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I I W. Marty Hartzell Project 803026 September 8, 2000 Page 4 IT proposes to implement a remedial strategy focused on aggressive source control and removal utilizing an sponging and soil vapor extraction in the former UST area. Air sparging involves the injection of atmospheric sir and" pressure into the subsurface. Air sponging has the combined ef'fct of physically removing cwtmn tmass from and and groundwater result of voladbizaamst of connotations into the air almost and mahaiing aerobic biologic activities by the addition of oxygen to the subsurfic Soil vapor extraction will be used to capture mil gas vapor Sour the unsaturated zone and the fuel-enriched air sparge stream. The and vapor extraction stream will be trailed to _ empty with regional Air District requirements; prior to discharge to the wnosphere. The combined air spargeosed vapor extraction system is projected to operate for six to eighteen morals in a high flow rate made until data indicates that physical removal of hydrocarbon mass has reached the limit of attentiveness. Following aggressive soume control via physics) removal processes, a accord mode of opemfion of the solace camrol system will be implemented. The second phase of opention will be an clanging for the purpose of oxygen addition to subsurface. The soil vapor extraction system will be dismadled cud the sit sparge system will be urn in much lower At injection rates. This mock of operation is oflm lammed bio-spargin& In this made, less than 10 cubic foul per minute (corn) of air is injected into the groundwater for the axle purpose of oxygenating the groundwater and unsaturated soils. This is performW to maximize the acerbic biodegradation off I compounds; further reducing the source zone fuel mass sod further enhancing natural attenuation of the bulk dissolved phase impacts. By maximizing source removal and eahaied namrat attenuation, the need for subsequent natural attnmuatis m processes to manage residual holsters will be minimized. The duration of this second mode of operative will be determined by evaluating the contaminant distribution at the site, the named attenuation parameters, and in-situ reapintion rates is the source crmml area. We expect that this second made of operation should require less than eighteen months of operation before the effectiveness may be limited by the moss of fuel-related hydrocarbons reasoning in the source zolm. EVALUATION OF THE VERTICAL GRADIENT BETWEEN THE IMPACTED ZONE AND DEEPER UNITS An additional gmumlwater momparing well (hdW-8) will be installed doxmgradieot and adjacent to existing well MW-6 to form a well pa'n for characteizing the vertical Student beneath (be site. The proposed well will he mamued outside of the source 'area to limit the potential for vertical migration of contaminants through the well seal. This well will also be included in the quarterly groundwater monitoring Program to evaluate the potential for vertical migration of impacted groundwater. The well will be installed vm.�,pn�e•niaow�mrawnawmau.mwvei nmlY�olNRoll Nfflmwol