The risk of overflowing wastewater mucking up post office operations in Merrifield should be alleviated sometime this fall.
That’s when the Fairfax County Department of Public Works and Environmental Services (DPWES) anticipates completing a project to upsize the sewer pipes near the Mosaic District.
Construction began in mid-May to replace an existing gravity sewer in Merrifield that carries wastewater from both the Mosaic District and the Dunn Loring Metro station area. Sewage from those neighborhoods flow to a chokepoint on the U.S. Postal Service’s property at 8409 Route 29 that has reached capacity, according to DPWES.
The new pipe will be 18 inches wide with the capacity to handle about 7.1 million gallons of water per day.
“The pipe was sized to accommodate the projected future development and population growth of the area based on the comprehensive plan,” DPWES spokesperson Sharon North said by email.
The Fairfax County Comprehensive Plan envisions Merrifield as a suburban center with denser, mixed-use development concentrated in “core areas” around the Metro station and Mosaic District. Other areas should “remain suburban in character,” though pedestrian, bicycle and transit improvements are recommended throughout to reduce people’s dependence on cars for travel.
Home to more than 11,000 people and over 1,600 businesses, as of 2021, Merrifield has seen development boom over the past two decades, with property assessments rising in value by 66.8% since 2005, according to the county’s Community Revitalization Section.
Though there hasn’t been a ton of new construction in the past few years, the county and developer Conifer Realty broke ground in June on an 80-unit affordable apartment building on Telestar Court. Additional development has been proposed near the core areas, including at the Alliance Center and Prosperity Business Campus.
On its project page, DPWES says the gravity sewer enhancements will alleviate the chokepoint near the post office, preventing potential overflows into the parking lot and engineering building, while also ensuring the area’s infrastructure is sufficient to support future growth.
Using a process called pilot tube microtunneling, the project is specifically enlarging pipes between manholes 58, 59 and 60, which are located respectively by the USPS engineering building, in the postal service’s mail carrier facility parking lot, and the adjacent PNC Bank parking lot:
Construction implementation using Pilot Tube Microtunneling will consist of drilling bore holes and tunneling underneath the ground to have the least amount of impact to USPS on the ground surface. The construction project will utilize two receiving pits (located at Manhole 60 in the PNC bank parking lot across from Caboose Brewery, and at Manhole 58 on USPS property). The jacking pit where the pilot tube microtunneling machine will bore from is located at Manhole 59 at the Mail Carrier Facility.
As of last Friday (Aug. 8), construction crews had finished installing a 36-inch steel casing pipe between manholes 58 and 59, and the pilot tubing work between manholes 59 and 60 were underway, DPWES said.
“Spacers are being ordered based on exact field measurements of the installed 36” steel casing and the gravity sewer pipe will be placed inside the casing pipe and supported by the spacers,” North said.
Because the gravity sewer pipe runs directly beneath the postal service’s mail truck loading zone, DPWES coordinated the design closely with USPS.
The Merrifield capacity upgrade is one of several wastewater projects that DPWES is currently working on. Other planned improvements include expansions in the Accotink Creek watershed and in Tysons.
In its most recent capital improvements plan (CIP), the county allocated over $50 million to gravity sewer capacity improvements for fiscal year 2026, which began on July 1. DPWES estimates that $388.64 million will be needed just for these projects to expand and replace existing sewer lines through FY 2034.
