Sewer gas odors in the summertime. Not what most people want to smell in or around their homes anytime, but especially not when temperatures and humidity are up.

Sanitary sewer pipes lie under or along most of our roadways, whisking away wastewater to treatment plants with rarely a problem. The pipes usually are situated far underground, and along low-lying stream corridors, where gravity does the job of conveyance from household laterals to the larger sewer mains, and then to the plants that daily treat millions of gallons of wastewater to local, state, and federal standards before the cleaned and disinfected effluent is discharged back into the river.

However, depending on weather conditions, or the occasional pipe blockage, the powerful odor of sewer gas reminds us that wastewater infrastructure is all around us, especially along popular recreational trails in stream valleys. Sewer gas complaints are handled by the county’s Department of Public Works.

Candy cane-shaped vents and large manholes can be seen along stream valley trails and, most of the time, the vents barely are noticed. However, noxious hydrogen sulfide (which forms naturally as organic matter decomposes) normally contained by the pipe system, can escape the gaskets designed to keep the odors in. That’s when you can smell it, and the complaints begin. The Department of Public Works and Environmental Services (DPWES) inspects more than 200 miles of pipe, and pressure cleans up to 500 miles of pipe each year. Defective components are repaired or replaced, and pipes are re-lined as necessary. The annual budget for infrastructure repair and replacement runs to millions of dollars each year, but odor can be especially vexing.

In the Bailey’s Crossroads area, where many odor complaints were recorded, staff installed a temporary system that injects calcium nitrate into a pump station wet well, to reduce odors downstream. That is an interim solution, while more investigation to determine the sources of the odor is underway. The study area encompasses a population of about 55,000 and includes shopping areas and 18 schools as well. Minimizing the creation and release of hydrogen sulfide is a public health responsibility and, while the source of the gas remains elusive, another round of testing is planned.

Gravity may be the culprit, as pipe elevation drops 80 feet near Columbia Pike, and the velocity of the wastewater flowing downhill pressurizes the pipes and forces the gas out of the downstream manholes. The temporary injection system for calcium nitrate appears to have reduced complaints, so a permanent injection system will be included as part of the pump station rehabilitation. More carbon filter odor cartridges may be added to affected manholes, as inspections and maintenance continue. Fairfax County’s entire wastewater system includes more than 3,200 miles of pipe, and 63 pump stations, and the Wastewater Trouble Response Center (703-323-1211) has staff on-call for rapid response to spills and other emergencies. These staff are the unsung heroes, providing services to county residents and businesses at all hours, year-round. For more information logon to www.fairfaxcounty.gov/publicworks/news.