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Implications of Winter Salt Application on LID Maintenance and Pollution Prevention Strategies
Phil James P. Eng, Credit Valley Conservation
Philadelphia Low Impact Development Symposium –Greening the Urban Environment
September 25th to 28th 2011
OutlineBackground• Urban watersheds and rising chloride levels• Issues associated with winter maintenance practices and implications to LID
Overview of Comparison Studies• Treated Salt versus Sand Salt – Public Road• Sodium Chloride versus Potassium Chloride – Parking Lot
Conclusions/Next Steps
• Rock Salt is one of the most commonly used winter de-icer on roads, parking lots and walk ways.
• Readily available, inexpensive and effectively depresses the freezing point of water to melt ice.
Sources of Chloride in our Watershed
Chloride concentrations – Sheridan Cr
0
1000
2000
3000
4000
5000
1976 1980 1984 1988 1992 1996 2000 2004 2008
Conc
entra
tion
(mg/
L)
Concentration, mg/L DW standard 75th percentile Linear Trendline
Cooksville Creek Real Time Monitoring
Chloride Levels September 2010 to March 2011
0
2500
5000
7500
10000
12500
15000
17500
20000
10/0
9/20
10 1
7:45
15/0
9/20
10 2
:45
19/0
9/20
10 1
1:45
23/0
9/20
10 2
0:45
28/0
9/20
10 5
:45
02/1
0/20
10 1
4:45
06/1
0/20
10 2
3:45
11/1
0/20
10 8
:45
15/1
0/20
10 1
7:45
20/1
0/20
10 2
:45
24/1
0/20
10 1
1:45
28/1
0/20
10 2
0:45
02/1
1/20
10 5
:45
06/1
1/20
10 1
4:45
11/1
1/20
10 0
:45
15/1
1/20
10 9
:45
19/1
1/20
10 1
8:45
24/1
1/20
10 3
:45
28/1
1/20
10 1
2:45
02/1
2/20
10 2
1:45
07/1
2/20
10 6
:45
11/1
2/20
10 1
6:00
16/1
2/20
10 1
:00
20/1
2/20
10 1
0:00
24/1
2/20
10 1
9:00
29/1
2/20
10 4
:00
02/0
1/20
11 1
3:00
06/0
1/20
11 2
2:00
11/0
1/20
11 7
:00
15/0
1/20
11 1
6:00
20/0
1/20
11 1
:00
24/0
1/20
11 1
0:00
28/0
1/20
11 1
9:00
02/0
2/20
11 4
:00
06/0
2/20
11 1
3:00
10/0
2/20
11 2
2:00
15/0
2/20
11 7
:00
19/0
2/20
11 1
6:00
24/0
2/20
11 1
:00
28/0
2/20
11 1
0:00
04/0
3/20
11 1
9:00
09/0
3/20
11 4
:00
13/0
3/20
11 1
3:30
Date
Chl
orid
e (m
g/L)
Chloride (mg/L) Draft Federal Guideline (128 mg/L)
Why is Pollution Prevention Important to LID?
Creek
Lake Ontario
Winter Maintenance
LID Features receiving road and parking lot drainage
Impacts: Chloride• Threat to Groundwater contamination in source
water protection areas (i.e. Reduces infiltration potential for LID);
• Sodium concentrations bind to the soil particles causing increased metal mobilization, ion exchange and decreased soil pH (Löfgren, 2001; Novotny et al., 2007 );
• Salt disrupts water and nutrient uptake leading to “drought like” conditions for the plant which is characterized by leaf scorch, leaf curling, leaf drop, stem dieback and plant death (Roth and Wall, 1976);
• In soil, salt application results in loss of fertility and permeability.
Impacts: Sand/Salt Mixtures• Only a small proportion of the sand is
collected in the spring through catchbasin cleaning, and street sweeping;
• Sediments within the sand/salt mixture come into contact with LID features such as bioretention facilities and permeable pavement;
Winter Maintenance Strategies
• Use a treated salt versus sand/salt mixture;
• Explore alternative de-icing materials that will result in a reduction of chloride;
• Anti-icing• Only plough• Education
Comparison Study: Sand Salt versus salt treated with magnesium chloride
Multiple Commercial Producers:
•Ice Ban Magic
•Magic Minus Zero
•Magic Salt
•Clear Lane
•Warwick Treated Salt
Comparison Study Evaluated Cl, TP, TSS, & Mg* Loadings in roadway runoff from 2008 – 2010 in partnership with the City of Mississauga, Environment Canada, and University of Waterloo
Sample Sites
4 Sample Sites:
2 Sand Salt Mix Sites (75/25 mix)
2 Sites with MgCl2 Treated Salt
Drainage Size: 2.0 – 2.5 Ha
Road Length: 1.8 km to 3.1 km
Primary Roads & Secondary Roads were Incorporated into the Sample Site Only
Primary Road Deicer: Rock Salt
Secondary Road Deicer: Sand Salt Mix or Treated Salt
Application Rates
Table 1: Deicer Application Rates Year Primary Road
Salt Application Rates (kg/l-km)
Sand Salt Application Rates (kg/l-km)
Treated Salt Application Rate Range (kg/l-km)
2008-2009 - 350 – 550* 130 - 150 2009-2010 130 - 600 400 – 800* 130 *Note: Salt accounts for 20 – 30 % of the mix based on material analysis
2008-2009 Cumulative Chloride Loads
Note* 2008 – 2009 Cumulative Chloride Loads Based Solely Upon on Sampled Events
Sources of Chloride at the Sand Salt SitesSite # Primary
Road Length (km)
Secondary Road Length (km)
Average Primary Road Salt Mass Spread Per Event (kg)
Average Secondary Road Salt MassSpread Per Event (kg)
Primary Road Contribution to Total Salt Input (kg)
Secondary Road Contribution to Total Salt Input(kg)
Bonny. 1.025 1.341 339 126 7,472 2,789
Eden. 0.000 2.175 0 176 0 4,241
Laurent. 1.628 1.595 510 109* 13,268 2,274
Pheas. 0.214 1.672 75 113* 1,958 2,350
* Note: Salt Load for Sites 3 & 4 Based Upon 75/25 Sand Salt Mix
•Higher salt input applied to primary roads does not seem to be a plausible explanation for Pheasant Run.
•Other reasons could be due to additional material application, cross connection with sanitary sewer, or groundwater contributions.
•Municipality noted that cul-de-sacs within Pheasant Run were spread twice with the sand/salt mix.
•Higher cumulative Cl loads correspond with higher cumulative TSS, TP, Mg loads
•Difficult to quantify the amount applied without detailed recording
Summary of Results• The sand salt sites had higher cumulative
loads of Cl, TSS, TP, and Mg;
• High Cl loads at Pheasant Run corresponds with high TSS, TP and Mg loads. Additional sand salt application at this site could be responsible for the higher Cl loads;
• The City chose to adopt treated salt on a city wide scale for secondary roads for the 2011/2012 winter season.
The purpose of the study was to evaluate alternative de-icing methods at a large parking lot along with measuring chloride residuals and other
water quality parameters in surface runoff.
Comparison Study: Sodium Chloride versus Potassium Chloride on a Parking Lot
Methods• Measured differences in residual chloride,
potassium and sodium concentrations
• Study took place between November, 2008 and April, 2009– Total of 6 sample events used out of 25 collected (many
challenges associated with winter monitoring programs);– Worked closely with the winter maintenance contractor.
Alternatives to NaCl
There are a number of factors for consideration when selecting an appropriate alternative de-icing material:
• Storage requirementsEquipment needs•Maintenance issues (i.e. staining carpets, slippery floors)• LIABILITY!
• Product effectiveness• Cost• Environmental Impact• Climate• Ease of use
ResultsGO Site Flow(L/S) vs Specific Conductivity (mS/cm) - February 2009
0
10
20
30
40
50
60
70
80
2009-02-01 00:00 2009-02-06 00:00 2009-02-11 00:00 2009-02-16 00:00 2009-02-21 00:00 2009-02-26 00:00
Sample Date/Time
Flow
(L/S
)
0
20
40
60
80
100
120
140
160
180
Spec
ific
Con
duct
ivity
(mS/
cm)
GO 1 Flow (L/S) GO 3 Flow (L/S) GO 1 Specific Conductivity (mS/cm) GO 3 Specific Conductivity (mS/cm)
Thermal Melt: Increased Flow & aDecrease in Specific Conductivity
Chemical Melt:Decrease in Flow & an Increase in Specific Conductivity
QA/QC -
Chloride
December 10, 2008 Sample Event (GO 1 Flux vs Cumulative Load)
0
2000
4000
6000
8000
10000
12000
11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30 18:00 18:30 19:00 19:30 20:00 20:30 21:00 21:30 22:00
Sample Time
Chl
orid
e Lo
ad (m
g/m
^2/s
)
0
10
20
30
40
50
60
70
Cum
ulat
ive
Load
(g/m
^2)
GO 1 Flux (mg/m^2/s) GO 1 Cumulative Load (g/m^2)
December 10, 2008 Sample Event (GO 3 Flux vs Cumulative Load)
0
2000
4000
6000
8000
10000
12000
11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30 18:00 18:30 19:00 19:30 20:00 20:30 21:00 21:30 22:00
Sample TimeC
hlor
ide
Load
(mg/
m^2
/s)
0
10
20
30
40
50
60
70
Cum
ulat
ive
Load
(g/m
^2)
GO 3 Flux (mg/m^2/s) GO 3 Cumulative Load (g/m^2)
KCl Site NaCl Site
Sodium
GO 1 Profile - Sodium Flux vs Cumulative Loading
0
5000
10000
15000
20000
25000
30000
2008-12-10 2009-01-18 2009-02-07 2009-03-07/08
2009-03-29 2009-04-20/21
Sample Date
Sodi
um F
lux
(mg/
m^2
/s)
-
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
Cum
ulat
ive
Load
(mg/
m^2
)
GO 1 Flux GO 1 Na Cumulative Loading (kg/m 2̂)
GO 3 Profile - Sodium Flux vs Cumulative Loading
0
5000
10000
15000
20000
25000
30000
2008-12-10 2009-01-18 2009-02-07 2009-03-07/08
2009-03-29 2009-04-20/21
Sample DateSo
dium
Flu
x (m
g/m
^2/s
)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
Cum
ulat
ive
Load
(mg/
m^2
)
GO 3 Flux GO 3 Na Cumulative Loading (kg/m 2̂)
KCl Site NaCl Site
Chloride/Sodium• Chloride/Sodium concentration, flux and loading were
greater from GO 1 (KCl) than GO 3 (NaCl);
• NaCl was also applied to the GO 1 parking lot nine times until January 17, 2009;
• Sodium concentrations after January 17 from GO 1 were comparable to those from GO 3– Could indicate that rock salt continued to be applied at GO 1 after
January 17
Potassium
GO 1 Profile - Potassium Flux vs Cumulative Loading
0
100
200
300
400
500
600
700
800
2008-12-10 2009-01-18 2009-02-07 2009-03-07/08
2009-03-29 2009-04-20/21
Sample Date
Pota
ssiu
m F
lux
(mg/
m^2
/s)
-
5,000.00
10,000.00
15,000.00
20,000.00
25,000.00
30,000.00
35,000.00
40,000.00
Cum
ulat
ive
Load
(mg/
m^2
)
GO 1 Flux GO 1 K Cumulative Loading (mg/m 2̂)
GO 3 Profile - Potassium Flux vs Cumulative Loading
0
100
200
300
400
500
600
700
800
2008-12-10 2009-01-18 2009-02-07 2009-03-07/08
2009-03-29 2009-04-20/21
Sample Date
Pota
ssiu
m F
lux
(mg/
m^2
/s)
0.00
5000.00
10000.00
15000.00
20000.00
25000.00
30000.00
35000.00
40000.00
Cum
ulat
ive
Load
(mg/
m^2
)
GO 3 Flux GO 3 K Cumulative Loading (mg/m 2̂)
KCl Site NaCl Site
Conclusions• The study found that winter parking lot runoff
is a significant source of chloride to the environment;
• Chloride losses from a parking lot treated with KCl were significantly higher than for a parking lot treated with road salt alone;
• Likely reasons for these observations are– 1) KCl product was applied at higher rates; – 2) Rock salt was being applied in addition to potassium
chloride.
Data Gaps
• The mass of deicer applied to the parking lot was not accurately measured
• This would need to be resolved to fully comprehend the environmental implications of potassium chloride application
Implications for Winter Maintenance Practices
• No “silver bullet” salt deicer that equates to a reduction in Cl levels;
• Reduction in Cl levels is only possible with a reduction in Cl based salts;
• Winter sand appears to have a bigger impact on water quality than what is assumed;
• Private and public landowners need to optimize salt use which includes roads and parking lots;
• Requires a shift: in the expectations of the public regarding bare pavement immediately following a snow fall event.– Dismantling of ‘black top’ policy– Need for public education and outreach– Need to link high Cl levels to impacts on drinking water and resident’s natural
environment
• Need for salt management plans, tracking salt use, snow storage areas, etc.
• Consider a flat rate winter maintenance contract versus per unit rate.
Implications for Winter Maintenance Practices
Next Steps
• Continued partnership with GO Transit to further explore alternatives to salt;
• Testing beet juice at CVC’s head office in Mississauga and using computerized spreaders to get an accurate measurement of the mass of material used;
• Upcoming parking lot retrofit project to look at opportunities to implement LID practices in groundwater sensitive regions.