Discharge of Storm Runoff 1

[beameupscotty]

I'm working on a site inside a Municipality with no storm sewer within a reasonable distance for the scope of work being designed. The existing soil is silt loam with high seasonal water table and slow permeability. I've thought about the idea of treating the runoff and releasing it into a sanitary sewer (this city doesn't accept combined sewer systems).

Does anyone have another idea I could try?

 

[bltseattle]

It seems to me you need to release water to the same place it goes now, not exceeding existing rates. This will likely mean that you need some level of detention (doesn't sound like infiltration will work on your site). Otherwise there is high liability for any future downstream flooding/sedimentation/erosion problems (even if not a result of your project, general public usually looks to recent upstream activity if flooding affects properties/resources, (even if it's the 100yr storm,) which can become a legal mess).

The local agency should really be giving direction to you for this issue.... this also puts some of the responsibility on the municipality for planning development in their jurisdiction to not affect downstream properties and resources.

 

[beameupscotty]

Thanks for the reply, bltseattle. You're correct this area was badly flooded even in 1996 (not a 1% event) and many lawsuits have been made.

 

[Maury]

Bitseattle gsve you the right answer. Discharging to the sanitary sewer system shouldn't be considered (I would hope the city wouldnt allow it). It is the hydraulic capacity of the sewer system and the treatment facility that is the problem, and treating the storm water doesn't solve that. Look to storm water detention and releasing the water where it goes now.

 

[beameupscotty]

Thank you for your reply, Maury.

I understand detention will lessen the immediate impact (in this case the difference between a 10-yr design event and a 5-yr existing conditions events) however these systems are design with overflow components usually designed for a 25-yr or 50-yr event. The existing point of concentration of this site is the shoulder of a turnpike road with no existing ditch or storm sewer within 500 feet. So, I guess an inexpensive solution would be to construct a settling basin outside the existing shoulder for the overflow and constricted (w/orifice) detention flow.

 

[WaterBear]

Collect on-site and pump to the gutter leading to the closest storm inlet. As you say, treatment may be required or desired to avoid NPDES citations. Look at the Vortechs System at vortechnics.com for guidance.

 

[Maury]

500 feet to a downstream inlet isn't very far. Have you considered extending the storm sewer or ditch to your site? State or local regulations should tell you an allowable release rate and how to calculate storage volume. A settling basin or treatment facility may be required to meet requirements for quality of the discharge water, but I understood your question to about the handling the quantity of discharge. Any pumping system should be a last resort. Gravity is more reliable, lower maintenance, and doesn't require standby power.