Geological Survey of Denmark and Greenland Bulletin 13, 2007
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Review of Survey Activities 2006, 65-68 |
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65
Experience and results from the Danish groundwater moni-
toring programme that has been carried out systematically
since 1990, have been used in a co-operative project between
Latvia and Denmark. The main objective of the project was
to obtain more detailed knowledge of the shallow Latvian
groundwater, to optimise the Latvian groundwater monitor-
ing programme and to support the implementation of Euro -
pean legislation such as the Water Framework Directive, the
Nitrate Directive and the Groundwater Directive in Latvia.
toring programme that has been carried out systematically
since 1990, have been used in a co-operative project between
Latvia and Denmark. The main objective of the project was
to obtain more detailed knowledge of the shallow Latvian
groundwater, to optimise the Latvian groundwater monitor-
ing programme and to support the implementation of Euro -
pean legislation such as the Water Framework Directive, the
Nitrate Directive and the Groundwater Directive in Latvia.
Comprehensive summaries describing the methodology
of groundwater quality monitoring as well as the major
results from the Danish groundwater monitoring network
can be found in GEUS (2005) and Stockmarr (2005). Until
recently only few data on Latvian groundwater quality were
available, but in a project running from 2003 to 2006, 800
samples from groundwater, springs and drains have been
analysed for a large number of components resulting in a
comprehensive overview of the status of Latvian groundwa-
ter (Fig. 1; Gosk et al . 2006).
results from the Danish groundwater monitoring network
can be found in GEUS (2005) and Stockmarr (2005). Until
recently only few data on Latvian groundwater quality were
available, but in a project running from 2003 to 2006, 800
samples from groundwater, springs and drains have been
analysed for a large number of components resulting in a
comprehensive overview of the status of Latvian groundwa-
ter (Fig. 1; Gosk et al . 2006).
The project
Agricultural influence on groundwater in Latvia
was carried out by the State Geological Survey of Latvia and
the Geological Survey of Denmark and Greenland (GEUS)
and was supported by the Danish Environmental Protection
Agency within the framework of the DANCEE programme
(Danish Co-operation for Environment in Eastern Europe).
As a spin-off of the project this paper compares groundwater
quality in the two countries.
the Geological Survey of Denmark and Greenland (GEUS)
and was supported by the Danish Environmental Protection
Agency within the framework of the DANCEE programme
(Danish Co-operation for Environment in Eastern Europe).
As a spin-off of the project this paper compares groundwater
quality in the two countries.
Groundwater use and agricultural load
Drinking-water production in Denmark is almost entirely
based on groundwater abstracted from both shallow and
moderately deep Quaternary and pre-Quaternary aquifers
covered by more or less protective layers of till of variable
thickness.
based on groundwater abstracted from both shallow and
moderately deep Quaternary and pre-Quaternary aquifers
covered by more or less protective layers of till of variable
thickness.
The annual groundwater recharge is relatively large in
Denmark and is on an average, national scale sufficient to
cover needs (Henriksen & Sonnenborg 2003). However,
cover needs (Henriksen & Sonnenborg 2003). However,
© GEUS, 2007.
Geological Survey of Denmark and Greenland Bulletin
13, 65-68. Available at:
www.geus.dk/publications/bull
Shallow groundwater quality in Latvia and Denmark
Edmund Gosk, Igors Levins and Lisbeth Flindt Jørgensen
Fig. 1. Sampling sites of Latvian groundwater.
abstraction exceeds recharge in some areas, especially around
the largest cities. Furthermore, diffuse groundwater contam-
ination by pesticides and nitrate has become an increasing
problem since the middle of the last century, and a number
of water-supply wells have been closed. Up to now it has been
possible tOFind new, clean groundwater resources, either by
drilling deeper wells or by moving wells to less impacted
areas.
the largest cities. Furthermore, diffuse groundwater contam-
ination by pesticides and nitrate has become an increasing
problem since the middle of the last century, and a number
of water-supply wells have been closed. Up to now it has been
possible tOFind new, clean groundwater resources, either by
drilling deeper wells or by moving wells to less impacted
areas.
More than 60% of the Danish territory is defined as arable
land. The impact of agriculture on water quality has been
known for many years, and measures aiming at a reduction of
nutrient load started in the 1980s with the adoption of the
first Action Plan on the Aquatic Environment. At that time
the average nitrogen load had reached 130 kg N/ha, which
resulted in a high risk of groundwater contamination and in
actual quality problems in some areas of the country.
known for many years, and measures aiming at a reduction of
nutrient load started in the 1980s with the adoption of the
first Action Plan on the Aquatic Environment. At that time
the average nitrogen load had reached 130 kg N/ha, which
resulted in a high risk of groundwater contamination and in
actual quality problems in some areas of the country.
Drinking-water production in Latvia is also primarily
based on groundwater. Only Riga Water Supply uses a sub-
stantial amount of surface water to produce about half of the
drinking water consumed in the Latvian capital.
stantial amount of surface water to produce about half of the
drinking water consumed in the Latvian capital.
The thick till layer that covers most of Latvia is charac-
terised by poor aquifer conditions where only little ground-
water abstraction is possible from small, local water-bearing
lenses. The centralised drinking-water supply in Latvia is
therefore typically based on confined aquifers screened at
depths greater than 50 m. In areas with intensive agriculture
(the southern and central parts of the country) the average
depth of wells exceeds 100 m.
water abstraction is possible from small, local water-bearing
lenses. The centralised drinking-water supply in Latvia is
therefore typically based on confined aquifers screened at
depths greater than 50 m. In areas with intensive agriculture
(the southern and central parts of the country) the average
depth of wells exceeds 100 m.
Due to the dramatic political and economical changes in
Latvia at the beginning of the 1990s groundwater abstraction
decreased by a factor of 2-3 resulting in a significant, still
progressing recovery of groundwater levels in the central and
south-western parts of the country. In the remaining parts of
the country groundwater levels have never been affected by
abstraction.
decreased by a factor of 2-3 resulting in a significant, still
progressing recovery of groundwater levels in the central and
south-western parts of the country. In the remaining parts of
the country groundwater levels have never been affected by
abstraction.
During the same period, the acreage of arable crops, the
use of mineral fertilisers, the number of livestock and other
parameters related to agricultural load, decreased by a factor
of 3-10 (Stålnacke et al . 2003). At present only 13% of the
Latvian area is under cultivation, and the average crop yield
is about half of the Danish figures.
parameters related to agricultural load, decreased by a factor
of 3-10 (Stålnacke et al . 2003). At present only 13% of the
Latvian area is under cultivation, and the average crop yield
is about half of the Danish figures.
Groundwater monitoring and knowledge
of diffuse contamination
of diffuse contamination
Due to the pressure from diffuse sources, groundwater mon-
itoring plays an important role in water management and
protection of groundwater resources in Denmark. More than
6000 drinking-water supply wells, a network of more than
1400 specially selected screens in 70 groundwater monitor-
ing areas, as well as five agricultural watershed monitoring
itoring plays an important role in water management and
protection of groundwater resources in Denmark. More than
6000 drinking-water supply wells, a network of more than
1400 specially selected screens in 70 groundwater monitor-
ing areas, as well as five agricultural watershed monitoring
areas equipped with a total of about 100 shallow screens
(Stockmarr 2005), together form the basis of the Danish
groundwater monitoring system. The detailed groundwater
quality monitoring includes analyses of 97 elements, com-
prising 14 heavy metals and 34 pesticides and their metabo-
lites (NERI 2005).
(Stockmarr 2005), together form the basis of the Danish
groundwater monitoring system. The detailed groundwater
quality monitoring includes analyses of 97 elements, com-
prising 14 heavy metals and 34 pesticides and their metabo-
lites (NERI 2005).
The regional groundwater quality monitoring network in
Latvia, established in the 1970s and 1980s, is based on 150
wells located within 45 monitoring stations. This network
was designed to control depression cones (quantitative mon-
itoring) rather than to monitor the various forms of diffuse
pollution (qualitative monitoring). Monitoring wells are typ-
ically screened in deep aquifers used for abstraction. Until
recently, the parameters analysed comprised major ions and
nitrogen compounds, but no analyses of heavy metals and
pesticides were made. Groundwater quality data from
abstraction wells consisted mainly of information collected
during drilling.
wells located within 45 monitoring stations. This network
was designed to control depression cones (quantitative mon-
itoring) rather than to monitor the various forms of diffuse
pollution (qualitative monitoring). Monitoring wells are typ-
ically screened in deep aquifers used for abstraction. Until
recently, the parameters analysed comprised major ions and
nitrogen compounds, but no analyses of heavy metals and
pesticides were made. Groundwater quality data from
abstraction wells consisted mainly of information collected
during drilling.
Monitoring of drinking-water quality in Latvia is almost
entirely limited to sampling of tap water. Although some of
the larger water-supply companies collect samples from
abstraction wells, the centralised data processing system for
this type of analysis is not yet established.
the larger water-supply companies collect samples from
abstraction wells, the centralised data processing system for
this type of analysis is not yet established.
The amount of groundwater data recently collected in
Latvia is much smaller than comparable data collected in
Denmark. However, a large amount of information on the
youngest groundwater in shallow aquifers has been collected
in the period 2003-2005 as part of the present project.
About 800 groundwater samples were analysed for a wide
spectrum of elements, including heavy metals and pesticides
(Gosk et al . 2006).
Denmark. However, a large amount of information on the
youngest groundwater in shallow aquifers has been collected
in the period 2003-2005 as part of the present project.
About 800 groundwater samples were analysed for a wide
spectrum of elements, including heavy metals and pesticides
(Gosk et al . 2006).
The determination of background concentration of vari-
ous elements was based on data from shallow wells located
outside local point-pollution plumes and urbanised and
industrial areas.
outside local point-pollution plumes and urbanised and
industrial areas.
Nitrates and pesticides
As expected, the distribution of nitrates in Danish and
Latvian groundwater differs considerably (Fig. 2A). In the
shallowest groundwater, the concentration of nitrates exceeds
the quality standards of drinking water (50 mg/l NO
Latvian groundwater differs considerably (Fig. 2A). In the
shallowest groundwater, the concentration of nitrates exceeds
the quality standards of drinking water (50 mg/l NO
3
) in
15% and 3.5% of the monitoring screens in Danish and
Latvian wells, respectively. Furthermore, the decrease of
nitrate concentration with depth is much faster in the
Latvian than in the Danish groundwater.
Latvian wells, respectively. Furthermore, the decrease of
nitrate concentration with depth is much faster in the
Latvian than in the Danish groundwater.
The differences observed are caused by a lower agricultural
load in Latvia as well as by a higher denitrification potential
and confinement degree of Latvian aquifers and aquitards
(Fig. 2B). A statistical comparison of the groundwater resi-
dence times is impossible due to the very limited number of
and confinement degree of Latvian aquifers and aquitards
(Fig. 2B). A statistical comparison of the groundwater resi-
dence times is impossible due to the very limited number of
66
age determinations of Latvian groundwater (27 water sam-
ples were analysed by the CFC method). However, it seems
that Latvian groundwater is about twice as old as Danish
groundwater from the same depth.
ples were analysed by the CFC method). However, it seems
that Latvian groundwater is about twice as old as Danish
groundwater from the same depth.
The recent investigations in Latvia revealed some unex-
pected results with respect to nitrate in shallow aquifers.
Latvian springs capturing the youngest and the most mobile
part of groundwater flow seem to be characterised by higher
average nitrate concentrations compared to shallow wells
drilled to the same aquifers (Fig. 3). Even springs located
within areas without obvious nitrate load show persistently
higher nitrate concentrations than neighbouring wells. After
recognition of this phenomenon several high-yielding springs
have been included in the groundwater monitoring network
to better understand flow patterns and problems of diffuse
nitrate pollution.
Latvian springs capturing the youngest and the most mobile
part of groundwater flow seem to be characterised by higher
average nitrate concentrations compared to shallow wells
drilled to the same aquifers (Fig. 3). Even springs located
within areas without obvious nitrate load show persistently
higher nitrate concentrations than neighbouring wells. After
recognition of this phenomenon several high-yielding springs
have been included in the groundwater monitoring network
to better understand flow patterns and problems of diffuse
nitrate pollution.
Investigations of contamination of Latvian groundwater
by pesticides have only just started, and the extent of this
problem is not fully clear. Vulnerable areas were identified in
the project, and 111 groundwater samples from wells in these
areas were analysed for a number of expected pesticides. In
30% of the samples, concentrations of pesticides exceeded
the quality standards of drinking water (0.1 µg/l). This figure
problem is not fully clear. Vulnerable areas were identified in
the project, and 111 groundwater samples from wells in these
areas were analysed for a number of expected pesticides. In
30% of the samples, concentrations of pesticides exceeded
the quality standards of drinking water (0.1 µg/l). This figure
is identical to the frequency in shallow Danish monitoring
screens (Stockmarr 2005). In Denmark the most often found
pesticide is BAM (2,6-dichlorobenzamide), a metabolite from
dichlobenil and chlorothiamide that prior to 1997 was com-
monly used as a total herbicide in urban areas, along roads,
railways and at farm yards. The triazine group is the second
most found pesticide group, but in Latvia this group comes
in third place, after the chlorophenoxy acids and trichloro -
acetic acid (TCA); the latter was the most widely utilised her-
bicide during the Soviet time and a by-product from the
chemical industry.
screens (Stockmarr 2005). In Denmark the most often found
pesticide is BAM (2,6-dichlorobenzamide), a metabolite from
dichlobenil and chlorothiamide that prior to 1997 was com-
monly used as a total herbicide in urban areas, along roads,
railways and at farm yards. The triazine group is the second
most found pesticide group, but in Latvia this group comes
in third place, after the chlorophenoxy acids and trichloro -
acetic acid (TCA); the latter was the most widely utilised her-
bicide during the Soviet time and a by-product from the
chemical industry.
As the investigation was focused on potentially vulnerable
areas and in the uppermost aquifers, an estimate of 30% occur-
rence of pesticides is highly pessimistic if the entire Latvian
groundwater is considered. Taking into account the smaller
acreage of treated areas and a higher confinement degree of
main aquifers, the risk of contamination of water-supply
wells by pesticides in Latvia should be significantly lower
than in Denmark. However, as the pesticides were mainly
used in the 1980s they may not yet have reached the main
Latvian aquifers containing groundwater older than 50 years.
rence of pesticides is highly pessimistic if the entire Latvian
groundwater is considered. Taking into account the smaller
acreage of treated areas and a higher confinement degree of
main aquifers, the risk of contamination of water-supply
wells by pesticides in Latvia should be significantly lower
than in Denmark. However, as the pesticides were mainly
used in the 1980s they may not yet have reached the main
Latvian aquifers containing groundwater older than 50 years.
Minor elements
In order to compare Danish and Latvian shallow groundwa-
ter chemistry, distribution curves of twelve selected minor
elements are presented in Fig. 4.
ter chemistry, distribution curves of twelve selected minor
elements are presented in Fig. 4.
Shallow Latvian groundwater is characterised by higher
background concentrations of aluminium and fluoride and
lower concentrations of bromide, lithium, manganese, phos-
phorus and strontium when compared to the Danish data. A
majority of the observed differences reflect the difference in
basic groundwater chemistry: the median values of the chlo-
ride, sulphate and permanganate indices in the Danish data
set (30, 45 and 3.1 mg/l, respectively) are significantly higher
than the corresponding values for the Latvian data set (10, 20
and 1.4 mg/l, respectively).
lower concentrations of bromide, lithium, manganese, phos-
phorus and strontium when compared to the Danish data. A
majority of the observed differences reflect the difference in
basic groundwater chemistry: the median values of the chlo-
ride, sulphate and permanganate indices in the Danish data
set (30, 45 and 3.1 mg/l, respectively) are significantly higher
than the corresponding values for the Latvian data set (10, 20
and 1.4 mg/l, respectively).
67
Fig. 2.
A
: Distribution of nitrate in Danish
and Latvian wells compared to screen depth.
Danish data from 719 monitoring screens
averaged for the period 1998-2003. Latvian
data from 717 monitoring and water-supply
wells averaged for the period 2000-2005.
B
: Distribution of dissolved oxygen in
Danish and Latvian wells as a function of
screen depth. Danish data from 706
monitoring screens are averaged for the
period 1998-2003. Latvian data from 160
monitoring and investigative screens are
averaged for the period 2003-2005.
Fig. 3. Distribution of nitrate in 85 springs and 358 shallow wells within
Latvian agricultural areas.
68
The anoxic and neutral conditions in the majority of
Latvian aquifers are unfavourable for migration of most
heavy metals, whose concentrations are well below the qual-
ity standards of drinking water. Exceptions are manganese
and arsenic that migrate in reducing environments. The con-
centrations of these elements exceed the quality standards (50
and 10 µg/l, respectively) in 22% and 1% of the samples.
Boron and selenium exceed the quality standards (300 and
10 µg/l, respectively) only in saline groundwater, where the
concentrations of sulphate or chloride are significantly higher
than quality standards for drinking water. In general, heavy
metals in Latvian groundwater are a smaller problem than in
Denmark where manganese and arsenic exceed quality stan-
dards of drinking water in 63% and 9% of the monitoring
screens, respectively. However, these compounds do not pose
a problem for the drinking-water supply in general in
Denmark due to sorption in natural sand filters at the water-
treatment plants.
heavy metals, whose concentrations are well below the qual-
ity standards of drinking water. Exceptions are manganese
and arsenic that migrate in reducing environments. The con-
centrations of these elements exceed the quality standards (50
and 10 µg/l, respectively) in 22% and 1% of the samples.
Boron and selenium exceed the quality standards (300 and
10 µg/l, respectively) only in saline groundwater, where the
concentrations of sulphate or chloride are significantly higher
than quality standards for drinking water. In general, heavy
metals in Latvian groundwater are a smaller problem than in
Denmark where manganese and arsenic exceed quality stan-
dards of drinking water in 63% and 9% of the monitoring
screens, respectively. However, these compounds do not pose
a problem for the drinking-water supply in general in
Denmark due to sorption in natural sand filters at the water-
treatment plants.
In Latvia, nickel concentrations higher than the quality
standard of drinking water (20 µg/l) were not observed in
groundwater below 10 m. In Denmark, high nickel concen-
trations locally create problems where large-scale depression
cones in the groundwater table result in oxidation of sulphide
minerals. Lowering of the groundwater table in Latvian
groundwater below 10 m. In Denmark, high nickel concen-
trations locally create problems where large-scale depression
cones in the groundwater table result in oxidation of sulphide
minerals. Lowering of the groundwater table in Latvian
aquifers occurs only in deep, confined aquifers rather than in
the vicinity of the groundwater table.
the vicinity of the groundwater table.
Conclusions
The distribution patterns of minor elements in Latvian and
Danish groundwater are somewhat similar and are governed
by the basic groundwater chemistry. In general, the back-
ground concentrations of aluminium and fluoride are higher,
and the concentrations of bromide, lithium, manganese,
phosphorus and strontium are lower in shallow groundwater
in Latvia compared to the Danish aquifers.
Danish groundwater are somewhat similar and are governed
by the basic groundwater chemistry. In general, the back-
ground concentrations of aluminium and fluoride are higher,
and the concentrations of bromide, lithium, manganese,
phosphorus and strontium are lower in shallow groundwater
in Latvia compared to the Danish aquifers.
The lower anthropogenic pressure combined with a
higher confinement degree of major water-supply aquifers
explains why diffuse contamination of Latvian groundwater
is lower than in Denmark. At present, the limited data on
pesticides and on the age of groundwater do not allow an
assessment of the extent of the pesticide problem in Latvian
groundwater with sufficient accuracy.
explains why diffuse contamination of Latvian groundwater
is lower than in Denmark. At present, the limited data on
pesticides and on the age of groundwater do not allow an
assessment of the extent of the pesticide problem in Latvian
groundwater with sufficient accuracy.
Acknowledgements
Our much appreciated friend and colleague, Edmund Gosk, passed
away on 24 November 2006 after a long struggle against cancer. We wish
to acknowledge his engaged involvement in this project in Latvia, as well
as in his many other tasks.
away on 24 November 2006 after a long struggle against cancer. We wish
to acknowledge his engaged involvement in this project in Latvia, as well
as in his many other tasks.
References
GEUS 2005: Grundvand 2004. Status og udvikling 1989-2004. København:
Danmarks og Grønlands Geologiske Undersøgelse (in Danish with
English summary). Available on: www.geus.dk/publications/grund
English summary). Available on: www.geus.dk/publications/grund
-
vandsovervaagning/1989_2004/index.html
Gosk, E., Levins, I. & Jørgensen, L.F. 2006: Agricultural influence on
groundwater in Latvia. Danmarks og Grønlands Geologiske Under -
søgelse Rapport 2006/85 , 98 pp.
søgelse Rapport 2006/85 , 98 pp.
Henriksen, H.J. & Sonnenborg, A. (eds) 2003: Ferskvandets kredsløb.
NOVA 2003 temarapport, 230 pp. København: Danmarks og Grøn -
lands Geologiske Undersøgelse, Danmarks Miljøundersøgelser, Dan -
marks Jordbrugsforskning and Danmarks Meteorologiske Institut (in
Danish with English summary).
Also available on: http://vandmodel.dk/ferskvands_2003_final.htm
lands Geologiske Undersøgelse, Danmarks Miljøundersøgelser, Dan -
marks Jordbrugsforskning and Danmarks Meteorologiske Institut (in
Danish with English summary).
Also available on: http://vandmodel.dk/ferskvands_2003_final.htm
NERI 2005: NOVANA - National monitoring and assessment programme
for the aquatic and terrestrial environment. Programme description,
part 2. NERI Technical Report 537/2005 , 137 pp.
part 2. NERI Technical Report 537/2005 , 137 pp.
Stålnacke, P., Grimvall, A., Libiseller, C., Laznik, M. & Kokoite, I. 2003:
Trends in nutrient concentrations in Latvian rivers and the response to
the dramatic change in agriculture. Journal of Hydrology 283 , 184- 205.
the dramatic change in agriculture. Journal of Hydrology 283 , 184- 205.
Stockmarr, J. 2005: Groundwater quality monitoring in Denmark. Geo l -
og ical Survey of Denmark and Greenland Bulletin
7
, 33-36.
Authors' addresses
L.F.J. & E.G. (deceased),
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
E-mail
: lfj@geus.dk
I.L.,
Latvian Environment, Geology and Meteorology Agency (LEGMA), Maskavas Str. 165, LV-1019 Riga, Latvia.
Fig. 4. Distribution of selected minor elements in shallow Latvian
groundwater (full lines indicate data from 477 wells and springs for the
period 2003-2005) and in shallow Danish groundwater (dotted lines
indicate data from 723 monitoring screens for the period 1998-2003).
