PCD site
Case reference EIR2024/00734
Received 5 August 2024
Published 10 September 2024
Request
Response
Information provided
1. Please can you confirm that this site is to collect road runoff from the A34 and filter it before it is released into the river Kennet?
Road runoff from the A34 is passed through the flow attenuation and treatment system at this location before discharge to the River Kennet. 3 As-built construction drawings are attached, titled:
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Drawing 003/RC/C/616/AB
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Drawing 003/RC/C/665/AB
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Drawing 003/RC/C/679/AB
Your description suggests there is a "concrete lined sediment collection pond" then a pond with reeds. For clarity, initial removal of silt occurs in a rectangular inlet chamber/silt trap located at the upstream end of a detention pond. There is only one pond. Please refer to drawing 0003/RC/C/665/AB. Also the detention pond is not designed as a reed bed, though reeds may grow within it.
2. Is there a separate silt collection pond?
Please refer to our response to question 1.
3. What maintenance, such as periodic emptying is defined in the design of the silt collection pond?
The requirement for pond maintenance is that the silt and all material that could impair operation is cleared every ten years, as per GM 701 - Asset Delivery Asset Maintenance Requirements.
Ponds are inspected every two years in accordance with the Required Level of Service (RLOS), Maintenance Requirements Plan (MRP) and GS 801 - Asset Delivery Asset Inspection Requirements.
4. Does this maintenance schedule for the silt collection pond form part of the license granted to you by the Environment Agency to discharge into the river Kennet?
There is no licence or permit for the discharge, nor is one required. Under Section 12(1) of the Environmental Permitting (England and Wales) Regulations 2016 (EPR) UKSI 2016/1154 it is not permitted to cause or knowingly permit a water discharge activity or groundwater activity, except under and to the extent authorised by an environmental permit.
The full definitions of 'water discharge activity' and 'groundwater activity' are given in Schedules 21 and 22 of the EPR respectively though they are essentially the discharge of pollutants directly or indirectly into surface waters or groundwater. However, road authorities in England and Wales are exempt from the need to apply for an environmental permit to discharge road runoff by virtue of the Highways Act 1980 and The Groundwater (England and Wales) Regulations 2009 UKSI 2009/2902. If pollution is occurring, the Environment Agency (in England) can serve a notice for the requirement of an environmental permit or serve an enforcement notice under Section 36 of the EPR.
5. When was this maintenance on the silt collection pond last carried out?
The inlet chamber/silt trap was inspected last on 3 April 2023 and no maintenance was required.
6. What maintenance, such as periodic emptying is defined in the design of the larger reed bed pond?
Please refer to our response to question 3.
7. Does this maintenance schedule for the larger reed bed pond form part of the license granted to you by the Environment Agency to discharge into the river Kennet?
Please refer to our response to question 4.
8. When was this maintenance on the larger reed bed pond last carried out?
The last inspection of the detention pond and ancillary items was in April 2023 and Condition rating was recorded as service level 2. Condition service level 2 is defined as "Superficial deposits with no loss of performance" ( CD 535 Table 3.4). Given that the inspection found no loss of performance, no maintenance was undertaken.
9. What regular monitoring do you do on this site? When was this last carried out?
There is no requirement to undertake water quality monitoring (sampling) at this location. In general, water quality monitoring is not carried out on a regular basis at our outfalls. Maintenance inspections of the pond are discussed in response to question 3.
10. Do you test the water in the ponds for pollution? When was this last carried out?
Water quality monitoring of the water in the ponds is not undertaken. The ponds are designed to reduce the pollutant load reaching the watercourse downstream.
11. Do you test the water leaving the ponds for pollution? When was this last carried out?
There is no requirement to undertake water quality monitoring of our outfalls unless there is a known pollution event within the highway drainage catchment.
12. Are the Pollution Control Devices purely used in the event of a pollution incident on the road?
The oil interceptor, silt trap, grass filter and pond at this site could be regarded as 'Pollution Control Devices' for routine runoff in that they are devices to control/reduce the pollutant load. However, the term 'Pollution Control Device' is generally used to refer to a device used to contain a spillage incident before it can reach the natural watercourse.
At this location there is a penstock upstream of the oil interceptor and a second penstock at the pond outlet chamber. This provides two opportunities at this location to contain the spillage before it reaches the river. It is unlikely that the penstocks would be used other than to contain spillages.
13. Are the Pollution Control Devices ever used during times of high rainfall and flooding to prevent runoff entering the river?
The PCDs (penstocks) are not used in these circumstances. The pond provides storage capacity for reducing peak runoff flowrates during storm events as shown on drawing 0003/RC/C/679/AB.
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