From arsenic in groundwater in SE Asia to implications of climate change in Danish catchments - A brief review of current and past groundwater research in Denmark

Abstract

Denmark has a long history of groundwater use strongly associated with groundwater research. As societal awareness of issues of groundwater quality and quality arose, especially during the second half of the twentieth century, a number of serious knowledge gaps were recognised in integrated (ground)water resources management, leading to a large number of research projects. The new knowledge and tools arising from this research has fuelled increasing exports of groundwater related technologies internationally. The purpose of this paper is to highlight and give a brief summary of key ongoing groundwater research studies nationally and abroad.

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9
European Geologist 40 | November 2015
From arsenic in groundwater in SE Asia to
implications of climate change in Danish
catchments - A brief review of current and
past groundwater research in Denmark
Lisbeth Flindt Jørgensen*, Klaus Hinsby, Jens Christian Refsgaard, Flemming Larsen, Kurt Klitten, Lærke Thor-
ling, Verner H Søndergaard, Walter Brüsch, Dieke Postma and Peter van der Keur
* Department of Hydrology, GEUS -
Geological Survey of Denmark and
Greenland, l@geus.dk
Since the adoption of what is probably
the oldest national water supply act
in the world in 1926, Danish water
supply has been increasingly based on
groundwater and today virtually all drink-
ing water supply is based on groundwater
resources. Groundwater suitable for drink-
ing water production can be found almost
all over the country at depths from a few
meters down to a few hundred meters
below surface, and the abstracted ground-
water ranges in age from a few years, with
anthropogenic impacts, to more than 10,000
years old, without human impact. Denmark
has a decentralised water supply structure
with many (>2,500) small and a few larger
water supply utilities equally distributed
across the country. is has called for and
ensured common eorts and a long tradi-
tion of research on groundwater manage-
ment, mapping and protection.
Denmark has a long history of groundwater
research strongly related to the increasing
importance of the groundwater resources.
As societal awareness of issues of ground-
water quantity and quality arose, especially
during the second half of the twentieth cen-
tury, a number of serious knowledge gaps
were recognised in integrated (ground)
water resources management, leading to
a large number of research projects. The
new knowledge and tools arising from this
research has fuelled increasing exports of
groundwater related technologies inter-
nationally. The purpose of this paper is to
highlight and give a brief summary of key
ongoing groundwater research studies
nationally and abroad.
Depuis très longtemps, le Danemark associe
usage de l’eau et recherche de l’eau souter-
raine. Comme la prise en compte sociale
des questions touchant la quantité et la
qualité de l’eau souterraine s’est développée,
en particulier pendant la seconde moitié
du vingtième siècle, un nombre de défauts
majeurs au niveau des connaissances a été
reconnu dans le cadre de la gestion intégrée
des ressources en eau, conduisant à un
grand nombre de projets de recherche. Les
nouvelles connaissances et outils dérivés de
cette recherche ont alimenté l’exportation
croissante de technologies liées aux eaux
souterraines sur le plan international. Le but
de cet article est de mettre en évidence et
de résumer brièvement les études actuelles
de recherche sur les eaux souterraines, au
niveau national comme international.
Dinamarca tiene gran experiencia en el
uso de las aguas subterráneas asociado
fundamentalmente con la investigación
hidrogeologica. Debido al aumento de la
conciencia social sobre los problemas de
cantidad y calidad del agua subterránea,
sobre todo durante la segunda mitad del
siglo XX, se indentificaron importantes
lagunas de conocimiento en la gestión
integrada de los recursos hídricos, dando
lugar a un gran número de proyectos de
investigación. Los nuevos conocimientos
y herramientas que surgen de esta inves-
tigación han impulsado el aumento de las
exportaciones de tecnologías relacionadas
con las aguas subterráneas a nivel inter-
nacional. El propósito de este artículo es
de recalcar y dar un breve resumen de los
principales estudios de investigación sobre
las aguas subterráneas en curso tanto al
nivel nacional como internacional.
Background
Denmark (43,000 km
2
, 5.5 million inhab-
itants) is geologically dominated by so
sediments such as clayey or sandy tills, and
meltwater deposits originating from Qua-
ternary glaciations, the latest ending only
around 10,000 years ago. e topography is
modest, ranging from a few meters below to
around 170 meters above sea level. e cli-
mate is temperate with moderate tempera-
tures, monthly averages from 1 °C to 18 °C,
and abundant precipitation during most
of the year, 37-91 mm/month (2001-2010,
DMI 2015). us, groundwater aquifers and
surface waters are usually replenished suf-
ciently although abstraction takes places
from around 20,000 irrigation wells and
10,000 water supply wells. However, this
has not always been the case; with increas-
ing industrialisation during the 1960s and
1970s, which also brought available and
aordable technology for the Danish farm-
ers to establish irrigation wells, water con-
sumption rose to almost 1.4 billion m
3
a
year, about twice as much as today (Figure
1). e use in the 1970s was well beyond
what in a recent study was estimated as a
sustainable abstraction of 1 billion m
3
a
year, taking ecosystem protection (e.g. envi-
ronmental ows) into account (Henriksen
et al., 2008). However, rising energy prices,
water saving campaigns, and requirements
on cleaning of waste water during the 1980s
and 1990s encouraged (or forced, though
legislation and gradually increasing levies)
industry, agriculture and private consum-
ers to reduce water use. is has led to a
signicant decrease in the water use since
the 1980s, as shown in Figure 1, although
the population has grown from 4.5 million
in the mid-1970s to 5.5 million today.
is does, however, not imply that the
groundwater abstraction in Denmark
always is sustainable, as heavy abstrac-
tion does not necessarily take place where
groundwater is abundantly present. is
may, especially in dry seasons, result in
unacceptable local eects on streams, lakes
and wetlands that are not in line with the
Topical - Groundwater research

10
Figure 1: Water use by sectors from 1970 to 2010 (Jørgensen et al., 2015) compared to an estimate
of the sustainable groundwater resource in Denmark (Henriksen et al., 2008). Data from 1970, 1977
and 1984 are estimates made by the Environmental Agency as there was no mandatory reporting of
abstraction before 1989. Data from 1990, 2000 and 2010 are averages of 5 years around each year.
good status objectives of the European
Water Framework Directive. In addition,
quality aspects play an important role, as
Denmark has a long tradition of perform-
ing only simple treatment (aeration fol-
lowed by ltering through sand/gravel to
remove iron, manganese, etc.) of ground-
water before distributing it to consumers
as clean drinking water. As good quality in
line with national and international quality
standards are of utmost importance for the
water supply utilities, and for dependent
terrestrial and associated aquatic ecosys-
tems, the protection of the Danish ground-
water resources are of interest for all par-
ties involved. e amount, location, and
protection of the quantitative and chemical
status of the Danish groundwater is crucial
for the Danish society, and this fact has for
several decades been the catalyst for initiat-
ing Danish strategic groundwater research
in collaboration among research institutes,
national and regional authorities, and pri-
vate companies.
Historical development
Probably the rst to investigate Danish
groundwater was Johan Georg Forch-
hammer (1794-1865), a German-Danish
geologist. He was a director at Copenhagen
Polytechnic Institute, today known as the
Technical University of Denmark, and later
professor at the Mineralogical Museum in
Copenhagen. He studied the water-bearing
chalk layers under a lake in the vicinity of
Copenhagen and concluded that the arte-
sian groundwater had a very positive inu-
ence on the water quality of the lake, which
at that time was a very important drinking
water reservoir for Copenhagen. Forcham-
mer’s experiences were later used by the
state engineer for Copenhagen, Ludwig
August Colding (1815-1888), when he was
given the responsibility of managing the
establishment of the Copenhagen Water
Supply Company constructed aer the Brit-
ish example, following a severe cholera epi-
demic in the 1853. With this, the citizens
of Copenhagen could enjoy clean drinking
water based on groundwater.
Groundwater investigations continued
at Copenhagen Polytechnic Institute while
the Geological Survey of Denmark (DGU,
today Geological Survey of Denmark and
Greenland - GEUS) was established in 1888.
However, groundwater research as a disci-
pline was not dened until the 1930s, when
groundwater chemistry caught the interest
of a few geologists at DGU working with
mapping of underground resources. e
research area slowly grew, mainly driven
by the requests from local and regional
authorities in charge of water supply.
From DGU, groundwater research spread
to the University of Copenhagen as well
as Aarhus University and also strength-
ened the groundwater investigations at
the Technical University of Copenhagen;
these four research institutes are the main
actors in groundwater research in Den-
mark today. Denmark participated in the
UNESCO initiated ‘International Hydro-
logical Decade’ (1965–1975) giving rise to
the rst hydrological cooperation between
research institutions, followed by a large
project on a regional river catchment in the
Eastern part of Denmark starting in the
mid-1970s (the Susaa project) as the Danish
contribution to the International Hydro-
logical Programme. At that time focus
was mainly directed towards the quantity
of groundwater, though also acknowledg-
ing the interactions between surface and
groundwater. Rather comprehensive studies
on the chemical and isotopic composition
of precipitation, groundwater and streams
were also conducted. In the 1980s the rst
strategic research programmes began with
funding targeting directly groundwater
quantity and quality, giving rise to more
solid cooperation between the dierent
research institutes, also involving semi-
private technology institutes/companies.
Highlights from current Danish ground-
water research
In the following, we will present a selec-
tion of a few recently completed or ongoing
research projects illustrating the diversity
of Danish research initiatives. It should be
noted that this does not in any way reect
the total portfolio of groundwater research
carried out in Denmark, as the scope of this
paper does not allow for that. us, issues
such as e.g. groundwater dating, groundwa-
ter–surface water interaction, groundwater
and medical geology, biogenic degradation
of pesticides or other xenobiotic substances
are not included.
Research activities related to groundwater
quantity
Mapping of the Danish subsurface with
geophysical techniques started as a research
discipline at DGU in the 1940s and has since
been used to locate and delineate our most
important groundwater resources. From
the late 1960s onwards Aarhus University
intensied its research activity, particularly
regarding further development of electric
and electromagnetic mapping methods.
In the late 1990s, a new water supply act
set the scene for a comprehensive and still
ongoing hydrogeological mapping task,
covering 40% of the Danish area. is was
encouraged by promising mapping results
obtained during the 1990s using improved
geophysical methods. However, the ambi-
tious plan of mapping a signicant part of
Denmark with ground-based geophysics
combined with drilling would be quite
time consuming. is inspired research-
ers at the Aarhus University experienced in
the progress and improvement of ground-
based transient electromagnetic methods
(TEM) to carry out further developments.
In 2002/2003 they were able to present a
new and more ecient TEM system, the
SkyTEM-system (Sørensen and Auken,
2004) being the rst airborne TEM system
developed specically for hydrogeological
mapping purposes. e Danish SkyTEM
system covers a depth range down to 400-
500 m below ground surface, and the spa-
tially dense SkyTEM data combined with

11
European Geologist 40 | November 2015
borehole information are used to produce
3D models of the geological layers, to
determine freshwater/saltwater bounda-
ries, etc. Today, SkyTEM is a commercial
system used worldwide and provided by the
company SkyTEM Surveys (http://skytem.
com), still being further developed and used
in research projects (see e.g. www.nitrat.dk,
Schamper et al., 2014).
Groundwater modelling in Denmark
started in the 1970s with a few research
and commissioned studies, but it was not
until the 1990s that groundwater modelling
became a regular activity in advisory tasks
for the authorities. e focus was initially
on groundwater ow and quantity, while
research related to groundwater quality
emerged in the 1980s. Today, groundwa-
ter modelling is a supporting activity in
the above-mentioned detailed mapping of
groundwater resources, launched in the late
1990s. Private companies conduct the map-
ping, while research institutes are involved
to ensure best practices. In addition, GEUS
has developed a national water resources
model (DK-model) (see Henriksen et al.,
2003, 2008; Højberg et al., 2013, or visit
www.vandmodel.dk). e DK-model is a
coupled surface water/groundwater model
using data from national databases on
geology, soils, climate, land use, and water
abstraction. e model has a 500 m spatial
grid, 10-15 geologically based layers and
16,000 km of water courses. Today, this
national model is used as a research plat-
form, e.g. to assess climate change impacts
on water resources using dierent future
CO
2
emission scenarios. In addition, the
DK-model supports the governmental and
local authorities in implementing the Water
Framework Directive in Denmark.
A river catchment with an area of 2,500
km
2
in the western part of Denmark was
selected as the site for a hydrological obser-
vatory (HOBE) in 2007. e research is
headed by the University of Copenhagen
with contributions from Aarhus Univer-
sity and GEUS. HOBE provides a site for
integrated and interdisciplinary measure-
ments and experiments at multiple spatial
and temporal scales with the opportu-
nity to establish high-density, multiscale,
high-quality, and long-term data sets that
can provide a platform for hydrological
research with interdisciplinary focus. is
can improve the scientic basis for better
water resources management decisions and
for reducing the uncertainty in the water
balance at catchment scale. A number
of novel measurements have been estab-
lished to supplement the existing state-of-
the-art monitoring of climate, streamow
and groundwater. e new measurements
include eddy ux measurement of evapo-
transpiration, soil moisture measurements
by in situ sensors, cosmic ray and satellite
based techniques, a variety of natural trac-
ers, unmanned aerial vehicles and new
techniques to measure stream-aquifer
interactions e collected data form the
basis for development of integrated and
physically based models for dierent scales.
Validated integrated hydrological models
will be applied for predicting the eects of
climate change and land-use changes. For
more information, see Jensen and Illangas-
ekare (2011) or visit www.hobe.dk.
Research activities related to groundwater
quality
As groundwater use for drinking water
grew during the 1960–80s, focus on ground-
water quality also raised, and a research
programme on nitrate, phosphorous and
organic matter in the aquatic environ-
ment was launched in 1986, including a
groundwater part. Following this, a national
groundwater monitoring programme was
established in 1988 as a part of a national
programme for monitoring the aquatic
environment to document eects of nutri-
ents regulations to improve water quality in
general in fresh surface water, groundwater
and in the marine environment surround-
ing Denmark. e still existing programme
is regularly adjusted to t the current (polit-
ical) challenges, and currently the objective
and monitoring design of the groundwater
part is being adapted to t the requirements
of the Water Framework Directive and the
Groundwater Directive. One of several
challenges is how and where to monitor
the quality of the groundwater that ows
into the Danish freshwater bodies and wet-
lands. Today, the monitoring programme is
dened as a non-research programme; how-
ever, data and ndings from the programme
are continuously used in research activities.
For more information, see Jørgensen and
Stockmarr (2009) or Hansen et al. (2012),
or visit www.grundvandsovervaagning.dk.
Groundwater quality is also monitored
in the Danish Pesticide Leaching Assess-
ment Programme (PLAP), an early warn-
ing system aimed at assessing the leaching
risk of pesticides and their degradation
products under eld conditions. e pro-
gramme was initiated by the Danish Gov-
ernment in 1998, and is still ongoing in both
monitoring and research activities, carried
out by Aarhus University and GEUS. e
objective is to provide a scientic founda-
tion for decision making in Danish regu
-
lation of pesticides by analysing whether
approved pesticides applied in accordance
with current regulations will result in leach-
ing of pesticides and/or their degradation
products to groundwater in unacceptable
concentrations (usually above 0.1 µg/L).e
programme focuses on pesticides used in
arable farming and monitors leaching in
ve agricultural elds, selected to be rep-
resentative of Danish conditions as regards
soil type and climate. Given the monitoring
design of the elds, pesticides and degra-
dation products appearing in groundwa-
ter below and downstream of the fields
can be related to the pesticides applied in
accordance with current approval condi-
tions (Rosenbom et al., 2015). For more
information on the programme, visit www.
pesticidvarsling.dk.
Historically, Denmark has been a farm-
ing society due to its favourable climate,
topography, and soil conditions, and today
still two-thirds of the country is agricultural
land with an average farm size of more than
60 ha. is poses a perpetual threat to the
aquatic environment, including ground-
water quality. Supported by comprehen-
sive research and monitoring programmes,
regulation of agricultural practices has led
to a 50% reduction in nitrate leaching from
agriculture between 1980 and 2005. is
has been based on uniform regulations
implying that the same regulation has taken
place in all areas, irrespective of the fact that
more than half of the nitrate leaching from
the root zone is reduced on the travel path
between the root zone and the streams and
that the location of this reduction varies
greatly depending on topography, geology
and functioning of drain pipes. Uniform
regulations are not cost-eective, as many
nitrate reducing measures are located in
areas where nature will reduce nitrate
anyway. Therefore, a government com-
mission recommended introducing spa-
tially dierentiated nitrate regulations so
that measures to reduce nitrate leaching
would be located in areas where the natural
reduction is low, implying that regulations
can be relaxed for areas with high natural
reduction. As this regulatory paradigm shi
from uniform, national based regulation to
spatially dierentiated regulations requires
new knowledge on local scale conditions, a
number of new research projects on nitrate
transport and regulation have been initi-
ated (Refsgaard et al., 2014, or visit www.
nitrat.dk, www.soils2sea.dk).
Salt water intrusion is an increasing
problem in coastal aquifers globally, and
the problems will increase in the future
due to increasing population, abstraction,
climate change and sea level rise (Hinsby
et al., 2011). Mapping, monitoring and
modelling of saltwater intrusion is ongo-
ing in many coastal aquifers around the
world and the results show that there is a
need for developing new innovative tools
Topical - Groundwater research

12
Future challenges
On a 5–10 year perspective, the ground-
water research areas mentioned above are
believed to be still relevant. Additionally,
some upcoming challenges are foreseen in
relation to scaling and parameterisation
in modelling activities, quantication of
uncertainty, and optimisation of solutions
e.g. in relation to climate change adapta-
tion, or emerging contaminants. Further,
we see a challenge for the research com-
munity in general to adapt to requirements
of the funding bodies, who seem to favour
supporting the development of innovative
solutions over funding process studies.
of people in Bangladesh, West Bengal and
Vietnam, and since 2004 GEUS has worked
together with Vietnamese universities on
capacity building and research activities in
the Red River delta plain in Vietnam. One
of the research themes has been to study
the geochemical processes controlling the
occurrence of elevated arsenic (As) in shal-
low, Holocene aquifers, and the ground-
water chemistry has been investigated in a
transect of 100 piezometers (Postma et al.,
2012) e research in this topic is ongoing,
and recently a large ERC Advance Grant
from the EU has been granted to GEUS
on a project entitled ‘Predicting the arsenic
content in groundwater in the oodplains
in SE-Asia’.
for mapping, monitoring and controlling
salt water intrusion in fresh aquifers sup-
plying drinking water for millions of people
as well as for food production (irrigation
of farm lands, etc.). ese are among the
main research topics of some recently
completed Danish-headed international
research projects: ‘Vietas’ (Tran et al., 2012),
‘CLIWAT’ - www.cliwat.eu (Hinsby et al.,
2011; Jørgensen et al., 2012), ‘Water4Coast’,
‘BaltCica’ - www.baltcica.org (Rasmussen et
al., 2013), as well as in a recently initiated
EU Horizon 2020 project called ‘SUBSOL’.
Groundwater contaminated with arsenic
of natural origin in concentrations exceed-
ing the WHO drinking water limit of 10
µg/L is a threat to the health of millions
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