***LOW PRESSURE SEWER INFORMATION DESPARATELY NEEDED***

[Norton1974]

I've done some pretty extensive research and believe I'm educated but professional validation is needed. My town has a low pressure, sealed, grinder pump system. It currently has back pressure/back flow on a consistent basis up through the laterals and right into the house to the only check valve in the system directly at the grinder pump. My lateral now has a leak, I understand that this would be my responsibility under normal circumstances. The leak due is traveling uphill against gravity and back into the home, its quantity far exceeds the 2 occupants internal usage of all water from the home. With the current rate of backflow/backpressure, the lateral is being taxed due to unregulated pressures. I believe that this situation makes the municipality liable at least to some degree. They fully admit to the backflow/backpressure but have denied any accountability by claiming these systems have backflow/backpressure by design. My understanding from common sense, research done, and general discussions is that this is 100% incorrect and goes against the purpose of the system as a whole. Am I correct that there is a minimal one direction fps flowrate necessary just for the self scouring aspect, and that once the grinder expels the slurry through the lateral that the lateral should not have anything coming back from the main? Even without a leak would the temperature difference from coming from outside back in not be a condensation and therefore moisture and mold catalyst. I've also attached the document I sent the Municipality to explain the situation and process, yet the claim is as said, PART OF THE SYSTEM BY DESIGN....Are they correct???

 

[swazimatt]

i am not sure what the design standard is for your location, but all the LP sewer systems I have been involved in have a boundary kit . This includes a non-return valve so if the lot owner's pipe develops a leak they would be able to isolate their section of pipe (within their property) and repair it

The system design will have back-pressure by design as pumps will be discharging into a common rising main while other pumps are pumping. Note, this is back pressure not back flow (which seems to be your issue). There should be no back flow
Even a system without a boundary kit (and no leak) should remain fully charged (if there is a check valve at the pump) ie full of sewage, until the pump starts up again. the portion of rising main from your pump to the junction with the common rising main should otherwise have zero flow and just sit there until you run the pump.

 

[bimr]

Not sure what you have going on as you haven't presented the equipment details.

Most of these systems have a grinder pump with 85 psi discharge pressure. You should have a check valve adjacent to the grinder pump that prevents the backflow.

If you have a leak in the lateral, it would appear that water would leak out of the lateral or sump pit, not flow back into the residence.

Suggest that you call a licensed plumber familiar with these systems.

 

[zelgar]

The only times I've heard of raw sewage backing up into houses/basements is when sewer lines are getting more water into the system than can be handled by the lift stations. This typically happens to areas that are designed to be 100% sanitary sewers but there is an inflow/infiltration problem during precipitation events (e.g., precipitation is getting into the system and overwhelming the sewer capacity). I guess this could also happen with a grinder pump, especially if it's overwhelmed or clogged. Has anyone evaluated the grinder pump to assure it is working properly and not clogged? Does every house have a grinder pump or are there many connected to it.

The sewer line that most laterals connect to are not a pressurized system since they typically rely on gravity flow. Once they reach a lift station, then they could be a pressurized system, but you would normally not connect a lateral to the force main.

Finally, I would contact your neighbors and see if they're having the same problem, and if so, how did they get things fixed.

 

[bimr]

The only times I've heard of raw sewage backing up into houses/basements is when sewer lines are getting more water into the system than can be handled by the lift stations. This typically happens to areas that are designed to be 100% sanitary sewers but there is an inflow/infiltration problem during precipitation events (e.g., precipitation is getting into the system and overwhelming the sewer capacity). I guess this could also happen with a grinder pump, especially if it's overwhelmed or clogged. Has anyone evaluated the grinder pump to assure it is working properly and not clogged? Does every house have a grinder pump or are there many connected to it.

The sewer line that most laterals connect to are not a pressurized system since they typically rely on gravity flow. Once they reach a lift station, then they could be a pressurized system, but you would normally not connect a lateral to the force main.

Finally, I would contact your neighbors and see if they're having the same problem, and if so, how did they get things fixed.

Suggest you review one of the grinder pump systems before you respond.

The poster is describing a grinder pump system, not an overhead sewer. These grinder pump systems consist of a 1.5" lateral from the residence that is connected to a 2-3" diameter manifold that conveys the sewage away. The sewage is eventually deposited in a manhole or lift station.

https://eone.com/images/files/eone-fairfield-glade-case-study-informed-infrastructure.pdf

 

[pointsman]

If I'm reading your post correctly, the grinder pump and its check valve are located in your house, and the lateral connects to the outlet of the grinder pump?

Grinder pumps are necessary when the downstream piping is pressurized. Otherwise, your lateral would not have a pump and your seweage would flow by gravity. Because the downstream sewer is pressurized, your lateral is pressurized and there is backpressure at your pump, regardless of whether there is flow or not. The backpressure is normal and your lateral is normally pressurized.

Without more description it's hard to tell with certainty, but I'm inclined to agree with the city that the lateral is designed to be pressurized. The leak would therefore be your responsibility.

From what you've described here, you have no evidence to assert that the lateral was taxed due to unmanaged pressures. In order to assert this you would need to take some pressure measurements.

 

[swazimatt]

If I'm reading your post correctly, the grinder pump and its check valve are located in your house, and the lateral connects to the outlet of the grinder pump?

Grinder pumps are necessary when the downstream piping is pressurized. Otherwise, your lateral would not have a pump and your seweage would flow by gravity. Because the downstream sewer is pressurized, your lateral is pressurized and there is backpressure at your pump, regardless of whether there is flow or not. The backpressure is normal and your lateral is normally pressurized.

Without more description it's hard to tell with certainty, but I'm inclined to agree with the city that the lateral is designed to be pressurized. The leak would therefore be your responsibility.

From what you've described here, you have no evidence to assert that the lateral was taxed due to unmanaged pressures. In order to assert this you would need to take some pressure measurements.

I wrote this yesterday and accidentally closed the tab before sending it!

As mentioned previously the system should be designed with a boundary kit. This is a chamber that sits on the lot connection (or lateral from pump to common/council rising main) and is a requirement of LP sewer systems here and should be included as part of good design. the chamber houses an isolation valve, a pump out connection and a check-valve. While the LP system will always be pressurized there should never be flow from the council system into the public system.
It sounds like the leak happened near the pump (within the private portion of the LP system) however if the pump was off and flow was backwards to the leak it should at most only have been the ww within the connection (pipe contents from pump to boundary kit). If it was more than this it sounds like one of 2 things have happened.
1. the LP system was designed without a boundary kit (or check valve on the boundary)
2. the boudary check valve is faulty and not closing on backpressure

The fact that @Norton1974 was able to repair the pipe burst indicates that there is at least an isolation valve downstream of the pump. possibly then a boundary kit with a faulty check valve

Here the boundary kit is owned by council and sits within the road reserve. (this is so they can close it when they are working on the common rising main). In your situation you would have to find out who is responsible for the boundary kit (and check valve) or ask the council why they have allowed a system without a check valve at your boundary

your pipe burst is also a bit concerning. The LP pumps generally pump up to 80m head, if the pump is able to pump (which it obviously is) you may want to confirm the lateral is the correct pipe pressure class to sustain at least 10bar

But the key here is that flow in a rising main of any sort should only flow one direction. If it is flowing backwards something is wrong