Increasing treatment capacity at an operational wastewater treatment works requires a solution that can be delivered efficiently without compromising accuracy or long-term performance.
At Garnswllt Wastewater Treatment Works, Naylor Concrete’s Sealwall precast tank system was selected for a new primary settlement tank forming a key part of a wider improvement scheme.
Project & Requirements
Dŵr Cymru Welsh Water commissioned Mott MacDonald Bentley to deliver a major improvement scheme at Garnswllt Wastewater Treatment Works in South Wales.
The site serves a predominantly domestic catchment south of Ammanford, receiving flows from several surrounding communities with a total population equivalent of approximately 30,000.
The improvement works were designed to increase treatment capacity, support future population growth and reduce phosphorus concentrations within the final effluent discharged to the Afon Llwchwr. Once complete, the scheme would increase the site’s pass-forward flow from 360 l/s to 431 l/s while reducing pressure on its existing treatment infrastructure.
A key part of the project was the construction of a new 25m diameter primary settlement tank. The additional tank was required to provide greater hydraulic retention and prevent the existing primary settlement tanks from becoming overloaded as flows through the works increased.
The Solution
Mott MacDonald Bentley selected Naylor Concrete’s Sealwall precast tank system for the new primary settlement tank.
Naylor supplied 75 precast Sealwall units to form the 25m diameter, 4m high structure. The units needed to be positioned accurately to achieve a tight tolerance of just 5mm across the completed tank.
Collaboration between the project team, Naylor Concrete and other Mott MacDonald Bentley framework teams allowed lessons from previous tank installations to be incorporated into the design and construction methodology.
Mitigations were designed into the tank to support an efficient and accurate installation, helping the site team achieve the required tolerances while significantly improving the anticipated installation rate.
Sealwall provided:
A robust precast concrete solution for the new primary settlement tank
Consistent dimensional accuracy across the 75 units
A fast and efficient installation process
Support for the project’s demanding construction tolerances
A repeatable solution capable of informing future settlement tank projects
The Outcome
The Sealwall installation progressed significantly faster than originally anticipated. The project team more than doubled the expected number of precast units installed each day, allowing the tank to be constructed in record time.
Despite the tight 5mm tolerance between units, the tank was delivered right first time and passed all testing and commissioning at the first attempt.
The construction methods developed at Garnswllt proved so effective that Mott MacDonald Bentley began developing internal standard design guidance and construction methodology using the project as a reference for future settlement tanks constructed with the Naylor Concrete system.
Now operational, the new primary settlement tank has improved hydraulic performance across the primary treatment stage and reduced overloading of the existing tanks. The wider scheme was completed on programme and within budget, enabling Garnswllt Wastewater Treatment Works to treat a pass-forward flow of up to 431 l/s.
A Proven Precast Tank Solution
The Garnswllt project demonstrates how a carefully planned precast solution, supported by collaboration across the project team, can improve installation efficiency while achieving demanding levels of accuracy.
By combining robust factory-manufactured units with an effective construction methodology, Sealwall helped deliver a durable primary settlement tank on programme and right first time.
Discuss Your Next Project
Planning a new liquid holding tank or wastewater treatment project? Speak to the Naylor Concrete team to discuss your requirements and find out how Sealwall could support your scheme.
Call 01226 320810 or email precast@naylor.co.uk for more information.
