BBC: Article on outfall monitoring

[c2R]

I thought it was interesting that there's so little awareness of this: https://www.bbc.co.uk/news/science-environment-68130715

There should be more emphasis perhaps on the merits of new road realignment schemes in the integration of balancing ponds.... it's clear that the part of the M4 in question is old and doesn't have this sort of feature built in, whereas most of the motorways built from the early to mid-80s I'd guess and onwards do mitigate in this way

[RichardA35]

A balancing pond balances and attenuates flow but does not necessarily contribute to pollutant removal unless retention areas and the entry or exit structures are engineered so to do. The settling of sediments and suspension loads can occur as a consequence of slowing the flow however.
The early motorway builds probably have some flow control as the prevailing standard was to attenuate run off to the greenfield run-off rate that would have been present before the road development.
However there was only rudimentary pollution control in the early days, well into the 1990's I would estimate. For example, on the M25 between junctions 7 - 8 on the top of the chalk downs, the run off is directed into the chalk aquifer via deep borehole wells. It was only with the widening project in c. 1996 some 10 years after opening that control structures were added to intercept oils or contain spillages.

[John McAdam]

I thought it was interesting that there's so little awareness of this: https://www.bbc.co.uk/news/science-environment-68130715
[...]

(My bolding.)

I thought the quotes from Jo Shepherd, a a former Environment Agency employee who now works with an organisation called Stormwater Shepherds, were pretty powerful:

"This little stream should be beautiful," Jo says as we look at what the map says is Syd Brook [by the M6 services at Chorley], at this point a murky pool of water topped with foam. "It's absolutely horrific."

When it rains, water from the M6 motorway drains directly into the stream. Jo shows me a plastic bottle full of brownish black water that she gathered during heavy rain the day before.

Her organisation Stormwater Shepherds has found tyre particles and dust from clutch and brake pads in the water.

"Because of the toxicity and the poisons in the sediment I would put this on a par with sewage (pollution) and to be frank, I'd probably put it above sewage," she says.

"Because they're not being monitored, no-one even knows the extent of the pollution and then nobody's doing anything about it. Nobody wants to talk about this."

(My bolding and underlining.)

A very real issue, that people don't want to talk about... because it's difficult and awkward.

[B1040]

It's one of the hidden costs of motor transport.
I'm not sure if there's an easy or cheap solution

[John McAdam]

It's one of the hidden costs of motor transport.
I'm not sure if there's an easy or cheap solution

Neither, I'd think. But that doesn't mean it should just be swept under the carpet and ignored, just because it's inconvenient.

[Ruperts Trooper]

A balancing pond balances and attenuates flow but does not necessarily contribute to pollutant removal unless retention areas and the entry or exit structures are engineered so to do. The settling of sediments and suspension loads can occur as a consequence of slowing the flow however.
The early motorway builds probably have some flow control as the prevailing standard was to attenuate run off to the greenfield run-off rate that would have been present before the road development.
However there was only rudimentary pollution control in the early days, well into the 1990's I would estimate. For example, on the M25 between junctions 7 - 8 on the top of the chalk downs, the run off is directed into the chalk aquifer via deep borehole wells. It was only with the widening project in c. 1996 some 10 years after opening that control structures were added to intercept oils or contain spillages.

One of the issues with more recent road schemes is lack of maintenance of the environmental protection features once the scheme has been built - sometimes the Highways Agency, Environment Agency, the local authority and the water board all deny liability for maintenance and in one instance that I know of, it was down to local residents to inform the authorities of the existence of such features.

[RichardA35]

A balancing pond balances and attenuates flow but does not necessarily contribute to pollutant removal unless retention areas and the entry or exit structures are engineered so to do. The settling of sediments and suspension loads can occur as a consequence of slowing the flow however.
The early motorway builds probably have some flow control as the prevailing standard was to attenuate run off to the greenfield run-off rate that would have been present before the road development.
However there was only rudimentary pollution control in the early days, well into the 1990's I would estimate. For example, on the M25 between junctions 7 - 8 on the top of the chalk downs, the run off is directed into the chalk aquifer via deep borehole wells. It was only with the widening project in c. 1996 some 10 years after opening that control structures were added to intercept oils or contain spillages.

One of the issues with more recent road schemes is lack of maintenance of the environmental protection features once the scheme has been built - sometimes the Highways Agency, Environment Agency, the local authority and the water board all deny liability for maintenance and in one instance that I know of, it was down to local residents to inform the authorities of the existence of such features.

Outfalls on more recent schemes (since mid 1990's) will have been permitted by the Environment Agency. If it's highway run-off then the highway authority should be responsible until it reaches the receiving watercourse. The can be some twists with developers having schemes adopted, uncertain local authority expertise and surface water drainage networks maintained by water companies

[baroudeur]

"This little stream should be beautiful," Jo says as we look at what the map says is Syd Brook [by the M6 services at Chorley], at this point a murky pool of water topped with foam. "It's absolutely horrific."

When it rains, water from the M6 motorway drains directly into the stream. Jo shows me a plastic bottle full of brownish black water that she gathered during heavy rain the day before.

Her organisation Stormwater Shepherds has found tyre particles and dust from clutch and brake pads in the water.

Ah! The lady with bare hands up to the wrist in the liquid she describes.

[Bryn666]

I remember being confused as a child what all the "interceptor" signs on the M65 meant when it opened in 1997. Being an era before I had the internet it took me a long time to work out it was all pollution control. Interestingly the signs have since been replaced by the now more standard PCD signs.

Highway run off is one of those huge externalities that no one really considers. I don't know enough about drainage to pontificate about it but it's another element of serious civils that the "just build a road so I can brrrmm brrrrm go fast cars more importanter than the ecological systems that we need to stay alive as a species" brigade don't appreciate.