More than three decades after its closure, the Virginia Key landfill will finally be sealed off, decontaminated and eventually turned into a park.

The project had been held up by a disagreement between Miami and Miami-Dade County over the cost of disposing of new trash. The years-long stalemate kept the county from releasing $45 million in bond money set aside for the clean up.

But the two sides have hammered out a deal that has found widespread support among the Miami City Commission. It comes up for a vote at City Hall Thursday.

“This is a win-win for the city and the county,” Miami Mayor Tomás Regalado said.

Under the agreement, Miami will extend its contract to use Miami-Dade’s waste-disposal system. The city had previously hesitated because of the price tag.

Had Miami chosen another vendor, city officials would have been responsible for sealing off the landfill. Miami-Dade was willing to do the job, and had set aside the bond money. But county officials said the plan also relied upon the income stream that would be generated by disposing of Miami’s trash.

While the two sides went back and forth, Miami-Dade sat on the bond proceeds, drawing criticism from the county inspector general and local activists.

The new agreement entitles Miami to the best rate available to any of the county’s clients. Also, Miami won’t have to provide a minimum amount of trash.

Miami City Manager Johnny Martinez called the deal “a good business decision.”

“The county is really the only game in town,” Martinez said. “If we didn’t go with them, our only other option would have been Broward County. Broward has a cheaper rate, but the cost of transportation and the overtime would have eaten into our savings.”

Miami also expects to save some money on its own. Solid waste officials say Miami will likely have less trash now that the city’s new recycling program is in full swing. Martinez estimates the cost of disposing of trash could dip to $7 million from $9 million annually.

Should the Miami and Miami-Dade commissions approve the agreement, it will jump start what will be a massive clean-up effort.

The 110-acre Virginia Key dump has been closed since 1978. At the time, closure meant covering the dump with a thin layer of soil. But testing later showed that the landfill was leaching toxic materials into the groundwater and hurting an already delicate ecosystem.

The plan now is to cap the dump with the more than 400,000 cubic yards of soil that came from the PortMiami tunnel dig. That should be enough to blanket the landfill with more than two feet of dirt.

The long-term goal is to build acres of park space on the site.

“We could put as many as 12 ball fields out there,” said City Commission Chairman Marc Sarnoff, whose district includes Virginia Key. “This could be a prime recreational facility for the entire city of Miami.”

The county will foot the bill for the landfill closure and decontamination, as well as coordinate the effort. The county has also agreed to spend $1 million annually to monitor the quality of the groundwater and reimburse Miami for money it has already spent on the site, said Mark Spanioli, Miami’s capital improvements director.

“The county has had this in mind for a number of years,” Spanioli said. “Working hand in hand is the way to go.”

Kathleen Woods-Richardson, the county’s public works and solid waste director, praised the two governments for working together.

“This was a hard-fought fight to make sure the best interests of the city and the county were protected,” she said.