The Solution

In collaboration with Dryp, a pilot project was launched in Kollund in May 2025. A total of 40 sensors were installed throughout the sewer catchment to collect data over a 12-month period.

The objective was to identify both misconnections and groundwater infiltration within the wastewater system, and thereby map where the largest volumes of unwanted water originated.

Before the sensor installation, an initial screening of existing pump station data was conducted across the catchment. This analysis helped identify operational patterns and determine which pumping areas required closer investigation. The screening revealed that some smaller pump catchments were so heavily influenced by rainfall that they could already indicate likely problem areas, while others were not considered relevant for detailed monitoring.

This pre-analysis made it possible to target the sensor deployment more effectively and ensure that measurement points were placed where they would create the highest value and provide the most accurate insights.

The target for the pilot area was to identify and reduce at least 100,000 m³ of unwanted water annually.

The data

The collected data clearly showed that the challenges across the catchment were unevenly distributed and consisted of both misconnections and infiltration.

Overall, Dryp estimates that approximately 150,000 m³ of unwanted water annually has been identified within the catchment, consisting of both misconnections and infiltration.

Key Observations

The analysis showed that the challenges in the Kollund catchment are highly unevenly distributed and vary significantly between areas. Rather than being one single issue, the catchment contains several local problem types that require different solutions.

North of Kollund, Hokkerup was identified as the area with the highest number of misconnections. Here, data indicates that a significant share of the unwanted water originates from incorrect connections between stormwater and wastewater systems, particularly during rainfall events.

In Holbøl, the situation is different, as the primary issue is infiltration. Water enters the sewer system through leaking pipes and manholes, creating a more constant hydraulic load independent of rainfall.

East of Kollund, especially around Østerskov, a combination of infiltration and misconnections contributes to large volumes of excess water entering the system.

Within Kollund itself, conditions vary considerably between subcatchments. Some areas perform well and remain relatively stable, while others experience significant challenges. This highlights how even small geographical differences can strongly influence sewer system performance.

Another important technical observation involved a dual-manhole system, where rainfall events caused unintended exchange between the stormwater and wastewater systems. This led to overflow and cross-contamination between the two systems and is currently being addressed through technical upgrades.

Results and Value

The project made it possible to identify specific problem areas down to street and subcatchment level, enabling Arwos to carry out much more targeted physical interventions.

In addition, the project:

Conclusion

The collaboration between Dryp and Arwos has established a new approach to managing inflow and infiltration in wastewater systems. Where previous efforts were often broad and generalized, this method enables precise and prioritized action based on concrete data.

The most important outcome is not only the identification of approximately 150,000 m³ of unwanted water annually, but the ability to transform data into a clear operational decision-making framework.

The project now continues with a focus on converting these insights into concrete physical interventions across the identified priority areas in Kollund.