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Just below the Huntington Power Plant, a coal-fired generating station at the mouth of the eponymous central Utah canyon, agricultural plots spread out along the right bank of Huntington Creek. For the past four decades, these bucolic 250 acres have been an integral part of plant operations, receiving wastewater to grow alfalfa, wheat and barley as part of scientific research aimed at developing low-cost ways of disposing of wastewater, according to published studies.

Scientists and regulators have concluded the practice recycles water without endangering the environment. The forage produced is safe, although one study found that the cattle eating it have "soft teeth and bone weaknesses," according to Esmaiel Malek, a former Utah State University professor who oversaw research at the plant's farm in the 2000s.

Yet concerns persist, and Rocky Mountain Power has agreed to phase out the practice. RMP now plans to divert some groundwater accumulating in its nearby shuttered Deer Creek coal mine onto the research farm.

Environmental groups have blasted Utah's largest utility and its parent, PacifiCorp, for applying wastewater to the farmland, alleging it is really a cheap way of dispersing pollution in violation of federal law.

Said utility spokesman David Eskelsen: "The Huntington Plant conforms to all regulatory rules and requirements regarding the processing of waste materials, regardless of the costs. Moreover, PacifiCorp has a lengthy and excellent record of meeting all environmental requirements and exceeding required measures where it makes sense to do so."

The utility's shareholders win at the expense of water quality, HEAL Utah and Sierra Club allege in various court filings and documents submitted to the U.S. Forest Service.

The Manti-La Sal National Forest recently authorized RMP's request to build a 5.6-mile pipeline from the mine's remaining portals in Rilda Canyon to the Huntington plant's large settling basin, which stores water to be used in the steam turbines. Last week, however, the Forest Service's regional office suspended approval pending a review of concerns raised by the environmental groups.

The groups' concerns lack merit and are based mostly on "supposition," rather than facts, according to RMP.

"Some of their claims are flatly false. We will sort those out as the litigation proceeds. Sierra Club was looking at material we report to [the Utah Department of Environmental Quality] and they didn't understand what they were looking at," said Eskelsen.

Federal authorities will not allow RMP to plug the mine or discharge the water into Rilda Creek, regardless of its quality. That leaves piping it out as the only option. The water would be stored in a large clay-lined settling pond until it is needed in the plant.

The utility has so far spent $60 million closing the mine, much of that dealing with the millions of gallons of groundwater filling the network of underground chambers and tunnels. Extensive water quality monitoring shows the water is safe except for elevated levels of iron, which leaches into the water from pyrite deposits, Eskelsen said.

Environmental groups say many unanswered questions remain.

"They can't blame us for being skeptical. If the water is safe, then prove it. There is a lack of information in the public record," said HEAL's executive director, Matt Pacenza.

While HEAL contends it would be better to treat the mine discharge water — nearly 1,000 acre-feet in the first year — RMP proposes using most of it in Huntington operations, rather than wasting it.

"Why build expensive ponds and treatment facilities to treat water that is useable in its current form?" Eskelsen said.

This water would offset "gallon for gallon" water that the power plant normally draws from Huntington Creek, according to the Forest Service's Environmental Assessment of the pipeline project. Three percent of this water — still amounting to nearly 10 million gallons in the first year — would be applied to the research farm.

Over a few years, the volume of discharge water would diminish, as would its load of iron contamination, reaching a point where it can be safely discharged into Huntington Creek, Eskelsen said.

The research farm factors in all of HEAL's charges over waste handing at Huntington, where RMP has long sponsored research by USU soils scientists. In carefully constructed experiments, the fields have been irrigated between April and October with spent cooling water, which has become saline after several cycles through the plant's cooling towers.

RMP's nearby Hunter plant has a similar farm.

"It was considered innovative in its time," Eskelsen said. "The plants were built [in the 1970s] to be the most environmentally sensitive coal plants of their day, and the research farms are part of that ethic. … The whole point of the farm was to carefully apply the water so that the plants used all of it" and none percolates into the ground or runs off the surface.

"If it works so wonderfully, why don't you keep doing it?" Pacenza said. "Coal has a lot of troubling things in it. There is a variety of pathways for it to become a problem. It doesn't have to run off the soil as you are applying it for it to be a problem."

The wastewater irrigation is governed under the Huntington plant's groundwater permit overseen by the DEQ. However, under the proposed terms of the permit's renewal, RMP has agreed to discontinue the practice because salt accumulations would soon render these soils unproductive for agriculture, documents show.

Red flags first appeared in 2004 when new monitoring wells revealed increasing levels of nitrate and boron in and around the research farm. Regulators suspected these contaminants could have migrated through the ground from Huntington's coal-ash repositories.

In a lawsuit filed earlier this year, HEAL and Sierra Club allege the utility could be diverting contaminated runoff from Huntington's massive coal-ash landfills into its ponds, which supply irrigation water to the research farms. For proof, they point to the boron, a marker for coal-ash contamination, cropping up in RMP's monitoring wells.

RMP denies coal-ash runoff ends up on the research farm and is vigorously challenging the claims in court.

"The 'farms' the wastewater is currently sprayed on are not designed to yield crops; instead they are designed to absorb pollution that PacifiCorp would otherwise have to pay to treat. The current crops from the 'research farms' are not fed to livestock, instead they are disposed of at the Huntington coal ash landfill."

Research suggests the forage is suitable to give cattle, but RMP opts to use it to control dust at the landfill, according to Eskelsen.

But the research does affirm one of the environmental groups' claims: The research farm does reduce RMP's wastewater costs.

It cost just 82 cents to dispose of 1,000 gallons of saline wastewater this way, versus $19.32 with evaporation ponds and $5.91 with reverse osmosis, one old study reported.

"The forage crops continue to thrive and yield within acceptable range of paired fresh water irrigated plots at the site; salinity and water distributions are indicative of crop water uptake, and illustrate the success of the managed accumulation approach originally designed for waste water management across all cropped sites receiving saline waste water irrigation," wrote USU soils scientist Grant Cardon in a recent report submitted to DEQ. "Wastewater application and management according to this plan will have continued desirable outcomes well into the future."

Brian Maffly covers public lands for The Salt Lake Tribune. Brian Maffly can be reached at bmaffly@sltrib.com or 801-257-8713.

Twitter: @brianmaffly