No abstract

No abstract

In Denmark the supply of drinking water is based almost solely on groundwater. During the past few decades Danish groundwater monitoring has encountered numerous instances of pollution with pesticides and their metabolites (GEUS 2003a). As a result, some hundreds of abstraction wells out of about 8000 in general water supply have been closed. With this background, there is a particular concern for reducing the leaching of pesticides into the groundwater. In the present study an approach for identification of areas potentially prone to pesticide leaching is described. The potential risk of leaching of pesticides from agricultural areas into groundwater is minimised through a procedure of approval; however, some leaching still occurs (GEUS 2003b). The Danish counties are therefore obliged to identify areas where there is a particular risk of pesticide leaching, and where restrictions in use of pesticides may be introduced to reduce the risk (Miljøstyrelsen 2000). The Geological Survey of Denmark and Greenland (GEUS) and the Danish Institute of Agricultural Sciences (DJF) have carried out a project, focusing on sandy agricultural areas, that attempts to establish the necessary background knowledge for identifying areas particularly prone to pesticide leaching. The project aims to distinguish vulnerable and less vulnerable areas, both locally and nationwide, in a cost-effective way.

Water profiles in soil columns were measured by the single-source gamma radiation method. Together with the normal attenuation equation, linear or parabolic equations for the relation between bulk density and volumetric water content were used. T o compensate for moderate changes in the bulk density during the experiment both initial and final bulk density and the water content were used in the water profile estimations.For a sandy loam soil, the radiation method without any corrections for bulk density changes resulted in a mean error of the volumetric water content estimation of 0.035 cm3 when the water content changed from 0.35 to 0.15 cm3 and3. By correction for changing bulk density by means of a linear or a parabolic equation the maximum difference between real and estimated water content was oaoog and 0*002 c m S ~m -~, respectively. Applying the latter method and a count of 106 the error of a single water content measurement was 0.004 cm3 Introduction IN studying water transport in soil columns, the water distribution and the changes in distribution are often measured by the gamma transmission method, using a single source (Gurr, 1962; Davidson