As the City of Cumberland has grown, its aging storm and sewer system has faced capacity problems, with excess effluent being released into the Potomac River. In an effort to end this dumping process, the city undertook an initiative to construct holding tanks to store excess effluent until it can be neutralized at a treatment plant. Carroll Engineering provided structural services to construct the $30 million Cumberland CSO Storage Facility, a concrete tank capable of holding up to 10 million gallons of wastewater. Located just west of the City of Cumberland Wastewater Treatment Plant, the tank measures 200 feet by 200 feet with a depth of 20 feet. The tank was constructed entirely below-grade, allowing for the usable space above ground to be converted into a basketball court serving the local park. CEI provided full structural designs for the entire project, including poured-in-place reinforced concrete walls, underground pipes connecting to the treatment plant, and a mat slab foundation.