 µg/L xylenes, 890 µg/L MTBE, and 52 µg/L TAME. The grab-groundwater sample collected from GP-3 at 39 fbg contained 0.51 µg/L benzene,0.91 µg/L xylenes,76µg/L MTBE,and 5.3 itg/L TAME. 2002 Monitoring Well Installation: On January 7 through 9,2002,SECOR supervised V&W Drilling,Inc.ofIsleton, California install shallow monitoring wells MW-5S and MW-6S and deep wells MW-5D,MW-6D,and MW-7D. No hydrocarbons were detected in soil, with the exception of 0.002 mg/kg MTBE in one sample (MW-5D at 51 fbg). 2003 Cone Penetration Test and Well Installation: On February 4 and 5,2003, SECOR supervised Gregg advance cone penetration borings CPT-1 and CPT-2 to assess soil stratigraphy and collected discrete grab-groundwater samples. Each boring was advanced to approximately 120 fbg. Three depth-discrete grab-groundwater samples were collected at each of the CPT boring locations. MTBE was detected in all six samples at concentrations ranging from 2 pg/L to 22 pg/L; TAME was detected in two of the samples at concentrations ranging from 0.9 µg/L to 0.5 pg/L. 2003 Monitoring Well Installation: On February 12,2003,SECOR supervised Spectrum Drilling and Exploration of Stockton,California install one 6-inch diameter groundwater monitoring well(MW-8)to a total depth of approximately 40 fbg. No samples were collected from this well due to its close proximity to CPT-2. 2004 to 2005 Remedial Action — Batch Groundwater Extraction: From August 2004 to June 2005, SECOR performed batch groundwater extraction events on wells MW-6S and MW-8. Integrated Wastestream Management (IWM),under the supervision of SECOR,extracted approximately 114,450 gallons of groundwater. During this time, the MTBE concentration declined from approximately 20,000µg/L to approximately 300 pg/L,and eventually below reporting limits. Approximately 3.8 pounds of MTBE was removed from the groundwater system. 2008 Soil Vapor Sampling: On January 17,2008,CRA observed Gregg Drilling and Testing,Inc.advance three soil vapor borings(VP-1,VP-2,and VP-3)using direct push GeoProbe®rig to a depth of 6 feet below grade(fbg). TPHg was detected in vapor from all wells at concentrations ranging from 270µg/m3 in VP-3 to 820µg/m3 in VP-1. Benzene was only detected in vapor from VP-1 at 4.0 µg/m3. Toluene was detected in vapor from wells VP-1 and VP-2 at 20 µg/m3 and 9.9µg/m3,respectively. No MTBE,ethyl-benzene, 1,2 DCA,or EDB was reported in vapor. Details of this investigation are presented in CRA's February 8, 2008 Soil Vapor Investigation Report. 2008 Site Closure: In May 2008 the Regional Water Quality Control Board, Central Valley Region, issued a No Further Action Required directive. 3 Worldwide Engineering,Environmental,Construction,and IT Services