SOIL-GAS OXYGEN-TENSION AND PENTACHLOROPHENOL BIODEGRADATION

Laboratory tests were conducted to determine the effect of soil gas ox ygen concentration on the degradation and mineralization of spiked C-1 4-pentachlorophenol and nonlabeled pentachlorophenol (PCP) present in soil taken from a prepared-bed land treatment unit at the Champion Int ernational Superfund Site in Libby, Mont. This soil was contaminated w ith wood preserving wastes including creosote and PCP. Degradation rat es of C-14-PCP and nonlabeled PCP were found to be enhanced under soil gas oxygen concentrations between 2 and 21% in the contaminated soil. Between 48 and 64% of C-14-PCP spiked onto the soil was mineralized a fter 70 days at soil gas oxygen levels between 2 and 21%. No statistic ally significant mineralization of PCP was found to occur at 0% oxygen concentrations. Mineralization of C-14-PCP in contaminated soil poiso ned with mercuric chloride was determined to be less than 0.2%. Degrad ation of indigenous nonradiolabeled PCP in the nonpoisoned soil was st atistically significantly greater than in poisoned soil. These results indicated that degradation of PCP was biological and would occur unde r low oxygen concentrations. Soil gas oxygen concentrations necessary for PCP biodegradation (2-5%) could be maintained, for example, using bioventing technology in order to achieve continued treatment of burie d lifts of soil while new lifts are added, thus decreasing the total t ime for soil remediation of the prepared bed.