GEOLOGY AND SEDIMENT GEOCHEMISTRY OF A LANDFILL LEACHATE CONTAMINATEDAQUIFER (GRINDSTED, DENMARK)

A landfill leachate affected aquifer was investigated with respect to the geology and sediment geochemistry (solid organic carbon, cation ex change capacity, oxidation capacity, reduced iron and sulfur species) involving 185 sediment samples taken along a 305-m-long and 10-12-m-de ep transect downgradient from the landfill. The geology showed two dis tinct sand layers (upper Quaternary, Weichselian and a lower Tertiary, Miocene) sandwiching thin layers of silt/clay deposits, peat and brow n coal. The organic carbon content (TOC) and the cation exchange capac ity (CEC) of the sandy sediments were low (TOC, 100-300 mu g C (g DW)( -1); CEC, 0.1-0.5 meg per 100 g DW) and correlated fairly well with th e geology. Processes in the contaminant plume caused depletion of oxid ation capacity and precipitation of reduced iron and sulfur species. H owever, some of these parameters were also affected by the geology, e. g. the oxidation capacity (OXC) was significantly higher in the Quater nary layer (OXC, 14-35 mu eq g DW-1) than in the Tertiary sand layer ( OXC, < 5 mu eq g DW-1). The intermediate layers (silt/clay and brown c oal) have significantly higher values of most of the parameters invest igated. This work demonstrates the need for a small scale geological m odel and a detailed mapping of the geochemistry of the sediments in or der to distinguish impacts caused by the contaminant plumes from natur al variations in the aquifer geochemistry. (C) 1998 Elsevier Science B .V.