Project Background

This project is for the renewal and rehabilitation of 1,200 linear feet of the Scott’s Run Siphon Facility. Fairfax County owns and operates three siphon pipes (14-inch, 18-inch, 24-inch) that convey the County’s wastewater flows across the Potomac River, through Carderock National Park and connecting to the DC Water’s Potomac Interceptor in Maryland. The trenchless rehabilitation method selected to renew this facility is the cured in place pipe (CIPP) method. CIPP is commonly used in similar applications due to its cost-effectiveness, schedule benefits and limited impact to residents and environment.

This project will be completed in two phases, with the first phase of lining taking place in Scott’s Run Nature Preserve and the second phase will occur in Carderock National Park. Fairfax County is coordinating with Fairfax Park Authority and National Park Services to ensure safety of the public and to minimize impacts to the trails.

Project Location

Scott’s Run Nature Preserve in Fairfax County, VA and National Park Service Carderock Recreation Area in Potomac, MD.

Project Phase

Phase 1 Construction began on February 16th, 2026, and included CIPP lining of the siphon pipes within Scott’s Run Nature Preserve. Construction was completed on August 10th, 2026.

Phase 2 is currently in design and includes the CIPP lining of the siphon pipes under the Potomac River into Carderock National Park. It is anticipating that construction will begin in fall of 2027 and full project construction limits will be confirmed during the design phase as well as a more refined construction schedule.

Timeline

What to Expect

During design, residents and trail goers may see Fairfax County Staff and their representative contractors completing non-invasive survey of the surrounding trail and trees or completing site walks.

During Phase 1 construction, the Scott’s Run Nature Preserve will be closed to visitors for a period of three months. Updates on the closure will be communicated on this webpage. Fairfax County is working with Fairfax County Park Authority to minimize project impacts. For alternate park locations and trails to explore during this temporary closure, residents are encouraged to use the Park Authority’s Park Amenity Locator and Trail Buddy tools. During Phase 2 Construction there will likely be a small portion of Carderock National Park closed off to the public along the sewer easement. There will be limited impacts Carderock National Park activities and amenities during construction of Phase 2.

Project Cost and Funding Source

This project is fully funded through sewer service charges from existing customers and availability charges, which are one-time fees for the initial connection to the system. No tax dollars are funding these improvements.

Contact

For more information, please email Jennifer Howells, Engineer IV Fairfax County Wastewater Collection Division at jennifer.howells@fairfaxcounty.gov or call our residential wastewater 24-Hour Customer Communications Center 703-323-1211 | TTY 711.