Shaped by a glacier and eroded by floods, Madison Valley has steep hillsides and a history of stormwater flooding and sewer backups in the neighborhood. We helped address the perpetual urban flooding problem, contributing geotechnical and environmental recommendations in the design and construction of a 1.3M-gallon, underground stormwater storage tank. Our input to the alternatives analysis resulted in a tunneled alignment with several jacking/receiving shafts. Working with soft landfill soils and resolving historical contamination, we designed excavation, shoring, and deep foundations for tank support. As a result of our subsurface studies, change orders were minimized providing a degree of surety in cost and schedule. Our attention during construction further helped keep the project moving forward and on schedule while minimizing impacts to the community.