Determining degree and spatial variation of tetrachloroethylene degradation in groundwater using compound-specific isotope analysis (CSIA) of carbon at the Blekingegatan site in Helsingborg

Abstract

Chlorinated solvents have been used as cleaning detergents in dry cleaners throughout the 20th century which has led to the spread of chlorinated solvents in the environment. Blekingegatan, Helsingborg, is a residential area where dry cleaning activities from 1930 to 1979 has led to vast emissions of the chlorinated solvent tetrachloroethylene (PCE). This has resulted in the formation of a groundwater contamination plume in the southwest direction from the source. The aim of this investigation is to establish if degradation of PCE is taking place in the contamination plume and if the magnitude of the degradation is enough to use monitored natural attenuation (MNA) as the remedial method. By measuring concentrations and conducting compound-specific isotope analysis (CSIA) in the sampled groundwater, the spatial variability of concentration- and isotope data could be determined. Results showed high concentrations of contaminants primarily in the source zone while values of the CSIA suggested that degradation is limited and mainly occurs downstream from the source. Furthermore, the values of the degradation product TCE indicated that TCE may be a primary contaminant as well. By constructing a Rayleigh plot it was concluded that dilution rather than degradation is the main contributor to the decrease of the contaminant concentration. Due to these results the extent of degradation was deemed as not sufficient enough to use monitored natural attenuation as the sole remediation method at the site.