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URS ' Ms. Kathy Amaru Page 2 of 6 Regional Water Quality Control Board—Central Valley Region ' May 8, 2011 Groundwater monitoring wells were installed to asses the extent of groundwater impacts. Monitoring wells MW-1-BP,MW-2-BP,and MW-3-BP were installed in 1987. Monitoring wells MW-4-BP through MW-10-BP were installed in 1988. Monitoring wells MW-11-BP through MW-15-BP were ' installed in 1994. Monitoring wells MW-16-BP through MW-18-BP were installed in 1995. Monitoring wells MW-1-BP, MW-5-BP,MW-6-BP,and MW-9-BP are currently used to monitor petroleum and chlorinated solvent-impacted groundwater at the site on a quarterly basis. ' In 2003,the Regional Water Quality Control Board(RWQCB) issued Cease and Desist Order No. R5-2003-0066 to DVI for exceeding effluence limits for their stormwater,most notably for chlorinated solvents. Part of the order was the repair of broken storm drain pipelines already identified ' as receiving infiltration of impacted groundwater. Emergency repair of the storm drain pipes was conducted in 2004. Sewer pipe rehabilitation was completed by January 2005. ' A groundwater remediation system was installed in accordance with URS' Operation and Maintenance Manual Addendum,dated June 9,2005. The system utilizes a groundwater pump installed in well MW-6,two liquid-phase granular activated carbon(LGAC)vessels,a holding tank, and a sprinkler ' discharge system. The system was installed and started on August 4,2005. The groundwater treatment system was shut off for the winter on October 2005. The system was restarted on Thursday,April 5, 2007, and operated for four months. ' On November 16 and 17,2004,URS drilled and installed five 2-inch-diameter groundwater monitoring wells (MW-19-BP through MW-23-BP)adjacent to the sewage treatment plant ponds. These wells are ' used to monitor potential groundwater quality impacts related to the sewage treatment plant ponds. On March 27, 2008, groundwater monitoring well MW-11 was destroyed to make way for the new sewer treatment plant. tMonitoring wells MW-1-STP through MW-4-STP, from the Sewage Treatment Plant, and MW-19-SP through MW-24-SP, from the Sewer Ponds,are now being used as part of the Burn Pit investigation. ' On March 30,2011,URS drilled and installed two groundwater monitoring wells(MW-24-BP and MW-25-BP), to serve as transition wells for the EOS pilot test. On April 19,2011, groundwater monitoring well MW-23-SP was destroyed due to previous damage. URS drilled and installed MW-23R-SP approximately 10 feet from the original well location. ' GROUNDWATER MONITORING ACTIVITIES ' The depth-to-groundwater and total depth of each well were measured,to an accuracy of 0.01 foot below ground surface(bgs),to a known surveyed point at each well location with an electronic water level indicator prior to purging. These measurements were used to calculate the purging volume and groundwater elevation for each well. H:\Wpm \RESMWA-Bum Pit\1011\ A-BP-1Qh l Re M,doc