Part I – Municipal Solid Waste
The trash or garbage that is collected from homes and businesses by our local governments is referred to as municipal solid waste. In the U.S., most of this waste or trash is placed in containment landfills that are designed to keep hazardous substances from seeping into the environment. Here heavy equipment is used to compact the trash and cover it with a layer of dirt each day. Notice in Figure 12.1 that a modern landfill is essentially a large excavation into the earth, where the bottom of the pit is located above the seasonal water table. For landfills that are still operating and have no permanent clay cap, rainwater is able to infiltrate through the trash and pick up bacteria, viruses, and various chemical compounds, forming a liquid known as leachate. To prevent leachate from escaping and then contaminating groundwater and nearby streams, modern landfills are lined with an impermeable fabric—similar to a vinyl-lined swimming pool. In addition to the liner, a system of pipes is used to collect most of the leachate that accumulates within the excavation. Pipes are also installed to remove methane gas that forms from the decaying trash and monitoring wells are used to detect whether any leachate is escaping from the landfill.
Figure 12.1 – Illustration showing the basic design of a modern containment landfill.
Ex 12 – Waste and Pollution
1) Because of their design, the amounts of water and free oxygen (O2) in modern landfills are kept to a minimum. Explain how the lack of water and oxygen affects the breakdown of waste within a landfill.
2) Does a modern landfill behave more like a decaying compost pile, or simply a storage area for our waste? Explain why.
3) What is the basic reason why landfill operators compact the municipal waste that is brought in each day?
4) Suppose you live in a town with a population of 25,000 where the municipal waste is sent to its own local landfill.
a) If each resident generates 7 lbs of trash per day, how many pounds of waste are sent to the landfill each day?
b) If the landfill operator is able to compact 45 lbs of trash into 1 ft3, which is typical, determine the volume of waste your town places in its landfill on a daily basis.
c) To adequately cover the daily trash with soil it takes about 1 part soil to 4 parts trash (i.e., 1 ft3 of soil for every 4 ft3 of trash). How many cubic feet of soil would be required to cover the trash each day in your landfill?
d) Calculate the total volume of trash and soil that would go into this landfill each day.
e) Suppose that your landfill represents a rectangular excavation that is 900 feet long by 900 feet wide by 20 ft deep. How many years will it take for the landfill to become full?
5) At some point our local landfill will reach its maximum holding capacity. When this occurs, the town must either build a new one, or begin shipping its municipal waste to a distant site.
a) If a local landfill where you live became full, would you be in favor of building a new one? Explain why or why not.
b) If you are in favor of building a new landfill, would your opinion change if the proposed site was located near your home? Explain why or why not.
c) If you felt it was better to start shipping the waste to a distant landfill, explain how this might affect the people living in the community where the landfill is located.
6) Figure 12.2 shows the number of active landfills in the U.S. between 1988 and 2007. Explain why there was such a significant decrease in the number of landfills during this period.
Figure 12.2 – Bar graph showing the number of active landfills in the U.S.
7) Describe how the decreased number of landfills has affected the way that local governments dispose of the waste they collect from area citizens.
8) Recycling programs have become quite common in municipalities across the U.S. Explain why local governments would bother to recycle when the cost of the programs oftentimes exceeds the value of the raw materials being recycled?
Part II – Waste and Pollution
In addition to escaping leachate from landfills, surface water and groundwater can become contaminated by the disposal of sewage and release of chemicals from industrial and agricultural applications. With respect to human sewage, most U.S. municipalities collect wastewater from individual homes and businesses via underground pipes, which then carry it to a centralized treatment plant as illustrated in Figure 12.3. Most of the organic matter and bacteria within the sewage are then broken down and removed before the treated wastewater is discharged into the environment—typically into a stream. However, the treatment processes are fairly ineffective at removing nutrients, such as nitrate (NO3-), and various pharmaceuticals (medicines) that pass through the human digestive system.
Figure 12.3 – Illustration showing a combined municipal sewer and storm water collection system commonly found in the U.S.
9) Suppose that your community has a large sewage treatment plant which is discharging nitrogen-rich wastewater into a nearby stream. Describe how the introduction of excessive amounts of nutrients (e.g., nitrogen) can affect the water quality downstream of the sewage plant.
10) As shown in Figure 12.3, sewage and stormwater drains typically share the same set of underground pipes. During heavy rains these combined systems often become overloaded to the point where untreated wastewater is allowed to discharge directly into a stream. Describe the type of downstream water-quality problems you would expect when this occurs.
11) Recent studies have documented the presence of a wide range of hormones and antibiotics in U.S. streams—these compounds originate from the medicines we take. Because streams serve as the water supply for many municipalities, large numbers of people are likely being exposed to these compounds. Although the concentrations are low, data are lacking as to the long-term effect on human health.
a) If the source of your city’s drinking water is a stream, what would you do until more scientific data becomes available? Note that bottled water may not be a solution as it is often times just city water.
b) How could you personally, as a citizen, help reduce the amount of pharmaceuticals that are entering our water supplies?
12) Figure 12.4 illustrates how a septic tank and drain field is used to treat household wastewater.
a) Explain why it is so important that the drain field and gravel bed of the septic system be located well above the water table.
b) Describe a common landscape position where people like to build homes, but where the geologic conditions make it nearly impossible for septic tanks to function properly.
Figure 12.4 – Subsurface view of a septic tank and drain field, which are used to treat wastewater for individual households not connected to a municipal sewer system.
13) Explain what inevitably happens when homeowners fail to have the sludge periodically pumped out of their septic tanks.
14) Figure 12.5 shows the drainage basin of the Mississippi River and the hypoxic or dead zone that has developed in the Gulf of Mexico. Here, excessive amounts of nutrients are being carried by the modern Mississippi and then discharged into the Gulf of Mexico, causing an oxygen-depleted (i.e., hypoxic) zone.
a) Describe at least two anthropogenic (human) sources for the excessive nutrients being carried by the modern Mississippi.
b) Explain how the oxygen-depleted zone in the Gulf of Mexico would impact both the marine life and human economy in the region.
Figure 12.5 – Map showing the drainage basin of Mississippi River and the hypoxic or dead zone in the Gulf of Mexico.
15) Describe how humans living in the Mississippi drainage basin might be able to reduce the amount of nutrients entering the drainage system, and thereby help minimize the oxygen depletion problem in the Gulf.
Supplemental Exercise – Note, instructors may wish to assign this one week in advance.
In an effort to reduce landfill costs, municipal governments have encouraged the development of recycling centers and curbside programs around the country. Below are some of the common types of materials that are being collected:
paper (newspaper, magazines, and corrugated cardboard containers) glass
plastic (# 1 & # 2 only)
steel cans scrap metal tires
used motor oil yard waste
1) For the next five days you are to examine the bags of trash from your home before permanently disposing of them. Estimate the percent volume of the following materials in each bag:
paper and paper products metals
organic waste (food scraps, rotten veggies, etc.) other
*Note, if you already recycle, include the volume of your recycled materials in your weekly averages for each of the above categories.
2) At the end of the five days, determine the overall average for each category—the volume total should come out to 100%.
3) Compare your list with the list of recycling materials provided at the beginning of this exercise. What percentage of your trash could be recycled?
4) Of course, not everybody recycles. List some of the pros and cons that might make one person choose to recycle and another not to recycle.
5) Figure 12.6 illustrates the various options in society for disposing of municipal waste. Note that in addition to recycling, individuals can help reduce the amount of trash being sent to landfills by reducing the amount of waste they generate in the first place, which is called source reduction.
a) Make a list of some of the ways you personally could reduce the volume of waste you generate at home and a work or school—this does not include recycling.
b) Some municipalities use incineration as a means of waste disposal (in some cases the heat is used to produce electricity). Although incineration has clear advantages over landfilling, it also creates some potentially serious environmental problems. Describe these problems.
Figure 12.6 – Waste pyramid showing the various options for disposing of municipal waste.