Sewage leaks into aquifer
An estimated 144,000 gallons of raw sewage leaked into the region’s drinking water aquifer late Wednesday after an underground sewer line ruptured in Hayden, Idaho
The sewage poses no immediate threat to nearby drinking water wells, but as the plume spreads it could endanger at least one well about 500 feet downstream, said John Tindall, with the Idaho Department of Environmental Quality.
“There is a concern about the impact” to the Spokane Valley-Rathdrum Prairie Aquifer, Tindall said. “As far as raw sewage spills go, it’s one of the bigger ones we’ve had in the area.”
The leak was discovered about 4:30 p.m. Wednesday near the intersection of Honeysuckle Drive and Reed Road, about one block west of U.S. Highway 95. Employees of the Hayden Area Regional Sewer Board worked with a contractor to stop the spill by 6 p.m.
The cause is under investigation, but officials believe the 15-inch-wide pipe broke after it was allowed to sag on uncompacted soil. The sewer line has been in place since the 1980s, Tindall said, but all the homebuilding in the area has meant several new connections to the system.
After the leak was discovered, lime was spread to disinfect the immediate area. About 144,000 gallons of untreated sewage could not be recovered and leaked into the nearby ground, Tindall said. The aquifer is about 250 feet below the ruptured line.
Although there’s some soil near the surface, most of what separates the sewage from the groundwater is gravel, which has little holding power or absorptive capacity. “We would assume that all of it gets down there, even though some of it gets stuck in the soil,” Tindall said.
The groundwater below the spill is part of the aquifer that supplies drinking water to more than 500,000 people in Kootenai and Spokane counties. Because of the massive size of the aquifer and the fact that the sewage will naturally break down over a period of “days and weeks,” Tindall said the spill does not appear to pose a threat to major municipal drinking water wells.
The aquifer near the site moves in a westerly direction at a rate of about 5 feet per day, Tindall said. The nearest well is about 500 feet southwest and serves at least 170 people in the Leisure Park development.
Experts are analyzing the possible health effects of the spill and should determine today if any special precautions are needed for downgradient wells. Raw sewage contains viruses and bacteria that can pose health threats, Tindall said, but the spill offers no immediate cause for concern.
Last year, at least 180,000 gallons of partially treated sewage sludge spilled into the Spokane River near Spokane when a storage tank collapsed at the city’s wastewater treatment plant.