Tailings storage facilities (TSFs) closed under historical practices are increasingly being reassessed to meet current regulatory requirements and modern risk management standards. Closure under a water cover has historically been widely applied, notably because it can, under appropriate conditions, support compliance with environmental water quality requirements.  At legacy TSFs, objectives related to geochemical performance and requirements for hydrotechnical, and geotechnical safety are often in tension. While a water cover may support water quality management, it may also introduce or prolong risks associated with long-term containment performance, including seepage losses, dam stability, freeboard management, and system response to extreme events. This paper presents a structured methodology for evaluating legacy TSFs operating under an existing water cover against alternative cover concepts. The approach integrates Failure Modes and Effects Analysis (FMEA) to establish a consistent risk basis, followed by an As Low As Reasonably Practicable (ALARP) assessment of the water cover configuration to define its reasonably practicable risk reduction envelope. The ALARP-optimized water cover is then compared against alternative cover concepts using FMEA-based risk outcomes and a broader multi-account evaluation framework, considering risk reduction effectiveness, geochemical performance, constructability, and long-term resilience.