Section Three
LANDFILLS-B. LEACHATE
22    PHYSICAL AND CHEMICAL CHARACTERISTICS OF
UNSATURATED PORE WATER AND LEACHATE AT A
DRY FLY ASH DISPOSAL SITE
Thomas L. Theis, Professor
Dept. of Civil and Environmental Engineering
Clarkson University
Potsdam, New York 13676
John A. Ripp, Principal
Atlantic Environmental Services
Colchester, Connecticut 06415
James F. Yillaume, Sr. Project Scientist
Environmental Management Division
Pennsylvania Power and Light Company
Allentown, Pennsylvania 18101
INTRODUCTION
With the continuing competition for dwindling space and the tightening of regulations on surface
water and groundwater discharges, the large surface impoundments being used by electric utilities for
the disposal of their high-volume coal combustion residues are slowly being replaced by managed
landfills and stockpiles. Even so, the waste water resulting from the operation of these landfills must
be managed so that local surface and groundwater supplies are protected.
Unfortunately, there is little reliable information available on these waste streams, in particular the
surface runoff and the bottom drainage or leachate. Previously, an engineer designing one of these
facilities had to rely on laboratory beaker or column tests, which are not always reliable indicators of
system behavior. Even such a basic property of the compacted ash as its surface infiltration rate,
which determines the sizing of any collection facilities, is largely unknown and certainly unverified.
Several years ago, the Electric Power Research Institute (EPR1) began a major research program to
develop computer models for predicting the natural attenuation of ash leachate in the subsurface
environment;1 but the results of this research were not expected to be available until well after 1990.
As a result, the Pennsylvania Power and Light Company (PP&L) began a research project in 1981
to develop basic information on the leaching behavior of fly ash in an actual landfill environment.
Initial work involved testing various surface runoff and leachate monitoring devices to determine
what would produce the most reliable data.2 This was followed in 1984 with the construction of a
large outdoor, heavily instrumented test cell of fly ash, which was designed to simulate the actual
disposal facility in all major respects.3 The ultimate goal of this latter effort was to characterize the
quality and quantity of the resulting waste streams so that suitable collection and, if necessary,
treatment facilities could be provided. Also, because there is no "standard" design for fly ash landfills,
it was hoped the project would provide basic information useful in improving the current design,
which was suspected of perhaps being overly conservative and therefore unnecessarily expensive.
The purpose of this chapter is to present information on the design, construction, and instrumentation of the test cell and the current hydrophysical and chemical data from the site.
TEST CELL DESIGN AND CONSTRUCTION
The test cell contains approximately 68,000 cubic feet (1926 m3) of compacted fly ash, initially
placed at 15% moisture by weight and a wet bulk density of between 90 and 120 pounds per cubic foot
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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