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1 <br /> URS <br /> Ms.Kathleen Amaru Page 2 <br /> Regional Water Quality Control Board—Central Valley Region <br /> ' July 31, 2009 <br /> the northern stormwater drainage subsystem.Further soil and groundwater sampling confirmed the Bum <br /> Pit as the source area of the chlorinated solvents. <br /> ' A total of 18 groundwater monitoring wells were installed to assess the extent of groundwater impacts. <br /> Monitoring wells MW-1,MW-2, and MW-3 were installed in 1987.Monitoring wells MW-4 through <br /> MW-10 were installed in 1988. Monitoring wells MW-11 through MW-15 were installed in 1994. <br /> Monitoring wells MW-16 through MW-18 were installed in 1995. The monitoring well network consists <br /> of wells screened in first groundwater(approximately 5 to 20 feet bgs)and in a deeper zone <br /> (approximately 60 feet to 80 feet bgs).Each of the 18 monitoring wells are sampled annually and wells <br /> MW-1,MW-5, MW-6, and MW-9 are sampled quarterly. Monitoring well MW-5 historically has been <br /> ' the most impacted well with PCE concentrations reported at 23 ug/L during the November 2007 <br /> sampling event. Since their installation in 1996,the deeper zoned wells(MW-16,MW-17, and MW-18) <br /> have never reported any constituents of concern. <br /> ' In 2003,RWQCB issued Cease and Desist Order No.R5-2003-0066 to DVI for exceeding effluence <br /> limits for their stormwater,most notably for chlorinated solvents. Part of the order was the repair of <br /> ' broken storm drain pipelines that were already identified as receiving infiltration of impacted <br /> groundwater.Emergency repair of the storm drainpipes were conducted in 2004. The sewer pipe <br /> rehabilitation was completed by January 2005. <br /> A groundwater remediation system was installed in accordance with the Operations and Maintenance <br /> Manual Addendum dated June 9, 2005. The system utilizes a groundwater pump installed in monitoring <br /> ' well MW-6, two liquid granulated activated carbon(LGAC)vessels, a holding tank, and a sprinkler <br /> discharge system. The system is currently not operating. <br /> ' In the letter from RWQCB dated May 2,2007,an ozone bench test workplan prepared by URS on <br /> January 10,2007,was approved. In the approval letter,RWQCB suggested that, in order to determine <br /> the competitive oxidant demand on ozone,the following also be assessed in the soil and groundwater: <br /> baseline chemical oxygen demand(COD),biological oxygen demand (BOD), and concentrations of <br /> ' non-target compounds such as petroleum hydrocarbons, organochlorine pesticides,polychlorinated <br /> biphenyls (PCBs), semivolatile organics(SVOCs),polyaromatic hydrocarbons(PAHs),nitroaromatics, <br /> and nitramines. Having this baseline data would assist RWQCB in assessing the effectiveness of in situ <br /> ' treatment of the chemicals of concern. <br /> In 2007,URS conducted a bench test to assess if ozone sparging could remediate the VOC-impacted <br /> ' groundwater.It was hoped that ozone could treat the groundwater more effectively than pump and treat, <br /> and reduce life cycle costs and remediation time. Laboratory testing confirmed that ozone is effective at <br /> destroying the VOCs,however, low concentrations of hexavalent chromium(up to 0.035 mg/L) were <br /> produced during testing. <br /> In addition, due to budget limitations, some of the aforementioned activities requested by RWQCB <br /> could not be conducted. However,the first ozone bench-scale study did establish the saturated soil <br /> ' K\Wp ms\RBSD\DVI-Bum Pit@009 Pusive SGWusive Soil Go Survey Repod.&c <br />