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RAPID CITY, S.D. (AP) — South Dakota officials are rethinking a proposal to dump coalbed methane water from Wyoming into the Cheyenne River.

South Dakota Environment and Natural Resources Secretary Steve Pirner said the proposal by ConocoPhillips would lead to more violations of the state's water quality standards in the Cheyenne River.

ConocoPhillips wants to drill 200 to 300 new coalbed methane wells in the southern part of the Powder River Basin southwest of Gillette. But to get to the methane, drillers first must pump out water from on top of the coal seam.

Pirner has asked his Wyoming counterpart, Department of Environmental Quality director John Corra, to revise the permit proposed for ConocoPhillips that would allow discharge of water from coal-bed methane wells into Wyoming's Antelope Creek. The creek flows into the Cheyenne River, which enters South Dakota northwest of Edgemont and flows through the Angostura Reservoir.

Wyoming currently is not allowing coal bed methane water to be discharged into the Powder River because of an agreement with Montana officials, Pirner said in a letter to Corra.

If Wyoming approves the permit, ConocoPhillips will pipe coalbed methane water from the Pumpkin Buttes area near Wright about 20 miles south to two reservoirs, where it would be held before being dumped into Antelope Creek.

Earlier this year, South Dakota Department of Environment and Natural Resources officials said they were satisfied with the permit request.

But on Wednesday, Tim Tollefsrud, DENR's director of the Division of Environmental Services, said the department was refining its position after getting more information on the project from ConocoPhillips and Wyoming officials at a May 16 meeting in Wyoming.

ConocoPhillips' own projections indicate its proposed releases would result in additional violations of South Dakota water quality standards, South Dakota officials said.

A high sodium adsorption ratio, which is a measure of the tendency of soils to accumulate sodium, can make clay soil impervious to water, ruining it for irrigation. Irrigators in Wyoming are among those opposed to the ConocoPhillips proposal.

ConocoPhillips' projections indicate the average sodium adsorption ratio of the Cheyenne at the border would increase from 8.3 to 10.9 with its proposal. South Dakota allows a maximum sodium absorption rate of 10.

The ConocoPhillips proposal would not violate state water standards continuously, Tollefsrud said. But it would lead to additional periods of violation.

DENR said current violations of salinity standards in the Cheyenne River are probably not the result of current coal-bed methane water discharges into Antelope Creek in Wyoming.

"The water quality of the Cheyenne is not great to begin with," Tollefsrud said.

DENR has begun a study with the Fall River Conservation District to quantify water quality in the river and identify pollutants that need to be reduced to meet standards, Tollefsrud said. Water in the Cheyenne has not met state standards at various times since 1967, he said.

Pirner has asked Corra to revise ConocoPhillips' permit, preferably by limiting the sodium absorption ratio at the discharge point to 10.

"This would ensure the ConocoPhillips' discharge is not contributing to further violations of South Dakota's surface water quality standards at the state border," Pirner said in a letter to Corra.

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