Pitkin County commissioners agreed last week to grant two transferable development rights (TDRs), now worth a total of about $350,000, to the owners of a property in Emma where evidence of prehistoric human habitation has been found.

The transaction marks the first time TDRs have been used to preserve an archeological site in the county, and it signals the evolution of the TDR program, which was established in 1994 to discourage development in rural and remote parts of Pitkin County located far from established infrastructure.

The program has since been used to spur the preservation of environmentally sensitive or historic sites, but archaeology is new territory.

“This is the first time, and maybe the last time, that TDRs will be used to protect a site like this,” said Pitkin County Open Space and Trails Director Dale Will, who orchestrated the arrangement.

Yet the Emma archaeology deal also exposes the sometimes imprecise and subjective way that Pitkin County has come to use TDRs, whose issuance is governed by a zoning and acreage formula in certain cases, but in others is simply determined by the druthers of the commissioners themselves.

In rural and remote areas, for example, the county code is clear: One TDR can be granted per 35 acres. But historic sites, areas that are “constrained” by environmental values or the Emma archaeological site are governed by a muddier standard: The code simply asks county officials to grant the number of TDRs that they think is “fair and equitable.”

In the Emma case, in exchange for two TDRs, property owners David Brown and Jody Anthes have agreed to forfeit their development rights on the property where the historic site is located. The land will be placed under a conservation easement managed by the county and an archaeological nonprofit group.

The couple can then turn around and sell their TDRs to a landowner seeking rights to build within Aspen’s urban growth boundary, or to someone who wants to expand the floor area of their home beyond the maximum of 5,750 square feet allowed by the county code.

Brown and Anthes purchased the Emma property in 2011 for $260,000, according to the Pitkin County Assessor’s Office. They also own a neighboring property, and have told the BOCC that they bought the land where the Archaic site sits in part to protect their privacy.

Fred Thiemer, an Aspen resident who owned the property before Brown and Anthes, said he had no idea that the site was home to such rare and scientifically valuable artifacts when he sold it.

“I didn’t have the money to build a big house on the property,” he said. “If I had done that, I guess I may have run across these artifacts. I never dug a hole on the property, but I always thought the land had a special energy about it.”

The roughly $90,000 difference between what Brown and Anthes paid for the property and the current value of the TDRs they will receive has prompted Board of County Commissioners (BOCC) chair George Newman to characterize the deal as a “windfall” for Brown and Anthes, a bit of good fortune he said the TDR program was not intended to provide.

“I don’t think it’s the intent of the TDR program to provide a windfall for an owner who wants to put their land under a conservation easement, and in this case the windfall is fairly substantial — it could be as much as $100,000,” said Newman at a BOCC meeting on Wednesday.

Throughout the process of reviewing the plan for the Emma site, Newman has argued that just one TDR would be sufficient to compensate Brown and Anthes for their development rights.

Calls to the couple seeking comment were not returned, but Aspen land planner Mitch Haas, who assisted them in securing a TDR deal with the county, said he disagreed with Newman’s assessment.

“Between the cost of the land, the time and cost of getting through the [county] review process, several archaeological consultants, and the cost of carrying the land in the time before the TDR is sold, at the end of the day, I think they’ll be lucky to break even,” Haas said.

He noted that in recent years, three other sites in Emma of similar size to Brown and Anthes’ 43-acre property have been conserved in exchange for two TDRs apiece.

Nevertheless, since the program began, trading TDRs for development rights has sometimes been fuzzy, according to Will, the open space director. That’s because the value of TDRs has never been tied to the actual value of the development rights they’re being swapped for.

“If you’ve got a mining claim in the backcountry, you’re entitled to one TDR per 35 acres, regardless of what the mining claim is worth,” Will said.

Rather than being tied to land values, the price of TDRs is simply determined by what private buyers and sellers think they’re worth when they are used on another site, or “landed,” a number that fluctuates constantly.

Before the economic crash of 2008, a single TDR could sell for up to $318,000, and by 2011 the price had dropped to $125,000, according to data from the county community development department.

The commissioners began discussing how to compensate Brown and Anthes to preserve the Emma site in 2011, and since then the price of TDRs has grown to around $175,000, an increase that significantly changes the calculus of how many TDRs is “fair and equitable” to trade for protection of the Emma site.

Newman said the BOCC plans to revisit the TDR program in the coming months, but in the meantime the program features all the unpredictability of the stock market: Landowners who receive TDRs can score a windfall or be hit with a loss, all depending on what their TDRs are worth when they sell them.

“Given the volatility of values in the TDR market,” wrote Will in a recent memo to the BOCC, “landowners and the county each accept some risk about the monetary proportion of the incentive this tool provides.”