Overview
The project involved comprehensive design, risk assessment, and a trade-off study to evaluate feasible mine infrastructure options for mine waste storage and clean water management in challenging terrain at the Watut Portal site in Papua New Guinea. The scope included the development of clean water diversion strategies, the design of a decline portal terrace, and a waste rock dump including PAF (Potentially Acid Forming) waste. Additionally, the project featured a detailed risk assessment and trade-off study to guide the client in selecting the most suitable infrastructure options.
Challenge
The key challenge was the project's location in a seismically active and high-rainfall environment within a narrow creek valley in Papua New Guinea. The site faced significant storm runoff from a large upstream catchment, which flowed through the valley where the underground decline portal was to be constructed. The region's steep, mountainous, and heavily forested terrain added to the complexity. A critical constraint was the requirement to fill the valley with run-of-mine waste, including Potentially Acid Forming (PAF) waste and borrowed materials. This restricted the natural flow of surface water from the upstream catchment. The primary challenge was managing stormwater flow through the site, along with handling the waste rock generated during operations, most of which was classified as PAF. This raised concerns about acid and metalliferous drainage (AMD), making its management a key focus of the project. Additional challenges included addressing the practical aspects of constructability and ensuring the long-term reliability of waste rock management and stormwater control systems in such a challenging environment.
Solution
A comprehensive Basis of Design was initially developed in collaboration with the client to outline key project requirements for the mine’s lifecycle. To manage stormwater risks, clean water diversion strategies were identified and designed, including two zoned earth-fill detention dams with clay cores to control flooding and reduce AMD risks. Diversion channels were designed to separate contact and non-contact water, ensuring safe surface flow management. For waste management, a Waste Rock Dump (WRD) was engineered to encapsulate Potentially Acid Forming (PAF) waste using Non-Acid Forming (NAF) waste. The design included an underdrain system to control groundwater flow and a cover system including a clay liner to minimize water ingress, creating a geotechnically and geochemically stable landform to effectively contain acid-forming waste. A Multiple Account Analysis (MAA) was conducted to evaluate and rank options, resulting in a cost-effective solution that addressed construction, operational, and regulatory risks.
Client Feedback
“Mohsen led a piece of work to optimise a major schedule and cost item within the project. Under his leadership, an innovative solution to the problem was developed and put forward for future analysis. The solution has the potential to unlock significant cost savings and schedule reduction with a subsequent major effect on the overall project NPV.”
Client
Wafi-Golpu Joint Venture (WGJV)
Location
Papua New Guinea, Morobe Province
Date
2019
Disclaimer: Project led by GeoTails Consulting’s founder, Mohsen, during previous consultancy engagements before founding GeoTails Consulting.
