AREA A/B ENGINEERING REPORT - Waste Management

Geosyntec Consultants
An extensive and growing body of research and practical knowledge exists to demonstrate the
long-term performance of landfills under different design, operating, and closure conditions. 1
Reviews of LFG 2 and leachate 3 composition from multiple sites have been published and appear
on Figure 1-3. These studies show that the most significant control on long-term leachate
generation rates is regulating how much liquid is permitted to enter the landfill. This is usually
associated with the installation of the final cover system. It is well documented that LFG
generation from MSW landfills decreases with waste age (i.e., after closure). Under normal
conditions, LFG generation rates typically reach a peak about one year after cessation of waste
placement, before tapering off in exponential form.
A number of factors affect the rate of waste decomposition in landfills and hence the rate and
quality of LFG and leachate production, including:
• Waste properties (e.g., composition, biodegradability, and physical state);
• Environmental factors (e.g., pH and alkalinity, availability of nutrients, and the presence
of inhibitors to microbial activity); and
• Operational and process-based factors (e.g., addition of degradation-enhancing
additives, and practices that optimize the high moisture content necessary for enhanced
waste degradation).
Biodegradability is mostly affected by the cellulose and hemicellulose content of the waste as
these two biogenic carbon sources contribute most significantly to waste decomposition.
Of the above, operational factors are the most controllable and arguably the most
important from the perspective of managing a landfill. By controlling or
promoting the processes of waste biodegradation, landfills can be managed to
enhance waste degradation to promote in-situ waste treatment, accelerate
exhaustion of LFG production, more rapidly reduce concentrations of leachate
parameters of concern, and reduce long-term potential environmental impacts. As discussed in
detail in Section 7.1, enhancing biodegradation within a modern managed landfill in this way is
most commonly achieved through use of bioreactor technology. This kind of proactive operation
of the landfill will likely diminish the need for containment (and reduction of infiltration through the
cover system) over the long term since LFG production will be reduced and leachate quality
improved to levels that protect the environment even in the absence of a tight landfill cover.
1 As documented by several noted peer-reviewed journal articles including Farquhar & Rovers (1973), Rees (1980),
Pohland & Harper (1986), Christensen & Kjeldsen (1989), Barlaz, et al (1990), Christensen, et al (1992), Bozkurt, et
al (1999 and 2000), Revans, et al. (1999) and Kjeldsen, et al (2003). See Appendix A for detailed discussion.
2 Including van Zanten & Sheepers (1995), Huitric (1999), Hsin-Mei & Kuo (2000), Green, et al (2000), Sullivan &
Michels (2000), Sullivan & Stege (2000), Barlaz, et al (2004a), and Sullivan, et al (2004).
3 Including Farquhar (1989), Christensen, et al (1994), Robinson (1995), Rowe (1995), Reinhart & Grosh (1998),
Knox, et al (2000), Christensen, et al (2001), Ehrig & Kruempelbeck (2001), Bonaparte, et al (2002a), Robinson &
Knox (2001 and 2003), and Gibbons, et al (2007).
MD10186.doc 22 29 March 2009