CHLORIDE IN THE 168 ENVIRONMENT A. Sources of Environmental 169 Chloride. B. Fate And Transport of 174 Environmental Chloride C. Legal Consequences of 179 Excess Environmental Chloride D. Elevated Chloride Concentrations 180 In Surface Water And Groundwater Result In Public Health And Environmental II. Legal And Policy 182 Options To Incentivize Optimal Chloride Use A. Incentivized Self-Governance 183 1. Program Origins 184 2. Certification Requirements 185 And Liability Waiver 3. Program Evaluation 186 4. Potential Evaluation 190 B. Information Dissemination 190 1. Informational Strategies 191 Intended For The Public-At-Large 2. Strategies Intended For 192 Salt Users C. Direct Regulatory Strategies 196 D. Chloride Alternatives 203 1. Green Infrastructure 203 2. Alternative Deicers 206 E. Integrated Watershed Management 207 F. Integrated Watershed Management 210 III. Conclusion 210 I. CHLORIDE IN THE ENVIRONMENT
For thousands of years, sodium chloride--commonly known as salt--has played a critical role in human civilization. Over the centuries, it has at times been central to human culture, trade, religion, economics, public safety, and even warfare. (1) Yet it has a complicated legacy. Only quite recently have scientists begun to analyze the potentially toxic effects of chloride accumulated in the natural environment. (2)
Chloride is the negatively charged ion of many salts, such as sodium chloride. It is naturally found in both fresh and salt water, and at modest concentrations is essential to biotic life. (3) However, excess chloride concentrations may inflict serious harm on human health and the environment. (4)
Sources of Environmental Chloride
Chloride from anthropogenic sources enters the environment via numerous routes, including snow and ice removal practices, salt storage facilities, wastewater treatment facility and septic system effluent, industrial facilities, agricultural operations, oil and gas wells, and natural sources such as atmospheric deposition.
Snow and ice removal practices. Chloride use in the United States has increased significantly since 1950, and the major factor has been the use of salt for deicing during the winter months. (5) Perhaps the most visible source to the environment, widespread use of chloride for snow and ice clearing began around 1960, (6) as transportation agencies began implementing "bare pavement" policies; (7) though by some accounts, the practice was first employed in New Hampshire during or just before World War II. (8) Before that time, vehicles had navigated snowy and icy conditions using tire chains or studded "winter" tires.
Chloride-based deicing and anti-icing agents such as sodium chloride are now routinely used to clear snow and ice on impervious roadway surfaces. (9) Regions classified as "snowy"--meaning that they receive more than five inches of annual snowfall--contain over 70% of the nation's population and road surfaces. (10) As of 2011, road salt application in the United States had risen to about 19.5 million metric tons per year (11) and now accounts for roughly 20% of state transportation maintenance budgets. (12) The use of deicers on travel surfaces has been extremely effective, "reducing accident rates by a factor of 8 on two-lane highways and [a factor of] 4.5 on multi-lane highways." (13) Obviously, this is highly important from a public safety perspective; each year, over 1,300 people perish and more than 116,800 are injured in vehicle accidents during winter precipitation events. (14)
Today, put simply, "[r]oad salts are essential to the transportation and highway maintenance industry in the United States." (15) Road salt performs two functions when used to clear snow and ice. First, it lowers the freezing point of water, often by several degrees: "The more salt is dissolved in the water, the more the freezing point is depressed. " (16) Second, it inhibits ice from forming in the first place. During the freezing process, water molecules arrange themselves into a more solid structure. Salt slows that process by adding impurities to the water and disrupting the water molecules' ability to organize." Although some alternative deicing substances are available, salt is typically considered the most effective and least costly substance for performing these functions. (18)
Some salt used for deicing is carried by runoff to surface water, and the resulting "[d]etrimental impacts... [are] evident on local, regional, and national scales." (19) According to some studies, essentially "all chloride ions that enter the soil and groundwater can ultimately be expected to reach surface water." (20) This occurs after disposal and melting of snow cleared from roadways, through dispersal by splashing and spray from vehicles, and via wind. (21)
Although its usage for deicing is often considered an issue for state or local governments, up to half of the salt used for winter maintenance enters the environment after being used to treat commercial or residential surfaces under private ownership such as parking lots, driveways, and sidewalks. (22) This complicates the legal and policy analysis due to the relative difficulty of regulating or otherwise influencing those sources as compared to public sector sources.
Salt storage. Chloride can also enter the environment via runoff from outdoor salt storage, especially when stored in uncovered piles. (23) Uncovered piles lose about 20% of their salt volume each year, much of it flowing directly into waterways via runoff. (24) Many states have promulgated regulations that mandate particular storage practices or facility construction requirements to prevent or minimize such runoff. (25)
Wastewater treatment facility and septic system effluent. Although most researchers have concluded that winter deicing runoff is the dominant source of chloride in surface waters, other studies reveal that treated wastewater can also be a major chloride source. (26) Chloride is "non-reactive," meaning that there is little or no loss when chloride in wastewater passes through wastewater treatment facilities or septic systems. (27) Instead, chloride "remain[s] in solution." (28) This is because it "cannot be removed using standard wastewater treatment technology; therefore, chloride that arrives in wastewater passes through treatment plants and enters natural water bodies as treated effluent." (29) It can enter the waste stream contained in food, beverages, cleaning products, and from water softeners. (30) An average person consumes about 4.7 pounds of salt per year, and releases about 2.9 pounds of that to wastewater discharges. (31) In contrast to these average discharges contained in human waste, "[w]ater softeners can release considerably larger amounts of chloride to the environment" through "septic systems, dry wells, or wastewater-treatment facilities." (32) One recent study showed that on average, home water softeners discharge about 0.56 pounds of chloride per day to wastewater systems. (33)
Industrial facilities. Some industries, especially food processing and chemical manufacturing, use or generate significant amounts of chloride and chloride salts. (34) Values for chloride discharges from publicly owned wastewater treatment facilities may include these sources. (35)
Agricultural operations. Agricultural operations use salt as a feed additive and in other products such as pesticides and fertilizers. (36) Researchers have recommended that improved agricultural practices that use less water could simultaneously reduce salt loading to freshwater. (37) The Colorado River Basin Salinity Control Program has effectively reduced salt loading to the river by about 1.3 million tons per year, largely through improved irrigation practices. (38)
Oil and gas wells. Oil and gas wells produce brine as an extraction byproduct (39) and are a "major anthropogenic source" of chloride in surface waters. (40) Excess chloride loading from oil and gas wells has led to high chloride concentrations in parts of the Colorado River. (41)
Natural sources and atmospheric deposition. Natural sources of chloride to surface and ground waters include the oceans, which themselves contain about 19,000 milligrams per liter (mg/L) of chloride; (42) soil/rock weathering interactions; (43) and minor levels of atmospheric deposition. (44)
The relative magnitude of these sources is difficult to evaluate because of highly localized variables. Studies undertaken in Milwaukee, Wisconsin watersheds appear to show that road salt is the dominant contributor due to winter spikes in chloride concentrations in surface waters. (45) Other studies claim that "[a]bout 70 percent of the salt consumed and dispersed to the environment each year is from sources other than deicing chemicals." (46) For example, in hard water communities, chloride concentrations in influent to treatment facilities are mostly composed of salt from water softeners, as shown in Table 1. Yet these results necessarily exclude the contribution of chloride-contaminated runoff that directly enters surface waters without passing through a treatment facility.
Fate and Transport of Environmental Chloride
Because numerous existing studies have demonstrated elevated chloride concentrations in surface waters and groundwater, the scope of this project did not include the collection of additional chloride data. Below, the results of existing comprehensive studies of chloride fate and transport mechanisms are distilled into nine principal findings that may be of special interest to policymakers selecting legal and policy strategies to address excess chloride issues.
Elevated chloride concentrations are observed during all seasons and reach maximum levels during winter months. Existing data bear out the intuitive expectation that chloride concentrations in waterways consistently increase (50) and eventually peak" (51) during the winter months; (52) after all, that is the time frame during which the...
REDUCING CHLORIDE DISCHARGES TO SURFACE WATER AND GROUNDWATER: A MENU OF OPTIONS FOR POLICYMAKERS.
|Author:||Strifling, David A.|
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COPYRIGHT GALE, Cengage Learning. All rights reserved.
COPYRIGHT GALE, Cengage Learning. All rights reserved.