Madison Department of Public Health

Background

The use of street and pavement deicing agents, consisting of the application of salt mixed with abrasives, was first recorded by the City of Madison during the winter of 1959-60. Despite the corrosive side effects of salt on vehicles, roads and bridges, the increased usage of deicing chemicals was encouraged by public demand for rapid return to normal conditions following a storm and the apparent economic advantage to a speedier return to bare pavement.

In 1962, the Common Council, concerned by the potential negative impact of deicing chemicals to our lakes and ecosystem, requested that the Madison Department of Public Health begin an aggressive monitoring program to record and document the levels of sodium and chloride in area surface waters. In 1973, the charge to the Heath Department was renewed in accordance with the plan to reduce the use of road salt in the Lake Wingra Watershed by 50%. This 50% salt use reduction plan was extended to the entire city in the winter of 1977-78. The 50% salt reduction goal was in proportion with the total tonnage of salt used in the winter of 1972-73 (5,691.25 tons used citywide).

The Madison Department of Public Health Laboratory was charged with monitoring the water quality of the area lakes and submitting an annual Roadsalt Report to the Madison Common Council. Data compiled from the years 1959-1974, found only slight increases of chloride content in area lakes, and our ongoing studies have determined that the chloride concentrations remain well below acceptable water quality standards for drinking (250 ppm) or swimming (Tables 1 & 2). While long term detrimental effects of chloride concentrations and deicing chemicals to lakes and streams, and to aquatic life has not yet been fully determined, the analytical data compiled in this ongoing study is absolutely essential in the overall analysis of the prolonged usage of road salt on city streets and sidewalks. Table 3 shows the yearly Sodium and Chloride levels in each of our area lakes from 1972 to the present.

Snow pack is the number one and principle enemy of our efforts to clear streets for safe and efficient use. This is caused by traffic on freshly fallen snow resulting in a temporary thaw and ultimate refreezing, forming a hard slippery crust that is impossible to remove with equipment, even heavy motor graders, without a very major and time-consuming effort. At near zero temperatures, salt is essentially ineffective and deicing chemicals that are effective at sub-zero temperatures are extremely corrosive. As we witnessed this past winter (2000-2001) on various city streets, the snow pack will remained for days after the storm. A 10-inch snowfall will deposit approximately 5,000 cubic yards of snow per mile of 30-foot city street (our average snowfall is 39± 15 inches). If plowing cycle time can be kept short, the formation of snow pack is reduced. Conversely, long periods between plow rounds enables considerable snow pack formation, which necessitates the use of larger quantities of salt/abrasives, and deicing chemicals. Approximately 45% of road salt will be carried away overland and flow to lakes or streams, while 55% is absorbed in the shallow aquifer below the surface and slowly moves to contaminate groundwater and deep water wells.

The use of deicing chemicals such as salt has become a cost effective means that allows us to remove the pack and return to safe bare pavement early on. It is our job to determine the most effective use of salt, thereby decreasing the amount needed for deicing. Computerized salt/sand spreader technology in use by the City of Madison has resulted in a more effective and judicious use of salt and abrasives, and has reduced the amount of salt used on city streets. Alternate deicing chemicals besides salt continue to be tested, but to date they have either been far too expensive or are ineffective. Salts are effective deicing agents and appear to be economical for control of snowfalls to depths of two to three inches. Application of salt or abrasives and plowing are the presently accepted methods for the control of ice and snow. The use of salt as a deicer, if done properly, provides a usable means of returning to bare and safe pavement with the least amount of time and cost.

The U.S. Environmental Protection Agency has identified nonpoint source pollution as the nation’s main cause of water quality problems. One significant source of non-point source pollution is the application of salt and other deicers in winter to streets, sidewalks, and parking lots. Chemicals in urban run-off during snowmelt pose a significant threat to the environment, particularly to groundwater, lakes, streams, soils, and vegetation. This threat is marked by increasing amounts of chloride and other chemicals in surface and groundwater as well as damage to roadside vegetation, road surfaces, and automobiles.

The current Wisconsin Department of Natural Resources rule, NR 105, has set 395 mg/L and 757 mg/L as the chronic (long-term) and acute (short-term) toxicity levels for chloride in fresh water, respectively. Comparison of these levels with the values reported in Tables 1 and 2 for area lakes and streams suggests that area surface waters are not yet impacted by past deicing activities. However, as seen in Table 3, chloride levels in our major lakes and streams are increasing.

While studies of the major lakes and streams in our area have shown limited impact from deicing, preliminary studies performed by students at Edgewood College have shown that chloride levels at storm water outfalls and in small retention ponds in the Lake Wingra water shed are approaching and exceeding the toxicity levels cited above (Table 4). In some cases, these ponds and creeks have extremely high levels of chloride, which would be expected to have toxicological effects on the ecology of these waters. Although these small bodies of surface water may not have the ecological significance of the larger lakes and rivers in the City of Madison, they may be an important indicator of future surface water quality. Edgewood College students determined the chloride level in their samples using the Hach test. While this method is different from the method used by the MDPH laboratory, analysis of split samples by both groups found chloride test results were similar.

It is also important to realize that deicing activities in winter also may degrade the quality of Madison’s ground water resources. Deep groundwater aquifers supply Madison’s drinking water and must be protected to ensure high quality water. As shown in Table 5, chloride levels are increasing in selected wells. Between 1975 and 2001, well # 6 has the highest average annual increase in chloride at 0.8 mg/L per year. Wells #10 and #17 have average annual increases in chloride of 0.1 and 0.4 mg/L per year. Wisconsin Department of Natural Resources enforcement standard (ES) and preventive action limit (PAL) for chloride in drinking water are 250 mg/L and 125 mg/L, respectively. Current chloride levels are much lower than these regulatory limits and do not yet pose an adverse health risk. However, continued salt application will likely result in ongoing increases in chloride levels in groundwater.

Sodium may also be added to groundwater as a result of Madison’s winter deicing program. Sodium is an essential nutrient. However, too much sodium in the diet is a concern due to the association between sodium and hypertension. Current dietary guidelines call for less than 2,400 mg of sodium per day in the diet. Sodium restricted diets may range from 2,000 to 1,000 mg of sodium per day. The US Environmental Protection Agency has issued non-enforceable guidelines that call for sodium levels in drinking water of 20 mg/L or less. Table 5 shows that average sodium levels in drinking water range from 2.3 to more than 14 mg/L in active wells. Sodium levels in excess of 20 mg/L have been observed in well #17.

The shallow groundwater aquifers in Madison are less closely linked with human health concerns due to the lack of direct exposure through drinking water. However, these shallow aquifers play an important role in surface water quality and may affect deeper aquifers. Research has shown that shallow aquifers are likely to be contaminated by salt applications during winter (Howard et al, 1993). Little sampling of Madison’s shallow aquifers has occurred. Samples collected by Edgewood College students and members of the Friends of Lake Wingra have found fairly high levels of chloride in natural springs in the UW Arboretum and the Lake Wingra Watershed in general (Table 6). Again, these samples were analyzed for chloride using the Hach test. Because these springs are supplied directly by shallow groundwater aquifers, these levels may be representative of the chloride levels in the aquifer itself. Additional analysis of the shallow aquifers throughout Madison is necessary to gain a better understanding of the impact of salt applications.

The detrimental impact of deicing chemicals on ornamental plants is likely to occur near salted highways, streets, driveways, and sidewalks. Snowmelt run-off damage to plants is categorized as follows:

A) Soil-borne salt accumulation

Street or sidewalk run-off from melted salt-laden snow washes into nearby soil. As salt is dissolved in water, the sodium and chloride ions are separated. Soil salt damage is slower acting than salt spray injury and plants may not show symptoms for several years.

B) Aerial Borne Salt Spray

Small droplets of aerosol spray are kicked up by fast-moving traffic on wet, salted roads. Spray can be lifted tens or hundreds of feet above the road surface with winds depositing the droplets on the foliage of nearby plants causing dehydration of tissues. Salt can enter plant cells or the intercellular spaces in leaves. Salt spray can damage thin barked trees and twigs but the primary damage is to broad-leaved and needle-leaved evergreens.

In addition to salt resistant plant selection, the City of Madison also considers terrace width a determining factor, as is whether or not a particular area is designated by the Street Department for limited salt usage for street deicing as in the case of streets impacting the Lake Wingra Watershed. Where terrace are narrow, the use of Maple should be limited due that species likelihood to experience summer scorch and ultimately decline and dieback.

The City of Madison Streets Division is responsible for salting and plowing streets within the city, and Dane County highway Department is responsible for roads of adjacent municipalities. Dane County contracts with the Department of Transportation (DOT) to maintain the Beltline along with other highways in Dane County.

Per snow event salt may be applied multiple times in repeat applications, dependent upon continuing snow accumulation, temperature and cloud cover, the effects of each salting, and the field observations of the plow/spreader drivers. Uncontrollable factors affecting the impact of a storm or our community include: a) Amount of snow, b) Rate of snowfall, c) Duration of fall, d) Wind conditions, and, e) Temperature.

During the 2000-01-snow season, the City of Madison applied a total record volume of 12,485.03 tons of salt and 7,818.43 Tons of sand on city streets. Since 1972-73, the fifty percent salt reduction goal has been met 5 times (Table 7).

Our record salt usage this past winter season was driven by the combination of heavy snows with below average temperatures. Other contributing factors include:

1. Annexation of roads from the towns - roads that have been and need to be salted.
2. Construction of additional streets that qualify as salt route streets - for example - the streets around the American Family complex.
3. Increased traffic on city streets. This puts pressure on us to de-ice the streets quicker.
4. Comparison with suburbs. Madison residents scream that Madison streets are covered with ice and the streets of adjoining suburbs (some times the dame street) are bare pavement due to the suburb’s salting policy.
5. General increased pressure by the motoring public to not have the bad weather affect their pace of life.

Of the total area drained by the Yahara River north of Lake Waubesa, only 30% is within the Madison City boundaries. Chemical and nutrient ladened street and urban runoff from adjacent areas continue to impact our surface and groundwater, and the immediate environs. During the 2000-2001-winter season, Dane County Highway & Transportation Department sold approximately 50,000 tons of salt, and 6,000 tons of salt/sand mix to surrounding municipalities and agencies with snowmelt runoff that directly impacts our area lakes (Table 8). At this time, the impact is not sufficient to cause observable ecological or human health problems. However, it is likely that continued use of road salt for winter deicing will result in increasing levels of chloride and sodium in surface and ground water.

The City of Madison is the only entity with a 50% salt reduction goal for winter street maintenance. We need to encourage a consorted and area-wide salt reduction plan for the entire watershed. Salt and sand use for winter deicing of roads is a countywide environmental issue that affects each of our communities, and should be addressed in the NR 216 permitting process, and included in area wide storm water legislation.

There initially needs to be better accounting by all parties on actual salt usage, application rates, etc. The stated policy on usage and actual usage may not necessarily coincide. I would like to see uniform standards for snow and ice control. It would be easier for us to trade services with surrounding municipalities if we had the same service standards, including when we plow, what streets we salt, how much salt is used, etc.