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Chapter 8 (Revised August 2013)
Winter Operations and Salt, Sand, and Chemical Management
8.1. Selecting Snow and Ice Control Materials to Mitigate Environmental Impacts

This section describes the use of various winter maintenance products for the prevention of ice bonding to pavement or for ice melting and removal, with a focus on their environmental footprint. Best practices of winter chemical usage are implemented to apply the right type and amount of materials in the right place at the right time for snow and ice control. Deicing agents can be found in a wide variety of snow and ice control products used on winter roadways to either prevent the bonding of ice to the roadway (anti-icing) or break the bond between ice and the roadway (deicing). The products (e.g., chlorides) melt ice and snow by lowering the freezing point of the snow-salt mixture. Prior to application onto roadways, liquid products can also be added to abrasives or solid salts to make them easier to manage, distribute, and stay on roadways (pre-wetting). For simplicity, the term deicer is used hereafter to refer to all products used for anti-icing, de-icing and pre-wetting operations.

According to a survey we conducted by Fay et al. (in review) the most commonly used winter maintenance product is solid salt (NaCl), followed by salt brine and then sand, grit or traction material. Liquid magnesium chloride (MgCl2) and liquid calcium chloride (CaCl2) were selected as being used by approximately 60% of respondents. The two products listed in the other category were - salt/sand mixed with potassium acetate (KAc) and calcium magnesium acetate (CMA) flakes for bridges. For anti-icing, deicing, pre-wetting and dry placement for traction, the most commonly used product was liquid NaCl, solid NaCl, liquid NaCl, and sand/grit/traction material, respectively.

There are primarily five types of products available in North America for snow and ice control on roads, i.e., NaCl, CaCl2, MgCl2, KAc, and CMA. All of these serve as freezing point depressants and have their own characteristics and impacts on the environment. Additives such as agricultural by-products (ABPs) or organic by-product enhancers are also blended with these primary deicers to improve their performances in snow and ice control. Known additives are corn syrup, corn steeps, and other corn derivatives; beet juice-sugared or de-sugared; lignin/lignosulfonate; molasses (usually from sugar cane); brewers/distillers by-product; and glycerin. Abrasives are also often used to provide temporary traction on wintery roads. While improving roadway safety and mobility, the use of these abrasives and deicers can lead to corrosion and environmental costs that should be taken into account (Shi et al., 2012).

8.1.1 Impacts of Salt and Chloride-Based Deicer on the Environment
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Chloride-based salts are the most common products used as freezing-point depressants for winter road maintenance applications. According to a 2007 survey, most state Departments of Transportation (DOTs) continue to rely on chloride salts and abrasives (Fay et al., 2008) for winter highway maintenance. NaCl, or rock salt, is the most widely used chemical due to its abundance and low cost (Fischel, 2001). It can be used as rock salt for de-icing, as salt brine for anti-icing, or added to sand or other abrasives to prevent freezing. A near record 20.3 million tons of NaCl were sold in 2007 in the U.S. (Salt Institute, 2008). The Salt Institute suggested application rates of NaCl at 100 to 300 pounds per lane mile (30 to 90 kg per lane km) of solid material, and at 45 to 165 gallons per lane mile (105 to 388 liters per lane km) of 23% liquid salt brine. However, NaCl is rarely used and minimally effective below pavement temperatures of 10°F (TRB, 1991).

Magnesium chloride (MgCl2) brines feature better performance at lower temperatures (Ketcham et al., 1996; Shi et al.,2009a). Laboratory data have demonstrated that relative to NaCl, the use of calcium chloride (CaCl2) for comparable deicing performance at 0 - 10°F within 1 hour would introduce 5 times less Cl- and 10 times less cations (Brandt, 1973). Field studies have shown CaCl2 to be more effective than NaCl, owing to its ability to attract moisture and stay on the roads (Warrington, 1998). At reasonable application rates, the effective temperature for CaCl2, MgCl2 and NaCl was reported to be -25°C, -15°C and -10°C, (-13°F, 5°F, 14°F) respectively (Yehia and Tuan, 1998). CaCl2 and MgCl2 are more costly than salt (NaCl), and they can be difficult to handle. Application of MgCl2 or CaCl2 on roads can lead to potentially slippery conditions on the pavement under certain relative humidity circumstances because of their hygroscopic properties (Perchanok et al., 1991; Leggett, 1999).

The environmental impacts of chloride roadway deicers depend on a wide range of factors unique to each formulation and the location of application. According to Ramakrishna and Viraraghavan (2005), the degree and distribution of the impacts in the highway environment are defined by spatial and temporal factors, such as: draining characteristics of road and adjacent soil, amount and timing of materials applied, "topography, discharge of the receiving stream, degree of urbanization of the watershed, temperature, precipitation, dilution", adsorption onto and biodegradation in soil, etc. A recent survey of winter maintenance practitioners found water quality to be of the greatest concern, with air quality, vegetation, endangered species, and subsurface well contamination also mentioned as highly relevant (Levelton Consultants, 2007). Recent research confirm that repeated applications of road salts (i.e., chloride-based deicers) and abrasives or "seepage from mismanaged salt storage facilities and snow disposal sites" may adversely affect the surrounding soil and vegetation, water bodies, aquatic biota, and wildlife (Buckler and Granato, 1999; Levelton Consultants, 2007; Venner Consulting and Parsons Brinckerhoff, 2004).

Known issues associated with the use of chlorides as deicers are increased salinity in adjacent waterways and soils, infiltration of cations (Na+, Ca2+, Mg2+, etc.) and chloride anion (Cl-) into soils and drinking water (TRB, 1991; Jones et al., 1992; Mason et al., 1999; Kaushall et al., 2005), and degradation of the environment along the roadside (Bryson and Barker, 2002; Miklovic and Galatowitsch, 2005).

Chlorides are readily soluble in water and difficult to remove, and thus concerns have been raised over their effects on water quality, on aquatic organisms, and on human health (TRB, 1991; Environment Canada, 2010). The chloride salts applied on winter roads can migrate into nearby surface waters and impact them via various pathways. Godwin et al. (2005) found that the Na+ and Cl- concentration of surface waters in Mohawk River Basin had increased by 130% and 243% from the 1950s to 1990s while other constituents had decreased or remained the same, likely attributed to the estimated 39 kg/km2 (54 lbs/mile2)-day application of deicing salt on roads within the watersheds. Generally, the highest salt concentrations in surface waters are associated with winter or spring thaw flushing events (Stevens, 2001; Ramakrishna and Viraraghavan, 2005). In addition to direct influx of road runoff into surface waters, chloride salts applied on winter roads can also percolate through roadside soils and reach the water table, thus posing an environmental risk for groundwater (Defourny, 2000; Albright, 2005). Research has shown that 10% to 60% of the NaCl applied to roads enters shallow subsurface waters and accumulates until steady-state concentrations are attained (Environment Canada, 2010). Improper salt storage has caused problems with well water and reservoir concentrations. Wells most likely to be affected are generally within 100 ft down-gradient of the roadway in the direction of groundwater movement (TRB, 1991). Watson et al. (2002) reported that Cl concentrations exceeded the U.S. EPA secondary maximum contaminant level of 250 mg/L for drinking water (EPA, 2006) at seven wells down gradient from the highway during late winter, spring, and summer samplings. The Cl limit was exceeded only in water from wells with total depth less than about 10 ft below land surface. Na concentrations in water periodically exceeded the EPA drinking-water equivalency level of 20 mg/L in both the uppermost (deicer affected) and lower one-thirds of the aquifer. The most common anti-caking agent used in deicers contains trace amounts of cyanide, which may add additional toxicity and impact aquatic organisms and present an environmental concern for the domestic water supply (Fischel, 2001).

Salt and other chloride-based deicers can pose an environmental risk for soils, as the salt concentrations in roadside soils have been found to positively correlate with the rate of salt application (Jones et al., 1992). Cunningham et al. (2008) found that in an urban environment Mg2+ from MgCl2 deicer application was the most abundant cation in soils adjacent to roadways even though NaCl was the most frequently used deicer. The Na+ was found to rapidly leach from the soil, decreasing toxicity to plants but increasing input to adjacent waterways. Green et al. (2008) found the use of chloride-based deicers to affect ammonification, possibly by increasing soil pH and by nitrification in roadside soils.

The elevated Na+ concentrations in soil tend to displace naturally occurring Ca2+, Mg2+ etc. and disperse the organic and inorganic particles in the soil pores, reducing soil permeability and aeration and increasing overland flow, surface runoff and erosion (Public Sector Consultants, 1993; Defourny, 2000; Fischel, 2001; Ramakrishna and Viraraghavan, 2005; Nelson et al., 2009; Environment Canada, 2010).

Salt and other chloride-based deicers can have detrimental effects on plants, in particular, roadside vegetation (NDOT, 1990; Bäckman and Folkeson, 1996; Fischel, 2001; Wegner and Yaggi, 2001; Environment Canada, 2004; Cekstere et al., 2008; Trahan and Peterson 2008; Munck et al., 2009). Roth and Wall (1976) suggested that roadside vegetation is subject to environmental stress and the elevated salt concentrations "can only further impair natural balances and accentuate this stress". Road salt exposure due to spray within 33 to 65 ft of the road was demonstrated to cause a greater severity of foliar damage than uptake through the soil alone (Viskari and Karenlampi, 2000; Bryson and Barker, 2002). Many studies have indicated that needle necrosis, twig dieback, and bud kill are associated with areas of heavy road salt usage, with trees and foliage down wind and facing the roadside more heavily affected than trees further away (Sucoff et al., 1976; Pederson et al., 2000). Field tests have shown that 20% to 63% of the NaCl-based deicers applied to highways in Sweden were carried through the air with 90% of them deposited within 65 ft of the roadside (Blomqvist and Johansson, 1999). Shrubs and grasses in general can tolerate increased NaCl concentrations better than trees (Sucoff, 1975). A study performed in Massachusetts evaluated the impacts of NaCl on vegetation near roadways (Bryson and Barker, 2002). Of the species tested, pines and sumacs had the most widespread, severe damage while grasses, ferns, maples and oaks were tolerant of high salt concentrations. Na concentrations in damaged pine needles were about 75 times as high as those in healthy pine needles. The highest Na concentrations associated with pine needles and maple leaves was 3356 mg/kg and 249 mg/kg, respectively at 10 ft from the road. Similar to NaCl, MgCl2 and CaCl2 can cause damage to vegetation such as growth inhibition, scorched leaves, or even plant death (TRB, 1991; Public Sector Consultants, 1993; Trahan and Peterson, 2008). Field and greenhouse studies have found direct application of MgCl2 to be more damaging to plant foliage than NaCl, causing decreased photosynthesis rates on exposed foliage adjacent to roadways (Trahan and Peterson, 2008). In wetlands with elevated deicer concentrations, a decrease in plant community richness, evenness, cover, and species abundances has been observed (Richburg et al., 2001). In wetlands specifically, reducing and/or halting deicer treatment can allow for native plant recovery after multiple water years, but this includes the re-introduction of non-native species as well (TRB, 1991; Moore et al., 1999).

Road salt may accumulate on the side of roadways following deicer applications and during spring as snow melts; in areas with few natural salt sources, this could attract deer and other wildlife to the road network (Bruinderink and Hazebroek, 1996). The presence of wildlife on roadways to glean deicing salts has led to increased incidents of wildlife-vehicle collisions (Forman et al., 2003). Chloride salts used for snow and ice control generally pose minor impacts on fauna, since it is rare for their concentrations in the environment to exceed the tolerance level of animals (TRB, 1991; Jones et al., 1992; Lewis, 1999; Silver et al., 2009). Nonetheless, ingestions of road salts have been associated with mammalian and avian behavioral and toxicological effects (Forman et al., 2003). Additionally, road salts may reduce wildlife habitat by reducing plant cover or by causing shifts in plant communities - in effect, decreasing food sources and/or shelter (Environment Canada, 2010). Field data and modeling of the effects of road salt on vernal-pool-breeding amphibian species found that embryonic and larval survival was reduced with increasing conductivity. The negative effects varied as a function of the larval density and the distance from the road, with the greatest impacts occurring within 150 ft of the road (Karrker et al., 2008).

8.1.2 Impacts of Acetate Based Deicers on the Environment
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The high cost of acetates (KAc, CMA, and sodium acetate - NaAc) and formates (sodium formate - NaFm, and potassium formate - KFm) have hindered their wider application by highway agencies (Vitaliano, 1992; Cheng and Guthrie, 1998; Fischel, 2001; Keating, 2001). Testing of soil, vegetation, and streams on the North Island of New Zealand where CMA was used for both anti-icing and deicing had shown no negative impacts (Burkett and Gurr, 2004). CMA generally works as a deicer similar to NaCl, yet it can require 50% more by weight than NaCl to achieve the same results (Wegner and Yaggi, 2001). Relative to NaCl, CMA is "slower acting and less effective in freezing rain, drier snowstorms, and light-traffic conditions" (Ramakrishna and Viraraghavan, 2005). Other disadvantages of CMA include the air quality impacts and poor performance in thick accumulations of snow and ice and in temperatures below 23°F.

The most pronounced environmental issue associated with acetate-based deicers is the biochemical oxygen demand (BOD) increase that reduces available oxygen for organisms in the soil and aquatic environments (LaPerriere and Rea, 1989; Fischel, 2001). The acetate ion happens to be the most abundant organic acid metabolite in nature and its biodegradation could lead to anaerobic soil conditions or localized dissolved oxygen (DO) depletion in surface waters (TRB, 1991; D'Itri, 1992; Horner and Brenner, 1992; Defourny, 2000). Data pertaining to a NaAc/NaFm-based deicer suggests that during the spring thaw runoff, short periods of oxygen depletion in receiving waters may occur, with potential danger in warmer weather (Bang and Johnston, 1998). Multiple studies have found KFm to cause no undesirable changes in the groundwater chemistry, owing to biodegradation in topsoil (Hellsten et al., 2005a, 2005b). An aquifer scale study on the fate of KFm (Hellsten et al., 2005b) found KFm to be easily biodegraded at low temperatures (-2 to +6°C (28 to +43°F)) in soil microcosms, whereas chloride ions from the deicing products used in previous winters had accumulated in the aquifer.

The effect of acetate-based deicers on plants can vary depending on the type of plant and the level of deicer usage. For Kentucky bluegrass, red fescue grass, barley and cress it was found that CMA was less toxic than both NaFm and NaCl, which were of equal toxicity (Robidoux and Delisle, 2001). CMA can enhance plant growth by improving soil permeability and providing needed Ca and Mg as nutrients, which may be a valuable characteristic in areas where heavy salt use has resulted in soil compaction (Fritzsche, 1992). A NaAc/NaFm-based deicer has been demonstrated to have positive impacts on pine and sunflower growth, acting as a fertilizer at concentrations of ~0.5 g/kg of soil. At higher concentrations of 4 g/kg, detrimental effects have been observed including low germination rates, low biomass yield, lateral stem growth, suppressed apical meristem growth, browning of leaves/needles, and senescence (Bang and Johnston, 1998). KFm concentrations less than 4 kg/m2 were found to have detrimental effects on vegetation (Hellsten et al., 2005a).

There are also mixed effects of acetate-based deicers on animals. In general, CMA has low aquatic toxicity while KAc and NaAc have greater aquatic toxicity (Fischel, 2001). A NaAc/NaFm-based deicer was reported to cause apparent fish disorientation, concave abdomen and spinal curvature, observed gill distention, and death (Bang and Johnston, 1998). Acetates and formates have been shown to promote bacteria and algae growth (LaPerriere and Rea, 1989; Bang and Johnston, 1998). For the invertebrate Eisenia fetida, CMA was found to be less toxic than NaFm or NaCl, which were of equal toxicity (Robidoux and Delisle, 2001).

8.1.3 Impacts of Sand/Abrasives on the Environment
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Abrasives (e.g., sand or grit) have been used for many decades for winter operations, as they can provide a temporary friction layer on the snowy or icy pavement. Abrasives are typically used on roads with low traffic and low level of service (LOS) (Blackburn et al., 2004). Abrasives, especially those not pre-wetted, had limited effectiveness on wintery roads with higher vehicle speeds; as such, the use of abrasives will not necessarily improve operations or mobility on many roads (CTC & Associates, 2008). Schlup and Ruess (2001) provided a balanced perspective on the use of abrasives and salt, based on their impact on security, economy, and the environment. The detrimental environmental impacts of abrasives are generally greater than those of deicers (Staples et al., 2004). It would take a significantly higher amount of abrasives to maintain a reasonable level of service, relative to the amount of deicer that would be required.

Abrasives used for snow and ice control are relatively inexpensive but costs of damage caused by their repeated applications, along with substantial clean-up costs, can make them less cost-effective. The use of abrasives can pose negative impacts to water quality and aquatic species, air quality, vegetation, and soil and incur hidden costs. Even after cleanup, 50% to 90% of the sand may remain somewhere in the environment (Parker, 1997). Depending on their particle size, abrasives may contribute greatly to air pollution, can potentially cause serious lung disease, and is listed as a carcinogen (Fischel, 2001; Nixon, 2001). Particles smaller than 10 microns (0.01 mm) in diameter, known as PM-10, are regulated by the U.S. EPA and may become suspended in the air and contribute to respiratory problems and cause eye and throat irritation. Communities with excessive PM-10 particles in the air may surpass limits imposed by the Clean Air Act and be categorized as "non-attainment" areas (Williams, 2001). In such communities, the use of abrasives is only allowed on a limited basis (Chang et al., 2002). Abrasives also pose significant risks for water quality and may threaten the survivability of aquatic species especially during spring runoff (Staples et al., 2004). The risks may include: increased water turbidity from suspended solids, clogging of streams and storm water drains, and reduced oxygenation within the stream and river beds. Particles less than 2 mm in size are especially problematic as they can block the movement of oxygen into streambed gravel. Increased quantities of particles less than 6 mm in size can smother macro-invertebrates and fish eggs, affecting both food chains and fish reproduction (Staples et al., 2004). Finally, abrasives used for snow and ice control can also exacerbate the environmental stress for roadside soil and vegetation.

8.1.4 Responding to Public Concerns/Complaints Regarding Contamination
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A number of studies have established the impacts of winter maintenance materials on the roadside environment, particularly to soils, plant life and aquatics (Mills and Barker, 2002; Hagle, 2002; Akbar, et al., 2006). While proper material storage, maintenance of equipment, appropriate application rates, and preventative procedures and specialized equipment have made great strides in reducing or eliminating the environmental impacts of winter maintenance materials, it is impossible at the present time to completely prevent all roadside contamination. The occurrence of contamination has led in recent decades to greater public concerns and complaints stemming from winter maintenance practices that transportation agencies must consider and address. Different approaches have been developed and used by agencies to address such concern/complaints, which are outlined in the following paragraphs. Some of these approaches are proactive and seek to address/minimize issues before they arise, providing agencies with a means to address public concerns by showing what is already being done. In other cases, a reactive approach is employed to address public complaints that arise from potential contamination.

The Environmental Protection Agency has laid out practices to prevent pollution to waterways from the operation and maintenance of highways (EPA, 1993). These practices included several specific to winter maintenance operations, and include:

  • Cover salt storage piles and deicing materials to reduce surface water contamination and locate such piles outside of the 100 year floodplain.
  • Regulate the application of deicers to prevent over application.
  • Use specialized equipment (e.g., zero velocity spreaders) to apply granular materials so that they remain on the roadway.
  • Use alternative materials such as sand and salt substitutes in sensitive ecosystems.
  • Avoid dumping snow into surface waters.

The Maryland Department of the Environment has also laid out best management practices for winter maintenance, including:

  • Avoid the use of salt and deicers when more than 3 inches of snow have accumulated.
  • Use treatment materials at an appropriate temperature for the specific product.
  • Use salt and deicers only when a storm is imminent, and sweep and remove materials from the roadway if a storm does not occur.
  • Apply materials only when and where necessary.
  • Calibrate equipment and train operators in proper application procedures.
  • Mix sand with granular materials for added traction and to reduce chemical use.
  • Consider alternative materials that require lower application quantities.
  • Store materials in a dry, covered area on an impervious surface (Maryland Department of the Environment, Undated).

The prior discussions have detailed proactive approaches to prevent and reduce environmental contamination. However, when such contamination does occur and the public contacts an agency regarding it, steps should be taken to alleviate and address concerns and complaints. The New York State Department of Transportation, in addressing public complaints stemming from site contamination from transportation facilities (e.g., maintenance yards), recommended the following steps be taken: (Venner Consulting, 2004)

  • Locate the contaminated site on a map and observe what highways or maintenance facilities are located nearby to determine potential sources of contamination.
  • Interview staff if a maintenance facility is located near the affected site to determine if materials were left uncovered and, if so, to recommend actions to address the issue.
  • Review historical data (photos, maps, and water quality data) to determine if past maintenance facilities may have contributed to the contamination.
  • Inspect the site and neighboring areas to determine whether other sources (e.g., septic systems) have contributed to the contamination and to observe whether any significant amounts of winter maintenance products are visibly present.

As these approaches indicate, both proactive and reactive measures should be taken to address public concerns and complaints regarding contamination. While it may be impossible to eliminate all contamination associated with winter maintenance, particularly treatment using deicers, it is possible to significantly prevent such issues from having an impact outside of the right of way and to address them in an effective manner when they do arise.

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Continue to Section 8.2 »
 
Table of Contents
 
Chapter 8
Winter Operations and Salt, Sand, and Chemical Management
8.0 Introduction
8.1 Selecting Snow and Ice Control Materials to Mitigate Environmental Impacts
8.2 Reducing Sand Usage and Managing Traction Materials
8.3 Strategic Planning for Reduced Salt Usage
8.4 Stewardship Practices for Reducing Salt, Sand and Chemical Usage
8.5 Precision Application to Manage and Reduce Chemical Applications
8.6 Monitoring and Recordkeeping
8.7 Winter Operations Facilities Management
8.8 Training for Salt Management and Winter Maintenance Operations
  References
  Appendix A - Acronyms
   
Lists: Examples | Tables | Figures
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