Lesson 12: MSW Landfills

Read: Text, Chapter 4 (pp. 121-128 & 133-143)

Review:

The Executive Summary (pp. ix-xix) and Section 2.0 Review of Design Equations and Techniques (pp. 3-11) of Reinhart, Debra R., and Philip McCreanor, " Implications of Time/Space Variable Leachate Head on Liner Leakage ," December 1999.

• Water Balance: P=I+R+ET+DS+W;
  • P = precipitation
  • I = infiltration
  • R = runoff
  • ET = evapotranspiration
  • DS = change in water storage
  • W = water consumed by reactions
• Darcy’s Law
  • Unsaturated flow implications
  • Channeled flow
• Saturated lenses
  • Variation of permeability with depth due to overburden pressure and increased waste densities
  • Heterogeneities
  • Low permeability daily cover materials
• EPA Hydrologic Evaluation of Landfill Performance (HELP) Model
  • Breaks landfill cross-section down into discrete horizontal layers
  • Leachate is routed through each layer based on its properties
  • Results include leachate production, head on liner, and liner leakage rate

• Liner
  • Composite (a geomembrane over a low permeability material)
  • Double composite
• Low permeability layer
  • Typically clay (hydraulic conductivity <= 10^-7 cm/s)
  • Review: Hydraulic Equivalency and Breakthrough Time; CLASS NOTES
• Pipe Spacing
  • Read: Requirements for Hazardous Waste Landfill Design, Construction, and Closure EPA/625/4-89/022, pp. 53-60
  • YOU MUST USE CONSISTENT UNITS!!!
  • l = length units (m,ft,in,cm); t=time units (sec,min,hr,day)
  • Without a Geonet
  • 
    1. H_max = heads on liner, l
    2. L = pipe spacing, l
    3. q = 25 yr, 24 hr design storm, lt^-1
    4. K= gravel hydraulic conductivity, lt^-1
    5. alpha =slope of LCS, degrees
  • With a geonet
  • 
    1. theta = geonet transmissivity, l²t^-1
    2. q = 25 yr, 24 hr design storm, lt^-1
    3. L = pipe spacing, l
    4. H_max = heads on liner, l
    5. a =slope of LCS, degrees
  • Calculating 'q' - divide the storm volume by the storm length. For instance, a 25 year, 8 hour design storm generates 4 inches of rainfall. The average storm intensity is 0.0212 cm/min [(4 inches)/(8 hours)*conversion factors ].

Landfill Composite Leachate Collection   System Installation (Note: Clay, Geo-   membrane, Gravel, and Sand Materials)	Landfill Leachate Collection System   Installation (Note: Geo-   membrane and Drainage Material)

Welding Sheets of HDPE Geomembrane   for Landfill Liner	Booting Leachate Collection Pipes   to Landfill Liner