Hydrogeological investigation for the PEGASUS project, southern Skåne, Sweden

Abstract: SLU (Swedish University of Agricultural Sciences) have had a project ongoing in a catchment area in southern Skåne for 20 years where they study how pesticide occurrence in surface waters correlate to the sort and amount used on the agricultural fields. A new project started by SGI (Swedish Geotechnical Institute) called PEGASUS (PEsticide occurrence in Groundwater, A Study for sustainable Use in Skåne) has begun an investigation in the same catchment to study the pesticide behavior and effects in the deeper groundwater. This paper is a geological and hydrogeological investigation of the catchment area for the PEGASUS project. The catchment area is located in a valley that is partly formed by a river and partly by faulting. The river’s course is anthropogenically modified by a culvert system draining the agricultural fields and the river emerges first in the SE part of the catchment area. The valley sediments consist of an upper and lower glaciofluvial sand divided by a silty clay layer. The surface sediments consist of a clayrich till which makes up 90 % of the surface sediments, the remaining 10 % consists of glaciofluvial sediments and postglacial sediments. There are two groundwater divides within the investigated aquifer, one in the northern part of the catchment area and one to the west of the catchment area. The groundwater gradient follows the surface water gradient which is SE and E towards the river. The recharge from surface water to the upper aquifer is low meaning that recharge likely occurs during heavy precipitation periods. The average age of the groundwater is c. 40-60 years. The hydraulic conductivity was calculated based on three different methods, Hazen’s method, slugtest and percolation tube test. The results varied between these methods but the general hydraulic conductivity of the upper aquifer ranges from 2'10-4 m/s, for the coarsest sediments, to 2'10-7 m/s, for the finest sediments.