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Water, Air and Climate Change Branch WATER QUALITY Roadsalt and Winter Maintenance for British Columbia Municipalities Best Management Practices to Protect Water Quality December 1998 Canadian Cataloguing in Publication Data Warrington, P.D. (Patrick Douglas), 1942 -
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Table
1. Roadsalt Application Rates
This document is one of a series that deals with non-point source (NPS) pollution problems in British Columbia by proposing BMPs to eliminate or reduce such pollution. It provides guidance and information to local governments and road maintenance contractors concerning BMPs that minimize the impact of roadsalt on roadside vegetation, transportation corridor infrastructure, surface water and ground water.
It is intended for public works departments and local environment committees which supervise or advise on the winter maintenance of roads and streets within municipal jurisdiction. The intention is to supplement, not replace, the current British Columbia Ministry of Transportation and Highways accepted practices which are documented in a technical maintenance manual (BC MOTH, 1995). Refer to this manual, which may already be used in some municipalities, for specific operational details.
This document reviews measures that British Columbia municipalities can use to reduce the pollution of the environment by roadsalt and de-icers without compromising road safety. These include a reduction in salt use by following application guidelines, replacement of some salt with sand or ploughing. Pre-wetting the salt or sand/salt mixture can make it more effective thus reducing the amount that needs to be used. Advanced equipment such as special snow ploughs, remote monitors, automated de-icer sprays, infra-red pavement temperature monitors, spreaders and pavement friction monitoring devices can also reduce salt use. Anti-icing techniques and materials can also be used. There are
alternatives to roadsalt which are more effective and less
damaging to water supplies and the environment but their
costs are significantly higher. However, the total cost to
society should be considered, not just the capital cost of
the roadsalt. One can also use alternative winter maintenance
practices. Changes in driver behaviour and expectations would
reduce the need for as much salt and maintenance if dry,
bare roads were not expected. Changing snow dumping practices
to eliminate dumping in sensitive areas would reduce the
environmental damage caused by what salt was still required.
Eliminating some contaminants in roadsalt would reduce the
harmful effects of roadsalt use.
In British Columbia, each municipality determines its own winter road maintenance operations, which, for many communities, relies heavily on the use of salt as a road and street de-icer. This BMP document attempts to provide guidance to BC communities so that they are better able to protect their natural resources and quality of living without compromising the level of winter maintenance services. Because road safety remains the top priority when looking at measures that reduce the flow of roadsalt into the environment, this document focuses on examples of successful, cost-effective initiatives that do not compromise safety. This document also provides technical information, resources and guidance to encourage and facilitate development of effective local plans to reduce the impact of roadsalt. Case studies
elsewhere demonstrate that levels of service need not suffer
due to changes or reductions in application of
roadsalt. Following these selected BMP's, local governments
may notice significant savings in addition to environmental
benefits. There are already many municipalities in British
Columbia that have advanced winter maintenance programs and
employ many of the measures outlined in this document. They
are an excellent resource for other communities that are
working to establish more conscientious winter maintenance
practices.
Winter maintenance is an indispensable operation that provides safe winter driving conditions for BC residents. The goal is fewer accidents and thus lower repair costs for automobiles, and reduced medical and job loss costs for people. There are a variety of tools used to clear roadways of snow and ice; plowing and road salting are only the primary ones. Since the early 1950s, roadsalt has been applied extensively in North America (14 million tons in the USA in 1996) to de-ice roads for the purpose of providing safe and convenient driving conditions. Over time, the use of roadsalt has become commonplace; the amount used in British Columbia increased rapidly. There was about a 40 percent increase through the 1980s (Bedford, 1992). In the 1970s, it became widely recognized that the ever-increasing use of salt to maintain clear roadways is not without costly consequences. Damage due to roadsalt on roadside vegetation, wildlife, soil, road surfaces, bridges and automobiles, as well as the contamination of surface and drinking water, have generated concern about the use of roadsalt for de-icing. Environment Canada evaluated the toxicity of various sources of stormwater and found that run-off from multi-lane divided highways with traffic densities over 100,000 vehicles per day had the highest frequency of severe toxicity of the sources tested. This was due to the quick contaminant release during snowmelt, enhanced mobility of metals in chloride-rich run-off and high concentrations of road salt (CWWA,1999). In parts of Canada and the United States, ground water has been contaminated to the degree that it is no longer potable and some lakes have suffered environmental impacts. The transfer of roadsalt and other de-icers from delivery trucks to the storage facility, and from the storage facility to the spreader trucks, may be of more environmental concern than the actual storage of the roadsalt. Ground water in Heffley Creek, BC (just north of Kamloops) was contaminated in 1994 by spillage during handling and storage at a salt storage facility. Salt and sand was stored in front of the storage facility and not under cover on an impervious surface. The incident demonstrated that communities in BC are susceptible to water quality degradation as a result of roadsalt. Generally, the spillage which may occur while transferring the salt to and from the storage piles is of more environmental concern than long term storage, when a proper storage facility has been constructed. This spillage must be cleaned up immediately to prevent chronic contamination of the local area.
Conventional
roadsalt is primarily common table salt (sodium chloride or
NaCl). Because of this, it is rarely viewed as potentially
toxic or harmful. In reality, roadsalt can be very damaging
to the environment. Roadsalt can have serious impacts on water
quality and specific BMP's have evolved to protect water resources.
In addition, a number of other chemicals are often added to
roadsalt to depress the freezing point, reduce the corrosion
of vehicles and structures and prevent the roadsalt from caking
or clumping so that it may be readily spread; roadsalt usually
contains various impurities as well. Environment Canada has
included roadsalt and other de-icers in their second Priority
Assessment List of potential toxic substances under the Canadian
Environmental Protection Act.
2.2 Impacts on Water Quality and the Environment The sodium chloride brine and solids enter the surrounding environment in runoff, spray, aerosols and dust from traffic, deposition from ploughing and snow removal. Negative impacts can include damage to vegetation, soils and wildlife, contamination of surface and ground water (including drinking water supplies) and corrosion of metals, concrete and other materials. This document is concerned principally with the impact of roadsalt on water quality and other impacts are not discussed. However, if less roadsalt is used the effects on soils, vegetation and animals will also be reduced. Recent studies in southern Ontario showed that only about 45% of the applied roadsalt runs off; the rest contaminates shallow aquifers. Considering the past and present rate of roadsalt application in Ontario, ground water will soon be contaminated with sodium and chloride beyond safe levels. Since there is a lag period before the salt shows up in ground water, the problem with contaminated drinking water will continue to get worse before it gets better, even if road salting stops. The accepted chloride level in drinking water is around 250 mg/L as set by the USEPA and the Ontario Ministry of Environment. Pore waters from the unsaturated zone adjacent to Metropolitan Toronto Highways had measured chloride levels of 14,000 mg/L in 1987 (Pilon and Howard, 1987). Mass balance and steady state calculations, based on current application rates in Ontario and measured loss rates, indicate chloride will reach 400 mg/L and sodium 250 mg/L (Howard et al, 1993). Ultimately the salt will start to show up in the Great Lakes (Howard et al, 1993; Toronto-1995). There are no similar studies available for British Columbia.
Sodium ions may bind to soil particles in roadside soils causing other ions, often heavy metals, to be released into the water in place of sodium. This exchange typically causes harmful changes to soil structure and properties. High concentrations of sodium in the soil and water may be toxic to plants. High concentrations of sodium in the human diet may lead to many conditions such as hypertension, cardiovascular disease, metabolic disorders, renal diseases and cirrhosis of the liver. However, water would become unpalatable to most people before these conditions would arise.
Chloride is relatively unreactive, but has been known to contribute to density stratification, as a component of dissolved salt in small lakes, preventing the ecologically important seasonal lake overturn. Chloride tends to be somewhat less toxic to animals and plants than sodium. However, too much chloride makes water unpalatable and eventually unfit to drink. There are abundant examples of extensive drinking water contamination resulting from applying sodium chloride to roads. In the United States, Massachusetts and New Hampshire in particular, the costly replacement and/or abandonment of wells due to chloride contamination has occurred often enough that, in many cases, applying salt to roads has been discontinued in problem areas (Chollar, 1996; Minsk et al., no date). A survey of wells near Ottawa, Ontario in 1979 showed that levels of chloride resulting from nearby application of salt to the roads exceeded the Ontario Ministry of Environment public water supply criterion (Minsk et al, no date). In British Columbia, the community of Heffley Creek suffered severe drinking water contamination from stored roadsalt and individual wells had the quality of their water impaired.
Iron cyanide may be added to roadsalt as an anti-caking agent at levels reaching at least 45 mg total cyanide per 1000 kg of roadsalt. Roadsalt containing iron cyanide (ferrocyanide or ferricyanide) as an anti-caking agent should not be used. There are other environmentally safe replacements for iron cyanide. This cyanide content may not be labelled or it may be called 'yellow prussiate of soda'. UV light breaks down the chemical bond releasing free cyanide.
British Columbia is a large and diverse province. There are significant differences in regional and site-specific climate, biology, geology and geography which are important in determining the impact of de-icing chemicals. For example, soil composition, drainage patterns, moisture content, timing and both total quantity of salt applied as well as the concentration of salt per km are a few characteristics recognized as important in determining the sensitivity of an area to salt damage. Because the impact of roadsalt is so site-specific, it is very difficult to make broad recommendations for all British Columbia municipalities.
Often, as was the case in Heffley Creek's 1994 water contamination, water quality degradation due to roadsalt goes unnoticed for years until the problem is relatively severe. Each community should examine its potential susceptibility to environmental damage from de-icing chemicals and implement winter maintenance strategies that will protect their resources.
3. Minimizing the Impact of Roadsalt on Water Quality In British Columbia, several coastal lakes are known to have had their normal calcium and carbonate dominated chemical equilibria altered such that sodium and chloride are now the dominant ions (Warrington, 1998). One lake is on the highway between Terrace and Kitimat and another between Port Alberni and Long Beach. These are lakes adjacent to highways with snow and ice problems which happen to have convenient scenic pullouts along the lakeshore where snow, containing salt, was pushed over the bank during removal operations or else roadside snow and salt simply ran directly into the lake during the spring thaw. The source of the Heffley Creek ground water contamination was inadequate salt handling and storage outside the storage facility that had been releasing salt into the soil for years. Heffley Creek residents were supplied with bottled drinking water, suffered damage to gardens and other vegetation and may also have suffered damage to water filtering systems, pipes and fixtures as a result of this contamination. The total remediation cost of the contamination was about $2,000,000 which included land purchases and construction of a new salt storage facility.
Nine strategies to reduce or eliminate the risk to water quality caused by roadsalt are discussed below. These are:
The state of West Virginia uses 100,000 to 140,000 tons of roadsalt, or more, in an average to severe winter. They may have up to 73,000 tons stockpiled at any one time. This salt costs them an average of $35.00 ton; it is the cheapest (capital cost) de-icing material available. In the USA,
highway de-icing accounted for 60% (20 million tons) of the
31.5 million tons of NaCl used in 1994. No other use exceeded
10% (WVDOT, 1997). Similar data is not available for British
Columbia but these examples give an idea of the magnitude of
roadsalt use. In addition to improved salt storage and handling,
the simplest way to reduce the environmental impact of roadsalt
is to reduce the amount of salt applied.
The services manual contains other useful information, and should
be consulted.
Applying water or some de-icing solution to roadsalt and/or sand before, or during, application is a process known as pre-wetting (Gustafson, 1992). The liquid coats the particles and, upon contact with the roadway surface, the salt or sand embeds itself in the ice or snow (Bodnarchuck et al, 1994). Pre-wetting
has a capital cost which must be weighed against the environmental
costs of not using this more efficient process. Pre-wetting
decreases the amount of roadsalt or sand required without decreases
in levels of service. However, the increased costs due to pre-wetting
and the decreased cost of using less salt and sand may not
be equal.
A variety of liquids may be used for pre-wetting roadsalt. These include sodium chloride, calcium chloride, magnesium chloride, potassium acetate, and calcium magnesium acetate in brine solutions. Water can also be an effective pre-wetting agent provided that the temperature is relatively high. Each
solution has different properties and may behave differently
due to the chemical characteristics and the method of pre-wetting
employed (for more detailed information, see the document FHWA-Effective
Anti-icing Program under the heading On-line References in
the Information Pre-wetting does not necessarily require large and expensive equipment purchases. There are three basic techniques of pre-wetting:
The Information Resources section of this document identifies documents that provide instruction on how to modify trucks, spreaders, and garages to facilitate pre-wetting. While there is an initial investment in time, experimentation and training required, the eventual savings in salt, time and money can be significant. The following are some of the benefits and concerns associated with pre-wetting:
The technology and equipment used in winter maintenance operations is advancing continually. There are an enormous variety of tools that can be used to increase efficiency and safety and to reduce costs. Some of these tools are discussed below: Special
snow ploughs
Materials used for blade edges include synthetic polymers, rubber, steel and carbide inserts. According to the Washington State Department of Transportation, polymer edges are useful for removing slush (Ketcham et al, 1996) from streets and highways. It is therefore only necessary to reduce packed snow to slush, rather than fully melt it, which requires only half as much salt (Ketcham et al, 1996; Kuusela et al, 1992). However, this environmentally beneficial reduction in the amount of roadsalt used has an economic cost since a second pass is required to remove the slush. There are also snowplough scoops designed to make snow plough operations more efficient. Note that ploughing after de-icing salt has been applied to snow and ice results in the deposition of salt off the roadway. This is both a considerable waste of salt and a potential threat to the environment which is not always avoidable.
Remote monitors that lie beneath the road surface can indicate pavement temperatures, in particular trouble spots, near or on a bridge for instance, so that action can be taken immediately when there is the risk of dangerous conditions. It is even feasible to have speed limits over bridges regulated by automated road condition monitors. Thermisters are used in several locations in British Columbia.
Having an efficient and precise spreading mechanism is one very effective way to mitigate the impact of roadsalt on the environment. An even distribution of salt, applied at a consistent, pre-determined rate, with minimal scattering of salt particles cuts down dramatically on the amount of material applied. Special spreaders also allow for the implementation of liquid de-icer, anti-icing and pre-wetting applications which, themselves, can be very effective means of reducing roadsalt application. Highway authorities in Finland report that a liquid roadsalt solution allows for 50 to 75 percent reductions in roadsalt application over granular roadsalt, because of application accuracy (Kuusela et al, 1992). Each community should examine its own needs and consider the most effective device for their own de-icing operations. Future savings in materials, wages, and community-wide salt damage should be considered when comparing the cost of various spreaders.
The term anti-icing is one that has emerged relatively recently to describe a new approach to winter maintenance that differs from traditional de-icing methods. Anti-icing is the timely application of chemical freezing point depressants to roadways before snow and ice accumulate. This prevents the formation of a bond between slippery snow and ice and the roadway, thereby facilitating mechanical removal (Ketcham et al, 1996). Anti-icing allows for a very high level of traffic safety at low cost and significantly reduces the amount of roadsalt used. Salt is no longer applied in quantities required to melt downward through a heavy layer of snow and ice. Because the required amount of de-icer is reduced, it then becomes feasible to use more expensive and more specific chemical alternatives to roadsalt.
To use anti-icing techniques, a winter maintenance operation may only need minor adjustments. Often, it is discovered that anti-icing is being practiced without it being recognized as such. Some of the more effective anti-icing tools include liquid anti-icing chemicals (liquid de-icers) and accurate local weather information. In some areas these techniques alone are sufficient to eliminate, or greatly reduce, the use of roadsalt. Liquid spreading mechanisms can be constructed at relatively low cost. These tools, along with experience of local road conditions, may be enough to achieve goals like improved roadway conditions, fewer working hours per week for winter maintenance operators and reduced impact on the environment (Keep et al, 1995). An essential component for a successful anti-icing program is operator training. Winter maintenance experts in North America and Europe alike stress the importance of training for anti-icing. Operators must have a good understanding of what the options available to them will achieve and use a systematic approach. Standards and calibration charts are important parts of an anti-icing operation but are ineffective without an operator who is aware of their function and impact. Operator training is one benefit of inter-community exchanges of information and resources that can be especially valuable. There are also consultants who may be contracted to educate crews and managers about anti-icing practices. The above material only summarizes some basic information on anti-icing. Further independent research on the topic is recommended. For references see the Information Resources section of this document.
3.5 Alternatives to Sodium Chloride Several freezing point depressants are available for road de-icing as alternatives to NaCl. Their efficiency as de-icers, and their relative effects on the environment need to be reviewed on an individual basis. The initial cost of NaCl is quite low compared to most alternatives, but studies have indicated that the real cost of applying roadsalt is much higher than the initial cost. The US Environmental Protection Agency reported that the actual annual cost of salt related damage for 1976 was 15 times the cost of purchasing and applying the roadsalt (D'Itri et al, 1992). Figures for the full cost of applying roadsalt in BC are not available, but they are likely similar and substantial. The high actual cost of salt damage has not been enough to dissuade most agencies in North America from using salt. However, the Washington State and Oregon State Departments of Transportation have eliminated or vastly reduced sodium chloride in their winter maintenance programs because of the high overall costs associated with its use (Keep et al, 1995). They have used anti-icing strategies, including the application of calcium magnesium acetate as the principal freezing point depressant.
There are various liquid and solid formulations of these chemicals. Each winter maintenance operation must determine the best choice for its own program. There are alternatives to roadsalt available that cause less environmental damage and more are being developed. Regular reviews of products available in the market and discussion with other communities regarding alternative de-icers are recommended. The Ministry of Transportation and Highways constantly carries out reviews and analyses of de-icers. Capital cost is usually the major problem with use of such materials.
3.6 Alternative Winter Maintenance Practices There are alternative ways to reduce impact of roadsalt to the environment. While simply modifying existing winter maintenance practices slightly is one technique, there are some other measures that can be applied. A few such measures are listed below:
One measure which would allow for vast reductions in winter maintenance would be to increase public awareness of the potentially harmful effects of de-icing chemicals on the environment and to secure the public's cooperation in reducing the need for application of salt on roads by lowering speed limits under icy conditions. In some places where the environment is very sensitive to human activity and important to the public, lower speed limits and other driving restrictions have been imposed. In Japan, commuters drive more slowly in the winter months and use special soft rubber winter tires that grip the road surface almost as well as studded tires (Minsk et al, no date). In parts of the Netherlands where drinking water quality is an issue, speed limits are sometimes controlled by road conditions and the public does not expect to drive the same speed all year round (Leppänen, 1996). Anti-lock brakes on vehicles will also help, to some extent, to reduce accidents on ice and snow.
In many cases, particularly in cities, snow cannot be pushed off the road-side, but must be picked up and dumped somewhere. What to do with large quantities of snow has always been a problem. In many places it has been dumped into water, rivers and lakes, which gets rid of it effectively but causes contamination (Scott, 1980). However, when it is scraped off the streets, snow includes salt, sand, organics, metals and debris and these contaminants are of concern Table 2. The quality of the snow may also be affected by the town and the contaminants found on the streets; snow from Trail had high metal levels and failed Daphnia and Selanastrum toxicity tests (Antcliffe and Colwell, 1998). If snow is left on the streets to melt and runs into storm sewers much of this material ends up in the rivers, although some solids do settle out in retention basins where these exist. If the snow is piled on empty lots the solids are removed but much of the soluble salts will eventually find their way into ground water or surface waters. There is no fully satisfactory solution, but there are some compromises which lessen the impacts to water and sediment quality. These include:
Roadsalt may contain a number of contaminants, some deliberately added and others incidental. The source of roadsalt used should be analysed to make sure it has no harmful materials in it. Anti-caking compounds are sometimes added and some of these contain cyanide which is very toxic and should be avoided. Do not assume roadsalt is just NaCl. The commercial grade used for roadsalt is impure and will contain contaminants, some of which may be toxic. However, apart from the cyanide the concentrations are generally too low to be of concern. When large purchases of roadsalt are going to be made, insist on an analysis of the product first. Testing by MOTH over the years indicates that the normal mixture supplied is about 99% NaCl and only 1% contaminants, mostly soil particles. Table 2 gives some contaminants in snow removed from roads in Toronto. Not all of these contaminants resulted from roadsalt application. With the obvious exception of the chlorides, most came from the roads and the cars themselves. After normal dilutions of at least 10:1 or 20:1 they would not constitute a water quality problem.
based on 5
samples of Toronto street snow.
Table 3. Contaminants in Melted Snow Removed from Trail Roads
based
on 4 samples of Trail street snow.
Roadsalt was often stored in piles near the stretch of road where experience indicated it would be needed. Often there were neither floor nor roof provided for the piles. Historically, ground water contamination by roadsalt was caused by runoff and infiltration of NaCl from these salt storage piles. A properly constructed storage facility, and transfer procedures which avoid spillage, should virtually eliminate the risk to water quality from roadsalt storage facilities. For | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||