We use our own groundwater for drinking water. In 2016, 94.8% of water users were connected to the municipal network and subjected to water metering, and the total water consumption was 7.7 Mm3 (approx. 65 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 122 litres/capita/day in 2016. The water supply system is effective. Today, 6.8% 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 0.68 kWh/m3 in 2016 (Fig. A3). Lahti Aqua is monitoring its carbon footprint (20.2 kgCO2/capita/a), which is small, thanks to wastewater treatment energy efficiency.
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 2015, all collected samples complied with the quality standardsof the 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. Some water towers are equipped with UV water purification systems. According to the yearly survey of Lahti Aqua, customer satisfaction is high.
Lahti is partially located on a moraine ridge, which is an important area for recharging groundwater (Fig. C2). Groundwater bodies under and close to the ridge are large. The water table is stable and the quantitative status is good. A Regional Groundwater Protection Plan has been in place, since 2012, to improve the quality.
Wastewater Collecting Systems
Virtually all urban areas have separate sewers for storm water and wastewater. In 2016, Lahti had 756 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) .
Storm Water Management and Floods
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). Currently, we are preparing urban storm water management systems using NBS’s.
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 [4, 5], 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, as a whole .
Quantity of Wastewater
The quantity of wastewater has decreased: 7.1 Mm3 in 2016 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).
Sludge Gasification and Energy Consumption of UWWTPs
Energy consumption, in 2016, was 0.82 kWh/m3 (Table A5), and 15 131 m3 of sludge were generated (dry measure).
The UWWTPs produce biogas (2.6 Mm³ in 2016), which is used for heat production (15.4 GWh). 51% was used at the UWWTPs and about 7.5 GWh was sold to the district heating network of Lahti Energy Ltd.
After anaerobic digestion (and gasification), the sludge is dried in a centrifuge. The dried sludge is sent to LABIO Ltd (9B).
Reducing Water Consumption
The reduction in water consumption is performed by improving metering and appliances, tariff policies, and raising awareness:
Improving Quality of Drinking Water
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 of Regional Groundwater Protection Plan (2012) :
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€.
Maintaining the Network
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 2013-2017, Lahti Aqua has built and is building 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, even if a problem should occur; 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.
The Nastola Municipality Water Utility has been developing the water management system in sparsely populated areas. Over 30 km of water supply trunk lines were built, with an investment of 4 M€. The projects were carried out in cooperation with neighbouring municipalities and towns subsidized by the government. In 2015, 3 km of distribution networks were built, with connections to the trunk lines.
Rescuing Our Sensitive Water Bodies
We have been restoring Lake Vesijärvi, since the mid-1970s, in co-operation with several municipalities, universities and other research organizations [10, 11]. 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. Two books on Lake Vesijärvi and its restoration story have been published (1992, 2010).
River conditions are improved through SuDS. The Porvoonjoki River is now cleaner, due to effective wastewater treatment. 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. We are reducing the negative impact on the Baltic Sea by improving the Porvoonjoki River’s condition.
Further actions to improve water bodies:
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€ :
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 all households and companies, annually. It serves as a waste management information package.
Sustainable Storm Water Management and Treatment
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 storm water, 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.
Water Management Plan
Main goals of the Water Management Plan (2010):
Many of these measures have already been achieved, e.g.: The Storm Water Management Plan, SuDS, connecting areas to municipal networks, upgrading UWWTPs and the sustainable use of sewage sludge. One of our future challenges is how to treat microplastics.
Improvement and Maintenance
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€.
Climate Change and Urbanization
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 and August of 2004.
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 other modern possibilities (e.g. green roofs). Old ditches need to be checked and cleaned or widened, if needed. 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.
Regional Groundwater Protection Plan
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.Discontinuing road salt use on groundwater recharging areas.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).Achieving of groundwater protection goals and measures is monitored by the Groundwater Workgroup.2017, road salt (NaCl) will be replaced with a biodegradable EcoMelter product (potassium and sodium formate) in the centre, increasing costs 250-300 000 € yearly.
We have initiated a project to apply for status as a UNESCO Global Geopark for the Salpausselkä Ridge around Lahti (C3) .
Clean Surface Waters
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 regarding management of storm waters.
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 .
To celebrate Finland’s Centennial year, we donated a new area for protection, the Sammalsillan suo (bog) . The associated nature path has been built to be accessible to everyone. Local residents have volunteered in the protection and restoration project.
The “Jokitalkkari” project will continue 2017-2018.
Investments and Budget
Specific actions and measures are determined yearly and based on the budget, strategies and plans. In 2016, Lahti City Group used 8 962 000 € for water protection and wastewater treatment. Investments were 4 022 900 €.
Additional information:1. Lahti - City of Clean Water video