1. Seasonal variation of chloride input from road salt application in a mixed urban/agricultural watershed in central Illinois
Lucas P. Chabela, Eric W. Peterson, Joe Miller
Illinois State University
Department of Geography-Geology
Normal, Il 61790

2. Background – Road salt
Compound containing chloride (Cl-) and either sodium, calcium, magnesium, potassium
Road salt (NaCl)usage has increased substantially due to growing population and urbanization since the 1950’s (Figure 1)
Chloride (Cl-) is a conservative ion
Figure 1: Road salt in End-Use from Deicing data obtained online from the United States Geological Survey (2005).

3. Background – Problems with Cl-
Chloride is also highly corrosive to steel and pipes used in water treatment plants and local bridges, which contributes to high and frequent repair cost (Kelly et al., 2012).
Secondary EPA drinking standard of 250 mg/L
High chloride concentrations can have negative even fatal effects on stream organisms and surrounding vegetation (Panno et al., 1999; Environment Canada, 2001; Corsi et al., 2010; Findlay and Kelly, 2011)
Stabilization of elevated chloride concentration in summer months (Ramakrishna and Viraraghavan, 2005; Corsi et al., 2015)
Figure 2: Photo of Little Kickapoo Creek located in central Illinois. Photo taken by Dr. Eric Peterson.

4. Background – Cl- storage
Chloride storage refers to a watersheds ability to accumulate Cl-
In the urban area of Chicago, Il, Kelly et al. (2012) estimated about 14% of the road salt (Cl-) is retained in the subsurface
Bester et al. (2006) simulated chloride transport and found well Cl- concentrations have not reached maximum concentrations after ~60 years
Positive relationship between Cl- storage and road salt application rates (Ludwikowski, 2016)(Figure 3)
Figure 3: Modeled chloride storage in net mass over time as road salt was applied for 60 continuous years over the winter months. Image obtained from Ludwikowski (2016).

5. Purpose
Modeling of a watershed can be helpful in understanding chloride storage
This project’s purpose is to:
1) Identify spatial and temporal changes in chloride loading on a small watershed scale
2) Establish a consistent data set for future GIS modeling of a watershed
Snow truck
Figure 4: A dump truck applying salt on roads. Image gathered from keffermazda.com.

6. Study Site/Methods Little Kickapoo Creek (LKC)
Low-gradient, perennial stream
Meanders through a glacial outwash valley
Background chloride concentration ~15 mg/L (Panno et al., 2006b)
Stream sampling occurs once every two weeks includes:
Discharge measurements
Water samples analyzed for major anions
7 sample sites along LKC
Figure 6: Little Kickapoo Creek sample site LKC2. Photo taken by Joe Miller.
Figure 5: Little Kickapoo Creek with sample site locations and land-use (Peterson and Benning, 2013).

7. Results
Figure 7: Temporal and spatial variation in chloride concentration through the 7 sample sites along LKC. The upper red line indicates the EPA secondary drinking standards of 250 mg/L and the lower red line indicates the background chloride concentration observed in the groundwater (Panno et al., 2006b).

8. Results
Figure 8: Box and whisker plots of seasonal and spatial variation of across the seven sampling locations at LKC. “X” represents the mean of these data and the line in the box is the median. The upper red line indicates the EPA secondary drinking standards of 250 mg/L and the lower red line indicates the background chloride concentration observed in the groundwater (Panno et al., 2006b).

9. Results
Figure 9: Scatter plot of seasonal chloride concentration plotted against temperature. The upper red line indicates the EPA secondary drinking standards of 250 mg/L and the lower red line indicates the background chloride concentration observed in the groundwater (Panno et al., 2006b).

10. Results
Figure 10: Upper graph shows precipitation in overall precipitation (blue) and snow (red). Lower graph shows maximum daily temperature (black) and average chloride concentration (orange) of the 7 LKC sample sites. Gray dotted line on the lower graph represents 32 degrees Fahrenheit and maximum temperatures below the dotted line represent potential times of deicing application. Maximum daily temperature and precipitation data obtained from the National Weather Service.

11. Results
Figure 11: Upper graph shows precipitation (blue). Lower graph shows chloride load in mg/s (black) and chloride concentration (orange) both at the LKC7 sample site. The red line indicates the background chloride concentration observed in the groundwater (Panno et al., 2006b).
Precipitation data obtained from the National Weather Service.

12. Conclusions Future work
There is an existing Cl- storage due to the concentration never returning to background groundwater levels
Cl- concentrations increase during the winter months (Dec – March)
Inverse relationship between Cl- concentration and temperature
Mobilization of chloride due to precipitation
Cl- should be recognized as an emerging contaminant due to human influences
Data collection will continue until May of 2017
GIS modeling projects to help characterize Cl- storage

13. Questions?
References Bester, M. L., Frind, E. O., Molson, J. W., and Rudolph, D. L., 2006, Numerical investigation of road salt impact on an urban wellfield, Groundwater, v. 44, no. 2, pg Corsi, S. R., Graczyk, D. J., Geis, S. W., Booth, N. L., and Richards, K. D., 2010, A fresh look at road salt: aquatic toxicity and water-quality impacts on local, regional, and national scales, Environmental Science Technology, vol. 55, pg Corsi, S. R., De Cicco, L. A., Lutz, M. A., and Hirsch, R. M., 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, vol. 508, pg Environment Canada, 2001, Priority substances list assessment report: Road Salts, Minister of Public Works and Government Services, Canadian Environmental Protection Act, Findlay, S. E. G., Kelly, V. R., 2011, Emerging indirect and long-term road salt effects on ecosystems, Annals of the New York Academy of Sciences, vol. 1223, pg Kelly, W. R., Panno, S. V., Hackely, K. C., 2012, Impacts of Road Salt Runoff on Water Quality of the Chicago, Illinois, Region, Enironmental & Engineering Geoscience, vol. 18, pg Ludwikowski, J., 2016, The transport and fate of chloride within the groundwater of a mixed urban and agricultural watershed, [M.S.: Illinois State University, 56 pg. Panno, S. V., Nuzzo, V. A., Cartwright, K., Hensel, B. R., Krapac, I. G., 1999, Impact of urban development on the chemical composition of ground water in a fen-wetland complex, Wetlands, vol. 19, pg Panno, S. V., Hackley, K. C., Hwang, H. H., Greenberg, S. E., Krapac, I. G., Landsberger, S., and O’Kelly, D. J., 2006b, Source identification of sodium and chloride in natural water: preliminary results, Groundwater, v. 44, no. 2, pg Peterson, E. W., and Benning, C., 2013, Factors influencing nitrate within a low-gradient agricultural stream, Environmental Earth Sciences, v. 68, no. 5, pg Ramakrishna, D. M., Viraraghavan, T., 2005, Environmental Impact of Chemical Deicers – A Review, Water, Air and Soil Pollution, vol. 166, pg U.S. Geological Survey, 2005, United States Geological Survey, (accessed September, 2016).