Chloride in groundwater in Finland
Chloride concentration in groundwater and road salting
Road salting is one activity that affects groundwater quality. In Finland roads have often been built in areas which are also important groundwater supply areas. In these sand and gravel formations, salt easily filters through into the groundwater and can raise chloride concentrations to higher than natural levels.
During the years 1975 to 1981 natural chloride concentrations were studied at 54 monitoring stations. The results are shown in the table below.
Chloride concentration in natural areas in Finland (Soveri 1985)
| Area |
Mean value mg/l |
| Fine-grained formations |
3.8 |
| Moraine areas |
2.2 |
| Coarse-grained formations (sand and gravel) |
1.4 |
| All data, total of 2286 samples |
2.1 |
A rise in the chloride concentration can cause groundwater to become corrosive. Because of the risk of corrosion, a recommendation of 25 mg chloride/litre has been set, otherwise 250 mg chloride/litre is recommended for water for household consumption In public waterworks the effects of corrosion can be reduced by raising the pH of the water.
The risks caused by road salting have been monitored in the whole of Finland during the years 1997 to 1998. Additionally, the effects of road salting on groundwater have been monitored regularly in about 50 special monitoring areas and the Finnish Road Administration has been monitoring chloride concentrations in about 150 areas.
Chloride concentrations in groundwater are still rising in many areas. Mathematical models have shown that in a single groundwater area changes in the groundwater can last even dozens of years, although salt is no longer permeating into the groundwater aquifer.
Use of road salt in Finland from 1959 to 2009 (Salminen, J. et al. 2010)
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References
Soveri, J., 1985. Influence of meltwater on the amount and composition of groundwater in quater-nary deposits in Finland. Vesihallitus 1985. 92 s. kuv., taul. Vesientutkimuslaitoksen julkaisuja; nro 63. ISBN 951-46-9056-7
Gustafsson, J. 2003. Teiden liukkaudentorjunnan pohjavesivaikutusten erityisseurantakohteet (The monitoring programme for the impacts of the road salting on groundwater). Suomen ympäristökeskuksen moniste 289, ISBN 952-11-1512-2 (pdf).
SYKEmo289
Tidenberg, S., Kosonen, E. and Gustafsson, J. 2007. Teiden talvikunnossapidon vaikutukset pohjaveteen (English abstract: Results of the effects of the winter maintenance of roads on groundwater quality). Suomen ympäristökeskus. Suomen ympäristökeskuksen raportteja 10/2007.131 s. ISBN 978-952-11-2664-2, ISBN 978-952-11-2665-9 (pdf) SYKEra10/2007
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