Highways Depot

Location: Highways Depot
Service: Drainage Design and Pollution Mitigation
Completion: Detailed Design – February 2025

Overview

Courous Ltd was appointed to design and deliver a drainage upgrade scheme at the National Highways’ Depot. The existing Class 1 oil interceptor had become non-functional, posing a risk of pollution to the local watercourse. A sustainable solution was needed.

Challenge

The depot’s drainage system was compromised by pipe defects (cracks, holes, and obstructions) and an overloaded wash-down tank that received runoff from both wash-down operations and surface gullies. Without action, the risk of pollution and maintenance issues would remain high.

Our Solution

A comprehensive design package was delivered including:

• Installation of a new Class 1 full retention interceptor (Spell P165) with 165L/s capacity

• Repairs to defective pipework throughout the depot following CCTV surveys

• Upgrades to the wash-down system, including disconnection of gully inflow and addition of an alarm

• New headwall construction at the outfall and ditch regrading for improved flow

• Maintenance path construction for long-term asset accessibility

Outcome

The proposed system ensures:

• Full separation of surface water and wash-down flows

• Improved pollution control through increased silt and oil interception

• Long-term maintainability and monitoring via new alarms and access provisions

• Compliance with CG501 and MCHW standards

Conclusion

This project exemplifies Courous Ltd’s capacity to develop compliant, low-risk drainage solutions for operational sites. By addressing pollution, capacity, and maintenance simultaneously, the scheme delivers sustainable value to National Highways’ estate.