The Stowell Complex consists of three main portals and two waste rock piles. VESTRA completed permitting, design, and construction inspection of remedial activities at the Stowell Complex. Remedial activities included excavation and consolidation of about 36,000 cubic yards of waste rock located on a steep slope immediately above Spring Creek.

VESTRA provided professional engineering, environmental, and geotechnical services to assist in the fast-track design and permitting of a Title 27 waste rock containment facility. The waste rock was relocated to a high-density polyethylene lined containment cell. When the Davis portal was uncovered during the waste rock removal project, VESTRA assisted with installation of a bulkhead seal.

In addition, VESTRA designed and inspected a system to inject compost behind the Upper and Lower Stowell portals to stimulate sulfate-reducing bacteria (SRB) activity. The compost was injected through the bulkhead seals and through boreholes drilled into the tunnels behind the bulkhead seals.

Additional remedial activities for which VESTRA completed permitting, design, and construction inspection included construction of a sprayfield to receive treated effluent from the treatment unit, installation of continuous monitoring stations in Spring Creek to verify the success of the remedial activities, and construction of a unit to treat residual discharge from three sealed portals. The treatment unit consists of five 5,000-gallon portable tanks connected in a series. The baffled tanks are filled with limestone and compost, and nutrients are added to stimulate SRB activity as needed. The capital cost per gallon per minute of treated effluent for these units is significantly less than the capital cost for constructing an open and lined treatment pond.

As a result of these activities, point source discharge from the Stowell Complex into Spring Creek has been eliminated. Waste Discharge Requirements have replaced the National Pollutant Discharge Elimination System Permit and Order, and except for the maintenance of the SRB treatment unit, remediation at the Stowell Complex is complete.