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Donegan Civil Engineering

Detention Tank and Screened CSO – Darwen WwTW and Clarence Street, Lancashire

A 15.00m diameter caisson detention tank and pumping station with over 1,000m³ capacity, plus a screened CSO chamber underpinned around a live 4.00m tunnel

By: Valentine Donegan

Published: August 6, 2026

Detention Tank and Screened CSO - Darwen WwTW and Clarence Street, Lancashire

Client: United Utilities

Project Description / Main Operations

This project was carried out by V J Donegan & Co Ltd direct for United Utilities, resolving unsatisfactory intermittent discharges at Darwen WwTW and Clarence Street.

Scope and method:

Construction of a 15.00m diameter shaft, sunk by caisson to approx. 15m deep, acting as a detention tank and pumping station with over 1,000m³ capacity for foul water.
Fit-out of the detention tank with 2 storm pumps and a scavenger pump feeding a set of twin 200mm diameter rising mains approx. 200m in length.
Underpinning of a 12.50m diameter shaft to approx. 10m depth around an existing 4.00m diameter tunnel, to act as a CSO chamber, within which a powered screen was installed.
Approx. 500m of open-cut gravity sewers ranging from 450mm to 750mm diameter, up to 4m deep, along with a number of manholes and in-situ reinforced concrete chambers.
Construction of an outfall structure within the embankment of the river.

For More Information, contact us at http://www.donegan.co.uk

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