Use of geochemical databases to delineate risk areas for contaminated groundwater

Areas of high risk for contamination of groundwater were delineated on the basis of element distributions in nation-wide geochemical maps of till, org anic stream sediments and stream waters. These areas were then compared wit h those in which concentrations of the same elements in groundwater wells w ere above water quality guidelines. All data sets are from the geochemical databases of the Geological Survey of Finland. Concentrations of several el ements (e.g. Cr, Cu, Mn, Ni and Zn) in the fine fraction of till were anoma lously high in five provinces. In many groundwater samples from these provi nces, the concentrations of Mn and Ni in drilled bedrock wells, and the con centrations of Ni and Zn in dug wells, exceeded the permissible limits. Con centrations of Cr and Cu in groundwater were slightly elevated in the same areas, but the recommended limits for these elements were not exceeded. Are as with high concentration of As in drilled bedrock wells correlated with a reas of high risk delineated on the basis of both till geochemistry and org anic stream sediments. Anomalies of F- were similar in stream water and gro undwater maps. High geogenic concentrations of potentially harmful elements in groundwater commonly occur in areas that can be delineated from geochem ical maps based on till, stream water and stream sediment sampling. However , not all of the wells with poor quality groundwater were identified from g eochemical maps at reconnaissance scale. (C) 1998 Elsevier Science B.V. All rights reserved.