SWANTON – Tom Vanacore grabbed a handful of grey dust before letting it roll back into a larger pile of crushed stone sitting idly in a Swanton warehouse. It was one of two such piles left in the warehouse, mined and crushed last year at the abutting quarry.

According to Vanacore, should everything go according to plan, that dust, pulverized into a fine powder at Shelburne Limestone Corporation’s Swanton quarry, could become the next tool for stymieing the flow of phosphorus into Lake Champlain.

Vanacore, of the Bridport-based Rock Dust Local, was one of last year’s awardees for Gov. Phil Scott’s Phosphorus Innovation Challenge (PIC), an initiative awarding grant funding to entrepreneurs with ideas for reducing phosphorus runoff into Vermont waterways.

A $25,000 grant was awarded to both Vanacore and the Shelburne Limestone Corporation (SLC), a mining company based out of Colchester with a limestone mine in Swanton, for developing marketable uses of a mineral capable of capturing nutrients like phosphorus and nitrogen.

“We had a proposal to use local minerals… and shown, experimentally, that it did capture solution phosphorus,” Vanacore said. “It picks up the phosphorus and nitrogen, and it seems to be working very well.”

Essentially, the minerals in question, two types of black shale mined from SLC’s limestone quarry in Swanton and a deposit in Shoreham, react with phosphorus to mineralize it, trapping that phosphorus in a mineral form where that reaction occurs.

Most of that phosphorus mineralizes in a form that can still be absorbed by plants, according to Vanacore.

Rock Dust Local’s and SLC’s proposal envisions the minerals used in everything from an engineered attachment to existing manure digesters to their incorporation into nutrient management plans for farmers, where their stone could be deployed “in the field to sort of manage, organically, the phosphorus.”

According to Vanacore, applications in farm fields have captured as much as 50 pounds of phosphorus per each tonnage of rock, the number initially cited in Rock Dust Local’s and SLC’s application for the PIC.

In the year that’s followed since their initial proposal was filed, Vanacore said they’ve actually exceeded those targets in some of their test fields scattered between Franklin and Addison counties.

“That is a tremendous amount of phosphorus,” Vanacore said.

Trapping phosphorus on a farm field rather than outright removing it is important, especially in some corners of Addison County where, according to Vanacore, farmers have sometimes found fields deprived of phosphorus.

Phosphorus, maligned for its role as a nutrient feeding the harmful blue-green algae blooms in Vermont’s waterways, is a vital nutrient for most living organisms.

Applying their brand of shale to farm fields, according to Vanacore and SLC’s Trampas Demers, could help farmers retain nutrients lost through runoff. “It will have the ability to grab the phosphorus and keep it where it belongs,” Demers said.

The results have, according to Vanacore and Demers, been “award winning crops” at some of their Addison test sites, including, Vanacore bragged, “14-foot corn in the middle of August.”

Other possible uses proposed by Vanacore and Demers included lining culverts and ditches with stone or possible applications in municipal wastewater systems.

The question Vanacore and Demers hope to answer through the next steps of the PIC, however, is whether or not they’d be able to market their phosphorus-catching shale now that it’s shown results.

The grant opportunity from the state was helpful, they said, but it still didn’t offset all of the costs behind their research, and, as Vanacore noted to the Messenger, “$25,000 doesn’t build an industry.”

Demers said he was confident it’d be easy to build the supply side of the equation, with both SLC’s mine in Swanton and the Wilcox Quarry in Shoreham already permitted for operation with room to expand.

SLC’s quarry in Swanton, where a large deposit sits below an actively mined deposit of calcium, is already serviced by railroad, and according to Demers, SLC already has the infrastructure needed for production. “We have everything in place to make this product,” Demers said. “We can offer this. We’re ready to go.”

SLC has around 50 employees serving in its administrative staff and in its three quarries.

Their products, titled “Swanton Black” after that strand’s hometown and “St. George Black” after the Wilcox Quarry’s owner George Wilcox, are certified organic and amended with a biological material called “biochar” capable of capturing carbon.

It’s the demand the two are worried about, which is why Vanacore is hoping the state will take their advice and consider integrating their mineral products into nutrient management planning for Vermont’s farmers and subsidizing the minerals’ use.

That state-led engagement, according to Vanacore, is especially needed today, when most of the state’s dairy farmers, the ideal market for Rock Dust Local’s proposed product, are struggling with their fifth year of milk prices sitting below the cost of producing milk.

Despite positive responses from farmers and tests in the field, “no one’s knocking my door down,” Vanacore said. “The farmers don’t have the money.”

“We have to assume the state is going to subsidize it,” Demers said. “We can’t create a market out of thin air.”

It’s something they hope to answer as they roll forward with the PIC, now wrapping up its second stage as participants create prototypes and craft business plans for their proposal.

Last year, the governor’s office awarded $240,000 to six proposals as a part of the phosphorus challenge. The next stage will see at least one of those projects funded for implementation.

Vanacore, previously a stonecutter whose work with using stone as soil amendment began with Rock Dust Local’s first iteration 30 years ago, sees their minerals as only a part of the state’s solution to continued water quality troubles.

Still, he was optimistic about his answer to the state’s water quality woes.

“We’ve found an answer to a vexing problem right here at both ends of the Champlain Valley,” Vanacore said.

Note: A previous version of this story erroneously reported Rock Dust Local’s product had captured “as much as 50 tons of phosphorus per each tonnage of stone.” It should read “as much as 50 pounds of phosphorus” and has been corrected.

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