Primary Gold Limited proposed the redevelopment of its Rustlers Roost and Quest 29 open-cut gold mines, involving expansion of existing pits, new mine infrastructure, haul road construction, waste rock landforms, processing facilities, a tailings storage facility, water storage, and site services. CDM Smith was engaged to prepare a Draft EIS and subsequently a Supplementary EIS (SEIS) for assessment under the Northern Territory Environment Protection Act 2019. The project required extensive technical studies, including hydrology and flood impact assessments, pit lake modelling, water balance analysis, and multiple environmental management plans. As the proposal evolved, CDM Smith integrated ongoing design refinements and addressed all public submission queries through the SEIS. The collaborative approach ensured a comprehensive, compliant, and transparent assessment process that supported the project’s progression through the NT EPA approval pathway.