Land Disposal of MSW: Protecting Health & Environment

Philip O'Leary & Patrick Walsh

This is the second lesson in the independent learning correspondence course on municipal solid waste (MSW) landfills. One lesson in this 12-part series will be published each month throughout the year in Waste Age magazine.

If you are interested in taking the course for 2 continuing education credits (CEUs), contact Phil O'Leary for a registration form and send a check payable to the University of Wisconsin for $149 to Phil O'Leary, Department of Engineering Professional Development, University of Wisconsin, 432 N. Lake Street, Madison, WI 53706. For more information, contact: Phil O'Leary at (608) 262-0493 or [email protected]. Website: www.wasteage.com.

Protecting the air, water, and land around a landfill is critical. The secret to success in operating a landfill is to properly design and operate the environmental management systems. In this lesson, environmental concerns will be described first, followed by environmental management systems.

Protecting Air, Land & Water

Creating a facility that is in harmony with the environment, while simultaneously serving the needs of the community is the primary aim of developing and operating a landfill.

Air quality, water quality and land quality are principal environmental considerations of a landfill. There are two types of air quality issues. One is the local impact that the facility may have on the environment immediately surrounding the landfill. This could include odors, dust and papers that might emanate from the site.

Generally, studies have not found significant health effects associated with air quality issues unique to landfills. Rather, global air quality issues result from the release of methane and other greenhouse gases into the environment. Landfills increasingly are being cited as significant sources of greenhouse gases.

The second area of consideration is the impact upon the water environment. This includes both discharges to surface waters and releases to the groundwater system. Groundwater quality concerns generally focus on protecting water supply systems that may be contaminated by landfill leaks. Surface water considerations usually revolve around the landfill runoff that is destructive to the aquatic environment within the stream.

Land issues normally are associated with using property, such as agricultural land, for a landfill site. Generally, this permanently removes the agricultural land from production. Land impacts normally involve the permanent disturbance of the land, or in land use conflicts that arise between the landfill and the surrounding area.

When considering the protection of the air, water and land in a landfill's vicinity, remember that it is a public facility that benefits the community. However, also remember that a landfill can be detrimental to the community if it significantly impacts a community's development, living conditions or its environment.

Waste Decomposition

The decomposition process that naturally occurs when waste material is buried is a principal driving force in the development, operation and closure of a landfill [See “Phases of Solid Waste Decomposition” on page 39].

MSW contains a large proportion of organic materials that naturally decompose when landfilled. This decomposition process initially is aerobic, but after the oxygen within the waste profile is consumed, it switches over to anaerobic processes. These are significant considerations when designing, operating and closing a landfill.

Both aerobic and anaerobic processes have byproducts. In the aerobic process, the main byproducts are carbon dioxide, plus contaminated water that flows toward the base of the landfill. In the anaerobic process, carbon dioxide and methane are produced as waste decomposes in the absence of oxygen. Liquid byproducts contain a large concentration of various contaminants that naturally move toward the landfill's base.

The decomposition process continues for many years. As this takes place, in addition to the principal byproducts already mentioned, trace quantities of materials that may have significant impacts upon the environment can be contained in both the landfill gas and in the leachate. These trace materials are generated until the landfill becomes completely stabilized. Although it isn't known long how this will take, some estimate between 300 and 1,000 years.

It is hoped that new aerobic and anaerobic systems shorten the time necessary to stabilize the waste, therefore reducing the amount of byproducts that are released into the environment. In addition, it is anticipated that each of these processes significantly reduce volume. Thus, larger quantities of waste can be placed in the same area, and the eventual landfill profile is more compatible with the surrounding land uses.

Environmental Concerns

A landfill's most noticeable concern is managing air emissions. For example, while not significantly harmful to the environment, wind-blown paper is the most frequently cited concern of many landfill's neighbors. While it is challenging to control wind-blown paper, the amount that escapes from a landfill can be minimized through management practices, such as having the operator pick up these materials or curtailing operations on high wind days.

Odors also may escape from the landfill. Odors generally result from decomposing waste and are difficult to entirely eliminate. To help, the amount of water that comes in contact with the waste can be minimized, and landfill operators should avoid accumulating ponds of water within the site. Good management practices, especially when recovering landfill gas, can minimize odors.

Controlling dust also presents challenges for landfill operators. Dust can best be managed by limiting the amount of soil that is directly exposed and is not covered with vegetation. Dust also may be better managed in the landfill's interior by dust control chemicals and spraying with water, as needed.

Carbon dioxide and methane are natural byproducts of decomposition. Approximately half of the landfill gas is carbon dioxide with the remainder being methane. Carbon dioxide is only a concern because it is a greenhouse gas. Methane, however, presents a number of problems, particularly as it migrates underground before escaping into the atmosphere.

Methane entering enclosed structures can cause an explosion. While many methane explosions have occurred around landfills, good management practices can virtually eliminate them. Care also must be taken when entering subsurface structures such as manholes that are located in or around the landfill. They very likely contain gases that can asphyxiate personnel who enter them. Standard procedures are available for testing, monitoring and venting these structures before landfill personnel enter.

Methane emitting into the atmosphere also has been cited as a significant source of greenhouse gases. The global warming potential (GWP) of MSW is estimated to be 2.32 tons of carbon dioxide per ton of landfilled waste. One ton of methane is equivalent to 25 tons of carbon dioxide from a greenhouse gas potential. So controlling methane is important to consider in the global warming debate.

Landfill gas also contains other organic compounds, generally in trace amounts. A number of these chemicals have been cited as having potential detrimental health effects to residents near the landfill. But controlling methane gas from migrating and energy recovery limits the impact of these potentially toxic organic compounds.

Noise may have a significant impact on the environment around the landfill. Operating equipment, alarm systems and blowers on gas recovery systems can be sources of noise. Good operation generally can minimize this.

Subsurface Discharges

Waste entering the landfill contains moisture that naturally, as well as by the pressure of successive layers of waste being placed, squeezes water out of the waste. Additionally, rainwater that enters the landfill, or the surface runoff that enters the site, increases the liquid materials quantity that can reach the landfill base. This liquid is referred to as leachate and is highly contaminated. If it is allowed to escape from the landfill, the leachate can contaminate groundwater resources located below the landfill [See “Groundwater Contamination by Leachate” on page 40].

Groundwater resources, when contaminated, are very difficult to decontaminate. When groundwater contamination occurs, the primary concern is that it will pollute drinking water supplies. The contaminated groundwater also may eventually discharge into surface water. Although serious, this is of a less concern than groundwater contamination. The contaminant concentrations in leachate are extremely high relative to other types of liquid waste.

In addition to escaping through the landfill cover, landfill gas (LFG) also may migrate underground, possibly entering enclosed structures. And LFG can become a significant source of groundwater contamination. This occurs when the gas dissolves in water that is migrating through the soil profile below the landfill. This newly contaminated water then may enter the groundwater, resulting in elevated concentrations of principally toxic organic compounds. This phase change of LFG into a liquid form has caused significant and very complicated groundwater contamination problems at some older, less well-managed landfills.

Surface Water Discharges

A landfill actually is a very large construction site and is subject to some of the same challenges of constructing other facilities where a large amount of soil is disturbed. The first consideration is soil erosion that may occur from the site. This could be detrimental to aquatic resources that are downstream from the facility. If erosion is severe enough, it is possible that waste contained within the facility may be transported off-site into surrounding water resources such as streams, lakes or wetlands.

In most severe cases, entire landfills have been washed away in floods where the landfill was inappropriately placed on a floodway.

A floodway is the area of a flooding river where the water is actively being carried downstream. This is compared to the floodway that is the area outside the main flow of a flood, and essentially is a storage reservoir that temporarily holds water as the flood crests.

A landfill actually may aggravate the local flooding of adjacent lands. Because a landfill usually is steeper than the surrounding topography, accelerated runoff may result. This runoff may exceed the capacity of downstream naturally occurring or constructed drainage structures, and thus cause localized flooding.

Land Use Considerations

In looking for a site to build a landfill, operators should consider how it fits into the surrounding landscape. Considerations generally fall into: ecological considerations and land use conflicts.

Ecological considerations include such things as disturbing sensitive areas that are important to wildlife or other ecological species. This could be forestland, wetlands or wildlife habitat. Often, the landfill developer will want to find a location that is somewhat isolated. But this, unfortunately, can result in the encroachment on sensitive areas.

Laws protect archaeological sites. It is important that these sites are identified before developing facilities to avoid disrupting them or delaying project development. In the wrong location, landfills can be detrimental to area's scenic beauty, such as high hills or in areas that can be viewed from parks.

The second land consideration is to minimize conflicts with the area's other land uses. Landfills often are referred to as “LULU's” (locally undesirable land uses). Land use conflicts can generate significant public opposition to new facilities. If the landfill encroaches upon an urban or residential area, those concerns must be addressed to avoid protracted legal challenges.

Legal challenges often center on environmental concerns because it is very difficult to show direct land use conflicts. Local zoning may allow developing a landfill, but the people in the area may simply oppose it as being a LULU.

Another consideration is the impact on the roads and traffic patterns that lead to the landfill. Truck traffic to a large site can be significant and must be considered when developing the facility.

The last issue is environmental justice, a relatively new area of controversy relating to landfills. Essentially, the argument is that waste disposal facilities and other undesirable types of developments are being located in economically disadvantaged areas where the residents are not as able as richer communities to actively oppose the development. Environmental justice arguments still are somewhat theoretical, but are receiving a significant amount of attention.

Control Mechanisms

Appropriate systems have been developed to eliminate or compensate for environmental concerns. Appropriate site selection is the first, and one of the most important, considerations in landfill development. Land use analysis should try to site a landfill where it has the least potential impact on the environment or surrounding land uses. This land use analysis usually examines various land attributes and evaluates the trade-offs of different sites.

A traffic assessment should parallel the land use analysis and consider the routes to be used for trucks arriving at the landfill and the condition of existing roads. This may lead to developing a new road or expanding existing roads to handle the truck traffic. Truck traffic also may be banned from side roads in residential areas that may be convenient but aren't appropriate for trucks.

The hydrogeologic conditions that exist around proposed landfill sites also should be evaluated. This includes a scientific study of the soil formations, geology and groundwater conditions that exist under a proposed site.

Finally, the site's seismic setting and presence of any faults or poor soil conditions that could cause a foundation failure should be considered.

Once a site has been selected, there are several environmentally related design elements to consider. First are surface water management systems. Any water that could flow toward the landfill should be diverted around the site to minimize the amount of liquid that may become leachate or runoff.

Diversion structures are conventional civil engineering improvements that manage water from precipitation on the site. In addition, erosion control structures should be constructed on the finished portions of the landfill, as well as downstream from it. These structures are used to minimize the sediment that may leave the site.

Many landfills now have detention ponds that receive the facility's runoff. Detention ponds allow sediment to settle, then release the water at a slower rate than would naturally occur. This prevents the deposit of sediments in downstream aquatic environments and minimizes potential downstream flooding.

To minimize the amount of water that enters the waste, all landfills now have covers constructed from either soil and/or geomembranes, which then are placed over the active portions of the cells. Covers are used temporarily, as well as when the landfill is closed.

In addition to protection from covers, a landfill liner and leachate collection system protect groundwater. These liners and collection systems minimize water leakage into the subsurface formations.

A gas management system often is installed at larger landfills to minimize off-site migration of LFG through subsurface formations, to minimize odors and to satisfy air quality regulations regarding greenhouse gases. A side benefit of controlling greenhouse gases is recovering energy in the form of electricity.

Methane in LFG can be used to fuel boilers and vehicles. An additional benefit of recovering energy from the landfill is reducing the amount of emissions from power production at other facilities, such as coal-fired power plants or gas turbine electrical generation facilities.

Operating Controls

Key when running a landfill is to monitor and control the composition of the waste entering the site. For example, if a waste collection vehicle contains a large proportion of liquid material, the driver can be asked to return that material to the waste generator.

There are tests to determine whether the waste is too wet to accept. Special wastes, particularly dusty wastes or materials that are difficult to compact, may be candidates for exclusion. Extensive regulations also exclude hazardous wastes from municipal waste landfills.

Managing any water that enters the site is another operating control to protect the environment. Uncontrolled water that enters the landfill or water that flows uncontrolled from it will have detrimental environmental effects. Using the diversion systems mentioned previously, as well as controlling high amounts of moisture waste entering the landfill, can help to limit damage to surface water resources and to minimize odors. Excessive amounts of water entering the site greatly increase the operating costs for the leachate collection and treatment system.

Wind-blown materials can be managed by constructing temporary fences, limiting the types of waste accepted and requiring proper covers for trucks coming to the site. If wind-blown materials escape from the landfill's immediate working area, work crews should manually pick them up before they escape.

Monitoring systems are very important in protecting the landfill's surrounding environment. Monitoring air quality for dust or organic compounds is important. Gas monitoring probes in the soil formation surrounding the landfill can determine whether off-site migration of methane is becoming a problem.

Groundwater is monitored with a series of small wells extending into the groundwater table. Samples collected from these wells indicate the presence or absence of any chemicals that may have escaped from the landfill. The collection of runoff samples from detention ponds can determine whether any undesirable materials are being carried off-site in surface water discharges.

A completely filled landfill enters the final closure phase. At this time, all of the necessary environmental controls must continuously limit the escape of any materials from the landfill. The final closure should place the landfill in a condition that will minimize long-term maintenance.

For example, a poor quality cover over a cell will result in more water entering the landfill, and eventually will increase the amount of leachate that needs to be collected and treated.

During final closure, it is important to strictly follow the original specifications used to receive permit approval. In some reported cases, the final closure did not conform to the original permit conditions and the owners had to reconstruct the final cover at great expense — after causing other environmental damage.

Monitoring all of the facility's environmental management features is necessary after the landfill is closed. This includes checking the drainage systems, the groundwater monitoring wells and gas monitoring system. The leachate collection and treatment system and gas recovery system must be operated until they are no longer deemed necessary. Few landfills that have been constructed using modern technology have reached the end of the long-term care period.

Regulatory Standards

An extensive set of federal laws control the development, operation, closure and long-term care of municipal and hazardous waste landfills. This federal framework generally is duplicated in state standards that have been developed to meet the conditions that exist within individual states. State standards generally are used to issue permits for landfill development, operation and closure.

Typically, state standards are similar to federal standards but may be more restrictive. They cannot be less restrictive unless a special exemption is obtained.

A large number of local regulations also impact landfill development and operation. These local regulations generally affect land use zoning, building inspection and traffic management. Together, the three regulatory levels provide an extensive and important system for protecting the environment when landfilling municipal solid waste.

Philip O'Leary and Patrick Walsh are professors with the Solid and Hazardous Waste Center at the University of Wisconsin.