# Storm Drain P-Trap?



## plbgbiz (Aug 27, 2010)

I need some insight from you big pipe commercial guys.

I am looking at replacing the storm drains for a parking garage. It ends up at the street connection 3' deep with what appears to be 16" Ductile Iron pipe. The problem is grade. It exits the garage at about 6' deep, runs under some chiller piping that I am not interested in changing, and then there are two street 90's that bring it up to the street tie-in height. The result is about 75' of the piping has standing water and the last 15'-20' is probably completely full. 

If we saw cut the garage, the whole system can be raised enough to get over the top of the chiller piping and eliminate the standing water. But to make that grade work, the last 100' (maybe less) would have to be dead level.


SO...


Other than poor communication between the ground crew, street crew, and engineer, is there a reason for that storm sewer to hold water?

I know having any length of drain pipe sitting level is asking for problems but it cannot be jetted or flushed effectively like it is now. Wouldn't level pipe be better than it standing full like a p-trap? 


Thanks... :blink::blink::blink:


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## supakingDFW (Aug 19, 2014)

With storm I would definitely rather have a flat line than one that is holding water...You're right, that's asking for trouble!...You never know how long that water may sit before the next rain...With no worry of solids or paper running through it, a little bit of a level line shouldn't be a problem...With situations like that, I've even had inspectors give me the OK..


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## Cuda (Mar 16, 2009)

We run into no grade SS lines all the time it seems like they are installed for the most part by excavation contractors who use the cheapest materials they can get away with and the logic that bellies don't matter because if the end outlet is low enough it will still function right. When we see those we recommend replacement but if the cost is too high for the parties that are involved we then will offer a reverse cleanout upstream and set them a maintenance schedule and pull all the debris downstream with the jetter it's there choice . also sometimes the bellie is not super bad and we offer to burst it to a larger size pipe to compat the grade issues.


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## Flyout95 (Apr 13, 2012)

What is the diameter of the main?


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## Unclog1776 (Feb 5, 2013)

I would be that line is half full of mud and debris from sitting full. What storm sewers lack in poop and paper they make up for in mud rock sticks and sometimes even oil.

If you can't make fall I would think a lift station would be in order


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## plbgbiz (Aug 27, 2010)

Flyout95 said:


> What is the diameter of the main?


3 - 300' runs of 6"

First two 6" runs combine to 12"

When it picks up the last run, it increases to 16" for the line exiting the garage to the street main.


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## plbgbiz (Aug 27, 2010)

From a function standpoint, I am perfectly okay with leveling off the the end of the line to keep it above the chiller lines and hit the street on grade. I want to be sure there is not some magic purpose in that existing offset at the end. 

It really just looks like they ran it out roo deep and then had a WTF moment when they got to the street.


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## plbgbiz (Aug 27, 2010)

Not so much a p-trap as it is a riser to get back to city main level.


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## plbgbiz (Aug 27, 2010)

....


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## plbgbiz (Aug 27, 2010)

It has 10 drains connected along each 6" run in addition to picking up drains from the second level. The end-of-line C.O. I am adding. Currently it has no C.O. access for maintenance.

The initial plan was for a pipe burst until we discovered the grade issue. Now it is looking like raising the whole thing up is the best solution.


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## Cuda (Mar 16, 2009)

Sounds like a good job to solve!


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## Flyout95 (Apr 13, 2012)

Yeah, that seems like the best idea.

Running it flat on a 16" line is nothing I would lose sleep over. 

Is there an interceptor/separator anywhere? I've put a few of those in parking garages, might be a way to grab some elevation.


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## jmc12185 (Aug 27, 2013)

It's not done properly now, and your considering doing all this work to redo it so the end result will still not be 100% correct. It may be better but not correct. With all those draining into it and the crap that comes down the line, it should really have proper pitch. Why not consider a lift station like mentioned earlier or maybe sub out the relocation of the chiller lines if that would even help you.

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## Will (Jun 6, 2010)

I'm no storm sewer expert, but would a holding tank(sand/grease trap) work? I'm talking about a big one. Might not gain any grade, but at least all solids would be caught and could be pumped for removal or irrigation purposes?


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## Unclog1776 (Feb 5, 2013)

plbgbiz said:


> 3 - 300' runs of 6" First two 6" runs combine to 12" When it picks up the last run, it increases to 16" for the line exiting the garage to the street main.


 At what point does the system run uphill? Only reason I ask is because a new construction parking garage here would have a separator pit with the thought being fluid leaks out of vehicles would be trapped there. If you could run the entire system into a large separator and drain that to a lift station you could decide your own elevations for the most part

Edit to add: I'm not sure if separators are required in parking garages in your area. Reason being here is our city is two decades into probably a 100 year war against old brick storm sanitary combo sewers. They are very strict about what gets hooked sanitary and what goes storm. 

Most of our brand new storms drain directly to waterways either natural rivers or man made surface run offs.


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## wyrickmech (Mar 16, 2013)

Saw cut and just run everything at .5% your still talking about being lower at the connection point so even if the last part has to go to dead level it's still down hill. Sounds like a good fix


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## plbgbiz (Aug 27, 2010)

The building has survived 30yrs without the separator so I am inclined to leave it out. If it were added, I suppose a job-built concrete box will suffice. Then have an aluminum hatch built. I have a source for that.

Maybe a small septic tank could be used for the separator.


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## PLUMBER_BILL (Oct 23, 2009)

plbgbiz said:


> I need some insight from you big pipe commercial guys.
> 
> <snip>
> 
> ...


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## PLUMBER_BILL (Oct 23, 2009)

*more on old stuff*

Going deeper into this post I found the following ...

I did post on this before but I think it was on PDL or PIPDL and I wrote a comment.

http://books.google.com/books?id=7t...QSBv4KoBA&ved=0CFsQ6AEwCA#v=onepage&q&f=false

Good book from the dead men.


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## justme (Jul 4, 2012)

Do the math and resize the system to see if it was over sized from the get go , you might find you can downsize from 16" to 12" and get the fall you need. One 12" pipe is equal to four 6" pipes . It might be worth a look. It's all going to depend on surface area being served by the system.


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## justme (Jul 4, 2012)

jmc12185 said:


> It's not done properly now, and your considering doing all this work to redo it so the end result will still not be 100% correct. It may be better but not correct. With all those draining into it and the crap that comes down the line, it should really have proper pitch. Why not consider a lift station like mentioned earlier or maybe sub out the relocation of the chiller lines if that would even help you.
> 
> Sent from my iPhone using PlumbingZone


I don't know you so I'm going to be as nice as possible , but a lift station on a storm sewer is a terrible idea , think about it . It's not just the size that would be needed (enormous) its the possibility of the power going out . Then all the bad things that could happen.


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## jmc12185 (Aug 27, 2013)

justme said:


> I don't know you so I'm going to be as nice as possible , but a lift station on a storm sewer is a terrible idea , think about it . It's not just the size that would be needed (enormous) its the possibility of the power going out . Then all the bad things that could happen.


 Was just throwing out other ideas to avoid running the pipe level. Maybe you didn't finish reading that sentence but the last part of it was "like mentioned earlier".

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## jmc12185 (Aug 27, 2013)

And you are correct about the power going out. There's is absolutely nothing you can do to run something when the power is out. Everything just shuts down. Maybe I'll invent something that runs off another form of energy like natural gas to power things when electricity is out.

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## Will (Jun 6, 2010)

jmc12185 said:


> And you are correct about the power going out. There's is absolutely nothing you can do to run something when the power is out. Everything just shuts down. Maybe I'll invent something that runs off another form of energy like natural gas to power things when electricity is out. Sent from my iPhone using PlumbingZone


Like a generator????


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## justme (Jul 4, 2012)

jmc12185 said:


> Was just throwing out other ideas to avoid running the pipe level. Maybe you didn't finish reading that sentence but the last part of it was "like mentioned earlier".
> 
> Sent from my iPhone using PlumbingZone


Maybe we should just stick with gravity drainage when it comes to storm waste you think.


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## jmc12185 (Aug 27, 2013)

Will said:


> Like a generator????


 Yes, like a generator.... I was being sarcastic.

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## plbgbiz (Aug 27, 2010)

justme said:


> Do the math and resize the system to see if it was over sized from the get go , you might find you can downsize from 16" to 12" and get the fall you need. One 12" pipe is equal to four 6" pipes . It might be worth a look. It's all going to depend on surface area being served by the system.


Actually the exterior storm sewer that ties into the main after all leaders are connected is 15"

I recalculated the load and verified 15" is right on the money.


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## david thompson (Sep 18, 2014)

t are involved we then will offer a reverse cleanout upstream and set them a maintenance schedule and pull all the debris downstream with the jetter it's there choice.


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