Over the past several years, Herrera has assisted the Wyoming Department of Environmental Quality (WDEQ) Abandoned Mine Division with the Wyoming Abandoned Mine Land Program (AML). This program aims to mitigate safety hazards and repair environmental damage from past mining activities by reclaiming thousands of acres of abandoned coal, bentonite, and uranium open pit mines in Wyoming. As part of the AML program, Herrera conducted field investigations and developed a reclamation plan for the Shirley Basin; a former uranium mill and mine site located in Carbon County, Wyoming.
Established in 1972 following the discovery of large uranium ore deposits, the Shirley Basin site consists of two solid tailings impoundments, the largest covering approximately 158 acres, and the smaller 135 acres. In addition, the site is adjacent to the Little Medicine Bow River, which was diverted to accommodate open-pit mining. The facility ceased mining activity in the mid-1980s, with reclamation taking place in 1992. These efforts regraded most of the lands impacted by mining and reconstructed the 3-mile-long river through the Shirley Basin site.
In 2007 and 2008, water quality studies conducted in the Little Medicine Bow River, indicated high levels of dissolved metals concentrations, posing a risk to human and aquatic health. With 26.2-miles of the river unable to meet Clean Water Act standards due to excessive sediment, the river was added to Wyoming’s 303(d) list of impaired and threatened waters in 2014.
With this, WDEQ tasked Herrera with conducting a field investigation of previous mine reclamation work in the Basin to evaluate the sources of erosion and sedimentation and provide recommendations for mitigation. Through this investigation, Herrera identified several sediment and erosion sources including the river upstream of the site, the reconstructed reach of the river, waste piles from former mining operations, reclaimed tributaries, and natural tributaries.
Based on the team’s field investigation and recommendations, Herrera established a reclamation plan to prevent unsuitable materials from entering the Little Medicine Bow River system and to reduce current levels of sedimentation in the river. This plan consisted of regrading the 400 Pile, the largest waste pile left behind by uranium mining, adding rock deflector grade-control structures within the existing channel alignment, and reducing erosion and promoting stabilization through site vegetation.
When regrading and stabilizing the 400 Pile, the team utilized the GeoFluveTM fluvial geomorphic landform design method and Carlson Natural RegradeTM software to mimic natural and local features. The regrade includes creating and armoring channels throughout the area to promote natural drainage and reduce erosion.
In addition, Herrera developed the revegetation and seeding plan, working with AML to deliver specifications for amendment usage and a Wyoming native seed mix of grasses, shrubs, and forbs that are well suited for survival in the limiting soil conditions. The mix is heavily based on species that survived initial revegetation efforts and those that are naturally invading. The revegetation plan follows new guidance developed by AML, called Wyoming AML Vegetation and Evaluation Standards (WAVES). The standards were developed to inform remediation techniques and minimize habitat fragmentation caused by historic mining practices in areas of ecological importance.
Part of the Shirley Basin project site lies in a Sage Grouse Core Area (SGCA). These areas were established by Wyoming’s Greater Sage-Grouse Core Area Protection Policy to preserve core sage-grouse population areas and restrict habitat alterations, while allowing existing land uses to continue. To further these conservation efforts, the reclamation design provides sage grouse brood rearing, nesting areas, as well as a new, natural lek area with vegetation and features designed for sage grouse strutting activities. Site construction on the 400 pile began in July 2021 and is estimated to complete in 2022. Revegetation monitoring will take place for a minimum of five years, or until vegetation meets the WAVES standards.
Herrera looks forward to continuing our work with WDEQ to further reclamation efforts in the Shirley Basin and across the state of Wyoming. Learn more about our mine reclamation work here.