Naturlig nedbrytning av klorerade lösningsmedel i grundvatten
Chlorinated solvents are common contaminants in soil and water. Under anaerobic conditions microbes are capable of transforming chlorinated solvents into ethylene which would result in a remediation of the contaminated area. In order to use natural attenuation as a remediation method evidence of continuous degradation is required. Furthermore, the degradation must occur at a sufficient rate and continuous monitoring of the site is needed until the demanded levels are achieved. A field study was performed on the basis of data from a dry-cleaning facility contaminated mainly by perchloroethylene. The purpose of the study was to define the existing situation regarding distribution and transformation of contaminant in order to evaluate the possibilities of using natural attenuation as a method of remediation. Degradation of perchloroethylene proceeds through successive removal of chlorine, with the formation of trichloroethylene, dichloroethylene, vinyl chloride and ethylene. There exists evidence of degradation as far as vinyl chloride on the site but whether transformation continues to ethylene is not established. The computer model Biochlor was used to simulate distribution and degradation of the contaminants. The site possesses a complex hydrogeology and the existing data are not sufficient to distinguish the effect of degradation from other factors such as spreading of contaminant between different layers of soil. Since degradation failed to be quantified, natural attenuation can not be recommended as a safe remediation method at the considered site without further investigations.