Salt

Excess salt located by a curb and next to a stormwater catch basin in a parking lot. Salt entering a catch basin is one of the many ways rock salt and elevated levels of chloride can enter the local freshwater system. Rock salt has major impacts on infrastructure, as it increases the rate of erosion/decay of supporting materials (rebar in concrete, etc.) and can lead to structural failure if overused (Wallace, et al. 2022). Photo Source: LSRCA, 2018.

Overview

Each year, Canadians spend over $1 billion on public and private roads, parking lots and sidewalks (Hossain et al., 2015). While the use of salt is essential to ensure public safety, there is a growing concern regarding the large quantities of salt (mainly chloride ions), being released to the environment.

In their 2001 assessment under the Canadian Environmental Protection Act, it was found that high releases of road salts from winter maintenance activities were having an adverse effect on freshwater ecosystems, soil, vegetation, and wildlife (Environment Canada, 2001). Based on this conclusion, Environment Canada developed its “Code of Practice the Environmental Management of Road Salts,” which focuses mainly on municipal and provincial road maintenance. This code, which requires the development of Salt Management Plans for those organizations using more than 500 tonnes of road salt annually, was released by Environment Canada in 2004 (Environment Canada, 2004). While the uptake of these guidelines has been successful, and many agencies have adopted best practices because of it, it is not generally applicable for companies that apply salt to private roads, parking lots, and roadways; and additional measures are needed to realize reductions in these areas.

There are studies and training programs that address these issues, which aim to educate private contractors about best practices, and how these can improve level of service, protect the environment, and reduce costs. However, uptake of these programs has been low.

To address this gap, LSRCA and its partner agencies identified a need for a guideline document that could be used by designers, regulatory agencies, owners, contractors, and others to consider design elements in the design and layout of parking lots and related infrastructure that can help to reduce the requirement for salt application. This effort culminated in the development of the Parking Lot Guidelines to Promote Salt Reduction.

The LSRCA commissioned study into salt management design strategies for parking lots can be read here: LSRCA salt guide. The report identified four key design strategies. They can be see summarized below:

Effective Grading

• Proper grading can minimize the freezing of wet pavement surfaces and prevent melt water from ponding and re-freezing, reducing the need for re-application of salt.
• Areas for vehicular and pedestrian traffic should be graded between 2 - 4 % to reduce the chances of depressions forming over time (maximum permitted 5% for AODA). Small depressions can result in ponded water icing over in the winter.
• Subbase should be well compacted for the same reason.
• In winter months efficient salt application should be made along the top of slopes; melting snow will carry the salt solution down-gradient.
• Effective grading can also direct melt water towards strategically placed stormwater collection infrastructure (i.e. catch basins, vegetated swales, bioretention features, landscaped areas), preventing salt application in heavy traffic areas that are also pathways for runoff.
• The key to effective stormwater collection during winter is to ensure that melt water from high traffic areas or snow piles does not have to travel great distances to a collection point.

Snow Pile Location

Not quite well graded enough; the puddle in the foreground will refreeze overnight.

• Snow piles should be strategically located to minimize the risk of melt water draining across high traffic areas and refreezing.
• Storage locations for snow piles should be around the outer edges of parking lots and downgradient from high traffic areas, in sunny areas where possible to accelerate melting.
• Consider grading the storage location to distribute the melt-water as sheet flow over a grass filter strip into an adjacent BMP, such as a bioretention cell or infiltration trench. In some cases, with careful vegetation selection and adequate drainage, the BMP itself can serve as a snow storage location. Designing specific drainage collection features for snow piles can ensure that melt water is quickly collected in the vicinity of the pile to reduce the opportunity for refreezing.
• Snow storage areas should be clearly marked for seasonal maintenance staff.

Sidewalk Design and Pedestrian Flow

• The design process should consider that pedestrians typically follow the path of shortest distance and do not necessarily use designed walkways. Walkways from adjacent residential areas and transit stops should be prioritized, and unnecessary walkways should be avoided.
• Sidewalks that receive infrequent use could be closed for the winter season.
• Maintained sidewalks should be ≥ 1.5 m wide to accommodate plowing and minimize the salting required.
• Using textured pavers can improve grip for pedestrians, again reducing the salt required.
• In busy areas around building entrances, covered walkways and heated mats also reduce salt requirements.

Landscaping Features

Trees

• Landscaping features (i.e. vegetated swales or landscaped islands) can lead to a reduced requirement of salt application by reducing the amount of paved surface.
• Specifying deciduous trees along walkways and near snow piles will maximize winter sunlight penetration. This will naturally enhance the melting of frozen surfaces, limiting the need for winter maintenance.
• Coniferous trees can be used to create treed wind breaks along the site perimeter to avoid snow drifts.

Other vegetation

Vegetation varies in its reaction to soils with high salinity:

• Salt in soil water generally makes it more difficult for roots to take up water. This phenomenon mimics drought conditions for the plant.
• If passing traffic sprays salty water onto plants it can reduce cold hardiness in buds and new twigs. These then become more susceptible to freezing, mortality or deformation.
• In high enough concentrations, sodium and chloride can also be directly toxic to plants. In some species the ions are absorbed by the plant and build up in the leaves causing them to die.

Generally, the vegetation growing closest to the source will be most strongly affected by salt. Plants actively growing in late winter (when salt levels are highest) are also more significantly affected. So, warm season grasses offer an advantage over cool season grasses, because they emerge later in the spring when excess salt has been flushed away. Resilient turf grasses are particularly useful in the design of vegetated filter strips, dry ponds and enhanced grass swales. The Ministry of Transportation have standardized a number of grass mixes. The 'Salt Tolerant Mix' is of particular value for low impact development applications alongside asphalt roadways and paved walkways.

Canada #1 Ground Cover (salt tolerant mix)

Common name	Scientific name	Proportion
Tall Fescue	Festuca arundinacea	25 %
Fults Alkali Grass	Puccinellia distans	20 %
Creeping Red Fescue	Festuca rubra	25 %
Perennial ryegrass	Lolium perrenne	20 %
Hard Fescue	Festuca trachyphylla	10 %

Picture showing an empty parking lot after a winter storm. An example of an area that could be closed off to users reducing the need for salting or other maintenance practices (shoveling, plowing services, etc.)

Other Design Features

Other options that can be considered to reduce the amount of salt that needs to be applied in a parking lot include:

• The use of permeable pavers: these improve drainage and prevent melt water from ponding and refreezing.
• Seasonally closing parking areas: many parking lots have areas that are infrequently used outside of the holiday shopping period. These areas can be closed and not maintained through much of the winter season, reducing both the effort and amount of salt required.

Additional Work

Parking Lot Friction Testing

Two of the main considerations contractors face in maintaining parking lots in winter are: what application rate should be used; and what is the level of service expected by the property owner, for which the bare pavement return time is a common measure (this is the amount of time it takes after treatment to achieve a bare surface). To better understand these questions in 2017 the LSRCA obtained a friction tester, with a goal of quantifying the effectiveness of various practices and salt application rates. Here we present some of the findings of this study.

This image demonstrates the two extremes of LSRCA’s friction testing: a perfectly clear and dry surface, with a µ value of 0.9 and the same surface covered in a light layer of snow, with a µ of only 0.11.

As can be seen in the inset table, the unit for measuring friction is ‘µ’, and the closer to 1.00 the µ value, the safer the surface. A high µ, however, is not the only measure of safety – many smooth indoor floors will have low µ values, in the range of 0.3 to 0.4, and they are generally not considered unsafe. Through this study, we measured the friction of several different surfaces, which received varying treatments.

Friction Values and Related Road Surface Conditions

Measured Friction Value (µ)	Road Surface Condition
0.8 - 1.00	Dry, New Asphalt
0.50 - 0.80	Wet Asphalt
0.30 - 0.50	Wet Sand on Ice
0.25 - 0.30	Dry Sand on Ice
0.25 - 0.25	Dry Ice
0.05 - 0.15	Wet Ice

Friction values for a properly treated surface (left) with a small amount of residue (µ =0.63) and an over salted surface right, which has a much lower friction value (µ =0.26).

High volumes of salt are often applied because contractors, property managers, and parking lot users feel that the more salt there is, the safer the surface is to walk or drive on. However, a surface that has been treated at an appropriate rate, (which is slightly wet with a small amount of salt residue) has a much higher friction value (μ); with the level of service achieved far more efficiently, than when compared to the same surface where rock salt has been heavily applied (over salted).

The picture above shows the same walkway where more than 10 times the generally recommended amount of salt was applied in the photo on the left, and only shoveling was done in the photo on the right, and both µ values were in the low 0.20s.

Through this work, as referenced above - LSRCA staff documented higher friction values on untreated surfaces than on surfaces with large volumes of product; the µ value of a surface may remain low if it has only been shoveled or plowed. While shoveling is an important part of the winter maintenance process, practitioners need to consider the site and predicted conditions on a day-to-day basis to determine how to attain the safest surface for vehicle and foot traffic. In many cases the sun or traffic may melt the residual snow on a shoveled or plowed surface without any further treatment being necessary (saving both time and money); while in other cases, some salt, applied at an appropriate rate, may be necessary.

Higher Costs, Little Benefit

Friction testing has demonstrated that bare pavement is safest, as it has the highest friction value, and that the over-application of salt does not always translate to safer conditions. Simply put, applying salt at the prescribed rate for the conditions and shoveling or plowing where appropriate will attain a higher friction rate than an overapplication of salt.

What is a reasonable amount of time to achieve the desired level of service?:

• Depending on the operating hours of the property being maintained, it may be possible to reduce the salt application rate without sacrificing the desired level of service.
  • For example, many commercial properties keep hours between 9:00 am and 9:00 pm, which would mean that the lot does not need to be clear until shortly before 9:00 am. The table below demonstrates the time it would take to reach bare pavement at typical industry-recommended application rates, in a situation where the temperature is between -7 and -9 °C, with between 0.5 and 1.5 cm of snow on the ground. The rate may need to be increased or decreased slightly to achieve the desired level of service depending on varying factors related to traffic, sunlight, type of snow, and/or pavement type.

Time to Reach Bare Pavement Scenario Comparison

Difference Among Scenarios	Time to bare pavement (hrs)	Application Rate (g/m2)	Volume of salt used for each application (kg)*	Total salt applied/season (tonnes)**	Material costs/season (assuming $100/tonne)
Scenario 1	2	87	13,050	913	$91,300
Scenario 2	3	58	8,700	609	$60,900
Difference	1	29	4,350	304	$30,400

As the "Time to Reach Bare Pavement Scenario Comparison" above demonstrates, significant salt and cost savings could be seen in a typical big box store, commercial business or institutional building's parking lot by simply reducing the application rate of rock salt and extending the time to bare pavement by one hour. To note, this is only the material cost of the salt (which varies, but has been higher than $100/tonne in recent years (Tumilty, 2018). Over-application of salt has been noted to cause significant damage to parking lot infrastructure, including issues with concrete, corrosion of railings, damage to landscaping materials, and damage to interior buildings' flooring. Reducing the application rate would decrease the rate at which this damage occurs, as a result helping to minimize the amount needed to repair or replace at a given property each year. All of this without sacrificing the safety of parking lot users.

Environmental Impacts

Salt contamination in freshwater (freshwater salinization) is a major concern to Ontarians wellbeing:

• Unpleasant taste in drinking water
• Health issue for those with hypertension issues
• Health issue for those who have experienced congestive heart failure
• Impacts to those with sodium restricted diets

A graph showing increasing average levels of chloride found in Lake Simcoe, and its watershed's rivers, streams and groundwater systems over the past few decades, due in part to increased use of rock salt in parking lots, roadways and commercial and residential properties. It is estimated that by 2120 the average level of chloride within the the Lake Simcoe watershed will exceed the 120mg/l guideline set by CWQG. (LSRCA, 2018)

Furthermore, salt can contribute to both biodiversity and habitat loss for numerous species. In Ontario, road salt was identified as one of the threats to drinking water under the Clean Water Act, 2006 - as well as a known toxin to wildlife species. Salt can impacts bird species, many plants and trees growth ability, and decrease size, function and fecundify in fish, mollusks (snail, mussels, etc.), amphibians and benthic invertebrate species. Staff from TRCA released an article in the January/February, 2022 edition of Water Canada magazine highlighting the effects of rock salt's over use and application across Southern Ontario's watersheds and is impact on freshwater environments and species.

Some of the key findings from the article highlight:

• In Ontario chloride concentrations (Cl^-) are measured monthly under the Provincial Water Quality Monitoring Network (PWQMN). Concentrations in the mouth of the Don River has showcased levels three times that of the Canadian Water Quality Guidance (CWQG) for long-term chronic effects to the environment and species.
• Although the PWQMN has been an excellent tool for following the long-term trends of median concentration levels in the province's watersheds the infrequency of sampling will at times miss peak and extreme values and outliers that result in excessive salt and chloride loadings in key areas with species at risk, etc.
• As a result, TRCA, along with its partners began a monitoring project at the mouths of the major tributaries within the GTA using high-frequency sensors, which make readings ever 15 mins.
• Some of the results from their monitoring work found
  • Highland Creek: 70 times the CWQG limit for chronic effects & 13 times the CWQG limit for acute effects of aquatic organisms.
  • Duffins Creek: 25 times the CWQG limit for chronic effects & ~5 times the CWQG limit for acute effects of aquatic organisms.
• These high values pose a considerable threat to fish, aquatic organisms, and ecosystem health overall - especially considering the frequency and duration of these values in major watercourses in urbanized areas of the province. The findings highlight the need for increased water monitoring efforts and requirements for new sensor technology to capture and accurate representation of the current state of our rivers and streams. (Wallace, et al. 2022.

External links

• Smart about Salt
  • The website of the Smart About Salt Council (SASC) that offers training, recommendations, research and up to date new articles about the importance of proper management and use of rock salt on Ontario roadways, parking lots, private and residential properties. Training is offered in both English and French.
• STEP Technical Brief: Alternatives to Salt
  • STEP released a technical brief on the alternatives to municipalities across Canada using salt as their primary deicer agent in winter, which has significant impacts (corrosion of infrastructure and other metal structures such as railings and doorways; damage to vehicles; contamination of surface and groundwater; impacts to roadside vegetation; increased wildlife collision rates; and large amounts of product waste due to blowing or bouncing off roadways). Numerous alternatives were tested to see what could feasibly replace the overreliance on rock salt which at a high-level include: chloride deicers, acetate deicers, and agricultural by-products (organics). Read more about the benefits, drawbacks, cost estimates and lowest working temperature for a given deicing agent.
• Procurement Guidance for Parking Lot Snow and Ice Management
  • STEP released a guidance document aimed at property owners, businesses and contractors to better understand their control over how much salt is applied through their snow and ice management contracts, and the diligence with which they manage and oversee these contracts. In this document, STEP describes various clauses and conditions that can be considered by these groups to be included in contracts to promote the responsible use of road salts. A summary of the measures are provided in with estimates of the impact on salt use, and the potential influence these may have on contract costs.
• LSRCA Technical Bulletin: Alternatives to Salt
  • LSRCA staff highlight in this brief about some BMPs have been developed specifically for winter maintenance in parking lots. Along with recommendations around the proper use and calibration of equipment, many of these practices relate to plowing the lot and walkways before applying salt, and applying the recommended amount of salt for the conditions. Several studies have been conducted, by industry and academia, to determine what the “right” amount is, and, while “proper” application can vary depending on temperature and conditions. This report talks about main considerations contractors face in maintaining parking lots in winter:
    • what application rate should be used?
    • what is the level of service expected by the client, for which the bare pavement return time is a common measure?
    • In order to better understand these questions; in 2017 the LSRCA obtained a friction tester, with a goal of quantifying the effectiveness of various practices and salt application rates. LSRCA’s friction testing showed that bare pavement is safest, as it has the highest friction value, and that the over-application of salt does not translate to safer conditions.
• Salt Application Best Practices for Winter Maintenance Contracts
  • STEP released a best practices document for winter maintenance contracts for private businesses to help reduce over-salting and ensuring that salt is applied responsibly on parking lots and walkways. The document highlights how an easy way to do this is by ensuring that businesses' snow and ice maintenance contract includes provisions requesting that industry best practices be employed and operators are adequately trained. Furthermore contracts should request evidence of knowledgeable contractor and property management staff, requiring training and certification through the Ontario Smart about Salt Program.
• LSRCA Technical Bulletin: Sand versus Salt
  • CVC developed a technical brief exploring the efficacy of the use of sand for winter maintenance, its associated environmental issues, and where its use is most appropriate. Sand although a known and regularly used alternative in some jurisdictions, tends to have additional costs and limited effectiveness when compared to rock salt. To read about these costs, effectiveness concerns and additional environmental impacts click the link to the technical bulletin above.
• Evaluation of Organic Anti-icing Materials for Winter Maintenance.
  • This study compares the performance of liquid road salt (brine) to three types of organic/semi-organic alternatives applied on a university parking lot in Waterloo, Ontario. Products are evaluated as anti-icers (applied pre-snowfall) based on the coefficient of friction (CoF). The results indicate that in general, anti-icing treatments improved friction levels by 10-40% relative to a control without any application of anti-icers. Despite containing less chloride, the organic and semi-organic products performed as well as traditional sodium chloride brine at similar application rates. Although organic anti-icers contributed less chloride into receiving streams, they contain higher concentrations of nutrients and organic content, which may limit their applicability in some context. To read more about these salt alternatives click the link above.
• LSRCA's Parking Lot Design Guidelines​
  • LSRCA has created a landing page with their partners, which include three key documents:
    • Fact Sheet - Parking Lot Guidelines: Highlights the impacts of elevated chloride levels in freshwater systems in the Lake Simcoe watershed and detailed, bullet-point descriptions of how to design parking lots to limit over application of rock salt.
    • Parking Lot design Guidelines - Full Report: Written in partnership with GHD the Parking Lot Design Guidelines to Promote Salt reduction is the primary document LSRCA uses to provide background on the issue of over salting roads and parking lots, primary design features for owners and contractors to consider, case study and site examples where the guidelines have been followed and Drawings of these sites that can be found on the main Parking Lot Guideline landing page.
    • Municipal Policy Template: This template document aids municipalities in the drafting of their own parking lot design and salt reduction policy document based on the findings and design guidance from LSRCA's Parking Lot design Guidelines - Full Report, 2017.
• Salt Application Verified Equipment Program: Managing Risk While Saving Money
  • The Salt Application Verified Equipment (SAVE) Program was developed to make the process of applying salt less subjective and encourage contractors providing snow and ice management services for parking lots and sidewalks to apply salt more efficiently. Through the program, salt spreading equipment is calibrated according to a standard test procedure, and contractors undertake in-field training to ensure familiarity with how to operate their equipment in a manner that achieves pre-determined target salt application rates. Equipment operators obtain annually renewable license and plate stickers to confirm that their equipment has been verified. The list of contractors with calibrated equipment is made available on-line for facility managers, property owners and property management companies to use in the procurement of snow and ice maintenance contracts for their properties. To learn more about the program click Here. And for further updates to the program's verification process visit SASC's page here.
• Good Practices for Winter Maintenance in Salt Vulnerable Areas. .
  • This guidance is a living document to help address the impacts of road salt, within specific vulnerable areas, and will be reviewed every two years to remain current with technological and legislative changes. There are several types of ‘salt vulnerable areas’, with various environment and human health goals including drinking water quality, wetland health, and fisheries that are identified within the document. This guidance currently prioritizes certain areas where municipal drinking water sources are known to be impacted by road salt, know as, ‘Issue Contributing Areas’ (ICAs) delineated under the Clean Water Act (2006).
• Winter Parking Lot and Sidewalk Maintenance Manual
  • The purpose of this manual By the Minnesota Pollution Control Agency (MPCA) is to deliver practical advice to those managing parking lots and sidewalks and help make proactive, cost-effective, environmentally conscious choices in winter parking lot and sidewalk management in the State of Minnesota. This knowledge will provide the opportunity to become a leader in the industry by operating more efficiently and reducing environmental impacts. The manual is based on the Minnesota Snow and Ice Control Field Handbook for Snowplow Operators, produced by the Minnesota Local Technical Assistance Program Center, and on the training materials for the MPCA's Winter Maintenance of Parking Lots and Sidewalks training class.
• A review of the species, community, and ecosystem impacts of road salt salinisation in fresh waters. .
  • This review study of the impacts of road salt on local ecosystems by Hintz and Relyea (2019), found that road salts negatively affect species at all trophic levels, from biofilms to fish species but the concentration of road salt where adverse effects were observed varied and the effects themselves ranged from reductions in fecundity, size and shape to alterations to nutrient and energy flow at an ecosystem level and increased greenhouse gas emissions from contaminated wetlands and altered hydrology and oxygen, nitrogen and carbon level dynamics in lakes and streams. concentration at which road salt triggered an effect varied considerably. To read mroe about their findings, click the link above.
• Chloride - Canadian Water Quality Guidelines for the Protection of Aquatic Life.
  • This guideline from the Canadian Council of Ministers of the Environment (CCME) is intended to protect against direct toxic effects of chloride, based on studies using NaCl and CaCl² salts. The guideline should be used as a screening and management tool to ensure that chloride does not lead to the degradation of the aquatic environment. Further guidance on the application of these guidelines is provided in the scientific criteria document (CCME 2011), which can be found here - Scientific Criteria Document - Cl Ion.
• Hamilton Salt Management Plan.
  • The City of Hamilton's 2021 Salt Management Plan is intended to set out a policy and procedural framework for ensuring that the Municipality continuously improves the management of road salt used in its winter maintenance operations. The plan is dynamic and allows the City to phase in new approaches and technologies in a way that is responsive to fiscal demands and the need to ensure that roadway safety is not compromised. To read more about the City's finalized plan that compares it's current practices to BMPs, opportunities for improvement and achievement metrics which can be replicated fore other Ontario municipalities click the link above.

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Ground depression acting as a flow control and water treatment structure, that is normally dry.

(1) The wearing away of the land surface by moving water, wind, ice or other geological agents, including such processes as gravitation creep; (2) Detachment and movement of soil or rock fragments by water, wind, ice or gravity (i.e. Accelerated, geological, gully, natural, rill, sheet, splash, or impact, etc).

Lake Simcoe Region Conservation Authority

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

a gently sloping, densely vegetated areas that treat runoff as sheet flow from adjacent impervious areas. They function by slowing runoff velocity and filtering out suspended sediment and associated pollutants, and by providing some infiltration into underlying soils.

Best management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.

Natural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).

A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

A mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.

A mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

The drainage area of a river.

An area of land that drains into a river or a lake. The boundary of a watershed is based on the elevation (natural contours) of a landscape.

Toronto and Region Conservation Authority

A biological community, including humans and their natural environment.

Sustainable Technologies Evaluation Program

The water below the surface, and typically below the groundwater table.

Credit Valley Conservation

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

A vegetated area such as a bog, fen, marsh, or swamp, where the soil or root zone is saturated for part of the year.