1. Prepared for: Dr. Joel Moore, Towson University
Prepared by: Jordan Sedlock, Towson University, GEOL 305, Environmental Geology
Topic: Increasing chloride trends in all seasons in snow-affected urban watersheds
Date: April 22, 2015
Source: Corsi et al. (2015) River chloride trends in snow-affected urban watersheds: increasing concentrations outpace urban
growth rate and are common among all seasons. Science of the Total Environment. 508: 488-497.
Statement of Issue
Increased river chloride concentrations are resultant of increased road salt application to
impervious surfaces during deicing periods.
A study conducted by Corsi et al. found that 29% of snow-affected urban watershed sites
examined, exhibited on average more than 100 days per year with chloride concentrations higher than the
EPA chronic criteria. The U.S. EPA defines chronic criterion for chloride exposure to be 230 mg/L on a
4-day average.1
Chloride concentration trends in urban watersheds are found to be increasing in deicing
conditions as well as present, now, in non-deicing conditions, suggesting that chloride is being stored
within hydrologic reservoirs (increasing baseline concentrations of chloride) and slowly released
throughout the year. The increases in chloride concentrations are attributed to increased road salt
application to the increasing urban land cover during deicing periods. The effects of increased chloride
are damaging to the environment and hydrologic systems as well as aquatic life in affected areas. This
excess sodium chloride increases salinity and threatens drinkability of surface water in affected areas;
within the next century, scientists predict that this source of water will no longer be potable and fit for
human consumption.
Historical Background
From the 1940s to the 1980s, rate of road salt application increased to an annual average of 9.6
million metric tons/year; from the 1980s to 2011, an annual average of 19.6 million metric tons/year.1
Also, from 1987 to 2010, road salt sales have increased by about 3.9%/year while urban land cover has
only increased by about 2.8%/year.1
Road salt sales have outpaced urban land cover by more than 40%.1
More road salt is being applied to impervious surfaces for deicing than is necessary, either, in attempt to
maintain longer, ice-free conditions, because density of impervious surfaces have increased per unit of
urban land cover, or differences in weather between the 40s and now could warrant different application
rates and different amounts of road salt. Also, increased usage of road salt has increased baseline
concentrations of chloride in shallow groundwater systems, indicated by present and elevated levels of
chloride observed throughout the entire year.
Potential Solutions
Potential solutions for this issue include reducing applications of road salt, providing training for
most effective use, pre-wetting salt to maximize retention to road surfaces, using carefully calibrated
applicators, implementing anti-icing techniques using organic glycols, for example, to facilitate plowing,
or using alternative chemicals such as organic salts like calcium magnesium acetate or sodium acetate. It
would be difficult to reduce application because of increased density of impervious surfaces however;
using carefully calibrated dispensers to evenly distribute salt could help reduce excess amounts applied to
roads. Pre-wetting is also an option that is effective and low in cost. Proper training for employees is very
important as well as relatively low in cost and more effective than not providing any type of informative
seminar prior to deicing. As far as alternative chemicals, organic compounds used for deicing tend to have
negative impacts on the environment similar to inorganic compounds. Environmental assessment is
recommended prior to implementing use of any new organic compounds for deicing.
Recommendations
1) Provide information seminar to ensure employees understand importance of proper application
2) Implement a pre-wetting technique to ensure maximum retention to road surfaces/ reduce runoff
3) Utilize carefully calibrated dispensers to evenly disperse salt/ reduce excessive application/
reduce runoff
4) Assess environmental conditions and consider implementing different chemicals to slow/ lower
increasing chloride concentrations