Deep Well Construction is a Series of Drilling and Testing

A deep injection well is built in stages, after detailed site studies, public hearings and a lengthy permitting process by the Florida Department of Environmental Protection, with the help of technical advisory committee.

Construction is performed from an impervious, concrete drilling pad, which prevents any contamination of shallow, freshwater aquifers by saltwater that might spill during drilling.

Crews assemble the rig, 150 to 200 feet tall, on the drilling pad. Once drilling begins, it usually is a 24-hour-a-day, seven-day-a week operation.

Drilling is performed in separate stages, with each stage designed and constructed to protect a specific portion of the aquifer being penetrated. Each successive well bore is smaller in diameter and extends farther down until the deep injection zone is reached.

Geophysical testing is conducted at every stage to evaluate the subsurface geology and to confirm the integrity of each section of the well before the next stage can be drilled. Water samples are collected to define water quality at specific depths in the well.

Here is the drilling sequence that Youngquist Brothers, Inc., uses to construct a typical, 24-inch diameter deep well in South Florida.

The first bore is 58.5 inches in diameter, drilled down to the base of the surficial aquifers, usually a depth of approximately 260 feet. Next, a steel pipe, one-half inch thick and 50 inches in diameter, is lowered into the cavity. Sulfate-resistant cement is pumped down to encase the entire length of the pipe and seal it to the surrounding rock.

Drilling of the second stage starts at the bottom of the first bore, at 48 inches in diameter, to approximately 1,000 feet below the surface. Another half-inch thick steel pipe, 42 inches in diameter, is installed inside the first casing and again sealed with cement along the entire length.

In the same fashion, the third stage is drilled 40 inches in diameter, to a depth of approximately 2,300 feet. A steel pipe, one-half inch thick, 34 inches in diameter, is installed and encased in cement to seal it to the surrounding rock and previous pipe.

The fourth and final casing stage is drilled 32.5 inches in diameter, to a depth of approximately 2,600 to 3,000 feet, depending on the formation at the site. A final, half-inch thick, seamless steel pipe, 24 inches in diameter, is installed and sealed with cement to the surrounding rock and previous casing.

For the fifth and final drilling stage, an open bore hole is drilled down into the cavernous "boulder zone."

Post-construction procedures include pressure tests, full scale injection tests, geophysical surveys and a television survey down the entire length of the well. The survey ensures there are no holes in the casing and no defective welds and establishes a baseline for future inspections of the well.

Upon final operating approval, the treated wastewater flows through the 24-inch pipe and down approximately 3,000 feet into the injection zone, where it dissipates into the extremely salty waters of the "boulder zone", safely away from the surface environment and from primary drinking water supplies.

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