International Geologiical Congress - Oslo 2008

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HYH-02 Groundwater resources and management Part 2

 

How to manage the drinking water source in the urban area? - The case of Ljubljansko polje aquifer

 

Branka Bracic Zeleznik, Public Water Supply and Waste Water Drainage Company (Slovenia)
 

 

The Ljubljansko polje aquifer is one of the most important bodies of groundwater in the state and in the same time the drinking water source for more than 300 000 inhabitant of Ljubljana and vicinity for almost one hundred and twenty years.

For the central position in the country and the geographical position of the area the gravel plan of Ljubljansko polje is where the interests of urbanisation, industry, agriculture and public drinking water supply intersect. Ljubljana has been developed in the last hundred years from a town of twenty thousand inhabitants to a city of almost three hundred thousand inhabitants.

The water fields were in the past situated far away from the city. Today the city is lying above the drinking water source and the water fields are surrounded with intensive urban areas and industrial zones. The anthropogenic activities modify the entire aquifer area, impact the hydrological balance, reduce aquifer recharge, influence groundwater flow characteristics and change the water source availability and restoration.

The progress of pipeline and sewage system has followed the city expansion. But in some parts of the city, especially on the borders, are still buildings and houses not connected to public sewage system. The drained area is 6576 ha, and the length of sewage system is 1039 km. The sewage system is predominantly combined (approximately 80 per cent) in average 30-40 years old, but several channels and main collectors are older than 50 years. In the areas on the margin of the city the sewage is built in separated systems, where the waste water has to be pumped in the main collectors and the precipitation water goes to the nearest recipient. Local the influence of the untied and damaged sewage system is detected in the groundwater quality. The presence of nitrate, chlorine, VOC, P, B, E. coli and some others pollutants show the influence of urbanisation on groundwater quality. The length of water supply pipeline is 1114 km. The groundwater abstraction was 27,6 mio m3 in 2006 and the 23 mio m3 of water were sold. About 30% of abstraction are losses in water supply system and present the urban drainage to groundwater.

In the present day, the groundwater quality indicates moderate ability to compensate the negative influences of heterogeneous land uses. The groundwater quality and quantity state in the last ten years will be presented. The efficiency of legislation on the state and local level that protected the drinking water sources will be analysed and some preventive measures will be presented in the paper.

 

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