Yukon Energy Corporation enlarged the Mayo Hydroelectric Facility from 5 MW to 15 MW within a two-year fast-track schedule. The complex design required 300 m of tunnel construction through poor bedrock conditions, under challenging artesian groundwater pressures. Tie-in to the 60-year old tunnel at the intake was difficult, complicated by proximity to full reservoir head. Careful mapping and characterization was required to support concurrent tunnel design and excavation, and slope stabilization. Precision LiDAR 3-D survey techniques and modeling were integral to the work. The project offset costly diesel generation, while annually eliminating 25,000 tonnes of greenhouse gas emissions.