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URS <br /> September 19, 2003 <br /> Page 7 <br /> 4.2.4 Aquifer Containment <br /> Aquifer containment refers to surrounding the contaminated aquifer and soil with a physical barrier such <br /> as a slurry wall or sheet pilling Containment would not reduce the mass, and installing a slurry wall, or <br /> sheet pilling around the entire site is not feasible given existing utilities and expense <br /> 4 2 5 Air Sparging <br /> Air sparging infects air into existing wells increasing dissolved oxygen in the aquifer and volatilizing <br /> hydrocarbons in the groundwater in the well It is a simple and effective method of remediation, <br /> especially if it is combined with other technologies, such as SVE <br /> 4.2.6 Monitored Natural Attenuation <br />' Monitored natural attenuation (MNA) would institute quarterly groundwater monitoring, tracking the <br /> concentrations and plume size, to establish a downward trend in plume concentrations MNA is a <br />' feasible alternative if there is no immediate risk to sensitive receptors that could be affected by the <br /> plume <br /> I5 0 REMEDIAL ACTION RECOMMENDATIONS <br /> URS recommends installation of a combination SVE with air sparging system to remove mass from the <br /> soil and groundwater at the site The contaminant laden air stream from the SVE system will be treated <br /> with catalytic oxidizer (Cat-Ox) technology Existing shallow wells VW-1A, VW-2A, and VW-3A will <br /> be used as extraction wells and/or air sparging wells, if practical Please refer to the site map (Figure 2) <br /> for the location of these wells Other wells may be installed where appropriate The SVE/air sparging <br /> system will operate continuously, except during rebound periods, until vapor concentrations decrease to <br /> the satisfaction of the County <br />' During system operation, vapor flow rates and vapor temperature will be recorded With vapor <br /> concentrations taken from analytical data, mass removed will be calculated and reported Vacuum <br /> gauges will be placed in surrounding wells to establish radius of influence lirruts <br /> 6.0 REMEDIAL ACTION IMPLEMENTATION <br />' Following San Joaquin County, Public Health Services Environmental Health Division approval of this <br /> CAP, a work plan will be prepared detailing the implementation of the recommended remedial <br />' alternative <br /> I <br /> I <br /> K 1WprocessV5 BP ARC01021861CAP Aug03\02186 CAP03 doc <br /> I <br />