Senate panel hears bill to clarify when mine detention ponds are in compliance after storms

Senate Natural Resources Committee members heard testimony on Senate Bill 365 on Jan. 20, when sponsor Sen. Barry Usher said the measure would clarify compliance determinations for mine-site detention ponds that overflow after back-to-back storms.

The bill would specify that a detention pond designed under current rule for a 10-year, 24-hour storm is not automatically out of compliance if a series of storms fills the pond, provided the pond was designed to rule specifications and the operator is working “towards dewatering the detention pond in a timely fashion.”

Proponents from the coal industry said the change is a technical clarification that preserves mines’ responsibility for water quality while avoiding automatic penalties. Opponents, including the Montana Environmental Information Center and ranchers, urged stronger language tying the bill to federal Clean Water Act obligations and expressed concern about reduced public notice and enforcement incentives.

"All SB 65 does is specify that as long as the detention pond is designed in accordance with the specifications outlined in rule and that the operator is working towards dewatering the detention pond in a timely fashion, the pond would be determined to be in compliance with permit conditions even during large storm events that may exceed the capacity of the pond," sponsor Sen. Barry Usher said in opening remarks.

Darryl L. James, representing Westmoreland Mining (operator of the Rosebud mine), said detention ponds are sized to capture a 10-year, 24-hour storm and that enlarging ponds to avoid every exceedance would be costly and could harm downstream users by holding back more water than necessary. "This is just a clarification in statute to make sure that if we design and construct a detention facility per code, that we are in compliance even if we have a series of storm events that exceed that design capacity," James said.

George Harris of the Montana Coal Council and Matt Vincent of the Montana Mining Association also testified in support, calling the bill a reasonable balance between environmental protection and operational predictability. Proponents repeatedly emphasized that the bill does not change the operator’s obligation to meet permitted discharge water-quality standards, including MPDES requirements.

Derf Johnson of the Montana Environmental Information Center said he would seek an amendment to make explicit that compliance under the bill does not relieve operators of Clean Water Act obligations. "If that's the case, I think that that should be included in this language," Johnson testified.

Ellen Pfister (Pfister), an opponent, said mine spoils are highly erosive and should be contained on site. "The permit means to keep the damages on the permit site, not leaving it," Pfister said.

Dan Walsh, division administrator for air, energy and mining at Montana Department of Environmental Quality (DEQ), told senators DEQ inspects coal mines monthly and documents pond capacity during inspections. He said DEQ receives regular reporting, including annual hydro reports, and that inspectors look at capacity and would follow up if ponds remained at or near capacity.

Senators asked how DEQ would retain enforcement "teeth" and whether monthly inspections and reporting requirements are sufficient to ensure timely dewatering and dredging. Walsh said DEQ retains discretion to find noncompliance if an operator fails to dewater and maintain ponds in a timely fashion; the bill would remove an automatic determination of noncompliance tied solely to design-capacity exceedance.

The hearing closed without a committee vote; Usher asked for a "do pass". The committee moved on to additional bills on its agenda.

Why it matters: Mining detention ponds are a primary control for silt and runoff on mine sites. The bill addresses how regulators and operators treat overflow after consecutive storms, a detailed technical point that proponents say avoids unintended penalties while opponents worry it could weaken enforcement or public transparency if not tied explicitly to existing water-quality law.