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leachate is recirculated, there are technologies available to treat ammonia and reduce its
concentration prior to leachate being entered back into the landfill (Berge & Reinhart, 2003;
Price, et al, 2003).
The body of knowledge devoted to the topic of metals reaction under various operating
conditions is considerable (e.g., Aulin, et al, 1997; Bozkurt, et al, 1997 and 1999; Flyhammer, et
al, 1998; Martensson, et al, 1999; Lagier, et al, 2001; Grischek & Bilitewski, 2001). According
to Christensen, et al. (1994), potentially toxic heavy metals do not constitute a frequent
groundwater contaminant problem at MSW landfill sites, partly because MSW landfill leachates
usually contain only modest concentrations of heavy metals and partly because the heavy metals
are strongly attenuated to waste by sorption and precipitation within the landfill. Bozkurt, et al.
(2000) developed a model to predict long-term emissions of metals from landfills and concluded
that heavy metals mobilization will not occur for thousands of years, if at all. Similarly, Belevi &
Baccini (1989) suggested that landfills contain sufficient buffer to maintain alkaline conditions for
more than 2,000 years and, therefore, did not expect significant remobilization of heavy metals
due to lower pH. This is consistent with recent independent reviews of heavy metals concentrations
in leachate from multiple landfills (e.g., Kjeldesen, et al. 2003; SWANA, 2004) in which
concentrations were typically at or below the drinking water MCLs, even at relatively “young”
landfill sites.
Characterization of xenobiotic organic compounds (XOCs) most frequently present in landfill
leachate has been extensive (e.g., Christensen, et al, 2001; Kjeldsen, et al, 2003). In a study of
leachate quality from over 60 landfill cells (Bonaparte, et al, 2002b), average XOC
concentrations were consistently lower in leachate from post-1990 landfills than from pre-1985
landfills. To evaluate long term trends in XOC leachate concentrations, several processes must be
considered, including volatilization to gas, diffusive losses, and leaching and degradation
(Deipser & Stegmann, 1994; Luthy, et al, 1997). Sanin, et al (2000), Kjeldsen & Christensen
(2001), and Kjeldsen & Jensen (2001), among others, describe the long term fate of XOCs, VOCs,
and haloalkanes (e.g., chlorofluorocarbons) in landfills.
Two recent studies evaluating data on inorganic ions, metals, and VOC trends as a function of
time have recently been completed. In the first (Gibbons, et al, 2007), a multi-year longitudinal
study used an expanded database of more than 1400 sample events from 101 closed landfill
cells of various MSW ages. Results indicate that a majority of constituents show a decreasing
trend with time in the post-closure period generally consistent with the major indicators such as
BOD. These results support findings in existing literature on long-term leachate constituent trends
using a robust data set with variability in climate, waste composition, the age of waste at the time
of capping and the predictability of leachate quality trends over time. A second study (Stratom,
et al, 2007) was conducted using over 12 years of leachate chemical data from a single lined
cell at a south Florida MSW landfill site and showed an overall declining trend in major ion
chemistry. Data collected after landfill closure capping showed an overall reduction in the
amplitude of short-term variations.
MD10186.doc 111 29 March 2009