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IS THIS A VALID SOLUTION TO A LOCAL DRAINAGE PROBLEM?
Carlh93
Posts: 7 Forumite
in Techie Stuff
I'm not sure if what follows is really "techie stuff", but I can't find a topic heading any closer to this subject. I can't find any "drainage forum" via Google, either, which seems surprising.
Our home connects to the local sewer as follows:-
1. From the inspection chamber ("manhole"), where our connection to the sewer starts, to a gravity feeder to the main gravity sewer.
2. This feeder, like two others in our section of the local sub-system, connects at about 90 degrees to the main sewer pipe, which also depends on gravity flow.
3. That pipe terminates at a pumping station which, as are the pipes, is the property of the sewerage division of one of the large utility companies.
4. The station pumps the sewage into a rising main (pipe under flow pressure), which eventually empties into one of the main public gravity sewers serving the town.
Our local system
This was originally a "private" system. Some years ago, national legislation was passed obliging the sewerage divisions of the regional water companies (eg, Anglian Water, Sever-Trent Water, etc) to adopt these systems.
The relevant utility is planning work on the connection of "our" feeder sewer to the main sewer. There are ten domestic connections altogether, five to one and five to the other side of this pipe.
These connections serve properties in two parallel cul de sacs. The feeder runs under five of the ten back gardens (of which ours is one) close to the back boundaries. This is not the usual position for such a pipe, but the builder who developed this area well over fifty years ago laid the whole system out in this way. So all of the main sewer into which the total three feeders drain, apart from its end section at the pumping station, also runs under back gardens. We are the fourth house on the descending gradient followed by "our" feeder. The fifth house, the last in the road connected to this feeder, has both feeder and main sewer running at 90 degrees to each other via some sort of tee, with an angled leg, under its back garden.
Apparently (not to our knowledge), householders at the low end of this feeder - though not, as far as I know, the owner of the fifth house on our side of the road, which has the lowest connection level on our side of our road - have complained to the water company about "flooding", which seemed to mean their drains ceasing to work due to periodic backing up.
As i understand the situation (we have lived here for nearly 45 years), the reported "flooding" is not due to any inadequacy in the pumping station, nor in the feeders, but to the flow capacity of the main sewer. This pipe, which the water company's plan shows as a 6" (150 mm) was fully surveyed by camera in 2000, and, I understand, reported to be a 4" (100 mm), like the feeders, in sound condition, but to have some considerable dips in its half-mile run. The sewerage pipes are not clay, but pitch fibre. This is a semi-plastic material, so can get crushed by the weight of the wet local clay subsoil without breaking. Its jointing is old-fashioned, so it is prone to leaking, allowing ground water to run into it under its own pressure when the water table is high.
As I have said, I was unaware of "flooding" complaints apparently having been made to the water company by some of my neighbours. We ourselves do experience, very occasionally, backing up from our feeder. We are not normally aware of this, but it does cause sewage water to stand in our inspection chambers - visible if I lift a cover. If the level in the chambers rises well above the inverts it pushes air back in the pipe from our downstairs WC, which is connected direct to the drains via a slow bend. This connection normally vents through the open-topped main (and sole) soil pipe: the one for the upstairs WC etc, which empties into the last of our three chambers. That chamber leads directly to the feeder. If that venting route back is blocked by a sufficiently high sewage level in all three chambers, this can cause the water in the trap of the downstairs WC to rise in the bowl. We do not experience sewer smell when this happens. And it is a very rare occurrence.
We consider this to be a minor nuisance only, caused by the flow inadequacy at peak times of the main sewer. As for the people who have complained about "flooding", there is only one other connection to the feeder as low down its flow path as ours, and only two that are lower. One of the latter is the fifth house in our road. I am baffled that none of these three neighbours has mentioned this problem to us if they have been affected.
The water company may, like me, believe that the state of the main sewer is the underlying cause of the problem, but the nature of the remedy which they have planned suggests that they are reluctant to undertake the huge amount of work, plus disruption to gardens, needed to renew/upgrade the main pipe, which is about half a mile long.
THE WATER COMPANY'S PLAN
I found out about this by chance when a man from the water company rang at our door last week, wanting access to the back garden at the fifth house in the road to check if there was a manhole there over the main sewer. His plan showed one. Our neighbour is usually our during the day, and was on that occasion. We know her well, so, having satisfied myself of the bona fides of the man, I showed him how to access her back garden (there is no locked gate), and kept an eye on him while he looked at the area where a manhole would be expected to be. He could not see one. It may have been hidden by a shed, or by a pile of old fence panels.
The plan that he described is to fit a one-way valve into the low end of the feeder pipe, just before it joins the main pipe. I was shown his copy of the plan, but this gave no detail. He said that this valve would be fitted into the outflow side of an (underground) chamber larger than a normal inspection chamber. When the main sewer pipe backed up, the valve would close, so sewage would not back up in the feeder and the domestic connections to it.
The man seem to have only modest technical and local knowledge. When I mentioned, if the main pipe flow became for any considerable time inadequate to take the inflow from the feeder, the risk that the holding tank would fill up, and simply delay the moment at which the domestic connections to it backed up, he assured me that this had all been calculated so that a "large enough" tank would be installed.
When we parted company I repeated that I was sceptical about the viability of the plan that he had described. I imagine he did not report what I had said when he returned to his depot because it appears that the plan is to go ahead as he described it. Or he did report what I said, and my comments were brushed aside?
But how large is large enough?. The man could not tell me the tank's planned capacity, nor how this had been calculated.
Before I contact the water company I need some informed opinion on whether or not my scepticism is well founded:-
a) As already mentioned, the main sewer flow may not recover before the holding tank is full. If this happens, the properties connected to the feeder will have inoperative drains, which is illegal because it is a health hazard.
b) When the proposed one-way valve closes, the much more numerous properties connected to the other two feeders will experience backing up of their own drains sooner than at present because the relief capacity provided by one of the three feeders (ours) is closed off. A few local properties (along the ends of the two cul de sacs) are connected direct to the main sewer, so they will also experience, sooner, more severe backing up resulting from the inability of sewage building up in the main pipe to flow back up our feeder.
The proposed plan may, or may not in practice, definitively improve the holding capacity of our feeder, but it does appear to reduce the holding capacity of the whole system once our feeder is closed off.
c) The water company man emphasised that the plan would not improve the backing-up problem for a small number of properties (the ten already mentioned, of which ours is one) at the expense of others. It had been drawn up with due diligence, he said. I am not convinced by this optimism. Nor am I convinced, in extreme conditions, where the holding tank over-filled with sewage rom our ten connections to the relevant feeder, that we would be better off than we are now. Indeed, as mentioned above, I worry that we could be worse off.
Please may I have some informed opinions on this from technically qualified and interested readers?
Our home connects to the local sewer as follows:-
1. From the inspection chamber ("manhole"), where our connection to the sewer starts, to a gravity feeder to the main gravity sewer.
2. This feeder, like two others in our section of the local sub-system, connects at about 90 degrees to the main sewer pipe, which also depends on gravity flow.
3. That pipe terminates at a pumping station which, as are the pipes, is the property of the sewerage division of one of the large utility companies.
4. The station pumps the sewage into a rising main (pipe under flow pressure), which eventually empties into one of the main public gravity sewers serving the town.
Our local system
This was originally a "private" system. Some years ago, national legislation was passed obliging the sewerage divisions of the regional water companies (eg, Anglian Water, Sever-Trent Water, etc) to adopt these systems.
The relevant utility is planning work on the connection of "our" feeder sewer to the main sewer. There are ten domestic connections altogether, five to one and five to the other side of this pipe.
These connections serve properties in two parallel cul de sacs. The feeder runs under five of the ten back gardens (of which ours is one) close to the back boundaries. This is not the usual position for such a pipe, but the builder who developed this area well over fifty years ago laid the whole system out in this way. So all of the main sewer into which the total three feeders drain, apart from its end section at the pumping station, also runs under back gardens. We are the fourth house on the descending gradient followed by "our" feeder. The fifth house, the last in the road connected to this feeder, has both feeder and main sewer running at 90 degrees to each other via some sort of tee, with an angled leg, under its back garden.
Apparently (not to our knowledge), householders at the low end of this feeder - though not, as far as I know, the owner of the fifth house on our side of the road, which has the lowest connection level on our side of our road - have complained to the water company about "flooding", which seemed to mean their drains ceasing to work due to periodic backing up.
As i understand the situation (we have lived here for nearly 45 years), the reported "flooding" is not due to any inadequacy in the pumping station, nor in the feeders, but to the flow capacity of the main sewer. This pipe, which the water company's plan shows as a 6" (150 mm) was fully surveyed by camera in 2000, and, I understand, reported to be a 4" (100 mm), like the feeders, in sound condition, but to have some considerable dips in its half-mile run. The sewerage pipes are not clay, but pitch fibre. This is a semi-plastic material, so can get crushed by the weight of the wet local clay subsoil without breaking. Its jointing is old-fashioned, so it is prone to leaking, allowing ground water to run into it under its own pressure when the water table is high.
As I have said, I was unaware of "flooding" complaints apparently having been made to the water company by some of my neighbours. We ourselves do experience, very occasionally, backing up from our feeder. We are not normally aware of this, but it does cause sewage water to stand in our inspection chambers - visible if I lift a cover. If the level in the chambers rises well above the inverts it pushes air back in the pipe from our downstairs WC, which is connected direct to the drains via a slow bend. This connection normally vents through the open-topped main (and sole) soil pipe: the one for the upstairs WC etc, which empties into the last of our three chambers. That chamber leads directly to the feeder. If that venting route back is blocked by a sufficiently high sewage level in all three chambers, this can cause the water in the trap of the downstairs WC to rise in the bowl. We do not experience sewer smell when this happens. And it is a very rare occurrence.
We consider this to be a minor nuisance only, caused by the flow inadequacy at peak times of the main sewer. As for the people who have complained about "flooding", there is only one other connection to the feeder as low down its flow path as ours, and only two that are lower. One of the latter is the fifth house in our road. I am baffled that none of these three neighbours has mentioned this problem to us if they have been affected.
The water company may, like me, believe that the state of the main sewer is the underlying cause of the problem, but the nature of the remedy which they have planned suggests that they are reluctant to undertake the huge amount of work, plus disruption to gardens, needed to renew/upgrade the main pipe, which is about half a mile long.
THE WATER COMPANY'S PLAN
I found out about this by chance when a man from the water company rang at our door last week, wanting access to the back garden at the fifth house in the road to check if there was a manhole there over the main sewer. His plan showed one. Our neighbour is usually our during the day, and was on that occasion. We know her well, so, having satisfied myself of the bona fides of the man, I showed him how to access her back garden (there is no locked gate), and kept an eye on him while he looked at the area where a manhole would be expected to be. He could not see one. It may have been hidden by a shed, or by a pile of old fence panels.
The plan that he described is to fit a one-way valve into the low end of the feeder pipe, just before it joins the main pipe. I was shown his copy of the plan, but this gave no detail. He said that this valve would be fitted into the outflow side of an (underground) chamber larger than a normal inspection chamber. When the main sewer pipe backed up, the valve would close, so sewage would not back up in the feeder and the domestic connections to it.
The man seem to have only modest technical and local knowledge. When I mentioned, if the main pipe flow became for any considerable time inadequate to take the inflow from the feeder, the risk that the holding tank would fill up, and simply delay the moment at which the domestic connections to it backed up, he assured me that this had all been calculated so that a "large enough" tank would be installed.
When we parted company I repeated that I was sceptical about the viability of the plan that he had described. I imagine he did not report what I had said when he returned to his depot because it appears that the plan is to go ahead as he described it. Or he did report what I said, and my comments were brushed aside?
But how large is large enough?. The man could not tell me the tank's planned capacity, nor how this had been calculated.
Before I contact the water company I need some informed opinion on whether or not my scepticism is well founded:-
a) As already mentioned, the main sewer flow may not recover before the holding tank is full. If this happens, the properties connected to the feeder will have inoperative drains, which is illegal because it is a health hazard.
b) When the proposed one-way valve closes, the much more numerous properties connected to the other two feeders will experience backing up of their own drains sooner than at present because the relief capacity provided by one of the three feeders (ours) is closed off. A few local properties (along the ends of the two cul de sacs) are connected direct to the main sewer, so they will also experience, sooner, more severe backing up resulting from the inability of sewage building up in the main pipe to flow back up our feeder.
The proposed plan may, or may not in practice, definitively improve the holding capacity of our feeder, but it does appear to reduce the holding capacity of the whole system once our feeder is closed off.
c) The water company man emphasised that the plan would not improve the backing-up problem for a small number of properties (the ten already mentioned, of which ours is one) at the expense of others. It had been drawn up with due diligence, he said. I am not convinced by this optimism. Nor am I convinced, in extreme conditions, where the holding tank over-filled with sewage rom our ten connections to the relevant feeder, that we would be better off than we are now. Indeed, as mentioned above, I worry that we could be worse off.
Please may I have some informed opinions on this from technically qualified and interested readers?
0
Comments
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Does not matter what we think the drains belong to the water company and they will carry out work that their engineers deem necessary to resolve the problem.
If you have concerns at the proposed solution having spoken with the engineer when he carried out an inspection (and taking into accounts his comments) then there is nothing stopping you contacting them and expressing your concerns.
They may actually listen to you but they are not interested in the sort of comments you may get on the internet. We are only expressing OUR PERSONAL opinions.
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Have you tried turning it off and then back on again???Drinking Rum before 10am makes you
A PIRATE
Not an Alcoholic...!0 -
Thank you for taking the trouble to reply, Grey-Critic,
Indeed I do intend to write to the water company to ask questions/express my concerns.
Of course, if their modification to the system causes more/different problems, they will be responsible. But getting things put right then might be a struggle - or worse.
As an interested party who is dubious about the validity of their "quick fix" solution (as I interpret their plan) I need to make them aware of my concerns.
But are my concerns justified - i am not a sewerage engineer?
So, before I write, it would be useful to have some informed objective opinion on whether their solution to the problem is one known to work well, or if my queries//concerns are rational and justified.
That's why I posted on MSE. I couldn't find an alternative forum with a more focussed remit.0 -
Try asking here.... Drainage - No.1 U.K. Professional Trade Forum, Plumbing, Gas, Electric, Tiling and Joinery Forum (uktradesforum.co.uk)Drinking Rum before 10am makes you
A PIRATE
Not an Alcoholic...!0 -
Thanks for your attempt to help.
To post on that forum I had first to register.
Registration required my email address which is ------@gmail.com. Error message stated "this email address not used on this forum".
Not very helpful. No explanation. Wonder if it accepts only addresses which show on a list of registered plumbers? I'm not a trader, and have never been a registered plumber!
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Drinking Rum before 10am makes you
A PIRATE
Not an Alcoholic...!0
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