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.
Highest levels in streams in the winter
In urban streams, the highest levels of chloride (as great as 4,000 parts per million, which is about 20 times higher than the recommended federal criteria) were measured during winter months when salt and other chemicals are used for deicing.
Increases over time
Increases in chloride levels in streams during the last two decades are consistent with overall increases in salt use in the U.S. for deicing.
Increasing chloride yields are linked to the expansion of road networks and parking lots that require deicing, increases in the number of septic systems, increases in wastewater discharge, and increases in saline groundwater from landfills.
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.
|Contact: John Mullaney|
United States Geological Survey