In summary
- The project forms part of a national programme to extend the life of 32 slow sand filter beds
- A new modular base and raised sandbar system increase filtration depth and reduce maintenance
- The refurbishment supports improved operational resilience in water treatment infrastructure
Project in numbers
67,000 modular porous blocks laid
600mm increase in sandbar height
The need
The existing slow sand filter had reached the end of its operational life. The concrete base limited maintenance options and contributed to a shortened skim cycle. Access was also becoming difficult.
As part of a wider national contract to refurbish 32 filter beds, we were appointed to upgrade the bed and extend its lifespan.
The solution
To improve the maintainability and lifespan of the filter bed, we removed the existing concrete floor and installed 67,000 porous concrete blocks. Compared to traditional poured concrete, the modular design offers faster installation, reduced embodied carbon, and the ability to complete localised patch repairs when needed.
We also raised the sandbar height by 600mm to support a greater volume of sand, increasing processing capacity and extending the skim cycle from 80 to 120 days. To enable this change, we rebuilt the concrete weir wall and replaced its supporting components.
The refurbishment also included high-pressure jetting to clean the filter walls and underfloor drainage, concrete repairs to the outer rim, and the installation of a new access ramp to support safer operation.
Pre and post-work CCTV surveys confirmed that debris had been thoroughly removed before installation began.
The benefits
Our successful gravel redistribution at Thorverton Gauging Station has achieved several benefits including:
- Modular block floor enables targeted future repairs and reduces material waste
- Increased sand depth extends skim cycles and reduces manual maintenance
- Upgrades support safer, more efficient operation of the filter bed
- Reduced embodied carbon through offsite manufacture and modular design
- Improved filtration performance through thorough cleaning and structural restoration
