The City Dump
Prior to the mid 1970s, dumps were typically deep holes where trash was simply tipped in until it could hold no more. These sites were not monitored, and few steps were taken to separate waste from the surrounding environment. Once the hole was filled, it was buried under a layer of soil and the city or county moved on to another site. This meant it was easy for toxic chemicals and gases to contaminate the nearby air, soil and groundwater. These areas also acted as breeding grounds for mosquitoes and other disease-carrying pests.
Dumps like these were usually sited in pretty much any large tract where the land was not considered desirable, including gravel pits, ravines, or undeveloped areas outside the city limits. Such laissez-faire practices often led to environmental damage, groundwater contamination, and infestations of rats and other vermin that together presented a host of health hazards.
The Sanitary Landfill
Modern Sanitary landfills are highly regulated and advanced replacements for the old-fashioned city dump, designed and operated to isolate waste until it is completely broken down, biologically, chemically and physically. Federal regulations often impose additional requirements, but the basic elements necessary to qualify as a sanitary landfill include:
- Full or partial isolation from the surrounding environment. In the US, this typically means that a landfill must be completely lined with two or more layers of an impermeable geosynthetic material to prevent contamination of local ground and surface waters.
- Designs based on local environmental and geological conditions, including isolation from vulnerable environments and population centers, and detailed plans for final disposal and restoration of the site.
- A permanent staff trained to manage and operate the site.
- A daily strategy for placing, spreading and compacting new waste, as well as covering it to minimize problems with pests and vermin.
Purposeful Design
Today’s design and management standards for most sanitary landfills in the US proactively address many environmental concerns, including avoiding unsafe or inappropriate locations and active management of harmful byproducts from organic decomposition. The impact of a newly commissioned sanitary landfill must consider the health of individuals operating the facility as well as nearby residents. The potential effect on the local environment must be studied, and vice-versa. For example, today’s landfills cannot be constructed near floodplains, wetlands, or geologically unstable areas like fault lines.
Some long-term concerns that are being actively addressed today include contamination of local groundwater, managing hazardous landfill gases, and the permanent loss of valuable land to landfill operations.
Groundwater
Rain, snow and even liquids produced naturally during decomposition trickle gradually through the waste heap, picking up pesticides, solvents, heavy metals, phenols, organic compounds and an excess of nutrients. If this liquid (leachate) is not controlled, it can seep into the environment, poisoning the soil, and eventually reach the underground water table, contaminating aquifers and surface waters like lakes and rivers. Today’s modern landfills employ sophisticated systems to contain, collect, and redirect leachate.
Methane Gas
Methane gas and carbon dioxide are both significant greenhouse gases which contribute to global climate change when released into the atmosphere. They’re also natural by-products of the decomposition process for organic materials, so they cannot be eliminated even in modern landfills. There are innovative management strategies, however, that can minimize the volume of greenhouse gases released from landfills, including systems to capture and destroy or even convert to energy sources.
Land Reclamation
Old style dumps were frequently covered with a final layer of soil and essentially abandoned. Problems with odors, fire hazards, contamination and even settling made many of those sites permanently unusable. In today’s climate of increasing urban density, land value, and the push towards public green spaces, a new requirement for today’s landfill designs is a well-designed closing and reclamation plan.
