Landfill Design and Operations Flashcards

What is the primary advantage of using geosynthetic clay liners (GCLs) in landfill liner systems compared to compacted clay liners (CCLs)?

Answer: GCLs are much thinner while achieving equivalent or better barrier performance

GCLs (typically 5–10 mm thick) can achieve hydraulic conductivity of ≤5×10⁻⁹ cm/s, matching or exceeding CCL performance while requiring far less material and installation space.

Under what condition must a municipal solid waste landfill owner install a gas collection and control system (GCCS)?

Answer: When the total design capacity exceeds 2.5 million Mg and the NMOC emission rate equals or exceeds 50 Mg/year

EPA's New Source Performance Standards (40 CFR Part 60, Subpart WWW/XXX) require a GCCS when design capacity ≥2.5 million Mg and non-methane organic compound (NMOC) emissions ≥50 Mg/year.

Which slope stability analysis method is most commonly applied to landfill side slopes to evaluate the factor of safety against circular failure?

Answer: Bishop's modified method of slices

Bishop's modified method of slices is widely used for landfill slope stability analysis because it accounts for interslice forces and provides accurate factors of safety for circular failure surfaces.

A landfill operator must relocate a solid waste boundary because excavation revealed the site is within a 100-year floodplain. This restriction primarily aims to:

Answer: Prevent interference with floodwater conveyance and protect waste containment integrity

Siting restrictions prohibit MSW landfills in 100-year floodplains to prevent flooding from disrupting waste containment systems and transporting contaminants off-site.

What operating record must a landfill maintain to document the quantity of waste received each operating day?

Answer: Waste acceptance and weight/volume records

Federal regulations require owners to maintain daily records of the types and quantities (weight or volume) of solid waste received to track airspace consumption and regulatory compliance.

When designing a landfill cell, which factor most directly determines the required capacity of the leachate collection sump pumping system?

Answer: The peak leachate generation rate based on water balance modeling

Sump pump capacity must match the peak leachate generation rate, typically estimated using water balance models (e.g., HELP model) that account for precipitation, evapotranspiration, and waste moisture.

What is the term for the practice of mining older sections of a landfill to recover buried materials, reclaim airspace, and retrieve soil amendments?

Answer: Landfill reclamation (landfill mining)

Landfill mining (reclamation) involves excavating previously disposed waste to recover recyclables, compost, and soil-like material while reclaiming valuable permitted airspace for additional waste disposal.