Outfall Pollution Assessment, Stafford Gate
Outfall Impact Assessment for Stafford Gate Development M6 Junction 14
Location: M6 Junction 14, Stafford
Service: Drainage and Water Quality Assessment
Date: July 2025
Overview
We were commissioned to assess the potential water quality and environmental impacts of the proposed Stafford Gate development near Junction 14 of the M6 motorway. The development would introduce a small extension of local highway (Creswell Grove) into the existing National Highways drainage system.
Challenge
The additional road area—totalling just 0.23 hectares—would increase the impermeable catchment draining to outfall SJ9025_1527c. Our objective was to determine whether this change would affect surface water quality, spillage risk, or groundwater conditions, particularly given the nearby Doxey and Tillington Marshes SSSI.
Solution
Using the Highways England Water Risk Assessment Tool (HEWRAT) and a precautionary modelling approach, we assessed both the baseline (existing) and proposed drainage configurations. We applied a highly conservative traffic load across the new catchment area to ensure robustness.
Key assessments included:
HEWRAT modelling for soluble and sediment-bound pollutants.
Spillage risk calculations using LA 113 methodology.
Groundwater risk profiling based on geological and hydrological data.
Outcome
The outfall required mitigation under both pre- and post-development conditions—indicating no additional water quality burden from the development.
Spillage and groundwater risks remained unchanged, with all assessments falling below required environmental thresholds.
The proposed development was deemed environmentally neutral, with no increased burden on the receiving watercourse or nearby protected sites.
Conclusion
Our findings supported the integration of the Stafford Gate scheme into the National Highways drainage network without additional mitigation needs beyond existing requirements. This case exemplifies our expertise in delivering precise, policy-compliant drainage impact assessments for complex infrastructure interfaces.