Lahti and Hollola are located above the significant I Salpausselkä groundwater reserves. Groundwater issues related to the construction of the Lahti southern ring road have been discussed with planners, Lahti Aqua Ltd, the authorities (Centre for Economic Development, Transport and the Environment; Regional State Administrative Agency) and the Urban Environment Service Area. The project entails the lowering of groundwater surface levels on the west side of Sokeritoppa by several metres from its natural level during construction. At this site, the groundwater surface level will be permanently lowered by approximately two metres. In the Liipola area, groundwater levels must be lowered by several metres because of tunnel construction, and the same applies to Patomäki.
In 2018, Lahti expanded the practice started in central Lahti in 2017 to use potassium and natrium formate as a replacement for de-icing salt to prevent slippery road surfaces. The impact of this change on groundwater quality will be monitored in the city centre over the coming years. The planning of joint monitoring of groundwater continued, and the monitoring will commence in the Lahti and Renkomäki groundwater areas in 2019.
On the basis of the hydrogeological surveys performed, the Centre for Economic Development, Transport and the Environment removed Kolava from the groundwater area classification. Ruoriniemi and Harvasaari were included as new groundwater areas. The Lahti groundwater area was redefined with respect to the Niemi area. Minor changes were also made in the Villähti groundwater area as well as the Nastonharju–Uusikylä A and B groundwater areas.
Water acquisition by Lahti and Hollola is solely based on groundwater reserves. The volume of water pumped for consumption in Lahti and Hollola totalled 25,000 m3 per day in 2018 All water samples taken met the quality requirements and recommendations set for household water, but the chloride content of some samples was above the quality recommendation level. Approximately 100,000 m3 of groundwater is formed in the Lahti groundwater reserves every day, which is around four times the daily consumption. Altogether, 23% of the groundwater areas are classified as being in a poor state.
|Nastola, Mälkönen abstraction site||172||190||215||190||220||220||200||200||210||213||220||195|
|Nastola Uusikylä (observation point GA1)||2,9||1,3||1||0,8||0,3||0,3||0|
|Lahti (HP137, trakcside)||1,6||2,2||2,3||1,2||1,8||2,6||3,15||3,7|
There have been no major changes in water consumption over the last few years. The specific consumption figure includes water consumed by residents and industry as well as loss caused by leakage. The figures for Lahti include Nastola and the figures for Hollola include Hämeenkoski.
|Lahti specific consumption||197||189||184||183||179||187||181||179|
|Hollola specific consumption||114||113||113||150||150||153||158||155|
|Nastola specific consumption||212||192||211||211||216|
|Lahti household consumption||127||125||124||122||121||120||119||120|
Future plans and challenges
The effects of climate change on groundwater quality and quantity (the RAINMAN project).
More efficient utilisation of modelling for the planning of groundwater protection.
Expansion of the joint monitoring programme.
Construction of the ring road below the groundwater surface level in Laune.
Monitoring the impact of the new de-icing method on chloride levels in groundwater.
Cleaning the groundwater areas that are in a poor chemical state
The need for water supply network renovations will increase as the pipelines built during Lahti’s years of rapid growth in the 1960s and 1970s will reach the end of their life cycle.