The list of sites for the so-called Earthpark project has been narrowed again, down to two.

Developers in Pella and Riverside have each lined up the 25 million dollars the Earthpark’s board had required in order to land the project. The Earthpark will consist of an indoor rain forest and outdoor exhibits highlighting Iowa’s environment. Developers of a site in Tiffin dropped out of the running Tuesday, saying they could not raise the 25 million.

Earthpark executive director David Oman says the board plans to decide between Pella and Riverside in September. “We’re probably within two months, perhaps a little less than that, in terms of a final decision,” Oman says.

The board’s final decision was to come in May, then June. Oman says they just couldn’t meet that “ambitious” timeline. “It became pretty clear that it was going to take a little more time to…really investigate and dig into the offers,” Oman says. “Various localities and development teams had very appropriate questions of us, about the project and what it would entail and what our needs were and all those discussions were part of a larger discussion of local visioning.”

Oman contends the project will bring in thousand of visitors and spawn development around the EarthPark. However, the Earthpark board is setting some restrictions for nearby development. Oman is vague about those restrictions, saying only that nearby development can be “contiguous, but not too close.” Oman suggests it might also entail requiring businesses nearby to be on the same, newly-created power grid. “We’re going to use sustainable building materials and expect to use alternative and renewable energy sources and technology to power the building and the life support systems on the inside,” Oman says. “We would be elated if the development around us could be a party to that technology as well. That might mean a district energy plant. It could be some shared utilities, etc. All of that has to be very carefully thought through.”

The Earthpark project is pegged to cost about $155 million dollars to build, and Oman says they’ve raised two-thirds of the money. He suggests businesses and individuals are weighing contributions, but concedes the board may seek a $10- to $15-million loan to get things started.

As for what criteria the board will use to decide between Pella and Riverside, Oman puts it this way. “You know, we’re (on) third base headed to home here,” Oman says. “There’s just a lot of information that’s going back and forth to give us the full ability to make a thoughtful decision.”

Critics of the project have dubbed it the Iowa Pork Forest and question whether it will deliver the economic side benefits backers claim.

Radio Iowa