On July 12, 2021, a small amount of sludge, approximately
20-40 gallons, was released during an EPA dewatering operation at the Susie
Adit site in Tenmile Creek, west of Helena, Montana. EPA estimates that a
100-foot stretch of Tenmile Creek was impacted by this release, which occurred
when a hose sucking up the discharge water at the adit site picked up excess
sediment and sludge material when the water level dropped in the area being
dewatered. This event was not a “blowout.” The sludge exited the Susie Adit
draining to Tenmile Creek in a manner similar to many previous discharge events
or “burps” over the past century in this heavily mined and mineralized area.
There are no observed or expected impacts to drinking water or aquatic life
associated with this discharge.
dewatering operation, which has been underway since July 8, was requested by
EPA’s Superfund Remedial Program and the Montana Department of Environmental
Quality in May 2021 to address a collapse of earthen material behind the
entrance of the Susie Portal. This collapse caused a blockage of mine-impacted
water within the tunnel, which without action to remove mine-impacted water and
prevent further degradation of the mine entrance, increases the risk of an
uncontrolled release to Tenmile Creek. EPA will resume the dewatering effort in
the next few days and will implement supplemental control measures to ensure
that additional sludge releases do not occur. EPA conducted water quality
sampling following the July 12 discharge and expects analytical results will be
available in the next 24 hours. Crews will also be removing sludge from
the creek at the point of discharge.