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N } 4 <br /> Former Shall Sanrloe Station(WIC No.204-7524-1408) j <br /> 141 N.EI Dorado Ave.,Stoddon,California G <br /> , <br /> Fu ro proposes to monitor the dissolved ox ;I en DO , vacuum response, and water <br /> 9 P P Y9 ( } <br /> levels at start-up of the groundwater oxygenatioan system, after two weeks, and again after <br /> four weeks. Groundwater samples will be collected from all monitoring wells during the <br /> next quarterly sampling event and analyzed to assess the effect of the GO system and <br /> the down-gradient wells (MW-4, RW-1, and RW-2). The data will be submitted to the <br /> PHS/EHD and permission to activate the air diffusers in the down-gradient wells will be <br /> requested. <br /> The PHS/EHD letter also expressed concernp that "the treatment system may not be <br /> adequately sized. to handle the concentrations removed-'..from -the subsurface". h <br /> "Breakthrough occurs frequently, which results'in system dc�wnliiri z urail"tkte cart n is <br /> replaced." ';' <br /> Hydrocarbon concentrations in soil vapors extracted from the site have decreased from <br /> 450 parts-per-million volume (ppmv) in July 19.93 to 51 ppmv on June 1, 1994. Fugro is <br /> using two 2,000-pound carbon vessels to treat the soil vapors. At the low influent <br /> concentrations, activated carbon is the most cost-effective treatment alternative. The <br /> addition of two more vapor extraction wells should increase both the removal of volatile <br /> hydrocarbons from soil and the radius of influence of the system. The carbon emissions <br /> control should continue to operate effectively within the projected range of influent <br /> hydrocarbon concentrations. <br /> The attached figure shows vacuum readings ;collected on June 10, 1994, prior to the <br /> installation of the GO system. Currently, there is a good vacuum response area to the <br /> existing vapor extraction system. <br /> 3 <br /> i <br /> e <br /> 93473011.ML7 2 <br />