STORM WATER INJECTION WELLS 1

[bocaeng]

Does anyone know of any design references for storm water injection wells for runoffs in parking lots.How are the pumps and pipes sized?What are the pressures at the subsurface point of ejection.Any help will be appreciated.

 

[bltseattle]

A few thoughts in no particular order....

Infiltrating stormwater is typically accomplished using gravity, not pumps. Infiltration rate controlled by the surface area of the infiltration system. Engineering analyses includes hydrologic modeling, level pool routing, and maybe groundwater mounding analysis, to ultimately determine the amount of storage that is needed since the area available to percolate stormwater will be less than what is needed to absorb site runoff "instantaneously" in almost all cases.

EPA regulates injection wells, see:

http://www.epa.gov/safewater/uic/pdfs/fact_class5_stormwater.pdf

For guidance in designing a pressurized system maybe consult with petroleum engineer types because oil drilling typically involves a water injection system, albeit at significant depth below the ground surface. When near the ground surface & using pressurized system I think you risk liquifying and destabilizing the soils so you should seek direction from the project's geotechnical engineer or a hydrogeologist if you are determined to use pressurized injection methods in the near-surface scenario.

What would happen if the pressurized water finds a geologic seam and emerges somewhere undesired (e.g. neighbors property, side of a hill)? In terms of liability, one could argue in a gravity system that water finding an underground geologic seam is a natural phenomenon, but in pressurized system you may be more liable for any damage (related to soil washouts or slope failure for example).

 

[cvg]

in addition to bltseattle comments regarding pressurized injection, there may also be a risk of contaminating an aquifer unless the stormwater is first treated. This would require capture and then tertiary treatment which would be quite expensive. For these reasons, and the risk of future liability, it is not generally recommended course of action.

 

[bocaeng]

Thanks for the responses to my request for information about injection wells .In City of Ft.Lauderdale,Fl. now injection wells are required for parking lot drainage rather than exfiltration fields or trenches.So.Fl.geology is basically sandy soils overlying a lime rock substrate with a high water table(-4 to -6 feet).At face value I guess to collect storm water at the surface and discharge 20 feet below ground surface you have to pump at least against the hydrostatic pressure of ground water.Any other thoughts would be appreciated.