1. Abstract
The use of road salt to deice roadways during winter and the subsequent runoff during spring months have
shown negative effects on aquatic ecosystems.1 Since the Fall of 2007, the chloride ion concentration of the Pike
River that flows through Racine, Kenosha and into Lake Michigan has been quantified. In 2012, sampling sites
on the Pike Creek, which flows through the northern portion of Kenosha, were added and monitored. Data from
2014 showed that two dates in late February and early March exceeded 500 ppm chloride in the river, while the
mean chloride concentration from late February to early May was 368 ppm, with a range of 205 to 622 ppm. Of
the 13 sampling dates in this time period, 12 of the dates measured a chloride concentration above the chronic
level of 230 ppm set by the EPA. During the same time period, the chloride values of the Pike Creek measured
50 to 70 ppm higher than the river. Baseline chloride concentrations of the Pike River measured in the fall have
shown an increase from 101 ±22 ppm in 2011 to 153 ±5 ppm in 2014. This data suggests chloride retention in
the river over time. Since Fall 2012, Carthage College has partnered with Root-Pike-WIN on the Pike River
Watershed-Based Plan. As a research institution in the watershed contributing chloride data, this research will
directly aid in setting outcomes to improve the water quality of the Pike River Watershed in the future.
Introduction
In snow laden areas of the United States, cities use sodium chloride to prevent the accumulation of ice on the
roadways. Over 90% of the salt added to bodies of water is due to run off from melted snow containing NaCl for
deicing.2 The United States annual sale of road salt increased from 0.28 million metric tons in the 1940’s to 16.0
million metric tons in 2008. The buildup of chloride ions has now increased to a point where it is a threat to the
health of aquatic ecosystems in areas that use road salt heavily.3 As set by the U.S. Environmental Protection
Agency (USEPA), the acute level for chloride in freshwater is 860 mg/L or parts per million (ppm) and the
chronic level is set at 230 mg/L. When the chloride concentration in the water exceeds the USEPA chronic or
acute levels, harm can be done to the aquatic life and may cause death.2
Chloride concentration, pH and conductivity were all measured on different sites along the Pike River and Pike
Creek. These measurements were recorded from September 2013 to December 2014, which is a continuation of a
study that has been conducted since 2007. Since 2007, chloride concentrations in the Pike River have increased
in spring months compared to the fall months due to the influx of sodium chloride used to deice the roadways in
the winter. An increase in baseline chloride levels in the fall has increased since 2007 as well, indicating chloride
retention within the Pike River. This poster will discuss the methods of research and the analysis of this data in
comparison to previous years and the relationship between conductivity and chloride in this part of Wisconsin.
Experimental Methods
Water samples were collected from the Pike River, Pike Creek, and Lake Michigan at sites shown in Figure 3.
Two samples were collected from each site and stored at 4˚C. A calibrated Ross Orion pH electrode was used to
measure pH of the water samples. To measure conductivity, a 2-point calibrated Oakton Waterproof EC Testr11
Dual Range Meter was used. Conductivity and pH measurements were measured the same day samples were
collected. Chloride levels were measured using an Accumet Chloride Combination Ion Selective Electrode (ISE)
after adding potassium nitrate to adjust the ionic strength. Prior to measuring chloride levels in the water
samples, a calibration curve of mean voltage versus the log of the chloride concentration was prepared using
known chloride standards ranging from 20.00 ppm to 1000.0 ppm Cl- depending on the season. The voltage
readings obtained for the water samples using the ISE were inserted into the equation of the line of best fit from
the calibration curve and used to determine the concentration of chloride in each sample (Figure 1, Table 1).
Figure 1: Chloride Calibration Curve for 10/23/14.
Site Mean Voltage
± Stand.
Dev. (mV)
Mean Chloride Concentration
± Stand. Dev. (ppm)
A 10.6 ± 0.8 126 ± 4
B 9.6 ± 0.9 132 ± 5
E 9.9 ± 0. 4 131 ± 2
F 9.9 ± 0.4 130 ± 2
L 4.2 ± 0.3 164 ± 2
M 57.7 ± 0.6 18.1 ± 0.5
PETS 10.3 ± 0.9 128 ± 5
W -2.75 ± 0.5 222 ± 4
X 69.9 ± 1.0 11.6 ± 0.5
FB 133.9 ± 0.5 0.88 ± 0.1
Table 1: Measured Voltage, Chloride Concentration
and Standard Deviation by Site for 10/23/14 Samples
Figure 3: Sampling Sites along the Pike River and Pike Creek.
Results
Figure 2: Mean Lower Pike River and Pike Creek Chloride Concentrations for Fall 2013 to Fall 2014.
Figure 4: Relationship between Cl- Concentration and Conductivity Data
Figure 5: Comparison of inches of snow, tons of salt applied and [Cl-]
for the past five years.
Chloride Calibration
(mV vs. log [Cl-], ppm)
Conductivity Calibration
( [Cl-], ppm vs. uS/cm)
% Difference
y = -56.488x + 153.89
R2 = 0.999
y = 0.281x + 8.4704
R2 = 0.996
Sample 1: 1820 + 19 ppm Sample 1: 1984 + 1 ppm +8%
Sample 2: 959 + 10 ppm Sample 2: 1104 + 1 ppm +13%
Sample 3: 508 + 10 ppm Sample 3: 491 + 2 ppm -4%
Sample 4: 295 + 4 ppm Sample 4: 312 +1 ppm +6%
Sample 5: 32.3 + 0.3 ppm Sample 5: 79 + 1 ppm +59%
Table 2: Analysis of Snow by Two Different Curves
[Cl- ], ppm
Tons of Road Salt
Inches of Snow
Figure 6: Mean Chloride Concentration for the Lower Pike River since 2008.
Discussion
The data in Figure 2 and 6 support the conclusion that road salt application increases
chloride concentrations in water samples during spring months from Fall 2013 to Fall 2014
and since Fall 2008. Data shows many sites measuring above the chronic level of 230 ppm
for multiple weeks, with some sites nearing the acute level which may cause long term
toxicity effects. Figure 5 further supports these data, showing the general trend that
increased snowfall results in higher road salt usage and higher chloride concentrations.
Furthermore, the Pike Creek consistently measured higher chloride concentrations
throughout the year in comparison to the Pike River due to the location of the Pike Creek in
a more metropolitan area with a drainage basin that is covered by a larger surface area of
impervious pavement.
Conductivity values are commonly measured to estimate chloride concentrations due to ease
of use and calibration. Table 2 shows the chloride concentrations of multiple snow samples
determined by two different calibration curves. Results deviated by greater than 50% at [Cl-]
< 100 ppm and by 8% at [Cl-] > 900 ppm. At higher chloride concentrations, when sodium
and chloride are the main ions present, a solid estimate of the chloride concentration from
conductivity measurements results. Figure 4 shows a moderate correlation (R2 = 0.71)
occurs between the measured chloride concentrations and the measured conductivity data
based upon data from Fall 2012 through Fall 2014 in the Pike River watershed. At
conductivities greater than 2250 uS/cm a better correlation results,2 but based upon the data
presented here, no clear estimation of chloride concentration results in this range of
conductivity measurement, which is most likely due to other ions impacting the conductivity
measurements. In addition to the influence of other ions in the water on the conductivity
measurements, a 1 or 2-point calibration of the conductivity meter may not be rigorous
enough to provide accurate data. A calibration curve based upon six standards (from 707 to
10000 uS/cm) only showed an R2 of 0.98. Conductivity measurements can be used to gauge
overall road-salt runoff from season to season, but detailed and accurate changes in chloride
concentrations is best determined by other methods.
Conclusion and Future Work
This research data supports the hypothesis that road salt increases chloride concentrations
within the watershed, especially during the spring months. Chloride concentrations are
consistently chronic in both the Pike River and Pike Creek during the spring months, which
could be causing harm to the ecosystem. The analysis of the relationship between Chloride
concentration and conductivity indicates some correlation of the results, but measurement of
only chloride concentrations provides the most accurate and precise data.
This research will be continued in the future and a new method using Ion Chromatography
to measure chloride will be developed in the next year and compared to the ISE analysis.
References
1 Novotny, E. V.; Murphy, D.; Stefan, H. G. “Increase of urban lake salinity by road deicing salt.” Sci. Total Environ.
2008, 406, 131– 144.
2 Corsi, Steven R., David J. Graczyk, Steven W. Geis, Nathaniel L. Booth, and Kevin D. Richards. "A Fresh Look at
Road Salt: Aquatic Toxicity and Water-Quality Impacts on Local, Regional, and National Scales." Environmental
Science and Technology, 2010, 44, 7376-7382
3 Kelly, Victoria R., Gary M. Lovett, Kathleen C. Weathers, Stuart E. G. Findlay, David L. Strayer, David J. Burns,
and Gene E. Likens. "Long-Term Sodium Chloride Retention in a Rural Watershed: Legacy Effects of Road Salt on
Streamwater Concentration."Environmental Science & Technology 42.2 (2008): 410-15.
Road Salt Tonnage data obtained from http://transportal.cee.wisc.edu/storm-report/weekly-reports/
Snow Fall data was obtained from http://premiuma.accuweather.com/premium/past-months.asp
y = -57.063x + 130.54
R² = 0.9994
-10.0
0.0
10.0
20.0
30.0
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50.0
60.0
0.000 0.500 1.000 1.500 2.000 2.500 3.000
Voltage,mV
Log [Chloride], ppm
Voltage, mV versus Log [Chloride], ppm for 10/23/14
y = 0.2903x - 86.942
R² = 0.7055
-100
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0 500 1000 1500 2000 2500 3000
ChlorideConcentration(ppm)
Conductivity (uS/cm)
Chloride Concentration vs. Conductivity
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2009-2010 2010-2011 2011-2012 2012-2013 2013-2014
RoadSalt(tons)
Chloride(ppm)andSnowFall(inches)
Year
Chloride Concentration, Tons of Road Salt and Inches of Snow