Landfill Design and Operations Flashcards

A landfill operator is managing stormwater runoff at an active municipal solid waste landfill. Which of the following is the most critical initial step to prevent surface water contamination and minimize leachate generation?

Answer: Constructing diversion berms and channels to direct run-on away from the waste disposal area.

The most effective and primary strategy for managing stormwater at a landfill is to prevent it from coming into contact with waste in the first place. Diverting stormwater run-on (water flowing onto the site from adjacent areas) around the active disposal area using berms, swales, or channels is a fundamental Best Management Practice (BMP). This minimizes the amount of water that can become contaminated leachate, reducing the load on the leachate collection and treatment system.

According to RCRA Subtitle D regulations, what is the primary purpose of applying a minimum of six inches of earthen material as daily cover at the end of each operating day?

Answer: To control disease vectors, fires, odors, blowing litter, and scavenging.

Federal regulations under RCRA Subtitle D mandate the application of daily cover primarily to address operational and environmental nuisances. Applying at least six inches of compacted soil or an approved alternative daily cover (ADC) helps to control the spread of disease by vectors (like rodents and insects), reduce the risk of surface fires, suppress odors from decomposing waste, prevent litter from being blown off-site, and deter scavenging by animals or humans.

Which two gases are the primary components of landfill gas (LFG) generated during the anaerobic decomposition phase?

Answer: Methane and Carbon Dioxide

During Phase IV, the mature, anaerobic stage of decomposition within a landfill, methanogenic bacteria dominate. These microorganisms break down organic waste, producing a biogas mixture known as landfill gas (LFG). This gas is typically composed of 45-60% methane (CH4) and 40-60% carbon dioxide (CO2), with trace amounts of other gases.

A new municipal solid waste landfill is being designed. What is the fundamental purpose of the composite liner system at the bottom of the landfill cell?

Answer: To prevent the migration of leachate into groundwater and underlying soil.

The primary function of a landfill liner system, particularly a composite liner as required by RCRA Subtitle D, is to act as a low-permeability barrier. This barrier is engineered to prevent leachate—the contaminated liquid that forms when water percolates through waste—from escaping the landfill and contaminating underlying aquifers and soil.

A landfill cell has reached its final permitted elevation and is ready for closure. Which component of the final cover system is specifically designed to collect and remove precipitation that infiltrates the topsoil before it can reach the low-permeability barrier layer?

Answer: Drainage Layer

A typical final cover system is a multi-layered design. Below the topsoil/vegetative layer, a drainage layer, often made of sand, gravel, or a synthetic geonet, is installed. Its purpose is to intercept any water that seeps through the top layer and channel it away from the underlying impermeable barrier (like a geomembrane or clay layer), thus preventing the 'bathtub effect' where water accumulates on top of the barrier.

When designing a landfill in a seismically active region, RCRA Subtitle D requires specific considerations. The design must demonstrate stability against the ground motion of the:

Answer: Maximum Horizontal Acceleration (MHA) with a 90% probability of not being exceeded in 250 years.

RCRA Subtitle D (40 CFR Part 258.14) specifies that new landfill units must be designed to resist seismic impacts. The standard for this design is the Maximum Horizontal Acceleration (MHA) in lithified earth material for the site. This MHA value is defined as the level with a 90% probability that it will not be exceeded in a 250-year period. This ensures the landfill's containment systems, such as liners and leachate collection, remain intact during a significant seismic event.