Risk assessment - Třebechovice-Bědovice

In the 2011 to 2012 period, the  Vodní zdroje Ekomonitor company was dealing with long-term pesticide contamination of the Water Resource of Třebechovice-Bědovice which prevented its use as a good-quality soft ground water by the population of Třebechovice pod Orebem.

As no contamination parameters had been available nor the source of contamination, it was necessary to make quite an extensive investigation of the hydro-geological basin of the Water Resources aquifer. Geo-physical investigation in the area aimed at mapping the thickness of the quaternary gravel sands and having a close look into the possibility of water penetrating from the chalk aquifer.

At points believed to be the sources of contamination, shallow probing was made. To supplement the network of monitoring hydro-geological structures, six more bore holes were made. Hydrodynamic tests and borehole surveys were made and flow rates measured in surface streams to establish the actual hydro-geological and hydrological parameters in the given territory. At the same time, annual monitoring was made of the quality of ground and surface waters. Altogether, this involved up to 26 hydro-geological structures and up to 6 profiles of surface waters.

Results of the monitoring were evaluated in respect to short-time development as well as, in relation to older data, from a long-term aspect. It became evident that on a long-term basis the ground water was only contaminated with   atrazine and its disintegration product desethylatrazine. The data thus obtained were used to create a hydraulic and transport model for the given area. The modelling helped to determine two source areas of atrazine and describe its transport by ground water into collecting zones. As a risk assessment proved that atrazine concentrations in ground water would pose an unacceptable risk to using the water for drinking, corrective measures were proposed. The most radical, but also most costly, proposal was to make a further survey as to the sources of contamination prior to decontamination work. As, at the moment, there are not sufficient funds for such a project, a protective hydraulic screen has been proposed by means of a hydraulic and transport model. This should, in a short time, ensure reduction of atrazine and desethylatrazine concentrations in the collecting area and make the use of the ground water for drinking possible.