[TowerTalk] How close does a vertical have to be to saltwater to see any benefit?

[Jon M Knodel]

Here is my question - Just how close does a vertical have to be to saltwater to see any benefit over typical ground?  We all know that a vertical over saltwater is excellent, but I want to know if it would be much of a benefit to put one up at my location.
 
I am located on a peninsula and my qth is about 1.25 miles from the ocean to the west and about 0.5 miles to a saltwater bay to the east.  Our soil is 100% sand and typically have a very high ground water table.  Would this proximity to saltwater give me any benefit over a station without any saltwater around anywhere with the same vertical antenna?  Or would it take the same vertical installed DIRECTLY over saltwater to see any benefit from the saltwater?  Any thoughts would be greatly appreciated.  Thanks.
 
Jon N7XW