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You should verify that laboratory measurements of total dissolved iron <br /> have been completed for groundwater samples from the site Use Exhibit <br /> . VII-12 to determine the range where dissolved iron is a concern for air <br /> sparging effectiveness <br /> Exhibrt VII-12 <br /> Dissolved Iron And Air Sparging Effec".,veness <br /> mso�ved lrcn C ancEntra#ian (mgll.) Air Sparging Effectrreness <br /> Fe`2 t 10 Air sparging effective <br /> 10 < Fe-2 <20 Air sparging wells require periodic testing <br /> and may need periodic replace hent <br /> Fe+2 > 20 Air sparging not recommended <br /> Field Piict-,SCale St£ldaa's <br /> geld pilot studies are rlecevsa -y to adequately design and evaluate <br /> any air s-.1w-ging system However, pilot tests should not be conducted if <br /> iree product is 'known to -yst at the g;c ur_dwater table, if uncontrolled <br /> vapors could migrate into confhned spaces. sewers, or buildings, or if the <br /> comrammated groundwater is m an unconfined aquifer The air sparge <br /> • well used for pilct testing is generally located in an area of moderate <br /> constituent concentrations Testing the system m areas of ext:ernely low <br /> constituent concentrations may riot provide sufficient data In addliion, <br /> because sparging can mduce migration of constituents, pilot tests ars <br /> generally not conducted in areas of e dremely hiMa constituent <br /> concentrations. The air sparging pilot study should include an SVE pilot <br /> study if SVE is to be included in the design of the air sparging system. <br /> Pilot studies for air sparging often include SVE pilot testing to <br /> determine if SVE can be used to effectively control the vapor plume. Plot <br /> studies, therefore, should include the installation of a single sparge <br /> point, several vapor extraction paints (if SVE is to be included in the <br /> design), and soil gas monitoring points to evaluate vapor generation <br /> rates and to define the vapor plume Fisting groundwater monitoring <br /> wells (normally not fewer than three to five wells around the plume) that <br /> have been screened above the saturated zone and through the dissolved <br /> phase plume can be used to monitor both dissolved and vapor phase <br /> migration, to monitor for changes in dissolved oxygen, and to measure <br /> changes in the depth to the groundwater table surface. Additional vapor <br /> probes should be used to fixrther define the vapor plume and identify <br /> any preferential migration pathways These probes should be designed <br /> and installed as discussed in Chapter II. Soil Vapor Extraction. <br /> October 1994 VII-13 <br />