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.