ORONOGO, Mo. — Four years after the Environmental Protection Agency began dumping truckload after truckload of mine waste into a mine pit in southwest Missouri, the work has had no visual effect and it’s unlikely the pit will ever be filled, an EPA official said.

The mine, near Oronogo, closed in 1948 and eventually developed into a lake 200 feet deep in some places, The Joplin Globe reported (http://bit.ly/2drfxEq ).

The EPA decided in 2012 to take mine waste from the region and dump it into the 12-acre mine pit, then cap it and leave a grass field. At the time, the agency estimated it would take 4 million cubic yards of mine waste to fill the pit. The EPA is using mine openings to hold mining waste rock, known as chat, which is contaminated with heavy metals such as lead, zinc and cadmium.

Mark Doolan, the remedial project manager for the EPA supervising the cleanup of the Oronogo-Duenweg Mining Belt Superfund site, said 2.5 million cubic yards of waste have been dumped in the pit since then and “You can’t even tell if we’ve put anything in it.”

The pit might not be filling as expected because it has several long, deep tunnels at the bottom and it is extremely deep, said Doolan, who added hopes of ever filling the pit have dropped.

More mine waste, he said, “is not going to make a difference.”

With just one more piece of property near Oronogo to be cleared, Doolan said the EPA is nearly finished dumping waste into the pit. It wouldn’t make financial sense to haul more mine waste to the Oronogo pit, he said.

The EPA will return the land to its owners, John and Regina Mueller, who will decide what to do with it.

Before the cleanup, the couple operated a recreation park and scuba dive shop at the site for more than 30 years. As part of an agreement with the EPA, the former mining company that owned the pit, reached a financial settlement with the Muellers for the loss of their business.

John Mueller said the couple had no interest in restarting the business and will likely sell the property. He said he always suspected the EPA would have trouble filling the pit and “now it just sits there.”

Information from: The Joplin (Mo.) Globe, http://www.joplinglobe.com