back    home

Lesson 4: MSW Landfills



  • Bulldozer
  • Compactor
  • Pans/Scrapers


  • Excavation method - ground water table (GWT) is distant from surface
    • Trenches are excavated, L = 100 - 400ft, W = 15 – 25 ft, D = 10 – 15 ft
    • SW is dumped into trenches
    • Tractors/compactors spread & compact refuse by pushing it up the working face - multiple passes are made to maximize compaction
    • Soil cover is placed on refuse, obtained from excavation
  • Above ground method - used when excavation method is not feasible
    • SW is unloaded and spread in long narrow strips (15-30 in thick)
    • Placement in strips is repeated multiple times until a predetermined cell thickness is reached (usually 5-20 ft)
    • Cover soil is applied (6-12 in) at end of day (geotextiles, foams, ground tires, compost, and other materials are often used)
    • Embankment (working face) slope - 3:1 or 4:1
  • Canyon/depression method
    • Similar operational technique to Above Ground Method
    • Used in areas where depressions (natural or artificial) exist, (canyons, valleys, ravines, borrow pits)


  • Compaction Efficiency
    • Number of passes
    • layer thickness
    • slope
    • moisture content

Daily Cover

  • soil
  • alternative materials (textile, geomembrane, foam, other)

Stormwater Control

  • Control of stormwater runon and runoff is required by Subtitle D of RCRA (Section 258.26).  Run-on control prevents the introduction of stormwater to the active area of the landfill, thus minimizing the production of leachate, erosion, and contamination of surface water.   Reducing run-on also limits the production of runoff from the landfill surface.
  • Run on can be prevented by diverting stormwater from active areas of the landfill.  Any facility constructed to control run on must be capable of handling peak volumes generated by a 24-hour, 25-year storm.  Typical measures to control run on include contouring the land surrounding the landfill cell or constructing ditches, dikes, or culverts to divert flow.

Runoff that is generated can be collected by swales, ditches, berms, dikes, or culverts that direct contaminated run off from active areas to storage and treatment facilities and uncontaminated run off from closed areas to detention facilities.  Run off from active areas must collect and control at least the volume generated from a 24-hour, 25-year storm.  Local regulations will dictate the design of uncontaminated stormwater management facilities.  For example in Florida, a detention pond must store the first inch of run off for 14 days.

Final  Cap or Final Cover Layer

  • Primary purposes:
    • Limit infiltration (leachate production)
    • Control gas emissions
  • Design based on:
    • Hydrologic principles to maximize runoff to limit infiltration
    • Geotechnical principles to prevent slope failures (see photo below)
      • If the drainage layer is not designed properly, pore pressure in the soil at the geomembrane surface will increase and the soil above the liner will slide down

Joining of Final Cover Membrane to
Leachate Collection System Membrane


Failed Landfill Slope


Monitoring Requirements

Groundwater monitoring
Statement of Federal Regulation:

  1. The requirements in this Part apply to MSWLF units, except as provided in paragraph (2) of this section.
  2. Ground-water monitoring requirements under 40CFR258.51 through 40CFR258.55 of this Part may be suspended by the Director of an approved State for  a MSWLF unit if the owner or operator can demonstrate that there is no potential for migration of hazardous constituents from the MSWLF unit to the uppermost aquifer (as defined in 40CFR258.2) during the active life of the unit and the post-closure care period.  This demonstration must be certified by a qualified ground-water scientist and approved by the Director of an approved State, and must be based upon:
    • Site-specific field collected measurements, sampling, and analysis of physical, chemical and biological processes affecting contaminant fate and transport, and
    • Contaminant fate and transport predictions that maximize contaminant migration and consider impacts on human health and environment.

Location of Groundwater Monitoring Wells

Air Monitoring

Explosive gases control:
Methane is explosive when present in a range of 5 (lower explosive limit, LEL) to 15 (upper explosive limit, UEL) percent by volume in air.   Methane is not explosive when present in concentrations greater than 15% however, fire and asphyxiation are still a threat at these levels.  Also, any dilution due to mixing with ambient air could bring the mixture back into the explosive range.

Statement of Federal Regulation:

  • Owners or operators of all MSWLF units must ensure that:
    • The concentration of methane gas generated by the facility does not exceed 25 percent of the lower explosive limit for methane in facility structures (excluding gas control or recovery system components); and
    • The concentration of methane gas does not exceed the LEL for methane at the facility property boundary.
  • Owners or operators of all MSWLF units must implement a routine methane-monitoring program to ensure that the standards of paragraph (1) of thes section are met.
    • The type and frequency of monitoring must be determined based on the following factors:
      • soil conditions;
      • the hydrogeologic conditions surrounding the facility;
      • the hydraulic conditions surrounding the facility; and
      • the location of facility structures and property boundaries.
    • The minimum frequency of monitoring shall be quarterly.
  • If methane gas levels exceeding the limits specified in paragraph (1) of this section are detected, the owner or operator must:
    • Immediately take all necessary steps to ensure protection of human health and notify the State Director;
    • Within seven days of detection, place in the operating record the methane gas levels detected and a description of the steps take to protect human health; and
    • Within 60 days of detection, implement a remediation plan for the methane gas releases, place a copy of the plan in the operating record, and notify the State Director that the plan has been implemented.  The plan shall describe the nature and extent of the problem and the proposed remedy.
    • The Director of and approved State may establish alternative schedules for demonstrating compliance.
  • For purposes of this section, lower explosive limit (LEL) means the lowest percent by volume of a mixture of explosive gases in air that will propogate a flame at 25C and atmospheric pressure.

Air Criteria:
Statement of Federal Regulation:

  • Owners or operators of all MSWLFs must ensure that the units do not violate any applicable requirements developed under a State Implementation Plan (SIP) approved or promulgated by the Administrator pursuant to section 110 of the Clean Air Act, as amended.
  • Open burning of solid waste, except for the infrequent burning of agricultural  wastes, silvicultural wastes, land-clearing debris, diseased trees, or debris from emergency clean-up operations, is prohibited at all MSWLF units.

Air criteria requirements are becoming a bigger issue for landfills as the control of greenhouse gases becomes more of a priority.  Both CH4 and CO2 are greenhouse gases.  CH4 is 10x more potent than CO2.  A potential benefit of aerobic landfilling is a reduction in the CH4 emissions however, aerobic processes produce NOX another greenhouse gas that is more difficult to treat than methane.  Landfill gas flares convert CH4 to CO2 and H2O.

Post-closure Care Requirements

  • maintenance of integrity and effectiveness of the final cover
  • operation of the leachate collection system
  • groundwater monitoring
  • gas migration monitoring


Page last updated July 2003 by Dr. Reinhart