Drainage Well

[djcbgn]

I am designing a stormwater injection well in South Fla. The stormwater runoff flows by gravity into the well. The depth of the well casing is about 70 feet below ground surface elevation and the open hole extends about twenty feet from the well casing. The groundwater level is about 4 feet below the ground surface. The well is along the coast and therefore the groundwater has high TDS (aout 30,000 ppm). How would you compensate for the density difference of the injected, and basically fresh, stormwater as compared to the denser groundwater? Thanks for the help.

 

[Dubliner]

Firstly I am wondering why you would need to inject the water so deep of the water table is shallow. Would a recharge pit not suffice? This would do away with many of your problems as the shallow water is unlikely to be as saline as the water at depth.

However, I would like to respectfully raise a few questions:

Have you considered the potential need to remove fines and other suspended particles before the water enters the well? In a short time I could imagine the well becoming clogged and requiring remediation.

Have you considered the possibility that the stormwater may have encountered pollutants prior to arriving at your well? Most road runoff will have some TPH contamination. I am not familiar with your environmental laws but regulators may take a dim view of polluted recharge.

Pure water has a density of 1000 kg/m3, sea water would have a density of ~1027 kg/m3. The injection could possibly cause plumes of less dense injected water to rise in the vicinity of the well. Is the shallow groundwater saline as well? If not it could become saline due to the rising plumes mixing with deep saline water or some kind of displacement mechanism.


Adam Beresford-Browne
Zenith International Ltd
zenithwater.com