Assessment of a groundwater contamination with vinyl chloride (VC) and precursor volatile organic compounds (VOC) by use of a geographical information system (GIS).

Regarding the health effects of volatile organic compounds (VOC) and their decomposition products (particularly vinyl chloride (VC)) under chronic low-dose exposure, VOC groundwater contaminations are seen to be an ongoing public health issue. This article presents results of a long-term investigation surveying VOC and VC groundwater contamination upstream of a large groundwater works in Cologne, Germany. For 10 years a contaminated aquifer has been monitored for different VOC and for VC. In total, 255 samples have been taken to assess both the 3-dimensional distribution and the temporal dynamics of the contaminants. VOC and VC precursor substances have been measured by means of pentane-liquid-liquid-extraction, GC and ECD, VC by means of derivatisation to 1,2 dibromochloroethane, GC, ECD, and by purge and trap technique and GC-MS-coupling. For spatial analysis all test results and additional hydrogeological attribute data have been transferred to a GIS. The spatial VOC distribution has been assessed by use of kriging interpolation indicating a decrease of the initial contaminants in time. A cluster analysis allowed to distinguish several independent contaminations within the large contamination area. The VC contamination was increasing. Anaerobic microbial dechlorination of VOC and subsequent VC accumulation were seen to be as credible from several indications (VC presence, downstream change of tetra/trichloroethylene-ratio and anaerobic conditions in the aquifer, high Fe(2+)- and Mn(2+)-concentrations). There was no statistically significant vertical differentiation of VOC and VC concentrations. The VOC load within the different water protection zones of the waterworks could be assessed.