Influence of petrographic composition/organic matter distribution of fluvial aquifer sediments on the sorption of hydrophobic contaminants

Quaternary fluvial valley deposits form major groundwater reservoirs for the drinking water supply, which are at the same time favorable urban and industrialized areas where contamination of the aquifers and their sediments occurs frequently. The transport behavior of dissolved hydrophobic organic contaminants (HOC) depends on the sorptive interactions (sorption isotherms, sorption kinetics) with the sediment grains and therefore on the sediment history in terms of source rocks (lithocomponents), petrographic composition, and depositional processes (lithofacies, e.g. grain-size distribution). The geological formations present in the source rock area already determine the variability of lithocomponents and thus the sorption capacities for organic contaminants in the valley (aquifer) sediments since they show distinct differences in organic carbon content (C-org) and nature of organic matter (both influence the sorption behavior of hydrophobic organic compounds). In general, Lithocomponents originating from sedimentary rock have higher C-org contents and thus higher sorption capacities compared to metamorphic and magmatic components, and the quartz and feldspar minerals. The petrographic composition of the samples is grain-size-dependent but very similar within a specific lithofacies. Higher fractions of sedimentary rock fragments occur in the gravel-dominated lithofacies, which therefore have higher sorption capacities. In contrast to this, the sand grain-size fractions (sand facies) are, due to decay and transport processes (sediment maturity), enriched in stable lithocomponents such as quartz minerals which consequently lead to lower sorption capacities for HOC. Attention has to be drawn to the impact of strongly sorbing constituents such as Tertiary coal fragments (local source rock area) present in some of the sand samples. (C) 1999 Elsevier Science B.V. All rights reserved.