Levels of chloride, a component of salt, are elevated in many urban streams and groundwater across the northern U.S., according to a new government study.
Chloride levels above the recommended federal criteria set to protect aquatic life were found in more than 40 percent of urban streams tested. The study was released today by the U.S. Geological Survey (USGS). Elevated chloride can inhibit plant growth, impair reproduction, and reduce the diversity of organisms in streams.
The effect of chloride on drinking-water wells was lower. Scientists found chloride levels greater than federal standards set for human consumption in fewer than 2 percent of drinking-water wells sampled in the USGS study.
Use of salt for deicing roads and parking lots in the winter is a major source of chloride. Other sources include wastewater treatment, septic systems, and farming operations.
"Safe transportation is a top priority of state and local officials when they use road salt. And clearly salt is an effective deicer that prevents accidents, saves lives, and reduces property losses," said Matthew C. Larsen, USGS Associate Director for Water. "These findings are not surprising, but rather remind us of the unintended consequences that salt use for deicing may have on our waters. Transportation officials continue to implement innovative alternatives that reduce salt use without compromising safety."
This comprehensive study examines chloride concentrations in the northern U.S. covering parts of 19 States, including 1,329 wells and 100 streams.
Land use matters
Chloride yields (the amount of chloride delivered per square mile of drainage area) were substantially higher in cities than in farmlands and forests. Urban streams carried 88 tons of chloride per square mile of drainage area. Forest streams carried about 6 tons of chloride per square mile.
Only 4 percent of the
|Contact: John Mullaney|
United States Geological Survey