DISTRIBUTION OF ORGANIC-COMPOUNDS FROM MUNICIPAL SOLID-WASTE IN THE GROUNDWATER DOWNGRADIENT OF A LANDFILL (GRINDSTED, DENMARK)

The distribution of organic compounds in the leachate plume downgradie nt of the Grindsted Landfill was mapped along two 300 m long transects (285 groundwater samples). At the border of the landfill, elevated co ncentrations of dissolved organic matter 30-110 mg of C L(-1) (measure d as nonvolatile organic carbon, NVOC) were found. In a distance of 13 0 m downgradient of the landfill, the NVOC had decreased to background level, which is 1-3 mg of C L(-1). More than 15 organic compounds wer e identified in the groundwater at the downgradient border of the land fill with benzene, toluene, ethylbenzene, and xylenes as dominating. N o pesticides were identified, but some phenoxy acids, which could be m etabolites of known pesticides, were found. In a distance of approxima tely 60 m from the landfill, most of the specific organic compounds we re no longer detectable. Since dilution and sorption apparently cannot account for the disappearance of the specific organic compounds withi n the first 60 m of the plume, it is proposed that the majority of the specific organic compounds were degraded in the anaerobic plume under methanogenic/sulfate-reducing or iron-reducing conditions. The invest igation indicates that the aquifer has a substantial natural attenuati on capacity.