How deep a well near Jacksonville is depends on which water it is drilled for

Three layers of water

Under most lots around Jacksonville the ground is layered. Sand at the surface holds the water-table aquifer, whose level rises and falls with the rain. Below it a layer of clay and clayey sand, the confining layer, holds the intermediate aquifer where one exists. Below that sits limestone, and inside the limestone is the Floridan aquifer, the regional supply that utilities and most drinking wells draw from.

A shallow well stops in the sand. A deep well is cased through the sand and the clay and opens into the limestone. The depth of the clay decides how deep a deep well has to be, and that depth is not the same across the service area.

Shallower inland, deeper at the coast

The limestone rises toward the west and south and dips toward the Atlantic. A Floridan well in Clay County toward Keystone Heights or in western Baker reaches rock far sooner than one at Ponte Vedra or on Amelia Island. The same standard of construction, cased and grouted through the confining layer, can differ by hundreds of feet between two towns twenty miles apart. That is the main reason well drilling is quoted per site rather than from a price list.

What the completion report tells you

Every permitted well has a completion report on file with the office that permitted it. It records total depth, casing depth and diameter, the static water level on the day, and often the yield. For a homeowner it is the single most useful document about the property's water, and for a pump replacement it is what the new pump is sized from. Where no report exists the depth and level can be measured, but it is cheaper to pull the file first.

Depth and chemistry go together

Shallow water-table wells tend to carry iron and tannins from the surface and move with the season. Floridan water is more stable in quantity and harder, with sulfate that can arrive as a sulfur smell. Choosing depth is choosing which set of problems to treat, and the treatment pages on this site are written around that.