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News Release


September 16, 2009
John Mullaney 860-291-6760 jmullane@usgs.gov
Diane Noserale 703-648-4333 dnoseral@usgs.gov

Chloride Found at Levels that Can Harm Aquatic Life in Urban Streams of the Northern U.S.--Winter Deicing a Major Source

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The USGS report and maps of monitoring sites are available online.

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.

Selected Highlights

Land use matters

Highest levels in streams in the winter

Increases over time

Sources can vary locally

Chloride in ground and surface waters comes from many sources including the use and storage of salt for deicing roads, septic systems, wastewater treatment facilities, water softening, animal waste, fertilizers, discharge from landfills, natural sources of salt and brine in geologic deposits, and from natural and human sources in precipitation.


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