From 9News.com (Brandon Rittman):
Denver’s Cherry Creek got saltier over the past decades, with chloride levels on pace to pose a danger to fish in the city’s iconic tributary of the South Platte River…
Cherry Creek’s winter average rose closer to that threshold, measuring 174 mg/l between 2006 and 2010, which is up from a wintertime average of 122 mg/l during the 1990 to 1994 seasons – a jump of 43 percent.
The USGS says as more areas become urbanized, the use of rock salt on roads and sidewalks increases, making its way into streams.
More importantly, the data shows the problem compounding year over year because stream systems are not able to flush out all of the salt during the warm months.
The effect is a higher baseline of salt content each year, allowing the levels to inch upward each cold season in urban areas.
Salt compounds like magnesium chloride and rock salt are highly effective at decreasing the hazards of icy surfaces.
“Deicing operations help to provide safe winter transportation conditions, which is very important,” the study’s lead author Steve Corsi said in a press release. “Findings from this study emphasize the need to consider deicer management options that minimize the use of road salt while still maintaining safe conditions.”
There are few true alternatives to road salt, and other treatments can come with their own pollution problems. For instance, applying sand to roadways can cause air pollution when cars grind the material into dust.
The USGS study found similar increases over the time period in other areas of the country, with the most severe chloride pollution levels measured in midwestern cities like Milwaukee, Chicago, Detroit, and Cleveland.
Salt applied in winter is a concern year-round. The study concludes, “elevated chloride concentrations in these streams through all seasons have implications on long-term exposures to chloride for aquatic organisms.”
The average summertime chloride level in Cherry Creek rose from 62 to 101 mg/l during the time periods in the study.
By contrast, the study found streams in less-developed areas of Wisconsin and Oregon were able to maintain average chloride levels measurable in single digits.
More water pollution coverage here.