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Salt-water intrusion in the limestone bedrock of South-Western Scania
Leander, B.; Person, K.M. (1999). Salt-water intrusion in the limestone bedrock of South-Western Scania. Natuurwet. Tijdschr. 79(1-4): 178-184
In: Natuurwetenschappelijk Tijdschrift. L. Walschot/Natuur- en Geneeskundige Vennootschap: Gent. ISSN 0770-1748, meer
Ook verschenen in:De Breuck, W.; Walschot, L. (Ed.) (1999). Proceedings of the 15th Salt-Water Intrusion Meeting Ghent (Belgium), 25-29 May 1998. Natuurwetenschappelijk Tijdschrift, 79(1-4). Natuurwetenschappelijk Tijdschrift: Gent. 307 pp., meer
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Rocks > Carbonate rocks > Limestone
Saline intrusion
Water > Ground water
Sweden, Scania
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| Abstract |
The possibility of salt-water intrusion in the limestone aquifer AlnarpsstrÖmmen in south-western Scania, south Sweden, is discussed. The aquifer is in close contact with the surrounding sea and the water extraction from the aquifer has decreased the groundwater pressure to levels below the sea-water level in some regions. That is why a number of long-term studies of the possible salt-water intrusion has been carried out and why its dynamics have been studied for more than 30 years.In the upper moraine layer of the area, the groundwater is unconfined. In the limestone formation, the water in general is confined. The confined groundwater is chemically reduced, with an iron content above 2 mg/l and typically hydrogen sulphide gas dissolved in the water. The concentration of ammonium ion may be above 0,5 mg/l. The composition of the reduced water is however not stable. Some boreholes display interesting shifts between nitrate and ammonium ions from one time to another. Groundwater is in general in calcium carbonate equilibrium with the limestone bedrock. Some regions of the bedrock contain groundwater with a molar concentration of magnesium higher than the molar concentration of calcium, although no dolomite is known in the region.A finite element model of the aquifer system has been developed. It simulates a two-djmensional steady state and transient groundwater flow with vertical leakage through confining low-permeable layers. An anticipated higher recharge rate or a lower water extraction quickly led to a change in water-table levels. The model has been verified when some smaller water works closed and the water extraction ceased in some areas of the aquifer. The extraction flow increases the sodium chloride as well as the calcium-carbonate content in the groundwater. When extraction ends, the sodium-chloride content in the well water decreases faster than the calcium-carbonate content, probably due to different origins of the ions. Sodium chloride originates either from sea water or upconing relict salt water, while calcium carbonate comes from the chemical equilibrium with the limestone bedrock. This equilibrium however also seems to be affected by the reduced sodium-chloride concentration; the total hardness decreases with a decrease in the sodium-chloride content. |
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