Summary of Studies for

Richard Statom, Fiessinger Scholarship Winner 2001

(Final Report - summer 2004)

In the final year of his research supported in part by the EREF Francois Fiessinger Scholarship, 12 ½ years of leachate data from seven lined cells at a municipal solid waste (MSW) landfill located in Palm Beach County, Florida were investigated to determine temporal trends and spatial variations in leachate chemistry at the site.  This work is a continuation of previous investigations into temporal changes in leachate chemistry (Environmental Geology, 2004, Vol. 45, # 7) and leachate transport within the landfill (Geological Society of America Annual Meeting, paper # 186-5).

In this third phase of the study, leachate chemistry at seven contiguous but temporally separable landfill cells was evaluated.  The results indicated that the leachates in the seven cells were similar, but spatial variations related to the age of the waste in the cell were evident; with the younger cells have generally higher contaminant concentrations than the older cells.  Overall declining or stable trends for major leachate constituents were observed in the cells as the waste aged, with the exception of the youngest cell.  The youngest cell showed increasing trends for several constituents during the study period, but an initial increasing trend when a landfill cell is first operated followed by a decreasing trend as the waste ages is typical for landfills.  There was also a relationship noted between leachate contaminant concentration and cumulative rainfall totals, such that increased rainfall levels precede lower contaminant concentrations.  This response to rainfall is found in all of the cells investigated, regardless of the age of the cells.

The flow regime within the landfill was determined to be one in which the majority of the leachate flows along preferential flow paths through the landfill, called a dual-domain system.  This type of flow regime is very similar to those found in structured soils, and effectively isolates the leaching processes to a small portion of the cell.  It was found that these preferential flow paths can change location over time and may cause leachate quality to change dramatically over the life of the landfill.

This work has provided some significant insights into the inner workings of MSW landfills, especially in the semi-tropical environment of Florida.  Future work will investigate if the temporal trends, spatial variations, and flow regime found at the Florida landfill are typical for landfills in other parts of the country.