Summary and conclusions, Miljøstyrelsen

Hydrochemical groundwater-surface water interaction

Summary and conclusions

Introductory work on implementation of the EU Water Framework Directive have outlined the criteria for classification of the physical-chemical status of groundwater and surface water bodies, knowing that the quantitative status of a groundwater body may have an impact on the ecological quality of surface waters interacting with that groundwater body. Implementation of Water Districts in Denmark (before end of the year 2004) will be accompanied by the definition of good or bad status of individual ground water bodies. During the same period a stream typology will be carried out to classify ecological quality of different stream types in Denmark. To obtain coherence between the two classifications it is nessesary to divide the stream valleys into components with unique parameter sets of physical, chemical and biological parameters.

The objective of this report is to present a methodology to classify stream valleys into type locations based on geologic and stream valley morphological principles. Groundwater and surface water interact differently in different types of stream valleys. The same is true for water soluble solutes that can be degraded by or desorbed from wetland sediments to ground water flowing through the stream valley aquifer. The key to understanding the complicated flow and degradation processes that occur in the stream valley aquifer is the identification of unique parameters values that characterize the individual stream valley types. Such an understanding is needed before the interaction between groundwater and surface water in stream valleys can be quantified.

A new classification of groundwater – surface water interaction types of Danish stream valleys is presented in this report and it has got the acronym GOI, which is identical with the English term GSI (Ground water - Surface water Interaction). It is necessary to define type locations in order to classify the hydraulic and degradation / transformation rates in the representative type areas. Stream valleys occurring in unaffected (natural) conditions and those impacted by anthropogenic conditions (such as artificial draining of wetlands) are represented in the classification system. Based on a comprehensive knowledge of Danish stream valley and wetland studies different field examples have been identified. In this report one example is presented to show that the methodology and working procedures are applicable to different GOI types along the Haller Å. This example shows that it is possible to a limited extent to determine the flow distribution of groundwater through the stream valley aquifer; the residence or contact time and the degradation potential of the individual stream valley types.. Therefore further testing, validation and operationalization of the typology is needed. It is recommended that additional Danish locations are examined based on the new classification system in order to determine the ranges of individual parameters under different stream valley conditions.

A field verification program has been developed to support the characterization of the representative parameter sets of individual stream valley types. The georadar method was tested at three type localities in the Gjern Å catchment to determine the functionality of the method for use in mapping geometric conditions and in analyzing the lithologic conditions of wetland sediments in stream valleys. The primary focus has been on determining whether georadar methods can identify water bearing sand horizons that are embedded in the less permeable organic rich materials.

This project is a continuation of a research and development project conducted for the Danish EPA by Geological Survey of Denmark and Greenland (GEUS) and The National Environmental Research Institute (DMU). The project was entitled "State-of-the-art of Groundwater – Surface Water Interaction" (Refsgaard et al, 2001). A catalogue of research needs was listed in this report covering different GSI issue. The present project was the highest prioritized research need outlined in the catalogue and is conducted by GEUS, DMU and University of Aarhus (AAU).