Sizing Sewer Question

[PGB1]

Hello All,

I apologize if this isn't a proper question, but I have confusion about sewer sizing.

There is a compromised area in the sewer under the paved driveway at my house. The servicing people (warranty contract company) accidentally identified the manual backwater valve as the broken section, removed 100 ft-sq of concrete (locator person missed) and removed the valve, installing a 4" Schedule 40 PVC jumper. The compromised part actually is farther down the paved driveway.

They believe that the rest of the sewer is a straight line to the city tap. It is 6" clay pipe. The building drain is 4" cast iron bell & spigot. All above ground piping in the house is 3" or smaller (except the below-roof increases for VTR) The pitch for the 6" isn't known. The building drain looks to be 1/4" per foot. (I forgot to check before back filling)

I did a Fixture Unit Count for the building and came up with 44 fixture units total. (The dishwasher and disposer are in the count even though they drain into the kitchen sink. Didn't know if that is proper)

The one item I don't know how to add to the fixture unit count is the storm water. (Combined storm/sanitary)
Under the basement floor is a network of 4" clay tiles. There is a pair of cleanouts next to each other in the basement floor. I think one of them is where the 4" clay network ties in. I don't know where the outdoor footing drains (also 4" clay) tie in.

WHY ASKING-
If it is a straight pipe from where the 6" begins, is it a good idea to sleeve inside the 6" with 4" schedule 40 PVC, connecting to the 4" building drain?
This will save me thousands of dollars of concrete.

The local plumbing inspector said "I'll ask someone and get back to you" & that many new houses are 4" all the way. So his ruling is pending.

If it's possible to do, does this plan sound reasonable?

Thanks For Sharing Your Knowledge,
Paul

 

[John Gayewski]

If you storm water wasn't tied into your sanitary sewer then yes downsizing would be appropriate.

I'm surprised your storm and sanitary sewer are allowed to be tied together. This is an old practice that is begging outlawed more and more. It ruins storm water that can otherwise be ran to a stream or river.

 

[Sponsor]

 

[PGB1]

If you storm water wasn't tied into your sanitary sewer then yes downsizing would be appropriate.

I'm surprised your storm and sanitary sewer are allowed to be tied together. This is an old practice that is begging outlawed more and more. It ruins storm water that can otherwise be ran to a stream or river.

Thanks John for your reply.

What I don't get is that the storm is tied at the 4". I expected a separate to the 6". The 4" carries sanitary and storm. Odd, isn't it?

The house is over 120 years. The city combined is from the 1920's, I think.
Maybe that's why storm and sanitary were combined. People with sump pumps discharge into the system, too. (Only grandfathered ones.)

New houses on the block are interesting. Their sanitary goes to the city combined in the front street. The storm has to be sent to the rear of the property and into a private catch basin (not connected to city). From there, it flows back to the front of the house to the combined. The pipes are perforated. The hope is that water will percolate into the ground. Unfortunately, we are all on clay.

Sadly, what you said about overflow going to a river is true. After a large rain or sudden snow melt, the local retention field overflows in to the river. Sewage & solids are carried with the overflow.

Thanks Again for your advice,
Paul

 

[John Gayewski]

Thanks John for your reply.

What I don't get is that the storm is tied at the 4". I expected a separate to the 6". The 4" carries sanitary and storm. Odd, isn't it?

The house is over 120 years. The city combined is from the 1920's, I think.
Maybe that's why storm and sanitary were combined. People with sump pumps discharge into the system, too. (Only grandfathered ones.)

New houses on the block are interesting. Their sanitary goes to the city combined in the front street. The storm has to be sent to the rear of the property and into a private catch basin (not connected to city). From there, it flows back to the front of the house to the combined. The pipes are perforated. The hope is that water will percolate into the ground. Unfortunately, we are all on clay.

Sadly, what you said about overflow going to a river is true. After a large rain or sudden snow melt, the local retention field overflows in to the river. Sewage & solids are carried with the overflow.

Thanks Again for your advice,
Paul

Sizing storm systems isn't something I commonly do and it's somewhat complicated. I can't say if downsizing to 4" will work for you, but it sounds like it could be worth it to possibly pay someone locally (or see if the city will) calculate it precisely for you.

 

[BrendanDaniels]

Figuring out sewer sizing can be a puzzle. From my experience, it’s essential to consider your current needs and any future expansions you might have in mind. You don’t want to end up with something too small, especially if you plan on adding more later.
One resource I found super helpful is pm247.co.uk . They have tons of info and advice on this topic, which can help you make an informed decision. Sometimes, getting the sizing right from the start is worth spending a little extra time. It’s much easier than having to upgrade or deal with issues later!