Chemical de-icer melting its way into aquifer

Chemical de-icers have become the weapon of choice for improving traction on roads and highways across the region. Their increase in use has also shown up in water samples taken from the Spokane Valley/Rathdrum Prairie Aquifer.

Experts in Idaho and Washington stress there’s little cause for concern, but agencies in both states say they are keeping a close eye on the chemical’s presence.

“It’s one of those things that has come up on our radar screen,” said Gary Stevens, an Idaho Department of Environmental Quality hydrogeologist. “We haven’t seen anything to indicate it’s a problem, but it’s on our radar screen.”

Beginning in the early 1990s, magnesium chloride replaced rock salt as the ice-fighting agent used by most governments in the Northwest. The chemical is more expensive than salt, but when applied correctly it sticks longer to pavement and can be particularly effective against black ice, according to highway engineers. In addition, the chemical can be sprayed on roads before storms to prevent ice. Magnesium chloride is also less harmful to aquatic life and plants than salt – magnesium, in fact, is actually beneficial to plant growth.

In Spokane County alone, about 175,000 gallons of magnesium chloride are now sprayed on streets and highways during a typical winter, said county engineer Ross Kelly. Another 150,000 gallons are used by the city of Spokane. The chemical is also widely used in Idaho.

In the 1980s, before the use of magnesium chloride, water samples from the aquifer would typically contain between 1 and 2 milligrams of chloride per liter. Since 1995, the average has risen to 3 to 4 milligrams, said Dale Peck, environmental response and technology director for the Panhandle Health District, which conducts regular tests from wells across the area. The drinking water standard for chloride set by the U.S. Environmental Protection Agency allows up to 250 milligrams per liter.

“This is obviously not a health threat,” Peck said. “It’s an indication of a rise.”

But the growing presence of chloride is also an indication of the growing human impact to the aquifer, which supplies drinking water to more than 400,000 people in the region. Dale Marcy, a chemistry and environmental science instructor and North Idaho College, said the aquifer has been placed under new strains because of the area’s growth. Fields once covered in grass are now growing houses, septic tanks, businesses and even a train refueling depot.

Chloride’s fingerprint “may be a better indicator of other substances that are mobile in the environment that are also moving toward the aquifer, things we haven’t thought yet of measuring,” Marcy said. This could include new pesticides or hazardous household chemicals.

Marcy said he expects the presence of chloride to only increase. “I imagine it will continue to go up,” he said. “Once it becomes bad then we’ll start doing something about it.”

Experts say magnesium chloride is likely the most environmentally friendly agent to treat icy roads. Traction sand dirties the air, cracks windshields and can even smother trout spawning beds in streams near roadways. Sodium from salt is particularly harmful to the environment and aquatic life. Not using anything doesn’t seem to be an option, Marcy said.

“Americans expect to drive very fast on the roads in winter,” Marcy said. “They want to be able to roll up to the stop signs and slam on the brakes.”

Marcy said he thinks the Idaho Department of Environmental Quality is being wise by keeping an eye on the potential impact of chloride from de-icers, even if the current levels are low.

The Idaho Transportation Department also is trying to track where its de-icers flow. In 2003, the agency began testing for chloride in soil samples along Interstate 90 and U.S. Highway 95 in the Coeur d’Alene area, agency spokesman Jeff Stratten said. The preliminary results are inconclusive, but they have so far been well below the potentially hazardous level, he said. Stratten also credited magnesium chloride for reducing the amount of wintertime crashes in the region, despite the booming growth in traffic.

“Our accident rates are staying at or lower than they have been in the past,” Stratten said.

In northeastern states, some freshwater streams and ponds are now a quarter as salty as the ocean because of the widespread use of rock salt to melt ice, according to a recent study conducted by researchers at the Institute of Ecosystem Studies, based in Millbrook, N.Y. Long-term records are showing that salinity levels are increasing and the environment is no longer able to flush all the chloride out of the system, said Peter Groffman, one of the authors of the study. Magnesium chloride might be safer than salt, but its use does not come without environmental risks, he said.

“The chloride seems to stick around longer than we thought,” he said. “If you’re making massive applications of de-icer, you’re going to end up with lots of salts in streams, lakes and perhaps the aquifer.”

Washington law prohibits any degradation of the aquifer, but the issue of chloride is tricky, said Mark Hepp, with the state’s Department of Ecology. Pinpointing the exact source of the chloride is one problem – water softeners in homes with septic systems also dump salt into the aquifer. And the level of chloride appears to be low in a pool of water believed to be vast.

“It’s a discharge of a pollutant but it may not be causing pollution. It’s a subtle difference,” Hepp said.

Much about the aquifer remains a mystery. Federal and state officials are now embarking on a massive $3.5 million data-gathering effort to map the aquifer and to provide management guidance to the governments charged with protecting the resource. Getting a handle on the impacts of de-icers to the aquifer is just one part of the mystery, said Reannette Boese, Spokane County’s groundwater coordinator.

“We don’t have good evidence because it moves through the aquifer so fast,” Boese said. “If you don’t sample on the right day, you don’t find it.”