Public Works and Environmental Services

Fairfax County, Virginia

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TTY 711

12000 Government Center Parkway
Suite 448 Fairfax, VA 22035

Christopher S. Herrington,

Slipline Replacement #1 (Old Mill Road)

(Project # WW-000028-002-E)

Project Background

The existing 12-inch sliplined gravity sewer along Old Mill Road was identified for rehabilitation due to its age and capacity. Initially constructed in 1955, the Old Mill Road Gravity Sewer (OMRGS) extends 2,170 feet and conveys wastewater to the Freund House Pump Station. In 1979, the initial 12-in-diameter pipe was rehabilitated with a high-density polyethylene (HDPE) liner, reducing the interior diameter to 10-inches. To address capacity and condition concerns, a Preliminary Engineering Report (PER) was completed in 2018. This evaluated the existing flow data and system hydraulics, regional development information, and analyzed alternative design solutions.

Photo: Final PER Overview Map of the OMRGS Study Area
Final PER Overview Map of the OMRGS Study Area


A design kick-off meeting was held in November of 2018 between the County and Engineer (Arcadis) to examine design options moving forward. Survey of the project area was performed by the County, and utility location and verification services evaluated potential utility conflicts. A tidal survey was also performed by the County to better understand tidal influences at the Douge Creek crossing that may impact design.

Design for Slipline Replacement #1, OMRGS, was completed in the Spring of 2020. It was determined that replacing 1,100 feet of the 10-inch sliplined gravity sewer with a new 16-inch sewer alignment would be the best long-term solution. Design decisions were also made to prevent disruption to residents’ sewer services and avoid sanitary sewer bypass pumping.

Photo: View of Old Mill Rd
View of Old Mill Road where the new sanitary sewer alignment will be placed under.

The project was placed out to public bid for construction in the Summer of 2021. Garney Construction was awarded the project and became the County’s general contractor in September of 2021. The Slipline #1 Replacement project has entered construction as of January 2022 with onsite work beginning in February of 2022.

Project Description

This project includes the installation of approximately 2,750 linear feet of new polyvinyl chloride (PVC) gravity sewer of varying sizes ranging from 4-inch pipe to 16-inch, as well as all associated manholes along Old Mill Road and on Mount Vernon Country Club property within the Mount Vernon District.

The primary goal of this project is to provide long-term solution to capacity concerns for surrounding neighborhoods and to accommodate additional flow from the neighborhood’s upstream sewer network. Ultimately, by replacing the existing sanitary sewer with a new alignment and a larger diameter pipe, the project will prevent future backup concerns and ensure quality collection of wastewater from neighboring homes.

Project Location

The project is located within the Mount Vernon District and along Old Mill Road.

Photo: Projects Limits and extent of work
Project limits and extent of work


Project Phase

This project is currently in Construction and is anticipated to be completed during the Fall of 2022.

Project Benefits

It is expected the improvements will serve the surrounding community for at least the next 50 years.

The Slipline Replacement #1 (Old Mill Road) project will:

  • Prevent costly emergency repairs
  • Provide residents with safe, reliable utility infrastructure
  • Reduce risks to public health and the environment


A Notice to Proceed was given to the contractor in November 2021. Site clearing and materials delivery began in February 2022. Trenching, installation of manholes and pipe, and backfill began at the end of February 2022. Work within the roadway of Old Mill Road is planned to begin the second week of March, 2022. Construction work is anticipated to be completed in Fall of 2022.

What to Expect

Residents may notice an increase in construction equipment and materials transported to the Old Mill Road construction entrance and staging areas located at Mount Vernon Country Club storage site. Temporary road closure and detour will take place for thru traffic. Old Mill Road will have one lane open with traffic controls in place so residents and students can still have access to their respective homes and learning centers.

Project Cost and Funding Source

Current Project Cost: $2,300,000

This project is included in the Fiscal Year (FY) 2022 - FY 2026 Adopted Capital Improvement Program (CIP) (With Future Fiscal Years to 2031). Funding is available in Project WW-000028, Gravity Sewers, Fund 69300, Sewer Construction Improvements.


For more information, please email, Senior Engineer III, Wastewater Design and Construction Division, Department of Public Works and Environmental Services, or call 703-261-4217.

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