Project Highlights

  • Ensero’s unique and custom designed water treatment plant uses direct Reverse Osmosis (RO) under pressure, to minimize fouling and metals precipitation, increasing RO membrane efficiency.
  • Combined mine dewatering, RO, and in situ treatment system achieved hydraulic control within the mine workings in 3 months.
  • Mine pool metals reduction goals were achieved in 6 months.
  • Ensero’s water treatment plant consistently meets the uranium MCL of 0.03 mg/l.
  • Early pilot study results show constructed wetlands treatment systems reduce uranium levels in mine water initially treated in-situ to a full order of magnitude below the MCL.
  • Ensero completed reclamation work in a difficult, narrow canyon to minimize impacts to all stakeholders and protect the endangered Prebles Jumping Mouse habitat.

The Challenge

The Schwartzwalder Mine is an extensive former underground uranium mine near Golden, Colorado. It was continuously dewatered and mined from the 1950s until 2000, after which the mine was flooded with natural recharge. In 2013, the mine owner was ordered to dewater the mine and achieve hydraulic capture to prevent diffuse seepage into Ralston Creek, located 4.8 km upstream of Denver’s water supply reservoir. Mine water contained elevated levels of uranium (as high as 14 mg/l), molybdenum, selenium, and arsenic. In 2018, Colorado Legacy Land, LLC purchased the mine, including the regulatory responsibility for ongoing environmental compliance with the Radioactive Materials License and ultimate regulatory closure. CLL reached out the Ensero Solutions (Ensero) for support.

Schwartzwalder Water Treatment Plant

The Ensero Solution

Ensero responded quickly with a multi-faceted approach including reclamation, mine dewatering, and both in situ and ex-situ water treatment and management. Our water treatment system was designed to mitigate the risk to Denver’s drinking water supply from the mine water. The system involves dewatering the mine to a designated level and then treating the water in an active water treatment plant (WTP) designed, constructed, and operated by Ensero. The design uses Reverse Osmosis (RO) as the primary treatment and ion exchange (IX) for polishing.

To maximize ex-situ treatment efficiency, Ensero utilizes WTP effluent concentrate to pre-treat mine water in situ. Concentrate is first mixed with a carbon source and barium chloride, then re-injected into the underground mine pool at over 1,100 ft bgs. Ensero’s patented in-situ treatment reduced underground uranium levels by 80% (to ~5 mg/l), thereby extending the RO membrane performance and directly addressing the contamination source.

Ensero developed a site-specific exit strategy to eventually transition from perpetual active treatment to passive treatment. We are currently pilot testing passive water treatment options. Initial results are favorable, and larger scale field testing is planned for 2022.

Schwartzwalder Reverse Osmosis Treatment System
Schwartzwalder Pilot Scale Constructed Wetland Treatment System
Schwartzwalder In Situ Treatment of Mine Pool

Physical reclamation activities include demolition and site preparation, impacted soil removal, waste consolidation, mine opening closure, stream restoration, and environmental monitoring. To date (August, 2020), Ensero has removed 31,000 cy of radionuclide-impacted soil from alongside Ralston Creek. The narrow canyon required Ensero to use specialized equipment to minimize environmental impacts. Excavated soil is disposed of in the underground mine, to reduce community impacts due to off-site transport and minimize client costs.

Ensero also designed and installed a storm water diversion channel to convey run on flows away from a reclaimed waste rock pile.

Once excavation is complete, Ensero will regrade, reseed, and restore the Ralston Creek Valley, which is critical habitat for the Preble’s Jumping Mouse.


For more information about the Schwartzwalder Project,
Please download a project summary and contact us today.

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