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To apply ISCO, ozone would be injected in permanent wells or temporary injection points that are strategically placed across the treatment area. The injection points would be at the depth where the bulk hydrocarbon mass is present. A skid -mounted process equipment would be used to inject the oxidant. Water quality data would be collected during injection from nearby monitoring wells or temporary monitoring points if no monitoring wells are available. TPH-g and BTEX concentrations would be monitored periodically from the monitoring wells after the injection to assess treatment progress. Typical monitoring frequencies would be from weekly to monthly after each injection event. A field pilot test would be required to determine the oxidant injection requirements, the number of injection points and injection events, and the time required between injection events. This information would also assist in developing a treatment performance monitoring plan. 4.4.1 Technical Effectiveness ' ISCO is capable of reducing the bulk mass of TPH-g and BTEX in groundwater at the site. Chemical oxidation is generally instantaneous and requires less time to achieve mass reduction and meet the target treatment goals than those involving primarily physical or biological removal ' processes. Its effectiveness will still be somewhat limited, however, when applied to silty and clayey soils due to the relatively low permeability of the soils that will limit the amount of contact the oxidant makes with the hydrocarbons. Usually, a greater number of injection points will be required in the silty/clayey soil stratum than in sandy soil to achieve the equivalent level of mass removal by chemical oxidation. Overall, the technical effectiveness of ISCO is ' considered moderate to high in meeting the treatment objective for the site. t 4.4.2 Implementability ISCO is expected to be easily implementable at the site. Ozone generators can be purchased from commercial suppliers to produce ozone onsite for injection via installed process piping. ' Because neither offgas emissions nor waste liquid will be generated, no aboveground handling and treatment of the offgas and waste liquid streams will be required, thus facilitating the ease of ' implementation. However, a permit might still be required from SJUAPCD for potential fugitive ozone emissions. Additional monitoring for ozone release in and around the treatment area might also be needed. A field pilot test will still be required as previously stated for full-scale treatment design, extending the timetable for the implementation. Overall, the implementability of this alternative is considered moderate. 4.4.3 Cost Major cost elements include those associated with conducting a field pilot test, procuring the ' oxidant generation equipment, installing injection piping and wells/points, and monitoring I FS Onsite Petroleum Hydrocarbon Remediation.doc 4-8 Shaw Environmental, Inc.