3.1 Main characteristics of the aquifer
The Krska kotlina aquifer covers an area of around 90 km2 located at the downstream portion of the Krka River sub-basin near the boarder with Croatia. It is composed of around 20 meters of quaternary sediments (the most important from a water point of view and highly permeable), of Pliocene sediments (between 0 and 600 meters of thickness) and of Miocene sediments with very low permeability. Rainfall in the area ranges from 900 to 1200 mm per year on average. And evapo-transpiration is estimated at 700 mm per year. The boundaries of the groundwater body (see Figure 3) do not coincide with administrative or surface water catchment boundaries. Indeed, the groundwater body area is shared between two municipalities (Krsko and Brezice) and between the catchment areas of the Krka River and of the Sava main river.
The aquifer is mainly recharged from precipitation, and to a much lower extent from the Sava River (average flow of 290 m3/s), the Krka River (average flow of 55 m3/s) and from small creeks. The groundwater body is connected to surface water, in particular wetlands along the Krka River, although little is known about the importance of this connection and how it affects the quality of the Krka River (if at all). The groundwater body also feeds into the most downstream part of the Sava river itself – the aquifer contributing to river flows during low flow periods.
Figure 3. Hydrological boundaries of the Krska kotlina aquifer (source: Krka Pilot project, 2006c)
3.2 Main groundwater pollution issues
The Krska kotlina aquifer is under pressures from different economic sectors and users.
Overall, the aquifer is under pressure from different sources of pollution in particular: (i) leakages from sewerage systems, (ii) inadequate sewage for dispersed settlements and malfunctioning sceptic tanks of individual households, (iii) leakages from landfills, (iv) inadequate management of farm yard manure, and finally and more importantly (v) high use of pesticides and fertilisers in agriculture. As a result of these pressures:
• Nitrate concentrations in the aquifer are currently increasing. Average concentrations are today just below the starting point for trend reversal of 37.5 mg/l (see Figure 4).
And if no additional action is taken1, water from the Krsko aquifer will become non-drinkable in the medium term with its concentration expected to reach 60 mg/l in the long-term (thus well-above the drinking water threshold of 50 mg/l – see Figure 5);
• Pesticides are also found in most parts of the aquifer, e.g. at all monitoring sites of the aquifer. Average pesticide concentrations remain low so groundwater is still drinkable. But concentrations of some pesticides (e.g. desetilatrazin and symazine) are increasing. Today, values higher than the threshold value of 0.1 µg/l are already found for desetilatrazine in the Drnovo abstraction well supplying water to the municipality of Krsko.
Some of the pollution of the aquifer might be transferred to natural areas and connected ecosystems which balance could then be threatened. However, there is much uncertainty on these interconnections and on the risk for connected ecosystems originating from groundwater pollution.
VTPodV KRŠKA KOTLINA: Nitrati
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00
1997 1998 1999 2000 2001 2002 2003 2004 2005
nitrati (mg/l)
Figure 4. Trends in average nitrate concentration for the Krsko kotlina aquifer (source: Krka Pilot Project, 2006a)
Figure 5. Expected future trend in nitrate concentration for the Krsko kotlina aquifer (source:
Krka Pilot Project, 2006d)
1 It is assumed that economic development and changes in the agriculture sector will be nitrate pollution neutral.
3.3 Groundwater abstraction
Groundwater from the Krsko kotlina aquifer is abstracted for municipal water use, industrial processes and agriculture use (irrigation).
With regards to municipal water abstraction and household water use, there are two wells supplying water to the municipality of Krško and abstracting groundwater from the Krska kotlina aquifer, namely the Drnovo well supplying water to the right river bank and the Brege well supplying water to the left river bank. The Drnovo well has a capacity of 50 l/s and it is supplying on average 35 l/s. The Brege well has a higher capacity of 60 l/s, but it is only supplying 25 l/s on average.
The Krško municipal water supply system also use water from other wells that are pumping water from other (shallow) aquifers and not from Krska kotlina. The same applies for the municipality of Brežice that only relies on wells pumping water from other nearby shallow aquifers.
The area above the Krska kotlina aquifer hosts several settlements as indicated in Figure 3.
However, many of their inhabitants are connected to drinking water supply networks which use other sources of water than the Krska kotlina aquifer. In total, 4 677 inhabitant are connected to the Drnovo and Brege wells abstracting water from the aquifer. This represents a total water use of around 388 000 m3 per year (2005 figures, see Krka Pilot Project, 2006d). In addition, many inhabitants still have their own wells (see Chapter 5), although water abstracted from these wells is always used in complement to water from the municipal network.
Groundwater abstraction for industrial water use is rather limited in the area that is mainly rural. Six wells, located in the municipality of Krško, abstract water from the aquifer mainly for small industries (paper and cellulose, construction…) and for the Krško Nuclear Power Plant (for drinking and cleaning – not for cooling). And this limited abstraction will not evolve drastically in the coming years as no significant industrial development is foreseen in the area.
In the area of the municipality of Brežice, there are four wells abstracting water from the aquifer used by Čatež Spa, a well-known spa center. Two of these wells are thermal wells pumping water at a depth of 564 and 532 m – thus not in the Krska kotlina aquifer. The two other wells are pumping water from the aquifer for drinking water purposes (for visitors and tourists).The average capacity of these wells is 7 l/s. And total yearly water use has been estimated at 220 000 m3 (Krka Pilot project, 2006d).
Abstraction for agriculture is made by two main wells used to irrigate vegetables (tomato, gherkin, paprika, lettuce…) and fruits (strawberries and apples). There are two other wells that are currently not operated and kept as “reserve” – and also a large number of small (illegal) wells. Overall, direct abstraction from the aquifer remains very limited as farmers are mainly abstracting water from the Sava River, the Krka River and from gravel pits.
Overall, the degradation of the quality of the aquifer because of increasing nitrate and pesticide pollution will not affect industrial water use and agriculture water use (irrigation).It will however become very problematic for municipal water use (water abstracted from the Drnovo and Brege wells) and for the thermal center of Čatež Spa as soon as pollutant concentrations are higher than set water quality standards.
As groundwater quality deteriorates, specific investments will be required by the municipalities and by the thermal center to ensure the water they supply to customers and visitors has good drinking water quality.
• Alternative solutions for ensuring good quality drinking water for the inhabitants connected to the municipal system abstracting water from the aquifer were investigated (Krka Pilot Project, 2006d). The analysis, comparing technical feasibility and costs, stressed that treating drinking water (using a system of ultra-filtration) would be the most cost-effective option (as compared for example to connecting customers to nearby existing water abstraction points with better quality raw water).
Overall, investment costs of such treatment is around 550 million SIT – with operation and maintenance costs accounting for 10% of investment costs. These costs will be paid by the water supply company and eventually passed to customers via water prices.
• Alternative solutions were also investigated for the thermal center of Čatež Spa.
Considering the potential pollution that will occur (pesticides, nitrates, ammonia, bacteriological pollution and possibly smell and taste), a reverse osmosis water purification process was considered as the best alternative and is already considered today by the private operator of the spa. The construction of two reverse osmosis devices with a capacity of 15 l/s will be sufficient to cover the drinking water needs of the spa. Investment costs of these two devices amount to 216 million SIT, with operating expenditures estimated at 96 SIT/m3. These costs will also be paid by the private operator of the thermal center – and eventually passed to visitors of the center via entry prices.
In conclusion, (current and future) water abstraction in the Krska kotlina aquifer does not pose any threat to the sustainability of the aquifer – as abstraction is minimal as compared to recharge. However, because of the degradation of the quality of the aquifer, significant investments will be required for the municipal drinking water supply and for the thermal spa to ensure good drinking water quality complying with set drinking water quality standards to customers and visitors.