Collection and Processing Equipment
No data (on a per ton of MSW transported) were found for the actual emissions generated by collection programs. Accordingly, information from a local community was used, and emissions were estimated on the basis of the fuel used.
No data were found on actual emissions during the construction and operation of landfills, including emissions from heavy equipment used for landfill compaction and operations and releases from MSW as it is compacted. Nor were data found on particulates and dust that may result from placing daily cover on landfills.
Landfill Air Emissions
No data were found on actual emissions from spraying leachate at the working face of the landfill, or from aeration in leachate treatment or sewage treatment plants.
No data were found on changes in the composition of trace organic components in landfill gas over long periods.
Statements were found that indicated that dioxins have been measured in the emissions from combusting landfill gas, but no quantitative data were found that indicate the amounts of those emissions.
No data were found on air emissions, if any, from ash monofills.
Landfill Water Emissions
No data were found to document changes in composition of leachate over 20 years or longer for use in estimating whether metal and organic concentrations decline or remain roughly steady. Comparisons of leachate during a landfill's acidic stage and during its methane-generating stage were found, but none of these data covered long periods. EPA data from the early 1970s analyzed leachate from the landfill types that were common at that time (Bogner, 1992). Those data might be useful for long-term comparisons.
Models exist to help predict the amount of leachate that would penetrate the bottom liner of a landfill, but few data were found. No data were found on the amounts and composition of leachate from shredfill or balefill operations.
No data were found on the amounts and composition of leachate from shredfill or balefill operations.
Long-term studies of leachate composition may eventually reflect the changing composition of the waste stream. The recent significant reductions of mercury in alkaline cells and the popularity of zinc-air cells as replacements for mercury batteries in hearing aids are examples of technological changes that will influence waste stream composition. Reduction of metals in inks is another example (Usherson, 1992) New laws in Europe and California also require elimination of lead from the 2 billion wine bottle caps produced each year that are made of lead (Andre and Karpel, 1991).
Ash Monofill Water Emissions
Leachate data for ash monofills are also inadequate. Although long-term, high-quality data on the composition of leachate have been reported, none of the sources reported on the quantity of leachate that is escaping through the bottom of the landfill. Data or estimates of leachate quantities are available for raw MSW landfills.
The amounts of metals and organic materials entering the ground below ash monofill liners have not been widely studied. Of the estimates presented here, therefore, these estimates have the fewest data to support them. The assumptions on which the estimates are based are discussed below, along with indication of gaps in the data.
Data are available on the composition of leachate from a closed monofill over 4 years, but not for the 20-year time frame of interest here. The data show that highly soluble materials- potassium, sodium, and chloride-appear in roughly the same concentrations each year. By extrapolation, it is assumed that the leaching of those ions is at steady state, and that the leachate does not become saturated with them. However, heavy metals like zinc and cadmium decrease sharply over the 4 years for which data exist; therefore, it has been assumed that the low levels noted in year 4 will be the maximum concentration for the next 16 years. It is believed that this is a conservative assumption.
It has been assumed that the depth of the monofill is the same as that for a regular MSW landfill. If an old quarry were used, for example, this assumption may be reasonable; in other situations, the ash monofill may be shallower.
The difference in volume between a raw MSW landfill and an ash monofill is known. To estimate the surface area on which rain will fall, it is necessary to assume a depth for the ash in the monofill. It has been assumed that the depths for both types of landfills are equal.
Data on MSW landfills provide estimates of the amount of rainfall on the closed, capped landfill surface that enters the landfill. The fraction of rainfall that is collected as leachate on the liner and the fraction that leaks into the ground below have also been estimated. Similar data for ash monofills were not found, and thus the proportions reported for raw MSW landfills were used for ash monofills as well. However, if the ash in the monofill hardens, as is frequently reported, it would be unreasonable to assume that rates of infiltration or of percolation to the bottom of the monofill were the same as those for MSW landfills. Because data on the amount of leachate that escapes MSW landfills were applied to ash monofills in this analysis, the estimates of leachate escaping to the ground in this report are likely to be overstated, and the estimates of the amounts of metal that are released in leachate may be too large as well.
Few data were found on the energy requirements for collecting and landfilling MSW; those data that do exist are based on truck capacity rather than on the actual tonnage collected. Nor were actual energy data (on a per ton of MSW basis) found for ongoing landfill construction, filling, compacting, and covering.
Engineering estimates that compare typical sizes of ash monofills with those of raw MSW landfills are available; however, comparisons of the actual depth and acreage of existing landfills and monofills were not found. Similarly, no studies provide guidance concerning land use for ash monofills after closure.
Research into beneficial uses of stabilized ash is frequently based on the relatively extensive research on the uses for flyash from coal-fired utilities. Some studies have evaluated use of the ash as a component of bituminous highway material. Other research is under way on uses in masonry block construction materials. Some processes vitrify or melt the ash into a glass that is extremely inert to leaching and can often be used beneficially as aggregate (see Appendix A page A-80, and DeCesare, 1991). Alternative uses for ash could save landfill space.
Materials Collection, Separation, and Recycling
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