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15 rune 1999 <br /> • AGE-NC Project No 98-0450 <br /> ' Page 18 of 27 <br /> ' strata in the saturated zone Air flow is retarded within fine-grained strata resulting in ineffective <br /> hydrocarbon recovery <br /> ' Also, IAS technology cannot be used to treat ground water in confined aquifer or confining <br /> subsurface conditions due to the injected air becoming trapped by the confining (clay) layer and not <br /> allowing the migration of hydrocarbon-impacted air to the vadose (unsaturated) zone for SVE <br /> ' removal Under confining conditions, the hydrocarbon-impacted air would be forced to migrate <br /> along the base of the confining layer resulting in spreading of contaminants <br /> I Use of this technology would require the installation of air injection points with screened intervals <br /> located approximately five feet below the water The IAS system must be combined with vapor <br /> extraction (SVE) to contain vapor stripped from the ground water The installation of extraction <br /> ' wells would also be required <br /> 5 13 Monitoring Activities <br /> Monitoring of IAS, SVE, and ground water monitoring wells would be required to assess the <br /> progress and effectiveness of the system One of the potential problems associated with air sparging <br /> is lateral spreading of the contaminant plume caused by either mounding of ground water above <br /> ' injection points or lateral air flow away from sparging wells To detect this problem, ground water <br /> elevations in monitoring wells and extraction wells (if appropriate) should be monitored on a <br /> monthly basis, at the minimum, to detect mounding and migration of organic vapor and to <br /> ' appropriately adjust the air sparge system <br />' 514 feasibility <br /> In-situ air sparging of dissolved hydrocarbons in ground water appears to be a feasible alternative <br /> based on subsurface conditions at the site As presented in boring logs (Appendix A) and illustrated <br /> on site cross-section A-A'(Figure 3), a sand unit is inferred from approximately 40 to 55 feet bsg <br />' near the apparent upper boundary of the saturated zone This unit represents a the water table and <br /> saturated zones <br />' An in-situ air sparging remediation was conducted by AGE for a site in Lodi The site is located _ <br /> approximately 3,000 fent east of the subject'property Installation of monitoring wells has revealed T <br /> very similar lithology between the two sites Two sparging wells were supplied with approximately <br />' 15 psi of air during the clean-up Induced pressure,organic vapor concentrations, ground water depth <br /> and dissolved oxygen concentrations were measured at surrounding monitoring wells Ground water <br /> samples were collected from monitoring wells before and after the remediation <br /> Advanced GeoEnriron mental,Inc <br /> 1 <br />