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419.Main Manteca <br /> April, 2006. <br /> Page 2 <br /> calculated a mass of 0.03.pounds of dissolved MTBE in groundwater,as opposed to 3.86 <br /> pounds.iri October, 2003. . <br /> Although the overall concentration of MTBE in groundwater has been in decline since late. <br /> 2001.and early 2002 when concentrations.were at the historical highs, the MTBE <br /> concentration in MW-11,and EW-1.is currently.still above.MCL levels...Also,as noted above, <br /> the contamination plume has not been fullyy defined in the northwest direction. .EHD.and <br /> RWQCB.agreed that the site is not quite.ready.for closure at this time; therefore,your request <br /> for no-further action is denied. .In order to.bring the site toward closure status,the following <br /> items.should first be addressed: <br /> • Complete definition of the lateral extent of the dissolved MTBE plume toward the <br /> northwest;grab samples.may be adequate. .. <br /> • Provide a fate-and-transport Model showing the path of travel of the plume before it <br /> reaches "background".levels, and provide an estimate,with technical support, of <br /> when background conditions.will be achieved.. <br /> Discuss and evaluate the risk of soil vapor intrusion to.all nearby structures, and <br /> compare residual contaminant concentrations.proposed to be left in place with the <br /> CHSSLs and ESLs.provided on the website of the San Francisco.Bay.Regional <br /> Water Quality.Control Board.. <br /> Since the MTBE concentration of MW-11.and EW-1 is still above MCL, some effort should <br /> be made to.reduce the concentration...EHD recommends.conducting a limited batch <br /> groundwater extraction at the affected well(s).. <br /> Please submit a proposal or work plan that will address the above-mentioned items to.EHD. <br /> by June 1,2006..If you have any questions,please contact Jeffrey.Wong at (209).468-0335.. <br /> Donna Heran,REHS,Director <br /> Environmental Health Division <br /> I � Z <br /> Jeffrey.Wong,.Senior REHS. Nuel C. Henderson,Jr.,PG. <br /> LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit N <br /> C:. RWQCB,Central Valley Region—James.L..L..Barton,PG <br /> C:. Condor Earth Technology-Lee Morse / David Wood <br /> i <br />