Abstract:
Assessment of present and future solid waste landfill design requirements and contaminant impacts on adjacent surface and ground waters requires accurate monitoring of the quality and quantity of leachate produced. However, due to field and laboratory constraints, landfill leachate is difficult to monitor. Resulting data is typically highly variable. This variability casts doubt on the reliability and diminishes the utility of the data. In addition, although the literature suggests that leachate quality changes as a landfill ages, evidence of a clear distinction between leachates from areas of different ages within a single landfill is not apparent in historical data from the site studied here.
Consequently, a monitoring plan was developed to investigate the short-term variability of leachate quality at a single municipal landfill, and to determine whether fill areas could be distinguished on the basis of age. Two locations were chosen: Site 1, an older area containing unlined source waste averaging 14 years old; and, Site 2, a younger area containing lined source waste averaging five years old. Site 1 had final cover in place whereas Site 2 did not. During the first sampling period, specific conductance and flow were monitored weekly over a period of two months. During the second sampling period, COD, TOC, and total recoverable Fe and Mn, in addition to specific conductance and flow, were monitored for 22 days at hourly, daily and weekly intervals.
Results obtained show large daily variation in concentrations of metals and organics at both sites. However, variation is similar forFE and Mn and for COD and TOC at each site, and corresponding concentration ratios remain relatively stable. In addition, trends are evident in relation to flow. At the older, unlined site concentrations of metals and organics decline with increasing flow, indicating that dilution or channeling occurs. At the newer, lined site concentrations are relatively constant over the range of flows observed indicating flow-proportional leaching. Magnitudes of all parameter concentrations also differ between the sites. COD, TOC, and Fe levels are two to three times higher while TDS and Mn are one-third to one-half lower at the older site.