Coffey is playing a pivotal role in the AMP8 upgrade of Penkridge Sewage Treatment Works (STW), a project designed to secure vital infrastructure for future population growth while protecting local water quality for generations to come.
Located just five miles south of Stafford, Penkridge STW is a medium-sized treatment facility serving a growing community. With a 30% population increase expected by 2038—rising from a population equivalent (PE) of 13,926 to 18,047—the existing site had already begun to experience Dry Weather Flow (DWF) breaches, highlighting the urgent need for capacity upgrades and environmental compliance.
A Collaborative Approach to Value and Innovation
Over the course of six months, Coffey worked in close collaboration with Severn Trent as part of an Integrated Project Team (IPT). This partnership focused on shared ownership and success, embodying our “Do It Together” ethos. The team successfully identified nearly £10 million in opportunities, delivering both programme efficiencies and enhanced value for the client and community.
Scope of Works
The upgrade project includes both immediate construction and forward-looking design elements:
- Modifications to the existing chemical dosing plant
- Construction of a new storm flow bifurcation chamber
- Installation of new storm tanks with cleaning systems and a dedicated wash water booster
- Integration with the existing storm return pumping station
- Site-wide civil and electrical works
In preparation for stricter environmental standards taking effect in December 2026, the outline design also includes:
- A new biofilter distribution chamber
- SAF (Submerged Aerated Filter) feed pumping station and distribution chamber
- Six new SAF units, with de-sludge facilities, access infrastructure, and ancillary pipework
- SAF collection chamber and a new control panel with expandable electrical infrastructure
Project Goals and Environmental Commitments
The primary objective is to ensure DWF compliance as the flow increases from 3,200 m³/day to 4,113 m³/day. This upgrade supports a 13% increase in Flow to Full Treatment (FFT), rising from 133 l/s to 150 l/s by 2038.
More critically, the works will ensure compliance with tightened final effluent permits:
- Total Phosphorus reduced from 1.0 mg/l to 0.75 mg/l
- Ammonia (NH3) from 10 mg/l to 4 mg/l
- Biological Oxygen Demand (BOD) from 20 mg/l to 15 mg/l
- Suspended Solids (SS) from 40 mg/l to 22 mg/l
These changes underscore our commitment to safeguarding local waterways and achieving long-term environmental resilience.
Programme and Investment
With a contract value of £3.28 million (expected to exceed £4 million), the project timeline is as follows:
- Design Phase: August to December 2025
- Construction Phase: December 2025 to October 2026
By integrating early, Coffey and Severn Trent are delivering a smarter, more resilient treatment solution that meets both current and future needs. Our customer-centric approach ensures added value, reduced risk, and meaningful community benefit.
For more information about this project or Coffey’s ongoing infrastructure work in the UK, contact us at 01925 818680 or info@coffeygroup.com.
