Any newly proposed landfill will have to go through several years of planning and design before it will be approved by local, state, and federal authorities. Specific goals and parameters must be agreed upon before planning can proceed:
What type of landfill will it be?
Conventional, or “Dry” Municipal Solid Waste facilities can be operated using a conventional model where no external moisture is allowed to enter the waste and leachate is constantly collected and removed. These types of landfills typically use a landfill cover to prevent any precipitation from entering the waste cells, while the leachate that does form is immediately drained, collected and removed for separate treatment. Waste maintained in such a dry state, however, produces an environment where waste degradation is prolonged and unpredictable.
Bioreactor landfills, in contrast, collect and recirculate leachate throughout the waste mass, promoting rapid decomposition of waste while simultaneously eliminating the need for expensive leachate treatment. This model is becoming increasingly popular as a sustainable alternative to older dry landfills.
Hazardous materials landfills are highly specialized according to the type and amount of waste being processed, the specific safety requirements and the impoundment times necessary of the materials present in the waste. Hazardous materials landfills are beyond the scope of this series.
What are some important factors to consider in choosing a location?
- Landfills should be located close enough to the area it serves that transportation costs are not prohibitive.
- Volume of the landfill, based on expected service life and predicted waste generation. Based on this, the necessary footprint and plot size can be determined.
- Traffic and access, both during construction and during operation. Potential issues related to noise, vibration, exhaust, dust, dirt and visual impressions should be considered. Traffic management, including the residential nature of access routes as well as potential damage to roads cannot be ignored.
- Studies of local topography, floodplains, utility maps, and land use, as well as presence of water wells, nearby wetlands and nature preserves, and proximity to airports are all necessary to make an informed decision.
- A complete understanding of the hydrology of sites under consideration is critical. Studies should provide an understanding of how water travels over and through soil on the proposed site.
- Specific regulations and permit requirements affecting the site under consideration.
How Should the Landfill be Configured?
The specific design of a landfill is usually based on the size (volume) of the landfill as well as the nature of local geography and topology.
- Area landfills sit entirely on top of the existing land. This is an attractive option in flat terrain with shallow groundwater, since it requires no excavation.
- Valley fills are a below-ground configuration commonly used in mountainous terrain.
- Above and below ground fills are a hybrid of the two types and are suitable for relatively flat ground without water table issues, and where lot size or footprint must be minimized while still maximizing storage capacity.
- Trench fills are also a hybrid system, typically used for small scale operations.
What do Daily Operations Involve?
In a sanitary landfill, only one cell is active at any time. Each cell typically represents only a small percentage of the total landfill capacity. Cells can be compared to building blocks. They're constructed side-by-side as the operation moves back and forth across the landfill space. Cells have an active face where the dumping, compacting and covering activities take place. Once a cell is filled, it will be covered and a new one will be activated. The size of the cell differs according to the design of the landfill.
Regardless of the size of an individual cell, the overall site layout is determined early, based on the site’s final footprint. Larger cell sizes may be 3 or more acres, while others may be less than 0.5 acre. The landfill is typically designed with multiple, semi-independent phases, which are constructed and filled one cell at a time. This practice minimizes the amount of landfill surface that’s open at any one time and minimizes problems with trash, vermin and accumulated precipitation. To maintain structural integrity, cells are stacked, compacted, and covered, one horizontal layer at a time. In well-designed and operated landfills, this practice of focused activity means that end-use plans might be implemented even while the rest of the landfill is still active. Another advantage in phased construction is that premature closure, for any reason, is more practical and economical.
