Project no. 401
A Low-Cost Largescale Investigation of Contamination
A. S. Sørensen
DTU Environment, Technical University of Denmark
Groundwater is the main source for drinking water in Denmark and is therefore vulnerable
for contamination. Low concentrations of contaminants is able to shut down large well fields
leaving behind a need for millions of cubic meter drinking water, rising groundwater tables
endangering nearby households and shutting down wells and waterworks worth many
THE CASE SITE
The waterworks in Bagsværd was constructed in 1921 when the area was mainly nature.
More buildings were built in the area and the area became a business district. Many drycleaning
facilities, machine shops and spray painting workshops are located in the district
and they all use chlorinated solvents. The chlorinated solvents were first found in the
drinking water abstraction wells in 1987. The contamination led to the closing of four out of
six wells. In 1993, a remedial pumping started to prevent the contamination reaching the
drinking water abstraction wells. In 2012 the waterworks was rebuild to include activated
carbon filters to clean the water as the contamination still reaches the wells. The cost of
running the remediation is almost 2 million DKK a year, which equals 1.33 % of the capital
regions budget for the environment. As the contamination is still reaching the wells with high
concentrations the coal must be changed more frequently resulting in high expenses.
Before the remediation can be optimized, a better understanding of the source must be
obtained. The most expensive part of investigations of contaminated sites is the drilling of
wells. Deep wells can easily cost hounded of thousands DKK. The capital region
investigates suspected contaminated sites, but it is limited to its cadaster. By collecting and
comparing data from multiple contaminated sites, a larger understanding is achieved. As the
investigations might be conducted in different years, the investigations cannot be compared.
The Geological Survey of Denmark and Greenland (GEUS) keeps a database (Jupiter) of
drilled wells which holds the coordinates of the well. By reusing old wells, a largescale
investigation can be conducted with solely the price of sampling.
When the spreading of the contamination is understood, the remedial pumping can be
reevaluated to capture more or all of the contamination through modelling. An advanced 3D
model is set up to find the best placements and pumping rates for remedial abstraction
wells. An optimal solution will ensure the quality of the water reaching the drinking water
abstraction wells thereby removing the need for activated carbon filters.
During the project was 87 outdated wells found out of 192. Some wells were hidden under
asphalt but reconstructed. Out of the existing and newly found wells, 25 were selected for
sampling. The results showed that contamination went under the remedial pumping, which
gave rise to implementing a highly conductive gravel layer in the advanced 3D model.