Point and non-point source leaching of pesticides in a till groundwater catchment

2. Site description

2.1 Site of investigation and land use

Types of landuse

The project area represents the groundwater catchment of Vester Vandværk in Skælskør, Figure 1. The total area is 226 hectares of which 75 hectares are Skælskør orchard and 140 hectares are agricultural land. Approximately 60% of the agricultural area is cropped with wheat while the remaining part is grassland, meadows and beach. Approximately 11 hectares of the project area is houses, gardens and roads.

Delineation of project area

The project area is delineated from the topography and the hydraulic potentials of the main aquifer (Figure 1). The area is confined so that the catchment area of the Skælskør water plant is included in the area.

Projektområde og lokalisering af punktkildeforurening, Skælskør frugtplantage og moniteringsparcel i plantagen

The southwestern limit of the area is the coastline. The western limit is along the topographical drainage area. The Northern limit is along the creek, Kobæk Rende. North of the water plant the boundary chosen is a line perpendicular to the equipotential lines of the main aquifer of the area. South of the water plant the topographic drainage area constitutes the boundary of the project area.

2.2 Geology and hydrogeology of the site

Prequarternary deposits

The geology is described from 9 wells in the ares (GEUS map 1412 I Skælskør). In the project area the prequarternary deposits consist of Bryozoan limestone of the Danian age in the northern part and of White chalk of Maastrichtian age in the southern part. The prequarternary surface has distinct topography, from to to 30 m below sea level. On a greater scale there is a depression in the prequarternary surface, now partly reflected by "Skælskør yderfjord" and cove.

Hydrogeology

The main aquifer of the Skælskør area consists of the Bryozoan limestone. The transmissivity of the aquifer has been calculated from pumping tests and is in the range of (0.2 - 1.4)·10^-3 m²/sec. The water table in the main aquifer has been monitored, Figure 2. Flow directions in the aquifer are towards the well field of skælskør Vester Vandværk.

The Quaternary deposits in the project area are 30 to 40 m in thickness. The deposits consist mainly of clay till. There are two approximately 1 m thick meltwater sand layers in the till at a depth of 8 - 9 m and 18 - 19 m below sea level. Locally a thin sand layer occurs on top of the Bryozoan limestone. Some minor postglacial freshwater peat and gytja plus marine gytja and sand deposits are situated in depressions of the slightly undulating landscape.