Environmental Protection

USGS Measures High Chloride Levels in 40% of Tested Streams

Levels of chloride, a component of salt, are elevated in many urban streams and groundwater across the northern United States, 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 recently 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.

Only 4 percent of the streams in agricultural areas had chloride levels that exceeded the recommended federal criteria set to protect aquatic life (compared to more than 40 percent of urban streams). Overall, 15 percent of all streams had chloride levels exceeding the criteria.

Chloride concentrations in shallow groundwater (not used for drinking) were 16 times greater in urban areas than in forests, and 4 times greater in urban areas than in agricultural areas.

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