On a winter’s drive into snowy mountains, we are privileged to admire from the warmth of our speeding car the vignettes of dark conifer forests huddled in bright snow. The beauty has a stark simplicity that momentarily shrinks our "to-do" list and inspires grand thoughts. Yet if we lose traction on a frozen spot, this landscape of dreamy simplicity can turn savage in a heartbeat. A few spinning seconds can bring terror and tragedy.
The sight of the gravel spreader is reassuring to those who travel in snow country. It’s good to know that when temperatures drop in the mountains, radios crackle at road maintenance stations and trucks roll. Equipment first hits the high-risk areas and emergency routes, then connects the road segments between them, spreading little shards of crushed rock that provide a temporary medium to help tires make contact with frozen, icy, or snow-packed roads. But with traffic, time, warming, and runoff, the crushed rock, which so recently came dancing out of the hopper, is washed off the road or kicked off by the buffeting of traffic and the spin of wheels. Throughout the winter, human life and safety will be guarded by repeated applications of road-sanding grits each time the radios crackle.Most people don’t have a reason to think about the ultimate fate of the crushed rock spread on roads and highways to increase winter driving safety. If they travel in snow country, they’re glad to see the gravel truck and pleased that a mechanical substitute for salt is being applied on mountain roads. But with the National Pollutant Discharge Elimination System (NPDES) and the Endangered Species Act pressing state and municipal road departments to assess maintenance and operations, the paths of road-sanding grits are getting some serious attention. Where sanded roadways drain to wetlands, streams, or sensitive habitats, concerns about cumulative sediment loadings are beginning to arise.
Assess Modes of Transport
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| Repeated applications of crushed rock make wintertime travel possible on icy roads. States and municipalities are finding ways to manage road-sanding grits after they have left the road. |
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| Residual gravels mount up over the years from snow pushed to the roadside. This might be regarded as an aesthetic problem, particularly in resort areas. |
It comes as no surprise that the vectors of these sediments–wind, creep, ravel, and overland flow–are the same familiar agents of erosion and transport that we face in every erosion analysis. So the first step of an assessment is to look at how these sediments go into transport.
Road-sanding grits leave the traveled surface by means of both active and passive mechanisms. Gravels are flicked to the roadside by the spin of tires and by the turbulent cells of air that large vehicles push ahead of themselves and drag behind–the same ones that in summer stir the roadside grasses, swoosh other roadside particles into the air, and make you wish you’d remembered your goggles for that bike ride. Rainfall sheeting off crowned or sloped road surfaces also transports road-sanding grits. The wider and steeper the road, the greater the energy that runoff is capable of gathering to transport loose materials in its exit path from the paved surface.
In road clearing operations, ice, snow, and gravel most commonly are pushed or blown into areas adjacent the road. When snow is pushed, residual gravels become concentrated near the road, usually in the right of way. Blowing scatters the gravels over a wider road corridor zone. In some areas, such as resorts and city centers, snow is loaded and hauled to disposal sites where the gravels are recovered. A few areas scoop snow into an ambulatory snow-melting machine that retains the gravels and sends the melt water to the storm sewer. But for the most part, pushing and blowing remain the order of the day when it comes to snow removal practices.
If we follow the pathways of sanding grit after it has left the road, we will find that much of it comes to a more-or-less permanent halt fairly nearby. Much reposes on road embankments but can be gullied when concentrated road runoff runs over the embankment on the way to the roadside ditch. Some becomes entrained in roadside drainage systems, where it can be transported quite efficiently before it comes to rest in wetlands or is delivered to streams.
Look at Impacts on Receiving-Water Resources
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| Road-sanding grits can have long-term cumulative impacts on streams and wetlands. |
Ask any wetlands ecologist what the effects will be of incremental filling of a wetland that is hydrologically connected to a small stream system. You will hear that watershed-regulating functions will be degraded in many ways. The capability of the wetland to store runoff for later release to base flows will be lessened. As a result, the receiving stream might have higher flows during the wet part of the year, but lower flows during the dry season. Channel responses will result, depending on channel materials and their influence on the ability of the stream to shift vertically and laterally. A widening stream might get warmer as it gets shallower and receives greater solar exposure. The pace of both chemical and biological activities will increase in the warming system. These will influence both water chemistry and biota. A deepening stream might grind away at its bed and banks, producing sediments that can become a chief factor in downstream water-quality impairment and simplifying aquatic habitats.
There’s more: The wetland’s ability to absorb background sediments might be reduced as wetland volume is taken up by the road-sanding grits. As the weight of these sediments displaces both air and water from the soil, plant species can change. The wetland may develop a distinct channel capable of passing background sediment loads right on through the system. The ability of the wetland to recycle inflowing nutrient loads might diminish. The changed nutrient balance of the receiving stream may be reflected by shifts in species of aquatic organisms, which in turn affect the species that eat them.
From the point of view of a Coho salmon that has swum upstream more than 100 mi. from the ocean to a cool, flashing mountain stream, the steady delivery of exogenous (from elsewhere), finely crushed rock to its spawning habitat is not just a housekeeping nightmare; it is more like a foreclosure. Just as space becomes unavailable in a living room piled high with boxes, stream habitat simply becomes unavailable where gravels settle out and stream pockets become packed with deposited gravels. As the small gravels migrate down into the spaces between larger alluvium of the streambed, the larger rock becomes "locked" in place, making it difficult for anadromous fish to build spawning redds or for eggs in the redds to receive enough oxygen.
One study estimated that 15 yd.3 of sanding grits were introduced annually into a half-mile segment of stream so small that a person could jump over it. In another, residual sanding grits that were blown onto a steep highway embankment were creeping back down after the snow melted, directly entering a salmon-bearing stream.
Fit the Solution to the Problem
Such concerns have prompted the development of a fresh batch of best management practices (BMPs) for managing roads treated with sanding grits, particularly in watersheds where threatened and endangered cold-water fish and other sensitive species are present. The solutions are as familiar as the agents of transport. They are prevention, interruption of overland flow, containment, and maintenance. As is the case with most BMPs, the practices are not rocket science but straightforward, commonsense, good-housekeeping actions that for the most part are affordable (see Table 1).
Table 1. Selected BMPs for Managing Road-Sanding Grits
Problem | Best Management Practice |
Storage. Grits freeze together in stockpile, requiring chemical deicers to load and spread. | - Timing. Crush rock during dry conditions.
- Containment. Store in covered shed.
- Site location and design. Storage and loading areas should be located such that grits and gravels will not be washed into drainage ditches, wetlands or streams. If necessary, such areas should be surrounded by containment barriers and/or a regular program of sweeping should be implemented.
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Access for maintenance. Lack of ownership of roadway corridor presents barrier to maintenance access beyond the road shoulder. | - Administration/funding. Obtain roadside rights of way so the department of transportation can access roadside areas and ditches to remove road-sanding grits.
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Transport in roadside drainage. Roadside ditches transport sanding grits to streams and wetlands. | - Construction. Retrofit roadside drainage ditches with settling basins for sediments. Space and size basins according to gradient, flow, ditch cross-section, sediment size, and load.
- Maintenance. Prepare a schedule for cleaning out and reshaping sediment basins. Consider late winter, before herbaceous vegetation becomes established in ditches.
- Adaptive management. Based on inspection records, revise maintenance frequency, spacing, and size of basins as needed.
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Unintended consequences of maintenance. After gravel is removed from ditches in seasonal maintenance operations, raw ditches produce and transport copious sediments during high-flow events. | - Temporary measure. Install temporary filtering barriers (such as BioBags, not straw bales) at appropriate intervals in ditches to slow down water and allow sediment settling. Remove after herbaceous vegetation has become established.
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Impacts of direct disposal into streams and wetlands. Gravels accumulate in wetlands where snow is blown. | - Designate disposal sites. Designate alternative locations to dispose of snow laden with road-sanding gravel.
- Different disposal requirements for "clean" or "dirty" snow. Determine which snow is clean and which is dirty, and key these to acceptable snow disposal techniques and areas. See Tables 2 and 3.
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Impacts of direct disposal on streambanks. Where snow is pushed repeatedly into streams, this operation frequently breaks streamside vegetation, lowering the capability of streambanks to withstand the erosive conditions of high flows. | - Designate disposal sites. Designate what areas are acceptable for pushing clean snow into streams. An example might be a cobble-bedded stream with rocky or cobbled upper banks and floodplain.
- Repair degraded streambanks. Degraded streambanks should be repaired by planting, live-staking, or sprigging native vegetation to encourage quick reestablishment of native, bank-holding plants.
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Lack of common standards and practices. Ski areas, transportation departments, and private snow-removal contractors might be practicing very different snow disposal methods, particularly with respect to stream and wetland protection. | - Develop snow management plan. Involve all entities connected with snow removal operations in developing a local snow management plan that includes standards and acceptable snow disposal methods and sites.
- Require licenses. License local snow-removal contractors and key their activities to appropriate disposal sites and methods.
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Indirect impacts. Gravel creeps from where it was blown onto bare cut bank or hillslope into roadside drainage ditch, wetland, or stream. | - Designate other disposal site.
- Revegetate or bioengineer steep cut banks or hillslopes. Use sprigging, planting, or bioengineering to establish dense vegetation on cut slope or hillslope so that road-sanding grits are held by vegetation.
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Roadway drainage design. Gravel washes from roadway or gravel-contaminated snow is pushed directly into stream or wetland from road. | - Retrofit stream undercrossings. Construct retaining walls or place jersey barriers at the edge of the roadway to prevent gravels from being washed or gravel-contaminated snow from being pushed directly into streams.
- Mark live stream crossings. Mark live stream undercrossings so that equipment operators can clearly see their locations, even in worst-case snowfall conditions. If the snow management plan requires the snowplow blade to be lifted or reangled in critical stream undercrossing zones, they will be clearly marked.
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Shoulder maintenance. Gravels often are swept or washed to the shoulder, where they migrate into roadside drainage systems. | - Replace washing with mechanical recovery.
- Recover and recycle. Sweep and pick up road-sanding grits from the road margin at the end of the season and reuse.
- Rework and recycle. Rework gravel-covered shoulders and embankments to retrieve gravels (annually or as needed), filter as needed, and reuse.
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Lack of specific codes and standards. Disagreements can arise if some people keep their snow on-site but others push it into public rights of way. | - Development codes and construction standards. Many snow-removal headaches can be resolved before they occur by means of codes that require snow that falls on residential, commercial, and industrial lands to be kept on-site. Standards can require a certain percentage of properties be kept available for snow storage. Underground parking might be required, or roof pitches might be prescribed that result in snow being stored on rooftops until it melts. Many preventative measures can be accomplished through codes and standards.
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Worst-case snow conditions. Snow disposal standards can be disregarded during the occasional "big dump." | - Designate emergency snow-disposal sites. Such sites might be school yards, large fields, and parking lots, even the medians of wide streets.
- Public outreach and education. Determine ahead of time how to communicate emergency snow-disposal sites.
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Lack of information. Lack of inspection records or of sufficient detail of records restricts evaluation of BMPs or their costs and inhibits the potential range of adaptive management. | - Keep detailed inspection records. Develop detailed inspection forms so that records can be analyzed to add, remove, or revise BMPs and so that maintenance expenses can be tracked. This is an especially important element in ensuring continuing institutional will and capacity to support a fully functioning BMP program.
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Training. Staff who will implement the BMPs and assess their function need training. They need observational skills as well as vocabulary to describe what they are seeing. | - Train staff to observe and record. People who will be monitoring the effectiveness of BMPs to control road-sanding grits need to learn to interpret the subtle indicators of sediment production, transport, and deposition, especially to evaluate whether sediments are being transported completely through the system.
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| Road-sanding grits can migrate into roadside drainage systems and be delivered by flowing water to streams and wetlands. |
But there’s a hitch: Wherever the new practices take a snow disposal site out of service, a compensatory area must be found. Snow managers have long appreciated the assistance they get from streams and wetlands–whose snowmelt capabilities can be impressive–when it comes to disposing snow. Large volumes of snow can be melted and dispersed by these natural systems, and thus, when wetlands and live waters are removed from snow management systems, there is an immediate need for an appropriate nearby snow disposal site capable of handling the volumes of snow delivered to it.
Determining what makes an appropriate snow disposal site can be a challenge. Most states and municipalities do not regulate snow disposal per se, so assessing the impacts of snow disposal depends in part on how federal, state, and local water-quality regulations are interpreted, carried out, and enforced at the local level. Stormwater research is beginning to look at the pollutants present in discarded snow and the likely impacts of these pollutants on aquatic environments and living things. A few studies have indicated that snow–particularly that which has been plowed from highways having high trip numbers, from high-volume parking lots, or into a huge pile to await the spring thaw–can have surprisingly high concentrations of pollutants. Likely contaminants in managed snow are listed in Table 2.
Table 2. Likely Contaminants in Managed Snow
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Pollutants associated with vehicle exhaust | Trash | Other metals shed by vehicles | Other vehicle fluids | Nutrients | Other organic debris |
Pollutants associated with wood-burning stoves* | Lead | Asbestos | Gravel | Bacteria | Sanding grits |
Deicing chemicals** | Copper | Oil and grease | Yard debris | Soil | Pet feces |
| * polycyclic aromatic hydrocarbons |
| ** chlorides, calcium-magnesium-acetate |
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| Some snow can contain roadway and atmospheric pollutants that produce a toxic pulse during initial snowmelt. |
According to some studies, however, the range of expected contaminants in snow varies according to where it falls, how long it stays before it melts, what atmospheric pollutants are or might become associated with the snow, whether other snow is added to it (such as at a snow disposal site), and whether runoff–particularly from snow storage or disposal sites–infiltrates or flows to wetlands or streams. Groundwater contamination by snowmelt might be a concern in wellhead areas for drinking water. Other local considerations may come into play in determining how clean or dirty snow is. These can include the acidity of snow and the potential for pollutants associated with melting snow to be adsorbed by local soils. For all of these reasons, it might be important to characterize levels of snow cleanliness in developing a local snow management plan. Table 3 provides a sample classification scheme and sample disposal BMPs for disposing of each "level" of snow. The scheme is offered with the caveat that some municipalities no longer dispose of snow in streams–no matter how clean the snow is considered to be. Others allow snow to be disposed in streams only if discharge is considered high enough for dilution.
Table 3. A Classification Scheme and Selected BMPs for Disposing of Clean and Dirty Snow
Probable Level of Contamination | Likelihood and Nature of Contamination | Areas Where Snow Should Not Be Disposed | Acceptable Means of Disposal and Acceptable Disposal Areas (BMPs) |
Level 1 conditions: Snow that has recently fallen on low-traffic, paved, residential streets that are not sanded or treated with deicing compounds or used for parking. This snow is removed within a few hours or a day of falling. | Low: Pet feces, street grit | Should not be pushed into creeks at unapproved sites. | - Push into creek at approved, adequately vegetated, or armored site
- Push to side of road
- Push to approved area adjacent to street right of way
- Blow to approved site (which might include a wetland)
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Level 2 conditions: Snow that has recently fallen on unpaved surfaces such as earthen or graveled parking lots, road shoulders, and unpaved alleys. This snow is cleared within a few hours or days of falling for parking, vehicle passage, or improved sight lines. | Moderate: Earthen materials (soil, gravel, roots, vegetative matter), vehicle fluids, trash, yard debris, burn-pile remnants, pet feces | Should not be pushed into creeks or blown into wetlands | If earthen parking lot: - Store cleared snow on-site
- Store in area where solids can be recovered and disposed
- Provide filtration and/or buffer if melt water drains to storm drain, wetland, or stream
- Remove solids at end of season
If road shoulders: - Retain on or close to site
- When pushing show in the shoulder area, avoid breaking vegetation
- Do not push into or pile within a predetermined distance of a stream or wetland
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Level 3 conditions: Snow that falls on arterial streets that might or might not be treated with road-sanding grits or deicing compounds and that might or might not accommodate parking | High: Road-sanding grits, vehicle fluids, trash, pet feces, and materials in snow pushed from parking and residential areas (soil, gravel, roots, vegetative matter, yard debris, and burn-pile remnants) | Should not be pushed into creeks or blown into wetlands | - Push and haul to appropriate, approved snow disposal sites
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Level 4 conditions: Snow that falls on areas with high volumes of parked vehicles and snow piles that accrue as a result of long-term storage of snow | High: Vehicle fluids, metals, and other materials shed by cars; pollutants associated with auto exhaust and wood stoves; trash; pet feces; sanding grits (even if grits are not applied to the lots; they tend to fall off the undersides of cars while they are parked); and incidental soil, gravel, roots, and vegetative matter associated with maintenance of unpaved edges | Should not be pushed into creeks or blown into wetlands | - Push and haul to appropriate, approved snow disposal sites
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For the most part, evaluation of snow disposal sites has not received a lot of attention, yet the potential exists that such sites could come to be commonly regarded as stormwater facilities under many municipal and state NPDES and total maximum daily load permits. Especially in settings near wetlands, drinking-water wells, or surface waters, where high groundwater or threatened, endangered, or sensitive aquatic species are present, snow disposal sites might need to be selected on the basis of assessment of potential environmental impacts. Public safety, noise, aesthetics, and economics will also figure in site selection. Table 4 lists selection criteria for snow disposal sites. Many of the measures listed are derived from South Dakota Department of Environment and Natural Resources, Watershed Protection (www.state.sd.us/denr/DFTA/WatershedProtection/snow.htm) and other sources.
Table 4. Selected Criteria for Evaluating Snow Disposal Sites
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Reasonable Access Is Available for Maintenance Equipment - Operators do not have to push snow uphill for unreasonable distances (less than 500 ft.).
- There are acceptable clearances for maneuvering of snow removal equipment.
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Public Safety - Snow storage sites are located to ensure that traffic intersections, site lines, and pedestrian crossing zones are clearly visible throughout the winter season.
- Snow storage sites are located such that piled snow does not present potential dangers to the public. Items to consider include the location of overhead wires and utilities, spontaneous recreational use that might occur, and traffic flow patterns.
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Aesthetically Acceptable Location - Snow storage sites and associated equipment, residual gravels, litter, trash, and snow piles should not be a visual blight as viewed from neighboring roads, residential areas, or areas that offer commercial lodging.
- The site is capable of being screened by vegetation.
- Noise from snowmoving and dumping operations at the site will not disturb areas where people are sleeping at night.
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Appropriate Soil Type - Soils are medium- to fine-grained (silts to clays) and/or contain a high percentage of organics in order to facilitate adherence of pollutants to the soil particles.
- Conversely, soils are not sandy, loose, and porous.
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Adequate Buffer From Stream or Wetland - The site is 50-100 ft. from a wetland or a water body, depending on slope steepness, quality of buffer zone, and size and nature of wetland or water body.
- The buffer can be maintained in a naturally vegetated state, and incursions into it will affect only 25% or less of its area over time.
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Distance From Drinking-Water Well(s) - There are no downgradient drinking-water wells in the vicinity (distance to be determined by municipality and/or state, based on groundwater analysis).
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Depth to Groundwater - Highest annual groundwater level is 2 ft. or more below the surface of the snow disposal facility. A groundwater or hydrogeologic analysis might be needed.
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Presence of Sensitive or Threatened and Endangered Aquatic Species - Snow management facilities should be located and managed in such as way that pollutants will not enter wetlands or streams.
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Learn From Others’ Actions
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| Wetlands and running streams often are used for snow disposal because they melt snow quickly and reduce the area needed for snow storage. |
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| However, when snow disposed this way contains road-sanding grits or other pollutants, receiving resources can be affected. |
Thousands of municipalities in snow zones now face stormwater permitting under NPDES II. Good resources for managers looking for ideas about how to deal with road-sanding grits are the annual NPDES reports of their state’s department of transportation and their region’s most populous cities. Many such reports contain BMPs for planning, operating, maintaining, and upgrading drainage systems associated with roads, and they contain sections on road-sanding grits.
A Web search will quickly reveal that control of residual gravels is but one of a nested set of related stormwater issues concerning snow management. As a result of rising concerns about toxic pulses associated with early-season melting of large snow-storage piles, some municipalities are managing snow as part of their solid waste and stormwater programs. Others have adopted detailed codes and standards to ensure that the relatively clean snow of residential areas is retained on the structures and properties where it falls in order to avoid contamination and costs associated with movement, storage, and runoff.
Although shouldering additional road maintenance BMPs under NPDES might seem onerous, some snow managers have remarked that the mandatory yearly analysis of maintenance and operations has been eye-opening. They have been able to identify opportunities to save energy, train workers, and conserve and recycle road-sanding grits. "We really have a better handle on our entire operations," remarks a colleague who is the only engineer of small town listed as a partner in a larger municipal NPDES permit. "Our housekeeping has gotten better. We understand where we are making progress and where we need to focus on improvements."