3.1 Background information about groundwater in Latvia
The territory of Latvia belongs to the Baltic artesian basin. Sedimentary rocks comprise water aquifers, which are situated in layers with different depths. The geological cross-section (from top to bottom) shows groundwater zones with different levels (active or slow) of exchange activities and chemical composition (freshwaters, mineral waters, saltwater). The overall zone of the active water exchange is more susceptible to potential anthropogenic pollution. Freshwater, which is the main source of drinking water supply in Latvia, originates mainly from this zone. This zone comprises quaternary (till 20 m depth usually), upper Devonian and middle Devonian aquifers or aquifer complexes. The total depth of the zone in Latvia varies between 10 to 400 meters.
There are two types of groundwater in Latvia – shallow groundwater and artesian groundwater.
• Shallow groundwater is the aquifer below the soil surface with no pressure or pressure lower than pressure at the soil surface. Shallow groundwater is spread in all upper quaternary sandy sediments at an average depth of 1 to 10 meters (in local areas even deeper). Shallow groundwater is not protected and at risk of surface pollution infiltration within the entire territory of Latvia. There is no recorded regional-wide pollution but a large number of localised polluted sites resulting from particular point source pressures or diffuse pollution (e.g. from urban areas).
• Artesian groundwater presents a natural pressure in contrast to shallow groundwater.
Artesian groundwater is spread in several groundwater aquifers and complexes. Existing monitoring data do not show substantial artesian groundwater pollution in Latvia. All recorded groundwater pollution is localised with limited impact on the quality of the overall artesian groundwater resources.
Overall, 16 groundwater bodies have been identified in Latvia (Ministry of Environment, 2004).
All groundwater bodies comprise both groundwater types – shallow groundwater and artesian groundwater. The identification of groundwater bodies has been carried out by the responsible authorities of Latvia as part of the implementation of the first WFD obligations.
3.2 First results of analysis of pressures on groundwater in Latvia
The main criterion for selecting a water body for the case study was whether it is at risk of failing meeting groundwater quality objectives, as the setting of threshold values will concern only pollutants at the origin of water bodies being “at risk”. It has to be noted that taking the local character of groundwater pollution in Latvia, there is not a single groundwater body that is characterized as being “at risk” in its entire territory, as usually only parts of water bodies are affected by anthropogenic pressures. That environmental problems identified in the selected water body are typical of groundwater problems in Latvia as a whole was also considered during the case study selection process. The Article 5 characterization report prepared at the end of 2004 and sent to the European Commission (EC) lists the following anthropogenic pressures affecting groundwater in Latvia (Ministry of Environment, 2004):
• Groundwater abstraction (mainly for drinking water needs and for industries)
• Pollution: infiltration of surface pollution from different point sources, urban territories and intensive agriculture areas
• Artificial recharge of groundwater (taking place only in one groundwater body).
The summary of the first risk assessment results for groundwater in Latvia is provided in Table 1.
It indicates the significance of each pollution problem causing the risk of failing good water quality for groundwater.
Table 1. Summary on the first risk assessment results for groundwater in Latvia
Risk category and pollution problem causing risk
From those, risk resulting from:
• Intrusion (of natural or anthropogenic origin)
• Artificial recharge
• Point source pollution
• Diffuse pollution
The groundwater body Q on the whole All – due to pollution from urban territories (due to pollution coming from industrial territories, transport infrastructure, communal services), affecting mainly shallow groundwater
“PROBABLY AT RISK”
From those, risk resulting from:
• Impact of agriculture activities
• Impact of urban areas
26 13 13
Agriculture territories of all GWB*
Urban areas for all GWB
Pollution affects only shallow groundwater
“NOT AT RISK” 2
13
Two very deep groundwater bodies (A and P – see Figure 3)
Natural territories of all groundwater bodies
* GWB – groundwater body
Source: Based on information presented in the 2004 Characterization report to the EC (ziņojums "Upju baseinu apgabalu raksturojums. Antropogēno slodžu uz pazemes un virszemes ūdeņiem vērtējums.
Ekonomiskā analīze.")
The results of the first groundwater risk assessment leads to several conclusions relevant to our analysis:
• The most significant pressure explaining groundwater bodies being “at risk” or “probably at risk” (including with uncertainty) is diffuse pollution originating from urban areas in priority and to a lesser extent from agriculture areas (see also Figure 3 presenting groundwater areas identified as “at risk” due to diffuse pollution in Latvia).
• At the same time, the problem of diffuse pollution (including pollution from urban areas) concerns mainly shallow groundwater and does not affect deep aquifers.
• Shallow groundwater is rarely used for (public) drinking water in Latvia. Shallow groundwater is used mostly by individual drinking water supplies in local districts of cities and in rural areas. But the number of inhabitants using shallow groundwater for drinking needs is expected to reduce in the future as a result of the extension of public water supply networks. Similarly, industry uses mainly artesian groundwater for water supply.
Thus, from an economic point of view, the “value” of shallow groundwater in Latvia overall is expected to be lower than for artesian groundwater because of the very limited importance of use values for shallow groundwater.
Urban territories Agriculture lands Nature territories Areas “at risk”: urban territories of cities Riga, Ventspils and Olaine
Borders of River Basins Borders of GWB
Figure 3. Groundwater areas identified as being “at risk” due to diffuse pollution in Latvia (Ministry of Environment, 2004)
Diffuse pollution from urban areas mainly concerns organic compounds, ammonium, chlorides, petroleum products and heavy metals, although the total spectrum of polluting substances observed in shallow groundwater is quite wide as many different pollution sources are concentrated in specific sites. The origin of these substances might include communal sewage (e.g. leakages from public sewage system), infiltration of pollution from individual sewage facilities and small gardens, transport infrastructure (e.g. petroleum products as run-off from fuel filling stations, roads, parking places) or industrial sites (mainly historical pollution).
3.3 Selection of the groundwater body for the case study
As a result of the information presented above, the territory of the city of Riga or the district D-2 of the groundwater body D4 was selected as case study. It is part of the groundwater body D4 shared between the four river basin districts (Daugava, Lielupe, Venta and Gauja) of Latvia. The district D-2 of this groundwater body belongs to the Daugava river basin district. It has been identified as a relatively discrete part of the water body D4 based on the area affected by pressures (although not as a separate hydro-geological unit).
The part D-2 of groundwater body D4 (the groundwater body D-2/D4 hereafter in the report) has been identified as being “at risk” in the Article 5 report (Ministry of Environment, 2004) due to diffuse pollution, mainly as run-off from urban areas. The selected groundwater body is the most significant area with pollution of this type in Latvia. Besides, the analysis will focus on shallow groundwater only (the Quaternary aquifer) as the problem of pollution concerns only shallow groundwater.
3.4 Identification of pollutant for the socio-economic assessments
The following criteria have been considered for the identification of pollutants for the Latvian case study:
• Whether the pollutant is causing or likely to cause a risk of failing water quality objectives for the particular water body;
• Availability of monitoring information for characterizing concentrations of the substance;
• Whether the substance is a typical pollutant representing high risk for groundwater in Latvia as a whole;
• Whether knowledge/investigations/work exist for this pollutant on background concentrations, quality standards, characterization of cause-effect relationships, potential measures and their effects etc;
• Whether the choice of pollutant enlarges the diversity of substances analysed in the BRIDGE (WP 5) case studies.
As a result of these different criterias, petroleum products have been selected for the socio-economic analysis in the Latvian case study.
3.5 Main characteristics of the selected groundwater body
The water body D-2/D4 selected as case study has a total area equivalent to the area of the city of Riga, i.e. 304.05 km2. Overall, the groundwater body D-2/D4 comprises both shallow and artesian groundwater, namely the aquifer complex Arukila-Amata (D2-3ar-am), which include several middle and upper Devonian aquifers at a depth of a few 10s to 330 meters
and Plavinas-Amula (D3pl-aml), which includes several upper Devonian aquifers at a depth of 20 to 80 meters. The following artesian aquifers are located in the area of the case study: the aquifers Gaujas, Amatas and Arukila (from the complex Arukial-Amata) and the aquifer Plavinu (from the complex Plavinas-Amula).
Because of the small depth of shallow groundwater, these water resources are very prone to surface pollution. The natural protection level of artesian aquifers is better overall. The existing thickness of tight sedimentary layers supports the assumption that artesian aquifers of the case study area are relatively well protected.
As mentioned above, the analysis focused on shallow groundwater of the water body D-2/D4. The depth of shallow groundwater varies. It is spread in all upper Quaternary sandy sediments at an average depth (thickness of the layer) of 1 to 10 meters, with higher thickness in scattered areas from 20 to 50 meters. The water level from the soil surface ranges between 0.5 to 3 meters on average, with deeper water levels reaching up to 5 meters or more locally. The upper Quaternary sandy sediments are formed of sand, sandy-gravel and clayey soils (loam).
All groundwater bodies in Latvia (excluding two very deep groundwater bodies – see the water bodies A and P in Figure 3) are connected to surface waters (mainly to the large rivers Daugava, Venta, Gauja and Salaca). Also connection to bogs (terrestrial ecosystems depending on the regime of groundwater) can be observed in many places. However this connection is poorly investigated and the most significant connection places or the most sensitive depending terrestrial ecosystems are not identified. At the same time, some pollution from petroleum products in the downstream part of the Daugava River (close to its outfall into the Riga gulf) is caused by local pollution from shallow groundwater discharging into the river. It indicates that direct connections between shallow groundwater and surface water are taking place in the case study area.
The main water uses related to groundwater in Latvia are water abstractions for drinking and industrial needs. This was the case for Riga in the past, with abstractions from the municipality and local industries being however higher than the recharge and threatening the sustainability of groundwater use in this aquifer and leading to the creation of a depression cone in the 1960-1980s. As a result, abstraction for municipal drinking water was changed and practically stopped. Today, around 200 individual bore-holes abstracting (artesian) groundwater are officially registered in the territory of the city of Riga. Water for municipal water supply is abstracted from the Daugava River (with adequate pre-treatment to bring surface water up to drinking water quality standards) and from artesian aquifers. Shallow groundwater is also abstracted but more marginally from bore-holes located outside of the territory of the city of Riga (at Zaķumuiža, Remberģi and Baltezers).
Groundwater is often used for individual water supply (mostly shallow groundwater), a situation that takes place also in the city of Riga. Indeed, households in several districts of the city do not have access to the public water supply system. However, the number of inhabitants using self-supply systems is relatively small (around 5% of the total population).
And it is decreasing due to the expansion of the public water supply network.