The Coal Authority identified a risk from rising mine waters to an aquifer, which provides drinking water each day to an estimated 30,000 people in the area.
Risks and challenges
The aquifer was particularly vulnerable because of the potential for mine water to rise through open mine shafts, or natural fissures and faults in the coal measures, leading to irreversible contamination.
The mine water contains more salt than sea water, which is known as hypersaline, and would significantly diminish the quality of the drinking water if mine water levels had remained uncontrolled.
A unique solution
This project was particularly challenging due to the:
quality and quantity of the mine water
limited availability of land
sensitive location, near a local nature reserve on the Durham Heritage Coast
local transport links, that include a rail line crossing and a nearby road
These factors made it impossible to follow our usual practice of constructing passive lagoons and reed beds.
To protect the aquifer a state-of-the-art active chemical treatment plant was constructed. This is housed in a building that has been designed to fit in with the local development. We recycled 89% of the waste generated during the construction of the plant, which was approximately 135 tonnes of material.
Each year the scheme treats approximately 2,200 million litres of mine water.
In early 2016, 192 solar photovoltaic panels were installed on the roof of the main building at the Dawdon treatment scheme.
The panels produce 50kw of electricity each hour and this electricity is being used to off-set the costs of pumping the mine water on site.
In 2011, heat exchangers coupled to a domestic heat pump were installed to capture the heat from the mine water.
The heating and hot water are provided to the offices, workshops and crew rooms, which form part of the treatment facility.
These incentives take us a step closer to reaching our vision of a zero cost mine water treatment scheme.