“We're standing on a giant reservoir,'' says Allan Bedwell, DEP's deputy secretary for regulatory programs. “If using it for a water supply reservoir makes sense, we should explore it.”

The fertilizer plant, abandoned in 2001, is situated in a region the Southwest Florida Water Management District has declared a water shortage area.

The first of four ponds is nearly drained, and work has begun on building up the walls around it to increase storage capacity.

Rainwater would be separated from the slightly radioactive gypsum by a layer of high-density vinyl, 2 millimeters thick, that could cover the bottom and banks of the 45-acre pond.

When filled, the converted gypsum pond could hold 270 million gallons. Although small compared to the 15-billion-gallon reservoir Tampa Bay Water is building in southeastern Hillsborough, Bedwell indicates the reservoir idea is a long-term prospect but could supply both Hillsborough and Manatee counties.

First, though, there remains 344 million gallons of the toxic waste the state has been trying to get rid of. The U.S. EPA denied the state's request to extend an emergency permit that allowed the dumping of partially treated wastewater into the Gulf of Mexico. The DEP now is sending it to nearby Bishop Harbor, a shallow, 525-acre aquatic preserve that connects to Tampa Bay. Serious concerns that heavy rains or a ruptured dike could lead to a catastrophic spill prompted the unprecedented dumping of phosphate process water into the harbor and gulf.

Barring extraordinary weather, two of the four ponds could be sealed by the end of this year, and the other two finished by the close of 2005. Work on the ponds' walls and the stack slopes would be completed in 2006.