Tank Overflow Piping 2

[bank]

The MEP engineer on my project wants to tie the overflow line from a fire water tank into the site storm sewer system. This is basically potable water (chlorinated) from the City water mains. My understanding is that the storm sewer system is for storm water only, and that water such as that from tanks should drain into the sanitary sewer system. Does anyone know if this is governed by any codes (Plumbing Code, NPDES, etc.), and if so, what the codes state?

 

[cvg]

keep it in the storm sewer if you can and I don't believe there is anything that says you can't put potable water into a storm drain. However, a direct connection to the storm drain is not recommended. The storm sewer cannot handle any pressure flow and you do not want to risk a cross connection either. Make sure you have an air gap to prevent pressure or back flow.

 

[GoldDredger]

I'd allow a connection to the storm system. I don't think we are talking a significant volume from an intermittent overflow of a fire reservoir. My guess is the flow would be gravity as well, once it begins its downward path from the overflow high point.

When fire departments or city water departments activate fire hydrants or blow off valves to test pressure or clear lines, that flow eventually ends up in storm systems.

Also, when you think about it, what your concerned about is that water fit for human consumption is too contaminated to put into a storm system.

That being said, I suppose I would check with the municipality just to cover yourself.

 

[bimr]

You should design the tank with the same standards as a potable water tank.

Storage tanks should not normally overflow. High alarm level on a tank is typically set at 90% full. The overflow is a contingency in case of failure to shut off the incoming water.

If you regularly drained water to the storm sewer, then you should dechlorinate. For an emergency occurence, it probably does not matter.

The overflow to drain connection should not be hard piped since you may be creating a cross connection.



"Overflow: Provide a ____ mm ____ (inch) steel pipe extended to grade with an overflow visible before spilling into a storm sewer inlet. The overflow shall be provided with an insect screen."

"Guidance: It is recommended that any discharge lines from tank overflow or drains be sloped for complete drainage so as to prevent any standing water in these lines. It is also recommended that these lines be separate from each other as well as separate from other discharge lines, such as from perimeter french drain system, and each be easily visible as required for the overflow line."

"If a drain is provided, it shall not discharge to a sanitary sewer. If local authority allows discharge to a storm drain, the drain discharge shall have a physical air gap of at least two pipe diameters between the discharge end of the pipe and the overflow rim of the receiving basin."

http://www.drinkingwater.utah.gov/documents/rules_ddw_version/R309-545_3-8-06.doc

R309-545-13. Tank Overflow.


All water storage structures shall be provided with an overflow which is discharged at an elevation between 12 and 24 inches above the ground surface with an appropriate air gap. The discharges shall not cause erosion.

(1) Diameter.


All overflow pipes shall be of sufficient capacity to permit waste of water in excess of the filling rate.

(2) Slope.


All overflow pipes shall Be sloped for complete drainage,

(3) Screen.


All overflow pipes shall be screened with No. 4 mesh non-corrodible screen installed at a location least susceptible to damage by vandalism,

(4) Visible Discharge.


All overflow pipes shall be located so that any discharge is visible,

(5) Cross Connections.


All overflow pipes shall not be connected to, or discharge into, any sanitary sewer system.

(6) Paint.


If an overflow pipe within a reservoir is painted or otherwise coated, such coating shall comply with ANSI/NSF Standard 61.

R309-545-14. Access Openings.

 

[RWF7437]

Is this overflow pipe ALSO a tank drain ?

 

[MiketheEngineer]

Check w/ local public works deprt. Some would probably wish that you dump it in the storm sewer.

 

[chicopee]

let the overflow pipe drain in a gutter which ultimately drains into a storm drain. It would not be any different than let's flushing fire hydrants, performing 2" drain test of fire sprinkler systems, all of which use potable water.

 

[JStephen]

As far as I know, most water tanks would be set up to overflow either onto the ground or into a storm sewer system, but normally not a sanitary sewer.

If you are using any kind of water treatment chemicals, you may want to look at it in more detail.