ARCHIVED REPORTS_FIRST QUARTER 2010 GROUNDWATER MONITORING REPORT

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URS Mr. James Barton Page 4 of 8 California Regional Water Quality Control Board, Central Valley Region April 29, 2010 continuous operation at the site until low soil gas levels justified treatment system shutdown in December 2003. By the end of December 2002,the system had recovered approximately 524 gallons of gasoline from the subsurface. Due to lack of funding, all work stopped at the site on January 31,2005. On September 12, 2003,ASE submitted the Workplan for Additional Groundwater Characterization proposing the installation of 13 wells north of the site. In response to the Regional Water Quality Control Board(RWQCB), Central Valley Region concerns presented in their letter dated September 22, 2003, ASE submitted the Workplan Addendum for Additional Groundwater Characterization on October 20, 2003. The addendum proposes an additional nine wells north of the site. ' URS was awarded the contract to provide environmental services in October 2006 and quarterly groundwater sampling was resumed in the first quarter of 2007. On August 9, 2007, URS submitted a work plan for additional off-site assessment. This assessment is required to complete the lateral and vertical delineation of MTBE-impacted groundwater. The work plan was approved in a letter from RWQCB dated August 28, 2007. The field activities will commence following RWQCB approval. SITE GEOLOGY Sediments beneath the site are primarily sand and sandy silt of relatively high permeability. The only significant low-permeability materials were clayey silt layers located between 26 and 32 feet bgs and 50 and 64 feet bgs. Neither of these layers has been considered a competent aquitard. rGROUNDWATER MONITORING ACTIVITIES On March I"through 3rd,2010,URS conducted groundwater monitoring and domestic well and treatment system sampling at the site,which included the following tasks: • Measure groundwater levels in on-site monitoring wells (MW-1 through MW-20),recovery wells (RW-1 through RW-5),piezometers(P-1 and P-4), and extraction wells (EW-1). • Purge and collect groundwater samples from all scheduled wells. • Purge and collect influent,mid-fluent, and effluent samples from domestic wells at the direction of RWQCB. • Submit groundwater samples to a California-certified laboratory for analysis of TPH-G; TPH-D; and volatile organic compounds(VOCs) including BTEX, MTBE,TBA, di-isopropyl ether (DIPE), ethyl tert-butyl ether(ETBE), and tert-amyl methyl ether(TAME). • Prepare this report summarizing the analytical results. The depth-to-groundwater and total depth of each well were measured to an accuracy of 0.01 foot bgs to a known surveyed point at each well location with an electronic water level indicator prior to purging. H:\Wprocess\RESD\Franks One Stop\QTR 10\IQMR10 Report.doc