Ofwat Chief Executive David Black has written to Wessex Water and South West Water to inform them that the Mendip Quarries strategic resource option (SRO) should continue to receive development funding for Gate three in the RAPID programme.

Image: Mendip Quarries solution schematic

The SRO solution owners Wessex Water and South West Water submitted their standard gate two reports in July 2023 for assessment.

The assessment process has been overseen by RAPID, with input from the partner regulators Ofwat, the Environment Agency and the Drinking Water Inspectorate. The Environment Agency, together with Natural England, have reviewed the environmental sections of the submissions, and provided feedback to RAPID. The Consumer Council for Water (CCW) provided input to the assessment on customer engagement.

The Mendip Quarries solution is being jointly developed by the water companies to provide resilient water supplies to the South West of England by addressing current forecasted resource deficits.

The Mendips Quarries SRO is s a reservoir arising from a re-purposed quarry located in the Mendips hills. The gate two work has concentrated on Torr Quarry, which is located between Frome and Shepton Mallet. The reservoir would have a useable capacity of 28.5 million m³; approximately 33% larger than Wimbleball reservoir. The reservoir would be fed by a combination of groundwater and surface water from an enhanced River Avon abstraction licence, providing a water resource benefit of up to 46 megalitres per day (ml/d). Two treatment and conveyance proposals have been developed:

1. Surface water will be treated to potable standards and transferred to an existing Wessex Water service reservoir, located near Warminster in Wiltshire.

2. Surface water will be treated to raw water discharge standards and transferred to the River Stour in Dorset for subsequent downstream abstraction and treatment to potable water standards at an existing water treatment works (WTW) supplying Bournemouth Water.

The final decision says that further funding should be allowed for the solution to progress to accelerated gate three and that June 2028 has been proposed as suitable timing for gate three.

The solution is chosen in Wessex Water’s and South West Water’s draft Water Resource Management Plans 2024, as a solution on their preferred pathways. However, despite being on a preferred pathway, implementation is delayed due to procurement of the site and that the quarry is still actively used. The solution will not be construction ready by 2030 but can be construction ready by 2030 -2035. Continued funding is required to develop the solution for delivery in time for the planned construction ready date option.

The assessment of the efficient costs as spent on standard gate two activities results in an allowance for this solution of £2.00m (of £2.00m claimed). The Mendip Quarries has therefore underspent its gate two allowance by £3.02m and can take this underspend forward to gate three, increasing the allowance available at gate three to £14.72m.

The assessment of the unit costs of delivering the Mendip Quarries is that they are “reasonable at this stage.”

Gate three timing

Wessex Water have proposed a date for gate three of June 2028 alongside a forward programme of gate four in September 2029, proposed planning application submitted in 2030, solution construction ready in the period 2030 to 2035, and solution operational in 2042. However, the assessment says that for gate four should be scheduled approximately eight weeks after the date when development consent order applications or local planning applications are projected to have been made. This should therefore be in 2030, after the proposed development consent order or local planning application for the solution has been made, not before.

The solution owners are required to meet one Priority Action by 31 March 2024 – namely, to ensure the water quality monitoring plan incorporates all emerging contaminants of concern and provide a water quality monitoring plan including the emerging contaminants to RAPID by 31 March 2024.

Click here to read the final decision document in full.