Case Study: Ducktown, Tennessee

One of my favorite environmental stories centers on Ducktown, Tennessee, where native copper was discovered in 1843, and where since 1854 metal sulfides mined from the Copper Basin were smelted in ovens to separate the copper [1], [2]. Trees from the local hardwood forests fueled the ovens, which emitted sulfur oxides that combined with water in the air to form sulfuric acid. The acid stung the eyes, damaged the lungs, killed local vegetation, and leached nutrients from the soil. Without vegetation, the soil eroded away, leaving behind a thin layer of hard, red, infertile soil covering the rocks. Thus, the area surrounding Ducktown looked like the surface of Mars for many decades; U.S. astronauts said it was one of the most recognizable features on the surface of the earth. For environmentalists the good part of the story is that, by 1903, the mining companies figured out how to reduce the environmental damage caused by smelting and at the same time make more money. They simply collected the sulfur oxides released during smelting, added water to make sulfuric acid, and then sold the acid for more money than they made from selling the copper. This is an example of one of those rare “win-win” situations that businesses should always look for.

Since the 1930’s the government has been trying to revegetate the Ducktown area to reduce erosion and the amount of toxic heavy metals being dissolved and transported into local streams [2]. However, the soil is so acidic and infertile that almost nothing will grow in it except a few hardy pine species.

1. Keller, E.A., Introduction to Environmental Geology. 3rd ed. 2005: Pearson Prentic Hall. 583.

2. Kaufman, D.S., The Effect of Pine Afforestation on Copper and Iron Movement Through the Recovering Soils of the Copper basin Mining District, Ducktown, Tennessee, in Geology. 1999, Vanderbilt University: Nashville, TN. p. 135.

Change Your Transportation

Transportation has a huge environmental impact, so society must focus on reducing that impact. Consider the environmental impact of a single automobile that travels an average of 100,000 miles in its lifetime. There is the damage that results from the manufacturing of the car and the mining and processing of the raw materials; from the drilling, transporting, and refining of the oil and gas that it uses; and from the emission of green house gases, NOx that contributes to acid rain, and ozone that causes photochemical smog. There are many other problems associated with automobiles. Driving a car is one of the riskiest activities we engage in, and cars make walking and bicycling much more dangerous on shared roads. Much of our country has been paved over by roads and parking lots, which has increased flooding risks but also uglified our landscape (I love Joni Mitchell’s song “They Paved Paradise and Put up a Parking Lot”). Driving in heavy traffic is very stressful, often leading to episodes of “road rage”. Yes, driving in the countryside without other cars can be very relaxing and enjoyable, but how often does that happen today, and is it worth all of the problems it creates? My prediction is that the most significant lifestyle change in the U.S. in the next two decades will be the abandoning of the car culture. That lifestyle won’t disappear completely, but it will become less prevalent as the price of fuel dramatically increases (due to peak oil and carbon taxes). The change may be traumatic, as 88% of workers in the U.S. travel to work by car, making the U.S. particularly vulnerable to peak oil [1]. People will choose smaller cars, cars that do not run on fossil fuels, or other modes of transportation including moped, bicycle, and mass transit. They will move closer to their jobs to decrease their transportation costs (I hope to buy a home within walking distance of my work before peak oil makes the cost unaffordable). They will take fewer long trips, and they will go to school closer to home. They will travel less for work, as companies try to cut costs. Telecommuting will become even more widespread, and in many cases, videoconferencing will make travel to meetings unnecessary. All of these changes will reduce traffic congestion and pollution, increase our national security by decreasing our dependence on foreign oil, reduce CO₂ emissions contributing to global warming, and I would argue, increase our health (more walking) and quality of life (less time wasted in traffic, better scenery).

Change What You Drive

The technology of automobiles hasn’t changed dramatically over the last 100 years. Most still use a standard internal engine fueled by gasoline. Throughout my life, U.S. auto manufacturers have presented prototypes of cars that were supposed to change the way we drive, but none of them ever came to fruition. Production and leasing of the EV-1 in the 1990’s signaled a potential shift to electric cars, but GM aborted that foray into new technology by confiscating all of the cars and destroying them, as documented in the film “Who Killed the Electric Car?”. However, contrary to general wisdom and the claims of some environmentalists, electric cars currently are not better for the environment. That is because the electricity used to power them comes primarily from the burning of fossil fuels, especially coal. Also, they are inherently less efficient, because any time you convert energy from one form to another you lose some energy. Converting fossil fuels into electricity to fuel automobiles is much less efficient than using them to fuel the car with an internal combustion engine directly. The same argument holds true for the now heralded hydrogen cars, which use electricity to produce hydrogen gas H₂, which in a fuel cell in the car reacts with oxygen gas O₂ to produce H₂O, releasing energy in the process. Although the hydrogen-fueled car emits only water, the process of producing the hydrogen requires lots of energy that usually comes from the burning of fossil fuels, which emits large amounts of CO₂ and other pollutants. So how can we make cars less harmful to the environment? First we must convert our primary source of energy from fossil fuels to renewable forms like wind and solar. Then we should use the electricity that is produced to fuel plug-in gas-electric hybrid cars, or eventually to produce H₂ gas for hydrogen-fueled cars.

Hybrid cars like the Toyota Prius have already raised the bar for energy efficiency. Hybrids have both a gasoline engine and electric motor. They produce electricity through regenerative braking, and automatically shut off the engine when idling. Another promising development is cars that run on biofuels such as ethanol and biodiesel. Flex cars can use ethanol or gasoline, but this is not a new technology, as it dates back to the original flex-fuel vehicle, the Model T, built in the 1910s. Many have concluded that production of ethanol from corn is not energy efficient, with some estimates showing that it requires more fossil fuel energy to produce the ethanol than is obtained from burning it. In addition, use of corn for ethanol production has increased the price of corn worldwide, which is a serious problem for the poor who depend on it for food. An increase in the price of corn causes increases in the price of all products for which corn is used as a feedstock. This problem of using food for fuel can be avoided by producing ethanol using switchgrass and wheat straw, which are also more energy efficient than corn.

So what can you do now? First, make every effort to decrease the number of miles you travel. Combine your errands. Never idle you car. Make sure your car is in tune and properly inflate the tires to maximize gas mileage. Carpool whenever possible. Make purchases online rather than driving to the store. Accelerate and decelerate slowly, and try to maintain a constant top speed. Ask your boss if you can telecommute one day per week. Vacation locally, or consider purchasing carbon offsets for the miles that you travel for vacation [2].

When the time comes to change your ride, buy a fuel-efficient hybrid as soon as you can, or even better, switch to mass transit. Encourage your employer to pay for your mass transit costs (like my employer, Vanderbilt University, they may be willing to do so because it means they will save money by building fewer parking garages). Imagine how much money you would save if you didn’t have monthly car and car insurance payments.

In the future, I envision a decentralized system of energy production for fuel-efficient homes and cars. Picture a windmill in your yard, and solar panels on your roof. The wind and the sun that power these energy sources are free and limitless. The electricity that they produce could be used to power your home and your plug-in electric car, or to produce hydrogen for the fuel cell in your car, all with zero CO₂ emissions or pollution.

1. Brown, L., Plan B 3.0: Mobilizing to Save Civilization. 2008, New York, NY: W.W. Norton & Co., Inc.

2. Jeffery, Y., L. Barclay, and M. Grosvenor, Green Living for Dummies. 2008: For Dummies.

Reduce Your Waste

In 1990 U.S. citizens generated over 4 pounds of solid waste per day, or over 1500 pounds per year. Individuals in most other developed countries generate only half that amount. Over 39% of municipal solid waste is paper, something we can easily reduce. Most communities dispose of solid waste in sanitary landfills by dumping it on the ground and covering it each night with a fresh layer of soil. Rainwater can infiltrate the waste and dissolve material to form a “leachate” solution, so modern landfills have liners and leachate collection systems that prevent the leachate from contaminating the underlying groundwater. However, unregulated and pre-regulation landfills have extensively contaminated groundwater aquifers. There are about 3,000 landfills in the U.S.. Most people don’t want a landfill sited near their home, an example of the NIMBY (Not In My Back Yard) syndrome. Also, because expansion of urban centers and overall population growth make it difficult to find suitable locations for landfills, the number of landfills and the capacity of landfills in the U.S. have been decreasing, and some cities are finding it hard to find places that can accept their waste. The most famous example was of a garbage barge that in 1987 could not find a facility to accept their waste, and after traveling over 5,000 miles over 112 days it finally unloaded its waste at an incinerator in Brooklyn, New York (http://www.nytimes.com/1987/07/11/nyregion/trash-barge-to-end-trip-in-brooklyn.html).

Two alternative approaches are to recycle and to incinerate waste. Until 2007, the city of Nashville burned their garbage and used the released energy to heat and cool metro buildings downtown. However, the smell of the garbage, the increasing value of the riverside property that the incinerator was located on, and the fear that the incinerator released heavy metals from its’ smokestack, led the city to close the operation.

Your effort to reduce waste must start at the beginning, when you are in the purchasing phase [1]. First, don’t buy a product unless you need it. Never buy disposable products or junk that will need to be replaced frequently. Next, buy products with minimal packaging, avoiding those that are “individually wrapped”.

Choose products that are made from recyclable materials, not plastics that can’t be recycled . When possible, buy products with provisions for returning or recycling the used product. Always remember to bring your reusable bags when you go shopping, and place fruit and vegetables directly in the bag rather than using the plastic bags in the produce department. Save some trees and use less paper: don’t subscribe to newspapers or magazines, since most of the information they contain can be obtained online. This semester I taught a class on Sustainability, and we went almost completely paperless (e.g., term papers were turned in, graded, and returned electronically). When you use paper in the office, always print double-sided, or reuse paper that has been printed on only one side.

The mantra for reducing waste is the 3 R’s: Reduce, Reuse, and Recycle, in that order (http://en.wikipedia.org/wiki/Waste_hierarchy). It’s best to reduce by consuming less. For example, I run a chemical laboratory at Vanderbilt University. We used to buy chemicals in bulk to reduce the cost per unit volume. However, we rarely ended up using all of the chemicals. When labs are closed down (when Professors retire), large amounts of chemicals, some hazardous, must be disposed of at great expense. When you consider that the environment was degraded twice, both in the production and disposal of the waste, and the fact that the chemicals were never used, it all seems very wasteful. Now we buy small quantities of chemicals, and purchase replacements when needed.

There are numerous references that give ideas on how to reuse and repurpose materials. For example, Jeffery et al. [1] suggests that we reuse plastic bags after washing, use empty glass jars as storage containers (it’s nice to see what’s inside a container without opening it), shop at second-hand clothing and book stores, and reuse wrapping paper. Reusing and repurposing items is also an opportunity for you to think “outside the box” and be creative. I personally always reuse disposable paper and plastic shopping bags. I store recyclables in the paper bags until they become unusable, and line garbage cans with the plastic bags. We forgo our reusable shopping bags only when we run out of disposable paper or plastic shopping bags. We donate our used clothes to Goodwill unless they are in bad shape, in which case we cut them up and use them as rags. Though I love books, I now avoid purchasing them, and instead sign them out of the library to save both money and paper.

Many charities accept used goods for reuse. This year we donated a computer to the National Christina Foundation. I personally found it rewarding to fix the computer up and then drop it off at a school for children from low-income families. Goodwill accepts many types of items and resells them in their stores. We have donated furniture and electronics to Amvets, and many charitable organizations are in need of used cars – you can claim a nice tax deduction for donating an old car instead of taking it to the dump.

Recycling is often the first concept that comes to mind when people discuss green living. That’s because we can recycle without really changing our lifestyle, so it is comparatively easy. Just throw the item in a recycle bin rather than a trash can. However, not everything can be recycled, especially when we consider cost. Moreover, not everything needs to be recycled, as I will now demonstrate. Students in my Sustainability class were upset when they learned that Vanderbilt recycles paper, plastic, and aluminum, but not glass. That got us talking about reasons for and costs of recycling. I noted that glass is a harmless material that is costly to recycle. Glass is made by melting beach sand containing silicate minerals like quartz (SiO₂). The sand melts over a range of temperatures, and isn’t completely molten until temperatures of around 1200°C (this temperature is lowered by addition of fluxes such as lime CaO, soda Na₂O, and sometimes Borate B₂O₃). To heat it to such high temperatures requires a lot of energy. It takes a lot of energy to remelt the glass during recycling, and because glass is relatively inert and won’t cause environmental damage when disposed of in a landfill, forgoing recycling was not as evil as they perceived. On the other hand, glass recycling uses less energy than manufacturing glass from sand, saving 315 kg of CO₂ for every ton of waste glass recycled (http://en.wikipedia.org/wiki/Glass_recycling), so recycling glass is still preferable. The best option is to reuse the glass, so it doesn’t have to be remelted.

The material that saves the most energy by recycling is aluminum. Aluminum ore is called bauxite, and it contains aluminum oxides that must be converted to metal. This means the Al³⁺ in the oxide must be reduced to metallic Al⁰ by adding three electrons, which requires a lot of energy because Aluminum prefers to be in the +3 state. This also means that Al metal will oxidize when in contact with oxygen in the atmosphere, but fortunately the process is very slow. Al metal has a very low melting temperature, so it takes a lot less energy to recycle the aluminum by heating and melting it than it would to mine more bauxite and convert the oxide to the metal.

The other thing to keep in mind is that it only makes sense to recycle materials when there is a market for the recycled product. For example, recycled paper is generally inferior to first-use paper, so different uses must be found for it. Fortunately, clever people are thinking of many new uses for reused and recycled products.

Whenever you are about to throw something in the garbage, think about whether that item can be reused or recycled. Repair it, or find someone who could use it, perhaps by selling it on eBay. Consider whether the waste is hazardous, which would require special disposal (we will discuss this in the next section). Don't just throw it in the garbage without thinking!

1. Jeffery, Y., L. Barclay, and M. Grosvenor, Green Living for Dummies. 2008: For Dummies.

Case study: DuPont Plant, New Johnsonville, TN

For a number of years I took students in my graduate course Aqueous Geochemistry to tour the DuPont Plant in New Johnsonville, TN, about two hours west of Nashville. The plant manufactures Titanium Dioxide TiO₂ by mining the mineral ilmenite FeTiO₃ and reacting it Hydrochloric acid HCl as follows: FeTiO₃ + 2HCl = FeCl₂ (aq) + TiO₂ + H₂O. The Titanium dioxide is a pigment that gives Kilz paint, Oreos, and many types of toothpaste their brilliant white color. There are two problems with this process. One is that the product solution is still very acidic. The other problem is that ilmenite contains many toxic heavy metals that are soluble in the acidic solution. In the 1960’s when people didn’t know better, DuPont was allowed to dispose of hundreds of thousands of gallons of this toxic acid solution directly into the Tennessee River, which of course killed all fish and bottom feeders downstream. Later they switched to the more environmentally friendly but more expensive process of deep-well injection. They drilled wells between 1000-2000 feet deep and then pumped the acidic waste into a confined, deep limestone layer. The thinking was that the limestone (which contains calcite CaCO₃ and dolomite CaMg(CO₃)₂) would neutralize the acid: CaCO₃ + 2H⁺ = Ca²⁺ + H₂O + CO₂. The confining (impermeable) layer above would keep the waste isolated from shallow aquifers that supplied drinking water. Once again, there were two problems with this plan, which my class would remind the DuPont engineers of every year, and every year they would claim ignorance. First, the acidic solution dissolves the limestone, which results in the formation of large caves deep underground. Eventually the weight of the overlying rock layers causes them to collapse, breaking into pieces, falling, and filling the caves. This shatters the confining layer and makes it permeable, so that the wastes can rise up into the aquifers. The other problem is that, as shown in the reaction, limestone dissolution produces CO₂ gas, and the pressure of that gas can build until it shatters the overlying rock and escapes. Either way, it seemed likely that the confining layer would eventually be compromised. So, to their credit, DuPont came up with a new solution that was even more environmentally friendly but (they claimed) even more expensive. Since around the year 2000 DuPont has been reacting the ilmenite with sodium carbonate, and according to the DuPont engineers the only by-product is harmless FeCO₃ (the mineral siderite), which is used to make bricks for construction. However, recently it was learned that this process produces dioxin as a by-product. Pure Dioxin is the strongest poison known to man (it is the neurotoxin in Agent Orange), and the New Johnsonville Plant is the fourth-largest producer of dioxin in the U.S..

This case study illustrates many different points. First, it is difficult to anticipate all of the potential outcomes of a complex industrial process. That is why ecologists advocate the precautionary principle. Second, industrial chemistry sorely needs to be “greened”. Green chemistry is a field just now coming into its own, and it has the potential to reduce greatly the environmental impact of the chemical industry. Third, despite repeated attempts at trying to “green” the chemical process, the production of Titanium Dioxide still causes serious environmental problems. DuPont is being sued by numerous plaintiffs who live near or work at their Titanium Dioxide plant in DeLisle, Mississippi, who claim that dioxin has seriously damaged their health or caused the death of loved ones (http://video.google.com/videoplay?docid=-7693391300780002092). At New Johnsonville, TN, many citizens are afraid to talk about the health risks posed by the DuPont plant because they work for the plant, their livelihood depends on its success, and they fear retaliation (http://www.dupontsafetyrevealed.org/newjohnsonville.htm). This raises many questions: Should we allow chemical companies to manufacture goods like Titanium Dioxide that are nonessential (it is simply used for aesthetic reasons) but that cause great harm to human health and the environment? Or should we close the plants, even if it meant that thousands of people would lose their jobs? The plants in New Johnsonville DeLisle are by far the largest local employers, so closing them would be an economic disaster for those communities. In fact, years ago when DuPont reapplied to the State of Tennessee for a permit for deep well injection, a representative of the Tennessee Environmental Council asked me if I would testify against the application. I refused, saying that deep well injection seemed to be the best of the alternatives known at the time, and that I couldn’t bear the thought of helping to put all of those people in New Johnsonville out of work. Yes, I am pro-environment, so I believe we should always be looking for ways to protect the environment, but the overall benefits of change have to outweigh the overall negatives, and in this case, the economic vitality of New Johnsonville seemed to me to outweigh the potential risks of deep-well injection.

The Behavior of Water Pollutants

In their textbook "Ecological Economics" (2004), Herman Daly and Joshua Farley say that the limits to human population growth may lie not in resource depletion, but in the waste absorption capacity of the environment. This can be understood with the following analogy. Water purification filters usually contain a resin that turns color when it becomes saturated, i.e., it cannot absorb any more pollutants. The interface between the two colors of resin (the reaction front) will migrate through the column from the inlet towards the outlet. Water flowing from the outlet will be purified until the interface reaches the end of the column, at which point the column resin is saturated in pollutants and cannot absorb any more. From that time on the outlet water will be just as polluted as the input water. In this case, the waste absorption capacity of the filter has been exceeded. Our environment acts as a filter, purifying water that passes through it, but eventually the filter will become saturated.

Let’s examine this in a little more detail. What happens when the concentration of a pollutant in a sediment-water system (lake or stream) keeps increasing? Examine langmuir 10-007. Imagine that we pour uranium U into a beaker containing water and sediment. Some of the U will dissolve in the solution, but some will adsorb onto the surface of mineral grains in the sediment. At first the proportions of U in solution and adsorbed to sediment will be constant as the total U concentration increases (move along a straight line away from the origin). As concentrations get higher the number of available sites for U to sorb onto mineral surfaces begins to decrease, and a greater proportion of U enters the fluid, causing the adsorption isotherm to level off and approach a slope of zero when the adsorption sites become “saturated”. Eventually even the solution becomes saturated, i.e., it can’t dissolve any more U. What happens then? Any additional U added to the system will precipitate out as a U-rich mineral (in this case Schoepite) that is added to the sediment and therefore causes the sediment concentration of uranium to begin increasing again. Note that as long as the solutions remains saturated in Schoepite, any additional U we add will go into the sediment, increasing the U concentration in the sediment. Conversely, no matter how much additional U we add, the concentration of U in the solution is fixed at its highest possible concentration. In this case, we have saturated our filter.

Let’s look at some slightly more complicated models in which the sediment but not the solution becomes saturated. Polluted water enters a beaker with sediment, equilibrates with the sediment, and then is replaced with another batch of polluted water. At first, a large proportion of the pollutant will sorb onto the sediment, causing the concentration in the solution to decrease substantially. As more batches of polluted water equilibrate with the sediment, the concentration of pollutant in the sediment will increase, and therefore the concentration of pollutant in the water that exits the beaker will increase in direct proportion. As the sediment approaches “saturation”, it can sorb less pollutant, so most of the pollutant remains in solution, and our sediment filter become increasingly ineffective.

What if we stop polluting? Can the system recover? Start adding batches of fresh water. You would observe that the water that exits the beaker would at first have high concentrations of pollutant because our sediment filter was saturated in pollutants. But with time, the concentration of pollutant in the sediment and in the exiting fluid would decrease and eventually go to zero. Thus, we can “flush” pollutants out of a sediment-water system such as a stream or lake, but it may take a long time and a lot of fresh water to remove all of the pollutant, especially if the pollutant strongly sorbs to the sediment (which is why PCB’s are still in Hudson River sediments after many decades).

Now imagine a reservoir such as a swamp with one stream entering and one stream exiting. If the stream entering the swamp is polluted, sediments near its entrance point will strip pollutants out of solution. With time, a concentration gradient will develop across the swamp, with high pollutant levels near the input stream and low levels near the output stream. As polluted water flows across the swamp, it encounters sediments with decreasing pollutant concentrations, so the concentration of the pollutant in the solution will continuously decrease. The water becomes increasingly pure as it traverses the swamp. In nature, swamps do an excellent job of filtering pollutants from water. However, if pollutants continue to enter the swamp, the total pollutant concentration in the swamp will keep increasing. Eventually sediments near the input stream will become saturated, and that “saturation front” will slowly migrate across the swamp until it reaches the output stream. At that point the entire swamp system has become saturated, and the output water will be just as polluted as the input water. As in our beaker example, if we stop polluting and the water in the input stream becomes pure again, then over time the process will be reversed, and the pollutants will slowly be flushed out of the swamp.

Water Pollution Case Study: Lake Erie

I grew up in Buffalo, New York in the 1960’s and 1970’s, when pollution was reaching its peak in the rust belt and the environmental movement was beginning. One of the watershed moments in the environmental movement was the discovery in 1978 of toxic waste underneath a school in Love Canal, near Niagara Falls and very close to Buffalo. Until I was six we lived down the street from Lake Erie, and I still recall walking along the shoreline with a clean-up crew. The Lake was very polluted at that time; signs posted near fishing areas stated severe limits on consumption of caught fish due to the threat of mercury poisoning. Not that there were many fish to catch; the only type of fish anyone caught was catfish. Why only catfish? Because catfish don’t need oxygen in the water to breathe; unlike other fish who use gills to extract dissolved oxygen from water, catfish obtain their oxygen by gulping air when they come to the surface. The problem in Lake Erie and many other bodies of water at that time was that it was eutrophic, i.e., oxygen-depleted. In the process of eutrophication, limiting nutrients like phosphorous and nitrogen added to the water cause algae blooms. When the algae die, they decompose:

C6H12O6 + 6O2 = 6 CO2 + 6H2O

This consumes the oxygen dissolved in the lake water. In temperate regions such as upstate New York, lakes have two layers: a shallow, warm, buoyant layer and a deep, cold, dense layer. In a eutrophic lake, the shallow layer in contact with the atmosphere is oxygen-rich, but the deep layer becomes oxygen depleted because the dead algae sink to the bottom of the lake and decompose. In the fall and spring the density difference between the two layers disappears and they mix together. The problem is that, especially in the fall, the deep water has no oxygen, so when it mixes with the shallow water the resulting mixture does not have enough oxygen for fish to breathe, and they die in large numbers. This is still a widespread problem in many areas of the U.S.. In fact, there is now a huge “dead zone” near the Mississippi delta in the Gulf of Mexico that formed because fertilizer-derived nutrients caused algae blooms and eutrophication. The good news is that there is a solution. Simply removing phosphorous from detergents in areas surrounding Lake Erie led to a decline in algae blooms, and now the lake has mostly recovered. No one is worse off for using phosphate-free detergents, but for some reason in areas where regulations allow it (including my current home state of Tennessee) most detergents still contain phosphates, and eutrophication is still a problem.

Lake Erie is still not without problems. In summers, beaches are often temporarily closed after rainfall events. Why? Because wastewater disposal systems have limited capacity, and during heavy rains they fill up and then overflow into local streams, which flow to the lake. You may have noticed that water treatment plants and pumping stations usually have overflow ponds with pipes near the top that drain into a stream. When it rains, you can observe the overflow ponds fill up. Once they are full, any additional wastewater flows out through the pipe and dumps into the stream. Ironically, water in streams is usually dirtiest after rainfall events. Currently many cities are in the process of upgrading their wastewater systems under federal mandate. The problem is the same problem we face with highways; you can add more lanes, but traffic will build until a few years later it as just as congested as it was before you added the lanes. Population growth means that the ideal size of a service system is a moving target, and these systems frequently require expensive expansion projects. The city of Nashville had to increase its water bill in 2009 in order to pay for the expansion of its wastewater system, which will cost hundreds of millions of dollars.