According to the U.S. EPA, the United States is expected to produce 220 million tons of garbage per year. So what do we do with it? There are three main types of waste disposal: composting, incineration and dumping. Composting is not currently used much in the United States, but is a form of recycling that involves taking organic matter, such as food or yard waste and letting it biodegrade into a soil that can later be used as fertilizer. Benefits of composting are that the garbage becomes reusable, and it is an inexpensive method of disposal. Incineration involves burning trash at very high temperatures. Incineration is a favored method of trash disposal because it can reduce the volume of waste by 75 to 95 percent. Also, the heat created from incineration can be used for energy. However, on the downside, incineration contributes to air pollution. Combusting or burning trash — like combusting gasoline or coal — can emit nitric and sulfuric oxides, which are known to cause acid rain. In addition, there has been a great deal of controversy over increased asthma and other respiratory diseases in communities near incinerators caused by inhaling the ash produced from incinerators. Fortunately, engineers have designed systems to reduce the pollutants emitted by incinerators; however, these practices are normally very expensive to implement. Lastly, there are open dumps and sanitary landfills used for trash disposal. An open dump occurs when waste is simply piled on any available land, without any engineered systems to protect the surrounding area from pollution. Open dumps are the oldest — and arguably the easiest — form of waste disposal, but are no longer used in the United States because of the pollution problems they create. Instead, we design sanitary landfills for the majority of our garbage. Sanitary landfills include engineered systems such as liners, leachate collections systems, and caps once the landfill is closed to help prevent air and water pollution.

Landfills, even well engineered ones, can cause air and water pollution. The predominant concern is groundwater and surface water pollution from runoff. Leaching is the process of water (normally in the form of precipitation; i.e., rain water) filtering through a landfill, which then carries whatever contaminants that are in the landfill out with the ground or surface water. After water has filtered through a landfill, it is called leachate. Leachate commonly contains high concentrations of chemicals, heavy metals and microbial life. Chemicals come from many different industrial wastes that are dumped at landfills or agricultural waste that contains large amounts of pesticides. Heavy metals, such as lead, can come from any number of items we throw away, including lead-based paint. The leachate then either flows over the ground into a nearby stream or lake or it filtrates through the ground into the groundwater bringing all the bad contaminants from the landfill with it. If leachate reaches the groundwater, it can migrate into the groundwater and create a plume of pullulated water. If the plume reaches a nearby well that is a source for local drinking water, people subsequently drink the contaminated water, which can cause many adverse effects for humans.

Another source of pollution from landfills is methane gas. Methane is created when microorganisms break down (or biodegrade) the organic matter that is contained in landfills. Methane gas often smells bad and can cause some respiratory problems for humans. In this lesson, we are going to concentrate on the groundwater pollution from landfills.

Because of the large number of old landfills that exist — such as the Fresh Kills landfill on Staten Island — and have caused a significant amount of pollution, the EPA has set up regulations for municipal solid waste landfills, including measures that will prevent or minimize pollution from leachate and methane gas. The regulations include: location, design, operating, groundwater monitoring, closure/post-closure care and corrective action and financing.

Location Restriction: Placement of a landfill is a definite problem. The EPA has restrictions based on the geology and ecology of the surrounding area. There are six total restrictions. A landfill cannot be placed in: 1) a floodplain, 2) a wetland, 3) a fault zone, 4) areas with high risk of earthquakes, 5) unstable areas, and finally 6) the immediate area of an airport. In addition to the above regulations, the hydrogeology and the demographics of the surrounding area must be considered. No one really aspires to live near a landfill, so it is important to examine how many people live near a potential landfill location and what affects that landfill may have on the community, such as whether or not there are any drinking water wells that could potentially be pullulated. Favorable hydrogeology will keep any pollution created from migrating or reaching any nearby wells. Factors that should be considered when choosing a landfill are topographic relief, location of the water table, amount of precipitation, type of rock and soil and location of the disposal zone in the surface water and groundwater flow systems.

Design: Modern landfills must be designed with pollution prevention in mind. Modern sanitary landfills must include a liner system, a runoff collection system, a methane collection system, a groundwater monitoring system, and after closure, a cap. Of particular importance is the landfill liner, as seen in Figure 1. Landfill liners have several layers: first, a layer of soil as a foundation for the waste; then, a geotextile layer that lets water through but filters out any little pieces of trash; then, a leachate collection system, which consists of gravel that allows water to filter down to pipes where it is collected; under the leachate collection system, liners are required to have a plastic layer in order to prevent leachate from reaching the groundwater; and finally, liners have an impermeable clay layer to stop any water that may make it through the plastic.

Operating: There are also rules for how landfill owners must operate their landfill. They must compact and cover the waste each day. A well-designed landfill will have a methane and water collection system, which are also part of the daily operations of a landfill. Finally, landfill owners must take measures to ensure that the area is restricted so no one can illegally dump hazardous waste.

Groundwater Monitoring: The groundwater down gradient of a landfill must be continually monitored for contamination. If the presence of a contaminant is detected, this could mean there is a leak in the liner or some surface water has been allowed to seep through the collection system.

Closure/Post-Closure Monitoring and Corrective Action: Once an owner or operator closes a landfill, they are still responsible for any pollution it may cause. Therefore, owners and operators are required to monitor the landfill after it is closed.

Financing: Owners and operators must prove that they can successfully finance the landfill.

When landfills are constructed today, a liner — specified by the EPA — must be installed in the landfill. The liners are engineered to stop water from filtering through the soil to the groundwater below the landfill, but in all sanitary landfills, water is found in the leachate collection system below the liner. Some landfill owners go above and beyond the call of duty and install a second leachate collection system below the clay since water oftentimes still manages to find its way into the clay layer. How can that be? There is plastic and impermeable clay — how did water still manage to get through these two layers? Well, many things can happen to cause this leakage. First, imagine trying to lay down plastic over an entire football field. Plastic that wide does not exist, so smaller pieces must be pieced together. Engineers take great care to make the seams as tight and leak- proof as possible using special machines (as shown in Figure 2, right), but as the students will discover in the accompanying activity, it is very hard to create perfect seams. Furthermore, piling tons and tons of garbage on top of liners creates a lot of pressure, and the seams could stretch and leak over time. Also, the liner is too big for a couple of people to just roll out and put together. Construction engineers use big trucks, such as the one shown in Figure 2 (left). Although necessary for installation, trucks are heavy and can easily puncture the liner, making a little hole through which the water can leak. Finally, some chemicals that are dumped in the landfill deteriorate the liner, causing leakage. Over time, most liners will deteriorate.

Figure 2. Pictures of the installation of a landfill liner. click for copyright

Brainstorm: Ask students what we should do with the garbage we produce every year. Allow students to answer generally and write all ideas on the board. If your classroom is not used to open discussion, go around the room and get one idea from every student. Repeat answers are permitted; just do not repeat the idea on the board. Once you have made a lengthy list of ideas on the board, go through and eliminate ideas that are not practical, such as sending garbage to the sun (most classes come up with this idea, and it is too expensive). Also, eliminate ideas that will pollute the Earth, such as do nothing or dump garbage into the sea. The idea is to come up with a list of what we actually do with garbage, including incineration, sanitary landfills, compositing and open dumps.

Question/Answer: Ask students the following questions. Call on different students to answer the questions.

1. What is the difference between a sanitary landfill and an open dump? (Answer: Sanitary landfills include engineered systems to prevent pollution, while open dumps are just piles of waste on existing land.)
2. What are the required elements of an EPA regulated landfill liner? (Answer: a geotextile layer that only allows water through, a permeable sand layer, a leachate collection system, a plastic liner and a layer of impermeable clay material)
3. Do engineered landfill liners still leak? (Answer: yes)
4. What are some things that cause landfill liners to leak? (Answer: Holes can be punctured in the liner during the installation, seams can leak, or the liner can deteriorate over time.)

Engineer a Landfill: Have students write a letter to the U.S. EPA regulator from the viewpoint of an environmental engineer, explaining what they have done on their landfill to insure that pollution is minimized. Students must included three things they do or have done at their landfill to minimize pollution. Some ideas include: built a liner, including all the different layers of their liner; monitored the groundwater and collected the leachate everyday; chose a site that had very impermeable soil and was not near people; or any combination of ideas that they can come up with are acceptable.