08/25/2026
Construction is nearing completion on the shaft and tunnel work for the Milestone Reservoir project in Loudoun County, Virginia, where a retired quarry is being transformed into a billion-gallon raw water reservoir.
The project takes an innovative approach to water supply resilience by transforming the quarry into a strategic water bank that can provide a backup supply when drought, storms, or poor water quality affect the Potomac River. By storing water when river conditions are favorable and drawing from the reservoir when conditions are less reliable, the project will give Loudoun Water greater flexibility in managing the region’s water supply.
The project includes a 300-foot-deep pump shaft and three intake tunnels at varying elevations, which will allow stored water to be withdrawn from the reservoir and conveyed to Loudoun Water’s treatment facility. A new 40-million-gallon-per-day pumping station will support the system. The multiple intake elevations will also provide flexibility in selecting water from different depths within the reservoir based on water quality conditions.
Converting a retired quarry into a functioning water-storage facility also requires specialized geotechnical and tunnel engineering. Schnabel is serving as lead geotechnical engineer and tunnel designer, supporting the project through design and construction. Our work includes the deep intake shaft and tunnels, as well as geotechnical considerations related to the quarry rock slopes. Steve Miller, Matthew Goff, and Eoin Durcan are among the Schnabel team members supporting these efforts.
Once complete, the Milestone Reservoir will provide up to two months of stored water for the region, helping Loudoun Water maintain a more reliable supply during droughts, storms, and periods when Potomac River water quality is impacted.
We’re proud to contribute our geotechnical and tunnel engineering expertise to this innovative approach to water supply resilience that will help provide reliable water for a growing community for years to come.
