Crossing Streams

[HVACMech]

Alright, here is a fun one. Had a client say they need some help redesigning their storm water system. They had recently been flagged by the city for putting too much storm water in their sanitary sewer system. In my head I snickered, because I feel like the term "too much" and "any at all" are interchangeable in this scenario. Anyone know of a random code exception that would allow you to combine storm and sanitary sewer?

 

[ME27272727]

I'm assuming it's not an older combined storm / sanitary sewer system?

 

[HVACMech]

I do not believe so (further investigation pending)

 

[PEDARRIN2]

This is a common problem in older municipal sewers where the storm portion of the discharge overwhelms the sewage treatment plant.

Close to where I live (not too close though), when this happens, the sanitary sewage treatment plant is "allowed" to dump not fully treated waste water into the river. They do not do it often and when they do, it is something they have to report and monitor closely, but I guess the rationale is it is better to pollute the river a little bit than to pollute the city streets a lot.

 

[dbill74]

I'm not aware of any IPC exception to allow storm and sanitary to be combined.
Query the city about their definition of "storm water". What you have to be careful of is municipalities that do not allow "clean waste" such as condensate from AHUs, water heater drains or other equipment drains going to sanitary. Pinellas County, Florida is one such jurisdiction that I know of. The restriction is hidden in their code of ordinances.

 

[HVACMech]

That is interesting dbill. I had not realized that some jurisdictions had that restriction. So do you just daylight your condensate, or do you put in floor drains and pipe to storm?

 

[ME27272727]

I've been hassled about running condensate to sanitary drain. Our argument was that the coils would be cleaned periodically, and we didn't want to send soaps and detergents into the storm water line. That has worked so far.

The city I live in has a combined storm / sanitary sewer system. After heavy rains, the treatment plants become overloaded, and discharge raw sewage into the local lake / river. It can become quite the stench.

 

[dbill74]

For the few jobs I did there, I think we piped to storm, but that was more due to where the drains were located. Either way was acceptable to the AHJ.
I heard the reasoning behind the ordinance was due to the sanitary treatment system being at capacity and they did not want to waste resources "cleaning" a waste stream that didn't need it. Been 10 years since I worked in that area.

 

[chicopee]

I was under the impression that all US communities had to separate storm water and sanitary sewage per EPA.

 

[PEDARRIN2]

In general, they do have to separate them, but they may still be combined out in the street.

The area I work with has a standard separation manhole they require which the storm and sanitary enter separately at different inverts, but are combined in the manhole to a single outlet.

When the municipality can pay for (at tax payer expense) separate sewer mainss in the street, they will come back and connect the extra inlet to the new sewer.

 

[lukaiENG]

Chicopee is correct in that new systems should be separated, however there are a number of old systems out there which have not been upgraded to the relatively new requirement due to the large cost.