DOT Maintenance staff generally develop winter management and operation plans that identify sensitive/critical areas , levels of service for roads and methods for maintaining levels of service during winter weather. NCHRP and AASHTO are producing NCHRP 6-16, Guidelines for the Selection of Snow and Ice Control Materials To Mitigate Environmental Impacts, which will be available in 2005. The objective of the project is to develop guidelines for selection of snow and ice control chemicals and abrasives, based on their constituents, performance, environmental impacts, cost, and site-specific conditions. The project will identify and justify methods for measuring the constituents and properties that determine the environmental impacts of the current range of snow and ice control materials, and present this information on available materials and significant properties in matrix format, with purchase specification and quality assurance test protocol for the evaluation of existing and future materials. Environmental impacts to be studied include effects on human health; aquatic life; flora and fauna; surface water and groundwater quality; air quality; vehicles; and physical infrastructure including bridges, pavements, railway electronic signaling systems, and power distribution lines. Guidelines will be developed that incorporate: [N]

A decision-making process for the selection of snow and ice control chemicals and abrasives, based on their composition, performance, environmental impacts, cost and site-specific conditions.

• The matrix of currently available products and their properties.
• The purchase specification.
• The quality assurance protocol.

For the purposes of this report, NCHRP 25-25(04), impacts of various snow and ice control materials and the background for use of recommended environmental stewardship practices are summarized below.

Road-salt use in the United States ranges from 8 million to 12 million tons of NaCl per year according to the National Research Council (NRC);Massachusetts, New Hampshire, and New York report the highest annual road-salt loadings, with Massachusetts the highest at 19.94 tons/lane-mile./yr.[N] Salt usage and impacts on the roadside habitat, water sources, fish and wildlife, and pavement are growing concerns in North America and abroad. Such concerns in Canada prompted the federal environmental agency, Environment Canada (EC), to conduct a comprehensive assessment of road-salt application to determine whether conventional deicers should be considered toxic substances under the Canadian Environmental Protection Act. [N] EC conducted a five-year, comprehensive scientific assessment of the environmental impacts of road salts that contain inorganic chlorides, such as sodium chloride, calcium chloride, potassium chloride, and magnesium chloride. The study found that high concentrations of road salts commonly enter the environment through roadway melt water and through seepage from mismanaged salt storage facilities and snow disposal sites.[N] Although not directly harmful to humans, the road salts can have harmful effects on the aquatic environment, plants, and animals. [N]

Much of the salt that is placed on a road during snow and ice control operations eventually runs off with the roadway drainage. While sodium may bond to negatively charged soil particles or be taken up in biological processes, chloride ions are less reactive and can be transported to surface waters through soil and groundwater. Road salts applied to roadways can enter air, soil, groundwater, and surface water from direct or snowmelt runoff, release from surface soils, and/or wind-borne spray.[N] Deicing salt reaches the natural environment in a number of ways: [N]

• Through salting practices in which some of the spread salt lands directly on or bounces onto roadside verges of footways.
• Through salt being thrown to the edge of the road by the action of passing vehicles or by the wind.
• Through dissolved salt running off roads and into drainage systems, which eventually discharge into natural waters.
• Through dissolved salt being splashed or sprayed onto roadside soil, vegetation, and surface waters by passing traffic.
• Through salted snow being blown or plowed onto the roadside by snow blowers or snowplows.

These salts remain in solution in surface waters and are not subject to any significant natural removal mechanisms. Their accumulation and persistence in watersheds pose risks to aquatic ecosystems and to water quality. Approximately 55 percent of road-salt chlorides are transported in surface runoff with the remaining 45 percent infiltrating through soils and into groundwater aquifers.[N] In the past, salt storage has led to contamination of local soils and watercourses. According to Hogbin, 0.125 to 02.5 percent of the initial weight of an uncovered stockpile is lost per year by leaching for each inch of rainfall on that stock pile.[N]

While wind deposition has received less attention than other areas of salt impact, study results have shown that roadside exposure to airborne salt was related strongly to the wind direction. [N] Bulk deposition was collected in a field adjacent to highway E4 in SE Sweden and related to wind characteristics and deicing activities on the road; chloride was shown to be transported several hundreds of meters away from the road and the amount of air-borne chloride deposited in the roadside environment was well correlated to the road-salting intensity.[N]

Salinity and chlorine-impaired streams are present in a number of Midwestern and Western states.[N] A Nevada DOT-Caltrans study in 1990 concluded that 15 percent of the trees observed along the Lake Tahoe Basin highways within both Nevada and California, were salt-affected, showing evidence of disease, bark beetle infestation, and the effects of four years of drought. [N] Roadside trees and other vegetation are affected by salt primarily through two mechanisms: 1) increased concentrations of salt in soil and soil water leading to greater root absorption; and 2) salt accumulation by foliage and branches due to vehicle splash and spray and windblown dry salt. Although deciduous trees have no leaves in winter, they can still be affected by salt spray as dormant twigs intercept the salt, which may reach living tissue by entering twigs through leave scars. In contrast to salt taken up by roots, salt spray rarely causes tree death outright, but annually recurring damage tends to keep the crowns narrow, stems thin, and plants short. Trees close to roads are generally the worst affected. Damage is most severe within five meters of the road but there is frequently a distinct injury gradient with distance; damage is minimal about 30 meters from the road. Trees on the downhill side of a road suffer more damage than those on the uphill side. On high-speed roads where salt spray instead of runoff is the major cause of injury, trees on the downwind side of the carriageway have the greatest injury. [N]

CDOT research on the environmental effects of chloride-based deicers found that aodium chloride, magnesium chloride, and calcium chloride may contribute to the mobilization of trace metals from the soil to surface and groundwater, though field evidence is limited. The chloride-based deicers have the potential to increase the salinity of the rivers, streams, and lakes. Since the dilution of deicers from the roadways to nearby streams is estimated to range from 100 to 500-fold, salinity increases are only likely to occur in slow-flowing streams and small ponds. Increased salinity was reported in groundwater at a distance of more than 300 feet from roadways. Damage to vegetation from deicing salts was reported to a distance of 100-650 feet. [N]

Sodium chloride crystals attract birds and mammals, which can contribute to road kills. Sodium-deficient wildlife sometimes travel great distances to ingest road salt. Many animals tend to overshoot their salt deficit and then drink salty snow melt to relieve thirst, which increases salt toxicity in blood and tissues.[N]

In contrast, magnesium chloride and calcium chloride deicers do not attract wildlife since the main chemical attractant is sodium. Acute toxicity tests show that there is slight oral toxicity of the chloride deicers to small animals.[N]

Further study of magnesium chloride deicer by the Colorado DOT and the University of Colorado concluded that application of Mag chloride at current rates is highly unlikely to cause or contribute to environmental damage at distances greater than 20 yards from the roadway. Even very close to the roadway, the study found that the potential of magnesium chloride deicer to cause environmental damage is likely much smaller than that of other factors related to road use and maintenance, including pollution of highway surfaces by vehicles and use of salt and sand mixtures to promote traction in winter. [N]

Caltrans found that Magnesium chloride, being a liquid, can be applied in a more uniform manner than granular salt, but must be kept in storage tanks. [N] Depending on service conditions experienced by automobile components, MgCl 2 is more corrosive than NaCl under humid environments, and NaCl is more corrosive under immersion and arid environments.[N]

Colorado DOT's study concluded with the following practice recommendations for Mag chloride: [N]

• Mag chloride may offer net environmental benefits if its use leads to a reduction in the quantity of salt and sand applied to roadways as long as concentrations of contaminants remain low and rust inhibitors containing phosphorus are avoided.
• Appropriate specifications for vendors and routine testing can ensure the continued environmental acceptability of magnesium chloride deicers.
• Deicers provided by vendors should be monitored independently by DOTs for chemical characteristics. Any significant changes in processing or source material should be disclosed by the vendor. Independent specifications should probably be developed depending on elevation in the state.

CDOT is conducting ongoing research (2005-2008) on innovative anti-icing and deicing chemical products on the market that could improve safety and mobility while protecting the environment. [N]

Acetate-based deicers are organic and have different kinds of effects on the environment than the chloride-based deicers. The acetate ions are broken down by soil microorganisms and may result in oxygen depletion of the soil, which can impact vegetation. The acetate deicers also have the potential to cause oxygen depletion in rivers, streams and lakes. Since the dilution of deicers from roadways to nearby streams is estimated to range from 100 to 500-fold, oxygen depletion has been considered likely to occur only in slow flowing streams and small ponds. [N] The aquatic toxicity of Calcium Magnesium Acetate (CMA) to fish and invertebrates is low. [N]However, the depletion of dissolved oxygen (DO) from the degradation of the acetate component of CMA has been a water quality concern, and studies have shown that CMA decomposition exerted a significant biochemical oxygen demand on receiving waters. [N] [N]

The acetate deicers Potassium Acetate, Sodium Acetate (NAAC), and CMAK have higher toxicity to aquatic organisms. The use of the acetate deicers results in the decrease of air pollution from the reduction in sand use. However, the solid acetate deicers CMA and NAAC may contribute fine particulates to the air and increase air pollution. The acetate deicers CMA and Potassium Acetate are not harmful to terrestrial vegetation at the concentrations typically used on the roadways. However, NAAC may potentially have an adverse effect on vegetation because of the presence of the sodium ion, which decreases the stability and permeability of the soil. The depletion of oxygen in the soil from the breakdown of the acetate ion can have a negative effect on plant growth. Slight acute oral toxicity to mammals has been reported for the acetate deicers. No studies have been conducted on whether the acetate deicers attract wildlife to roadways. [N]

Oregon DOT has decided to tightly control and potentially avoid the use of calcium magnesium acetate (CMA) and potassium acetate (KA) in the following areas:

• Those where receiving waters will not provide 100:1 dilution during the runoff season, or if the runoff occurs in the late season when the receiving waters may have warmed and protected aquatic species are present;
• Those where a larger highway runoff volume can directly reach a small, shallow pond, lake, or wetland, particularly if the receptor is ice covered. A 30-foot vegetation buffer may be adequate;
• Those where there is no vegetation buffer between the road and receiving waters, and the waters should be protected from oxygen depletion. Present DOT standards for vegetative buffers are adequate;
• Those known to have heavy metal concentrations, coarse soils overlying sensitive aquifers, or percolation devices such as French drains and drywells: when CMA or KA is used in any of the above situations due to over riding concerns for highway safety, water quality should be carefully monitored for possible problems.

Caltrans tests of CMA found the compound less effective than salt for deeper snow packs, resulting in a delay in the melting of ice and snow pack, particularly at temperature below 24 degrees F though the consistency of the snow pack was changed such that it was easier to plow. [N] CMA can cause respiratory distress and eye irritation for personnel required to handle it, thereby necessitating the use of protective gear. CMA costs over 10 times more than salt and typically requires an application rate 50 percent over that of salt for CMA to be effective. [N]

The National Research Council conducted a study to examine the full economic costs of using salt and CMA for highway deicing. The report, TRB Special Report 235, Comparing Salt And Calcium Magnesium Acetate, defines the true cost of salt; estimates of monetary costs involved in mitigating environmental damage from road salt; and summarizes field performance, infrastructure and environmental impacts, production technologies and costs of CMA. [N] Other studies have investigated the effects of different deicers on concrete deterioration. [N]

Sand is not a deicer, but has been used for snow and ice control since the early 20th Century. Agencies tend to spread sand many times throughout the winter months, an expensive process that can create large debris deposits on roadways and require road sweeping and subsequent disposal as solid waste. Sweeping picks up only a small percent of the total sand applied during a typical winter. An Oregon DOT study found that 50 to 90 percent of sand applied to pavements remains in the environment after cleanup. [N] The rest remains in the environment, much of it in catch basins or on or around roadways. Much of the sand not retained in catch basins stays in drainage pipes, decreasing their capacity. Abrasives can clog stormwater inlets and sewers, requiring cleanup in urban areas, on bridge decks, in ditches, and where aquatic environments are at risk. The materials may wash downstream and end up in streams and lakes.

Resource agencies have determined that roadway sand contributes to sedimentation in streams and impacts fish and other aquatic resources. Sand has a negative effect on water quality as a result of the increased turbidity caused by the presence of sand particles in water. Sediment impairment is the most widespread cause for waters of the state to fail to meet water quality standards. [N] The increased water turbidity can result in mortality of fish and bottom-dwelling invertebrates that may be covered by the sand. The increased turbidity will also reduce or inhibit photosynthesis in aquatic plants.

Air pollution from particles less than 10 microns in size (PM 10) has been documented from winter abrasive use. Vehicle grinding of sand allows fine particulate matter, PM 10 (or PM 2.5), to become airborne when dry, and causes river silting during snow melt via surface drainage. Sand used for snow and ice control increases air pollution and has been estimated to contribute approximately 45 percent of the small particulates present in air. [N] A 1995 study documented "The Contribution of Road Sanding and Salting Material on Ambient PM 10 Concentrations" in Albany, NY; Denver, CO; and Reno, NV, the impacts of wintertime road sanding and/or salting on ambient particulate loadings and found the following: [N]

• Albany. In 21 6-hour sampling periods, sanding contributed more than 44 percent of the total PM 10 particulate loading, with a high of 75 percent. Motor vehicle emissions contributed approximately 22 percent and deicing salt was as low as 1 percent, averaging 24 percent.
• Denver. In 24 samples analyzed in the study, the sand loading contributed over 59 percent to the ambient PM 10 levels, with a high greater than 89 percent. Motor vehicles contributed 19 percent and deicing salt just over 1 percent. Shortly after the study was completed, EPA approved the State of Colorado's air quality improvement plan including a new section dedicated to "Improved Street Sweeping" which requires "that any entity responsible for applying street sanding material within the Denver Central Business District shall clean all streets using vacuum sweepers or a more effective technology within four days of each sanding episode."
• Reno. In 20 samples analyzed, sand contributed an average of 57 percent to PM 10, similar to Denver, with a high of 80 percent. Motor vehicles contributed 22 percent and highway salt approximately 1 percent.

Last but not least, recent studies have shown sand to be of limited value on icy roads. The Iowa DOT and the Iowa Highway Research Board completed a study on "The Use of Abrasives in Winter Maintenance" and concluded that "… applying abrasives dry is of limited value in providing lasting friction enhancement. This represents a substantial change in current practice. Nonetheless, the results of a variety of studies are unequivocal in finding that abrasives applied to roads where significant traffic travels at high speeds are swept off the road rapidly, remaining in place (and providing friction enhancement) for somewhere between 10 and 100 vehicle passages, at most." The effects of sanding are temporary, whether spread dry or prewetted. Abrasives do little to improve driving conditions on roads with high traffic volume. When dry sand is spread, 30 percent of it immediately scatters. Over time, cars usually displace most of the remaining sand. As few as 8 to 12 vehicles can sweep it from snow covered highway surfaces. Even with light traffic, friction gained from dry sand is quickly diminished. University of Iowa (UI) researchers have drawn similar conclusions about methods to prewet abra­sives with a chemical deicing brine . [N]

If a complaint suggests that a DOT may be responsible or involved in the alleged contamination NYSDOT has recommended the following steps or practices to respond to public concern and address the environmental issue:

• Site Location. Locate the contaminated property or area on a map and observe if transportation facilities or major roads or highways are located near the affected site. Sometimes, we observe salt contamination in aquifer areas adjacent to salt storage (including former or temporary) facilities or more rarely, along major highways such as highly traveled State roads or interstates. Salting of smaller or low traffic volume roads generally does not cause significant groundwater contamination.
• Interview. Discuss with Regional Transportation Maintenance staff whether salt (or salt/sand mixtures) is or has been stored at or near the affected site. If so, find out if the salt pile is or was uncovered, and for how long. If stored salt is in contact (even occasionally) with rain or surface water, then recommend or perform actions (i.e., cover the pile with tarpaulins when not in use) to avoid such contact. Inadequate salt storage often results in aquifer salt-contamination.
• Photo, Map, and Background Water Quality Review. If possible, review historical aerial photos, soil/geological maps, and area background water quality data. Aerial photos may show previous salt piles. Soil/geological maps may suggest the location/orientation of potential geological conduits for the contaminants to migrate in the subsurface. Background water quality data from nearby wells will help in interpreting and deciding whether the water quality results received with the complaint could relate to salt-contaminated groundwater from DOT activities.
• Inspection. Inspect affected residences and ask residents for well data (well type and depth, soil/rock type, etc.). Look for water treatment system connections, if any, and identify where the system effluent goes. Typically the effluent discharges to the septic system. Also, inspect any nearby DOT facilities and evaluate past or current salt storage practices or conditions. If uncovered salt-, salt/sand mix- piles, or significant amounts of spilled salt are observed, recommend that regional transportation maintenance staff immediately cover or relocate the piles or remove the spilled salt.[N]