U.S. flag

An official website of the United States government

Dot gov

Official websites use .gov
A .gov website belongs to an official government organization in the United States.


Secure .gov websites use HTTPS
A lock () or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Susie Adit

Site Contact:
Todd DeGarmo


Site Location:
Rimini, MT 59626

The Susie Mine is located within the Community of Rimini, in Lewis and Clark County near Helena, Montana. The mine is located within the 53-square mile Upper Tenmile Creek Mining Area Superfund Site, which includes approximately 150 active and abandoned mines. Mining for gold, lead, copper, and zinc began in the area in the 1870’s and continued through the 1930’s. Waste rock containing heavy metals was used as fill for roads, yards, and local waterways, resulting in soil and groundwater contamination with heavy metals.

The Susie Adit discharges acidic mine-impacted water containing heavy metals and arsenic at a rate of 4 to 10 gallons per minute with a pH between 3.5 to 4.3. The portal of the mine tunnel has partially collapsed causing mine-impacted water to accumulate behind the blockage.  This blockage creates the potential for a sudden, uncontrolled release of mine-impacted water (i.e. “blowout”) and sediment into Tenmile Creek. EPA Region 8 is working with the Montana Department of Environmental Quality to mitigate the risk by reducing the volume of mine-impacted water pooled behind the blockage and removing the blockage. Additional drainage structures will also be installed.  This work is scheduled for July – August 2021.

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. EPA estimates that a 100-foot stretch of Tenmile Creek was impacted by this release, which occurred when a hose removing water from the adit site collected excess sediment and sludge material as the water level dropped in the area being dewatered. This event was not a “blowout.” The City of Helena drinking water will not be impacted by this event as there are no City Water intakes downstream of this area.  

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. Water quality sampling following the July 12 discharge was conducted  analytical results will be available soon and crews will also be removing sludge from the creek at the point of discharge.



For additional information, visit the Notices section.