Highways Depot
Drainage Design and Pollution Mitigation
Detailed Design – February 2025
- Completed
Project 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.
Challenges & Solutions
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.
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