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• Both air sparging and vapor extraction tests were performed at the site in <br /> August 2000 Both of these tests showed that these technologies could be <br /> successful at the site For this reason, ASE recommends that an air sparge <br /> vapor extraction system be installed at the site <br /> 4. 3 Groundwater "Pump- and Treat" <br /> Groundwater "pump and treat" technology is currently being used at the <br /> site to contain the groundwater plume at the site Groundwater is being <br /> extracted from five recovery wells and is then treated with granulated <br /> activated carbon The treated water is then discharged to the City of <br /> Manteca's sewer system This method has been effective in lowering <br /> hydrocarbon concentrations in the wells across West Yosemite Avenue, <br /> except for monitoring well MW-20 to the west Soil borings BH-A and <br /> BH-B, drilled on-site near recovery well RW-1, also showed that <br /> contamination to the west extends past the capture zone For these <br /> reasons, ASE recommends installing two additional groundwater recovery <br /> wells west of recovery well RW-1 to enhance the capture zone <br /> performance <br /> iASE recommends that additional recovery wells be installed to the west of <br /> recovery well RW-1 to further capture groundwater and keep the plume <br /> from flowing off-site to the northwest toward the domestic wells ASE is <br /> not, however, recommending "pump and treat" remediation as the sole <br /> treatment for the site since (a) it is relatively expensive for carbon <br /> replacement when the majority of hydrocarbon mass may be removed <br /> with less expensive methods and (b) "pump and treat" will not remediate <br /> unsaturated soil and therefore additional soil remediation will also be <br /> required <br /> 4-.4— In-Situ Bioremediation <br /> In-situ bioremediation was considered as a remedial option at the site <br /> There are several options to achieve this form of remediation, which <br /> involves increasing the amount of dissolved oxygen in the groundwater to <br /> enhance naturally occurring aerobic bacterial degradation of petroleum <br /> hydrocarbons in-situ It has been known for some time that naturally <br /> occurring bacteria readily degrade (digest) petroleum hydrocarbons into <br /> harmless byproducts Although anaerobic bacteria will degrade <br /> petroleum hydrocarbons, the rate is much slower than with aerobic <br /> . bacteria Depleted levels of oxygen appear to be the primary limiting <br /> factor for aerobic bacterial activity Two common methods of increasing <br /> Frank's One Stop Remedial Action Plan — August 2001 <br /> -15- <br />