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Hydrological modelling helps in the search for new well fields

Hydrological modelling helps in the search for new well fields for a water-secure future
Novafos is a large utility company in Denmark that supplies drinking water to the outer-suburban residents of Copenhagen. Due to increased water demands, there is a need to search for suitable locations for new well fields. One such location is on the peninsula of Hornsherred on the island of Zealand in eastern Denmark. Ramboll was tasked to provide insights into the groundwater resources in the area. Using an integrated groundwater model created with DHI’s technology, Ramboll has successfully helped Novafos to find one new well field, and more are on the way.
 
Challenge
Utilities need to search for new well fields to ensure a sustainable and reliable supply of drinking water for residents. This need arises due to various factors such as population growth, increased demand for water, changes in land use, contamination of existing water sources and the impact of climate change on water availability. By proactively seeking out new well fields, utilities can mitigate risks associated with water scarcity. As a major water utility in Denmark, Novafos needed a solution that could identify suitable locations to establish new well fields to ensure the long-term viability of their water supply systems.
 
Solution
Ramboll used hydrological modelling to understand the groundwater dynamics in Hornsherred. They developed a comprehensive fully dynamic MIKE SHE/MIKE HYDRO River (now MIKE+ Rivers) groundwater model spanning 260 km2. By inputting data such as geology, precipitation, evaporation and soil characteristics into the integrated MIKE SHE groundwater model, Ramboll was able to calibrate the model to fit observed groundwater levels and stream discharge, and hence find optimal values for various hydraulic parameters, ex. hydraulic conductivities for the different geological units in the model.
 
The finished model is used to run different abstraction scenarios, helping Novafos to assess catchment areas, potential impacts on the groundwater resource, changes in the groundwater table, phreatic surface variations and their effects on protected natural areas and streams, in line with the requirements of the Water Framework Directive, a European Union (EU) legislation that sets out rules to achieve good status for Europe’s rivers, lakes and groundwater.
Additionally, the model was fed with climate data to predict the future effects of climate change using the RCP 4.5 emission scenario. The RCP 4.5 emission scenario has been described by the Intergovernmental Panel on Climate Change (IPCC) as a moderate scenario in which emissions peak around 2040 and then decline. An ensemble of model runs has been performed based on different regional climate models to assess the long-term sustainability of extracting water from the area, considering factors like recharge rates and the impact of pumping on nearby wells.
 
Results
The model results reveal that due to increased winter precipitation in the future, the groundwater head levels in the limestone aquifer will slightly increase, and hence will not be a problem for the groundwater resource in this area in terms of water quantity. The forecasted climate scenarios also show that the impact of establishing a new well field or increasing the current abstraction is larger than the impact of climate change. By using hydrological modelling with MIKE technology, Ramboll has provided Novafos with valuable insights into the dynamics of groundwater systems, helping them make informed decisions about where to establish new well fields, and facilitated the process of applying for abstraction permits at the municipality.

How Söråker WWTP used a coupled groundwater-sewer model for a comprehensive evaluation with detailed insights 
 
The Söråker wastewater treatment plant (WWTP) in northern Sweden, operated by the water utility MittSverige Vatten, faced significant challenges due to high inflow and infiltration flows, particularly during snowmelt periods. These issues were exacerbated by the village's high groundwater levels, aging infrastructure and anticipated population growth. But by implementing a solution that integrates advanced technology with practical engineering, MittSverige Vatten has gained a detailed and holistic overview of hydrogeology and sewer networks for more efficient reduction of inflow and infiltration.
 
Challenge
Söråker's location on a slope near the Baltic Sea, combined with its glacial till soil composition, naturally led to elevated groundwater levels. Additionally, the village's infrastructure, including basements with drainage connected to the sewer network, contributed to excessive groundwater leakage into sewer pipes. Previous efforts, such as field surveys and scattered pipe relining, provided limited insights into these complex issues, jeopardising the WWTP's treatment efficiency and posing risks to residents and the environment.
 
Solution
In collaboration with DHI, Söraker WWTP implemented a multi-step approach:
 

Development of a coupled MIKE SHE groundwater-sewer model that allows detailed digital investigation of inflow and infiltration from groundwater and stormwater into the sewer network
Calibration of the model against groundwater monitoring points and total inflow to the WWTP
Evaluation of future scenarios involving strategies like deeper ditches, additional drainage and sewer pipe relining
Assessment of scenario impacts on inflow, treatment efficiency and groundwater levels. The integration of MIKE SHE and MIKE+ sewer models enabled detailed, physically based simulations, offering insights beyond traditional methods

 
Results
Söraker WWTP gained actionable solutions for informed decision-making that will enable them to accommodate the need for new housing areas at a reasonable cost and simultaneously reduce environmental impact on surrounding water environments. And by enhancing the operational and environmental efficiency of the existing WWTP, costly investments in upgrading the sewer network can be avoided. The implemented solutions are expected to alleviate the WWTP’s environmental load, enhance water quality and mitigate flooding risks. Results include:
 

An estimated investment savings of EUR 14 million by eliminating the need for costly investments in conventional sewer separation
A 30% reduction in biological oxygen demand (BOD) load to receiving waters, minimising environmental impact
Accommodation of new housing areas within existing WWTP permits thanks to reduced environmental impact from the WWTP


Exploring the potential of counter-current AB process (CCAB) applications in Denmark
Treatment of wastewater is required to reduce the carbon content as well as pollutants in the wastewater to mitigate eutrophication of the receiving water bodies. This process requires significant amounts of energy for pumping and aeration. Harvesting carbon (measured as chemical oxygen demand – COD) in the primary stage at the WWTP could be a cost-efficient way to lower energy requirements while using the removed carbon for biogas production. DHI received funding from the Market Development Fund to develop a new concept for COD harvest and to implement it in the primary stage at Esbjerg East WWTP, Denmark. With input from other Danish utilities, DHI developed the new counter-current AB process (CCAB), which increased COD harvest in the primary clarifier from 30% to 62%.
 
Challenge
The Danish Water and Wastewater Association performs a yearly benchmark of Danish WWTPs, which has revealed that in recent years, an increasing number of utilities have become energy neutral. This trend is expected to continue as it corresponds with local and national political goals. While WWTPs need significant amounts of energy for pumping and aeration, fortunately, utilities can claim major savings by improving treatment efficiency and increasing on-site energy production through anaerobic digestion of the primary sludge.
Existing technologies for increased COD harvest are costly and require high maintenance
 
Two commercially available technologies for increased COD harvest from municipal wastewater dominate the market: fine-mesh sieving (filtration) and chemically enhanced primary clarification. Both offer increased COD harvest compared to traditional methods, but unfortunately include significant downsides. Filtration requires advanced machinery with costly maintenance, while chemically enhanced clarification produces a high amount of inert chemical sludge that does not contribute to biogas production and generates additional load on the sludge handling systems.
 
Solution
Laboratory tests were carried out to determine the potential of CCAB operation before full-scale implementation and during full-scale operation at Esbjerg East WWTP. Good correlation was shown between lab and full-scale results. This allowed DHI to use lab-scale tests as an indicator of COD harvest potential of the technology. Advanced online process control was installed to ensure stable operation and sampling campaigns were performed to determine the actual COD harvest and used as input to model the CCAB process.
 
The modelling software WEST was used to run simulations of the baseline (current) operation of four WWTPs in Denmark. The results were compared to three alternative technologies with primary COD capture. The simulated scenarios included filtration, chemically enhanced clarification and CCAB systems. The endpoints for evaluation and comparison of the different scenarios were: (i) COD load provided for anaerobic digestion, (ii) power consumption for aeration and (iii) external carbon dosing to meet denitrification needs.
 
Results


Higher COD harvestLab-scale tests and full-scale operation showed comparably high COD harvest in the primary stage, from 30% to 62%. This number compares favourably with other commercially available technologies.


Potential for increased efficiency (WEST results)The CCAB process showed a positive impact on the energy production due to a doubling of the COD harvest in the primary stage. Furthermore, removing COD in the primary stage proportionally reduces aeration needs in the biological stage. A comparison of the test period with a similar period during baseline operation showed approximately 40% increased energy efficiency.


Significant savings with short ROI timesThe business cases evaluated favour CCAB operation in three out of four plants. CCAB operation is economically feasible at plants with existing primary clarifiers (ROI &lt; 2 years) but also in cases where primary clarifiers would have to be built (ROI &lt; 6 years). In all three cases, the yearly savings were higher for CCAB compared to any other scenario.



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