Authors: Lundmark, K; Abranovic, D; Kafle, A

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Lundmark, K, Abranovic, D & Kafle, A 2023, 'Design and regulatory approval of a novel in-situ salt cap for final closure of contaminated wastewater ponds at a brine mining operation', in B Abbasi, J Parshley, A Fourie & M Tibbett (eds), Mine Closure 2023: Proceedings of the 16th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth,

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A novel closure technology was developed and approved by regulators for the final closure of a series of large (over 4 sq km) earthen evaporation ponds at a brine mining operation adjacent to the Great Salt Lake in Utah, USA. The cap design included in-situ precipitation of a salt cap (primarily sodium chloride) to prevent contact between humans and wildlife with contaminated sediments and mine wastes contained in the facility’s wastewater evaporation ponds. The salt cap is a nature- based solution that is designed to mimic naturally-occurring salt beds present regionally in the Great Basin and is preferable over traditional closure approaches (soil cap, consolidate and cap, or off-site disposal) for the following reasons: 1) saturated wastes and sediments in the ponds are not suitable for traditional earthwork equipment operation; 2) long haul distances for waste disposal or importing cap materials; and 3) the size of the wastewater evaporation ponds and large volume of wastes / sediments. Salt cap design parameters including annual salt deposition rates (in centimetres), brine requirements, and salt weathering rates were estimated through a multi-year field-scale pilot test at a salt accumulation test cell constructed within the footprint of one of the wastewater evaporation ponds. Pilot testing also evaluated effects of brine source on salt deposition rates, where brine was obtained either from Great Salt Lake or from solar evaporation ponds brine feedstock for the mining operations. Key technical challenges that were addressed during salt cap design included: construction of interior partitions, irregular/sloping beds and groundwater discharge areas within the wastewater evaporation ponds, expected timeframe for construction, and potential for contaminant leaching upward into the salt cap. The salt cap closure was approved by the USEPA as the approach for final closure of the wastewater evaporation ponds under both Superfund and RCRA programs. This technology also uses sustainability best management practices to limit the use of natural resources and energy, reduce negative impacts on the environment, and minimize or eliminate greenhouse gases to the greatest extent possible.

Keywords: innovative technology, capping, nature-based solution, contaminated site, sustainability

Utah Division of Forestry, Fire, and State Lands (DFFSL). 2013. Final Great Salt Lake Comprehensive Management Plan and Record of Decision. Prepared by SWCA Environmental Consultants. March.
ERM. 2019. Draft Tier 1 Treatability Study Report. Prepared for US Magnesium LLC and USEPA Region 8. February.
ERM. 2021. Salt Cap Closure and Post-Closure Plan. Appendix 4A to Consent Degree for United States of America v. Magnesium Corporation of America, et al., Civil Action No. 2:01CV0040B. January.

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