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

3

4

QEW

Royal Windsor Blvd

2007

1944

Then & Now

Southdown Rd and Lakeshore Dr

• 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

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Concentration, mg/L DW standard 75th percentile Linear Trendline

Cooksville Creek Real Time Monitoring

Chloride Levels September 2010 to March 2011

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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

Sample Site Set Up

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

2009-2010 Cumulative Chloride Loads

2009-2010 Comparison of Cl Input-Output

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

2009-2010 Cumulative TSS Loading

Cumulative Loads Based Solely on Sampled Events

2009-2010 Cumulative TP Loading

Cumulative Loads Based Solely on Sampled Events

2009-2010 Cumulative Mg Loading

Cumulative Loads Based Solely on Sampled Events

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

GO 3

GO 1

Study Area

ResultsGO Site Flow(L/S) vs Specific Conductivity (mS/cm) - February 2009

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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

)

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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)

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Sample Time

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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)

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Sample TimeC

hlor

ide

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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

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2009-03-29 2009-04-20/21

Sample Date

Sodi

um F

lux

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GO 1 Flux GO 1 Na Cumulative Loading (kg/m 2̂)

GO 3 Profile - Sodium Flux vs Cumulative Loading

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2009-03-29 2009-04-20/21

Sample DateSo

dium

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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

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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

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m^2

/s)

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ive

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GO 1 Flux GO 1 K Cumulative Loading (mg/m 2̂)

GO 3 Profile - Potassium Flux vs Cumulative Loading

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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

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m^2

/s)

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ulat

ive

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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.