Establishing on-site sewage facilities (OSSF) for the Municipality of Næstved

Many residents of the Municipality of Næstved will have the option of establishing an OSSF system because the municipality has made a thorough qualitative survey of the groundwater. The financial resources of both residents and utilities are now being put to more effective use – without harming the environment. Sweco was responsible for making the survey and assessing the possibilities for on-site wastewater percolation.


Customer: The Municipality of Næstved and NK Forsyning

Period: 2016

Location: Næstved


The Municipality of Næstved has 4,701 rural properties that need to upgrade their sewage solution to improve the condition of watercourses, lakes and fjords.

Sweco assessed NK-Forsyning's and Næstved Municipality's options of on-site percolation of wastewater from these properties as part of the revision of the municipality's wastewater management plan. This led to the current situation where many properties that were originally supposed to have been connected to the sewer system now have the option of establishing a much less costly solution: an on-site sewage facility.

Based on the assessment, the municipality and the utility have prepared a new administrative basis to enable flexible case processing by the municipality for residents. At the same time, the municipality and the utility now have a common perception and understanding of the options available to residents. This makes it easier to explain which solution is best for them.

In the administrative basis, the statutory 300-metre protection zone around waterworks wells has been widened to a 500-metre zone. As a result, the waterworks will also have the option of establishing new wells near the waterworks in the future.

Sweco supplemented the existing survey of nitrite-vulnerable areas with areas where the groundwater is also vulnerable to household wastewater and other substances. This makes it easier for the municipality and the utility to intensify their efforts to protect the groundwater.

In addition, a map of the expected depth to the groundwater table has been prepared. Together with a screening of soil conditions down to a depth of two meters, this provides an overview of the specific areas of the municipality where on-site percolation and local drainage of rainwater is possible.

Customer quotes

"We experienced that far too many of the properties that were connected to the sewer system should have been able to get a different solution, so we joined forces with the municipality and Sweco to assess the situation. As a result, many of the properties that were originally supposed to have been connected to the sewer system, because that was the only solution, now have the option of establishing an on-site sewage facility instead. This will generate savings of more than DKK 100 million – and this is a conservative estimate."
"Having Sweco review the groundwater surveys and compare them to GIS analyses enabled us to set up specific scenarios, which improved our capacity to make well-founded decisions."