Landfill Systems and Infrastructure
The mounds at Fresh Kills are the result of 50 years (1948 - 2001) of land-filling household waste. By 1997, two of the four mounds were closed and covered with a thick, impermeable cap. The remaining mounds stopped accepting waste in 2001 and are expected to be fully capped between 2008 and 2011.
The final cover placed over the solid waste is constructed in phases. The essential design goals are to provide for hydraulic performance, slope stability and long-term integrity or durability of the landfill and its systems. This is achieved by minimizing surface water infiltration, preventing erosion, promoting proper surface water drainage, and separating the waste layer from the environment to protect public health. It also captures and prevents the emission of air polluting gases.
The final cover is made of a series of layers, each with distinct functions, which are described below.
- Final Grading / Soil Barrier Layer - Before the final cover can be placed, final grading must be completed. An intermediate cover material, sometimes called the cover foundation level or sub-base, is graded and compacted to the appropriate angles. Before the final cover is placed on the landfill, slopes may need to be adjusted to meet the minimum and maximum required grades (4% to 33%) set by the New York State Department of Environmental Conservation (DEC) to maintain slope stability and promote proper drainage.
Impermeable Plastic Liner - The impermeable plastic liner or hydraulic barrier is placed on the sub-base material. This is the most crucial component of final cover. It prevents water from entering the waste directly by stopping the flow of water and indirectly by promoting storage or drainage of water in the above layers. This layer also prevents the upward flow of gas into the atmosphere except in controlled places. It is made of low permeable and/or plastic material.
Drainage Layer - The drainage layer is needed in some portions of the final cover. This layer reduces the pressure of water on the barrier layer and increases friction, thus reducing the risk of sliding. It drains the overlying protection layer, increasing water storage capacity and reducing the risk of over-saturating the cover soils above.
Barrier Protection Layer - The barrier protection layer protects the hydraulic barrier from the extremes of weather that could cause the underlying layers to crack or heave. This layer stores excess water until it is either used by overlying plants or drained off. This layer is composed of soil and has a minimum thickness of 24 inches.
Planting Soil Layer - The planting soil layer or top soil layer must have a minimum thickness of six inches. It is specified to be fertile. The soil used is a sandy loam, selected for its potential to prevent soil erosion and to provide a good growing medium for the vegetation layer. The primary objective of the vegetation layer is to protect the integrity of the Final Cover through erosion control. A network of plant roots hold onto the soil, providing stability.
Environmental Control Systems
Solid waste breaks down over time. The main products of this decomposition are landfill gas and leachate. Fresh Kills is highly engineered, with sophisticated systems in place to collect and treat these by-products, and to protect public health and the environment.
Landfill gas is methane, carbon dioxide, water and other organic compounds. The Landfill Gas (LFG) System collects and controls gas emissions through a network of wells connected by pipes below the surface that convey the gas through a vacuum. Once collected, the gas is either flared off (burned) or processed to pipeline quality (recovery for domestic energy use) at an onsite LFG recovery plant. Gas emissions, non-methane organic compounds (NMOCs) and other hazardous pollutants are reduced by almost 100%. LFG and its odor are prevented from entering the atmosphere. In addition to this active gas collection and recovery system an additional safety system is in place to prevent the migration of gas off site.
Leachate is the liquid by-product of the breakdown of household waste. Once the final cover is placed on the landfill, the quantity of leachate produced diminishes considerably because the amount of water that comes in contact with refuse is minimized. The goal of the leachate management system is to remove pollutants by containment, collection and treatment of leachate before it reenters the environment. All treated water is cleaner than the nearby Arthur Kill, into which it is released.