Lahti Aqua Ltd (part of Lahti City Group) is in charge of drinking water and waste water management . Groundwater is used as only drinking water source. In 2017, 95% of water users were connected to the municipal network and subjected to water metering, and the total water consumption was 7.5 Mm3 (approx. 45 m3/capita/a) compared to 7.8 Mm3 (approx. 79 m3/capita/a) in 2006 (Fig A1). Water consumption has mainly decreased as a result of decreased use by apartment building residents, industry and the service sector. In 2006, residents consumed 139 litres/capita/day compared to 119 litres/capita/day in 2017. Today, 7.1% of water is lost in pipelines (Fig A2), while in 2006, the loss was nearly 11%. Effectiveness is achieved using modern control and digital information systems. The energy consumption of drinking water production was 0.69 kWh/m3 in 2017 (Fig. A3).
Drinking water quality is excellent. In 2010, 98% of the samples complied with the quality standards. Lahti Aqua has upgraded the purification technology, and in 2017, 100% of the samples complied with the quality standards (Drinking Water Directive). Due to the groundwater’s good quality, only minimal treatment is needed. The groundwater in Lahti is soft (pH 6.5). Therefore, calcium oxide or sodium hydroxide (50%) is added to prevent pipeline corrosion. Bacterial growth is prevented with a small amount of sodium hypochlorite (10%) or ammonium chloride. All water towers are equipped with UV water purification systems.
Virtually all urban areas have separate sewers for storm water and wastewater. In 2017, Lahti had 767 km of wastewater sewers and 454 km of storm water sewers. Combined sewers remain in the area adjacent to the Lahti Market Square. The amount of storm water runoff, from this area, has been estimated by Lahti Aqua as being approximately 50 000 m3/a (1% of the runoff from the city centre).
The Storm Water Management Plan (2012) promotes the use of sustainable drainage systems (SuDS) . For all new development areas and sites, a specific plan must be presented for storm water management. Alternative solutions are often necessary in the southern parts of Lahti, due to the soil type (clay/silt).
Flood risk areas were mapped, for Lahti, in 2010. Possible flooding is not expected to cause significant damages, since vulnerable areas are generally not inhabited and are excluded from future construction.
The Lake Vesijärvi and seven other lakes have a “moderate” status, six lakes have a “good” status and one has a “poor” status. There has been a Vesijärvi Action Plan since 2009, and a regional action plan to improve the condition of rivers and lakes. There are four rivers in Lahti, two have a “moderate” status, one has a “good” status and one has a “poor” status.
A Water Management Plan (2010) is in place to develop water management.
The quantity of wastewater has decreased: 7.5 Mm3 in 2017 and 8.4 Mm3 in 2006 (Fig. A4).
94.6% of households were connected to a sewage network in 2016. Close to 2 000 citizens or 600 buildings in the rural areas of Lahti used onsite sewage facilities. The methods vary from simple septic tanks to modern facilities. The most common method is a combination of a septic tank and a drainfield, which results in about 80-90% of nutrients from wastewaters being removed. Sewage sludge from tanks is transported to UWWTPs. Properties that are situated within the sewage network area must connect to the sewage network system (Fig. C1).
The reduction in water consumption is performed by improving metering and appliances, tariff policies, and raising awareness:
• The “Water School” website for children: water consumption, purification and wastewaters (Fig. B1).
• The water saving competition by Lahti Housing in 2012 and 2014; reduced consumption 10-19%.
• Water prices have been raised to cover running expenses and the upgrading of pipelines, and to motivate reducing water consumption.
• Water losses in pipelines have been reduced (9A).
Lahti Aqua has renewed water towers and added UV water purification systems. In 2013-2015, the Laune well was upgraded, to remove pesticides from the groundwater, with an activated carbon filter and a UV water purification system. Groundwater protection plans are in place for all wells. Lahti Aqua hands out information guidelines about permitted and prohibited activities on groundwater areas.
Since 1990, groundwater protection has been coordinated and implemented by a Groundwater Workgroup. The first groundwater protection plans were implemented in 1995 (Lahti) and 1999 (Nastola). Examples of actions:
• Oil tanks cannot be installed underground in important groundwater areas and the existing ones need to be inspected at least every 10 years.
• Oil tanks have been mapped (2012-2015).
• Since 2015, companies that are not required to have an environmental permit are checked for activities that could impair groundwater bodies.
• All springs were mapped in 2016.
• Protecting groundwater is carefully considered in the Master Plan (2016).
• 2017, road salt (NaCl) was replaced with a biodegradable EcoMelter product (potassium and sodium formate) in the centre, increasing costs 250-300 000 € yearly.
• The contaminated soil underneath the Market Square was cleaned in 2013-2015 (Fig. B2).
• Lahti has invested about 3.5 M€ for cleaning contaminated land, over the past 10 years.
• Biocides are only allowed, with a special permit, if other measures have failed (no biocides used in 2015-2017). A non-toxic hot foam system has been tested for controlling weeds and invasive plants.
Construction of a UV disinfection facility in Nikula was completed in 2015. All purified wastewater from two UWWTPs are directed to Nikula’s wastewater equalization basin (Fig. B3) and disinfected before release into the Porvoonjoki River. Permits require a purification efficiency of 90%, and Lahti Aqua Ltd aims to reduce the load of bacteria so that the treated wastewater is in a good state, according to the Finnish bathing water ordinance (EU Bathing Water Directive); an investment of 2 M€.
To increase the efficiency of the biological treatment, Lahti Aqua upgraded the operation of the aeration basins in 2010-2012; an investment of 0.3 M€.
The total network was 2 053 km in 2016, with 584 km gained from Nastola. Freezing temperatures may cause pipes to burst. Maintaining the network is crucial to prevent accidental pollution. Due to the hilly landscape, Lahti Aqua Ltd has pumps to direct wastewaters towards UWWTPs. In 2011, a project to upgrade the pumps was initiated, with an investment of 1 M€. In 2015-2016, six other pumps were upgraded. The renewal of the wastewater monitoring systems and pumps was completed in 2012. All wastewater pumps have monitoring systems and backup solutions. In 2017, 3.1 km of network and 3 pumps were renovated.
In 2013-2017, Lahti Aqua has built a backup system for the tunnel directing treated wastewaters from the Kariniemi UWWTP to Nikula. This ensures that waters are disinfected before being released into water bodies; an investment of 5 M€.
The sewer network is constantly widened to cover new residential areas and to reach households using onsite sewage facilities. In 2010, Lahti Aqua drafted a plan that covers the renewing and widening of the pipeline network stretching to 2030; an investment of 2.9 M€ in 2016.
We have been restoring Lake Vesijärvi, since the mid-1970s, in co-operation with several municipalities, universities and other research organizations. The yearly restoration investment is over 250 000 € and is covered by the City of Lahti, Lahti Aqua Ltd and Lahti Energy Ltd. Past measures included improving wastewater treatment and biomanipulation. The current restoration stage involves mapping pollution sources, eliminating wastewater sources from private dwellings, constructing retention ponds and wetlands, aeration and biomanipulation (Fig B4). In the past, Lake Vesijärvi was not suitable for swimming, but today, it has many public beaches.
River conditions are improved through SuDS. The river’s condition (including water quality, fish, fishing and benthic fauna) has been monitored, together with other municipalities, companies and non-governmental organizations, for over 20 years. The fraction of cyprinids has lessened and the population of more demanding fish has increased.
Further actions to improve water bodies:
• 2012-16: The “Jokitalkkari” project aims to improve river conditions so that salmonid populations will increase or return.
• 2017, 2018: The ”Jokitalkkari”; The previously canalized stream site was restored and a small fishway was constructed at the Seestaanjoki River at two locations.
• 2016: Lahti Catering offered fish patties to children at school made of Lake Vesijärvi’s roach.
• 2016-2018: Lake Vesijärvi Week, used to bring residents, companies and organizations together and increase the conception of the lake’s value with events and activities.
• Monitoring and management of small lakes.
• Lake Kymijärvi management agreement and research projects.
• Every year, we stock Lake Vesijärvi with 10 000 critically endangered eels, and then to secure their migration, they are caught and moved to the Gulf of Finland.
• Waste water counselling project.
The biogas production and refining plant of LABIO Ltd (owned by Lahti Aqua Ltd and Päijät-Häme Waste Management Ltd) was completed in 2014, making it Finland’s largest biowaste treatment plant; at an investment of 17 M€:
• The sludge is composted with biowaste.
• After digestion, the mass goes on for composting.
• Biogas is sold to be utilized as fuel. Lahti Aqua owns 35 biogas cars.
• The residual is composted and the end product is used to create soil or fertilizers.
• The yearly capacity is 80 000 tons of biowaste and a biogas production of up to 50 GWh.
Sewers Are Not Garbage Bins
Lahti Aqua informs residents, via the media, about not throwing food and other waste into the sewer network, to avoid blockages. The City has an environmental counselling unit and a special eco-van Kaisla, which enables us to advise residents all over the region and at various events. Päijät-Häme Waste Management Ltd distributes a calendar to serve as a waste management information package.
Sustainable drainage systems (SuDS) are important for adapting to climate change and improving the quality of water bodies. About 1 500 kg of phosphorus and 12 000 kg of nitrogen are added to Lake Vesijärvi through stormwater, yearly.
Over the past 10 years, we have constructed about 20 retention ponds or wetlands (Fig. B5). Our SuDS are estimated to reduce nutrient loads efficiently. Green roofs are promoted.
Figure B5. New stormwater retention pond in the Länsi-Hennala area.
Main goals of the Water Management Plan (2010):
• Comprehensive risk management.
• Upgrading and renewing pipeline networks and equipment and their monitoring and management.
• Upgrading and renewing UWWTPs, ensuring sufficient purification levels and energy efficiency.
• Improving the network of separate sewers.
• Connecting 100% of buildings that are in use most of the year (Fig. C1).
• Ensuring good water management for residents outside the public network.
• Processing sewage sludge sustainably and energy efficiently.
• Improving operational reliability during electricity shortages.
• Managing heavy rain events by delaying and planning flood routes.
• Lessening the negative impact of storm waters on water bodies.
One of our future challenges is how to treat microplastics. University of Helsinki is currently researching how to treat storm waters with plant fiber to prevent microplastics discharge.
Lahti Aqua is aiming to lessen leakages by monitoring the condition of pipelines and renewing pipes. Blockages are unclogged with a high-pressure water jet. Lahti Aqua’s Plan for Developing Sewer Network (by 2030) aims to maintain the sewage network in good condition. The annual allocation is 4.5-5 M€.
Urbanization, land use densification and climate change are a reality in Lahti. Heavy rainfall events caused flooding of some locations, including the city centre, in July 2004 and 2018.
Managing heavy rain events will be enhanced by improving the current separate sewer network, and delaying and planning flood routes. If technically possible, the storm water should be infiltrated on site. As a result, loading on sewer networks and water bodies will be reduced, while also enabling groundwater levels to recharge (Fig C2). New developments should consider SuDS or NbS. New retention ponds or wetlands will be constructed in new urban residential areas.
UWWTPs of Kariniemi and Ali-Juhakkala have a sufficient capacity to manage the increased wastewater loads from an increasing population. The current assessment for 2020 is based on data from 2005-2007. Lahti Aqua requires separating property owners’ storm water from wastewater, when pipeline networks are upgraded.
The plan includes an extensive list of measures to improve groundwater quality, but it takes a lot of time. The groundwater body of Lahti can be cleaned to a good state by 2027 and other groundwater bodies by 2021. Measures include:
• Directing gasoline stations and other risky actions away from groundwater recharging areas.
• Rehabilitating quarries immediately after mining has stopped.
• Cleaning and removing old oil tanks.
• Installing additional groundwater protection systems along roads.
• Connecting remaining households to municipal water networks.
• Avoiding further construction on the Salpausselkä I Ridge (Fig. C2, C3).
• 2018, use of EcoMelter (potassium and sodium formate) to replace road salt (NaCl) continues in the centre, increasing costs 250-300 000 € yearly. 2019-2020 area to use EcoMelter will be extended.
We have initiated a project to apply for status as a UNESCO Global Geopark for the Salpausselkä Ridge around Lahti (C3).
Climate change is well-considered in measures for achieving or maintaining the good state of water bodies. Rainfall is expected to increase significantly and winters will be warmer (less snow), resulting in increased urban runoff. Then again, spring flooding from melting snow will probably lessen. Lahti is aiming to manage the heavy rain events by delaying and planning flood routes.
Our Storm Water Management Plan aims to:
• Improve storm water management (i.e. avoid floods and ensure that building foundations remain dry).
• Ensure groundwater quality and recharging.
• Improve storm water quality and reduce negative impacts on receiving water bodies.
• Add biodiversity and increase its value.
• Improve co-operation and knowledge of storm water issues.
• Develop new best practices.
New construction projects in the city must follow the requirements set by the plan.
Several measures are being planned to reduce storm water pollution. The new residential area, within the city centre (Fig. C4), will be built utilizing the recent knowledge of NBS (Fig. C4-C5). Additionally, an auxiliary transport pipeline, which is under construction, will provide the option of redirecting storm water overflows, from the city’s two largest storm water sewers, to nearby constructed wetlands, where adequate capacity exists for their retention, infiltration and filtration . It will be carried out in co-operation with the University of Helsinki’s Department of Environmental Sciences and the Lake Vesijärvi Foundation.
Specific actions and measures are determined yearly and based on the budget, strategies and plans. In 2017, Lahti City Group used 9.6 M€ for water protection and wastewater treatment. Investments were 6.5 M€.