Motorway ponds data covering the past 24 months
Case reference EIR2025/01365
Received 9 July 2025
Published 25 September 2025
Request
Please will you send me the most recent data covering the past 24 months re; the disclosures made in 7760 7760:
Please will you:
- tell me how many treatment ponds and balancing ponds are located around the M25 to manage motorway runoff
- provide a list of them, including their locations
- tell me when each of them was last maintained, when accumulated sediment was removed and when upstream sediment capture devices such as oil/water separators were last emptied
Response
Please find attached the requested information in the form of a PDF entitled “FOI_Ponds_UPDATE_July2025”.
This update shows the following information:
• Pond name
• Last pond condition inspection date
• Location information (easting and northing)
• Date of the last sediment removal
• Date of the last inspection of the interceptors
• Date of the last clean of the interceptor
Please note that not all ponds require sediment removal due to the design of upstream silt capture devices, for example if the pond is only used for flow or river balancing. Sediment removal is based on condition inspection results.
Some ponds do not have interceptors and these are marked as N/A. This is normally due to the pond being exclusively for flow or river balancing, or are ponds for natural purposes only.
Documents
This is National Highways' response to a freedom of information (FOI) or environmental information regulations (EIR) request.
You can browse our other responses or make a new FOI request.