Ejector Pump System for Urban Townhouse-Feedback Please

[WishIwasAplumber]

Longtime lurker, but new poster. Can someone offer feedback on this ejector system that our sewer authority is proposing for urban water backup? See attachment for details.

For background, our town is very dense (mostly attached rowhouses), 95% impermeable, with tiny old sewer lines (some are still wood!). We are right on the coast, with exposure to massive storms. Henri and Ida which dumped 2-3" in an hour! Our sewer systems backup at 0.8"/hour.

Because of our old sewer lines and extreme storms, the majority of our town's homes have storm water backup from the roof. Main sewer line backs up, so the roof water has no where to go; it pushes up in utility floor drains or outdoor drains, which then flow in under doors.

The sewer authority said they cannot afford to upgrade the sewers, so they are proposing the attached system. In short, there would be check valves to keep sewer water from main line out. Between the check valve and the home, there would be an overflow drain that goes into a pit. The pit would have an ejector pump that connects to the house lateral after the check valve, thus forcing the water from the overflow into the main sewer line.

(I am just a housewife, so please know I never in a million years would have thought I'd be talking about check valves and pits.)

I'm active in our community. Local plumbers and architects are skeptical. I can't find a single person who's installed this before. Our sewer authority said it's new (for us at least) and that no one has done it here yet. So...Any thoughts about whether this will work and what kind of plumber would be able to install this? Any feedback on this system?

For example, many of the house laterals are still clay, so lining them will definitely be something ppl have to consider.

Thank you!

 

[Reach4]

1. Is "Existing Building Drain" just your roof/gutter stuff, or does it include your sink and toilet waste
2. Is that pit in the basement or buried in the front yard?
3. Do you have a separate sanitary sewer and rainwater drainage line running by your house? I will answer that-- no; the drawing says "combined sewer"
4. The pit, if in the basement, will need to be sealed and have a vent through the roof. If this is a big pit in the yard, that roof vent is not needed. That is actually a pretty good system. There will be a tray up top that holds grass, but can be lifted off for inspection and service.

Most places don't let you put gutter water into the sanitary sewer system at all. They want it to go into the yards, which may slowly flow to the street.

You don't want to be the only person NOT doing this, because your sewer lines will become pressurized.

https://www.floodexperts.com/wordpr...4/08/flood-control-and-seepage-prevention.jpg

 

[Sponsor]

 

[WishIwasAplumber]

1-

1. Is "Existing Building Drain" just your roof/gutter stuff, or does it include your sink and toilet waste
2. Is that pit in the basement or buried in the front yard?
3. Do you have a separate sanitary sewer and rainwater drainage line running by your house? I will answer that-- no; the drawing says "combined sewer"
4. The pit, if in the basement, will need to be sealed and have a vent through the roof. If this is a big pit in the yard, that roof vent is not needed. That is actually a pretty good system. There will be a tray up top that holds grass, but can be lifted off for inspection and service.

Most places don't let you put gutter water into the sanitary sewer system at all. They want it to go into the yards, which may slowly flow to the street.

You don't want to be the only person NOT doing this, because your sewer lines will become pressurized.

https://www.floodexperts.com/wordpr...4/08/flood-control-and-seepage-prevention.jpg

Thanks for your reply, Reach4. I see that I forgot the most important detail. Our town mandates all lines, including storm, go to the sewer. And, our sewer is a combined system. I know this is unusual, hence our many issues here. To answer other questions,

1. Yes, "Existing building drain" would include storm and sanitary. Most people have them combined and have one house drain that goes to main sewer. (Hope I'm using the right terminology!)
2. Pit would be buried in "front yard," which for us is usually bluestone or concrete. There would be a grate or manhole cover over it for maintenance.
3. I actually have a separate sanitary and storm line, which combines in the front of the house. But you're right, most people have it combined in their house.
4. Could the pit just vent in the yard? Lots of people have some kind of vent, candy-cane shaped, in their front yards. So it would not look out of place.

What does this mean "You don't want to be the only person NOT doing this, because your sewer lines will become pressurized"? I think it means if you don't have a check valve, you'll get backflow?

So glad you think this is a good system! What are some common pitfalls we should look out for? (For example, many homes here have old clay pipes. I assume we need to line them. Also, many homes connect low to the sewer, so I imagine it would be smart to have the new discharge line connect high.)

Also, I am not exaggerating when I say that no one in town has done this yet. We has consulted the sewer authority, architects, and the town engineer. Our local plumbers are skeptical. So we don't really know where to start to find someone.

Thank again. I will share your reply with my neighbors.

 

[Reach4]

I am not a pro.

4. Could the pit just vent in the yard? Lots of people have some kind of vent, candy-cane shaped, in their front yards. So it would not look out of place.

I think normally the house vents provide at least part of the venting, but the system I am familiar with does not have the candy cane that you describe.

What does this mean "You don't want to be the only person NOT doing this, because your sewer lines will become pressurized"? I think it means if you don't have a check valve, you'll get backflow?

Yes, but even with a check valve, there are still problems. If the water rises to the check valve, even a good normally open check valve will not let your house waste from leaving. But at least it is not other people's stuff coming up. If the check valve is a "normally closed" valve with a hanging flapper, those leak predictably after a while. A solid will keep the flapper from closing all of the way.

One good normally-open valve is probably better than two (redundant) flappers if the electricity goes out, but either can work.

Your proposed system has two flappers with cleanouts I think. But what makes these work ok is that whatever flows back gets added to the pit with the house waste. Then the pump injects the pit contents downstream of the flappers. The pressure helps close the flapper, but also the pump can overcome the leakage with higher flow than the leak.

If the electricity goes off, the pit can accumulate waste for a while. You should stop adding house waste. The capacity of the pit bottom is considerable but still limited.

Also, I am not exaggerating when I say that no one in town has done this yet. We has consulted the sewer authority, architects, and the town engineer. Our local plumbers are skeptical. So we don't really know where to start to find someone.

Find somebody to engineer the setup or somebody to construct?

The pits are usually made in one of two ways. One is concrete blocks, and the other is a pre-cast concrete thing for the walls. Precast costs more, I was thinking due to the need for lifting equipment. But maybe the delivered precast unit itself is the main reason for the extra cost. I think in either case, the bottoms are poured in the systems I have looked at. I expect it could be practical to pour the walls in place.

These systems are usually lower cost alternatives to overhead sewers retrofitted into basements. With overhead sewers, the ground floor and above sewage is re-routed to exit the basement wall near the frost line. Sometimes some sewage is run around the house to join in the front yard. That can avoid a pipe crossing the basement ceiling. Basement waste flows into a sealed septic pit that gets pumped up to join the higher waste at above ground level.
If you don't have basements, then this is a different use.

Whenever you have yard deep digging, remember that you want to end up with 4 to 6 inches of topsoil on top. A lot of subsoil will not support grass growth. I guess that depends on your subsoil.

 

[WishIwasAplumber]

Thanks, Reach 4. I hope you had a good Thanksgiving. I, for one, am thankful for people like you who help strangers!

I read your post several times and will show it to whoever we find to implement this. I finally found an engineer who can draw it and a contractor who has done it in the next town over. Fingers crossed.

 

[Jeff H Young]

what's the skepticism? just do nothing is better ? I suppose I'd put it in most likely city requires it. why not talk to engineer that drew this up?
basically you have a failed over loaded sewer and no one is replacing the whole system so this is the fix either pump or put up with no drainage when it rains

 

[Breplum]

Flawed concept from the start, to have combined storm and sewer. S.F. in CA has this and it is eternally stupid, expensive and expected to pollute the coast with every big storm because there is no way in the world to handle peak storm flow.
Battery back-up pumps for extended storms or automatic generators, on top of the expense of all this improvement...I can't imagine the community doing that.
Better to seek funding to redesign the community infrastructure with separate storm drain system request from a federal or state grant.

 

[Jeff H Young]

Yes replace the entire infrastructure if you have the final say and you aren't the one paying for it. unless you can just dump all the storm drain in the street and not use your drainage system plumbing facilities in home during these events the pump is the only thing you can do as homeowner , until (if ) upgraded system is installed