4.4.2.3 Long-Term Effectiveness and Permanence -- Alternative 2 The long-term effectiveness of dechlorination and HTTD was assessed in terms of the risk remaining after treatment. Risks may be posed by chemicals not removed from the contaminated material during treatment. Performance data, factors that influence performance, and limitations of the dechlorination and HTTD technology are discussed below. Dechlorination and HTTD Performance One PCB-contaminated Superfund site has been remediated using dechlorination and HTTD. In May 1991, the SoilTech ATP treated 104 tons of soil at the SITE demonstration performed at the WBD site. The average total PCB concentrations in soil were reduced from 28.2 to 0.043 mg/kg, a 99.8 percent removal efficiency. The test indicated that an average of 23.1 頜/dscm of PCBs was discharged from the stack to the atmosphere. During the WBD site remediation, the ATP treated 42,000 tons of soil containing 10 to 100 mg/kg PCBs. The treated soil PCB concentrations were less than 2 mg/kg (EPA 1993c). A pilot-scale demonstration of the SAREX THERM-O-DETOX system was conducted under EPA's SITE Program in September 1993. The demonstration consisted of four replicate test runs in the MTTD and two replicate test runs in the LTR. Feed soil consisted of a dry, clayey silt that was processed at a rate of 250 pounds per hour in the MTTD at 800 澹. The retention time was approximately 1 hour. The oil in each LTR test run was batch processed for 6 hours at 650 澹 (EPA 1994g). The results of the SAREX THERM-O-DETOX SITE demonstration indicate that treated soil met the cleanup goals of 95 ppm for PCP and 7 ppb for dioxins and furans. The MTTD achieved removal efficiencies of 99 percent for PCP. The MTTD achieved removal efficiencies of 92 percent or better for all dioxins and furans except for total TCDD, because the total TCDD concentrations in influent soil samples were just above sample detection limits; therefore, precise calculation of the removal efficiency was not possible. All SVOCs were well below TCLP limits in treated soil. The LTR batch tests reduced concentrations of dioxins and furans by 99 percent. The LTR batch tests reduced PCP concentrations by 97 percent (EPA 1994g). Limited bench-scale tests on dioxin-contaminated oil conducted by SoilTech indicate that BCD can effectively dechlorinate dioxins. Dioxin concentrations were reduced from 3,800 頜/kg in the untreated oil to less than 0.21 頜/kg in the treated oil. Factors that Influence Performance The degree to which an HTTD system is able to remove contaminants from wastes and is cost effective depends on certain key characteristics, including the moisture content of the waste, the boiling points of the contaminants, the hydrocarbon content of the waste, and the particle size distribution and soil classification of the waste being treated. These factors are discussed in Section 4.4.1.3. The factors that influence dechlorination performance are halogenated contaminant concentration and metals concentrations in the soil. Larger reagent doses will be required for high concentrations of halogenated contaminants. High metals concentrations may interfere with the dehalogenation reaction unless additional base is added. The tertiary treatment sludge may contain high concentrations of metals; therefore, treatability tests should be conducted to determine necessary reagent doses. System Limitations The HTTD limitations of this alternative are similar to the HTTD limitations of Alternative 1 (see Section 4.4.1.3). Limitations of dechlorination are discussed below. If APEG is used, the remaining glycol in the treated solids may need to be removed by a secondary treatment process. The treated solids would also need to be neutralized. If APEG reagents are sprayed on contaminated materials before they enter the HTTD unit, the HTTD unit may corrode. Organics present at high concentrations in the feed may react with the base, such as sodium hydroxide or potassium hydroxide, to form a semiliquid, gelatinous material