Landfills
Arlene Mand
Institute for Environmental Studies
presents
Dave M. Kargbo
Senior Hydrogeologist/Regional Soils Expert
U.S. Environmental Protection Agency
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Problems Associated with the
Use of Sulfidic Clay Soils
to Cap Landfills
______________________________
Abstract: There is extensive literature on the interaction between
waste chemicals and clay liner materials and how it influences waste
migration. However, attempts to incorporate as design components, the
effects of sulfidic (sulfide-bearing) clays on the integrity of clay caps
have largely been ignored. Currently, the only requirement for cover
soils in landfills and surface impoundments is that the soil attain,
upon compaction, a very low hydraulic conductivity of 10 -7 cm/second or
less. Sulfide-bearing clays used to cap some landfills have been observed to:
increase acidity in the vegetative cover, clay cap, and vertically down
the landfill profile; kill vegetation on the downslopes of the cover;
increase the permeability of the cover to percolating moisture; and
enhance erosion of the clay cover. Consequently, it is suggested that
clay cap designers test the acid-generating capabilities of potential
clay cap material before exploiting these earth formations. This can be
accomplished quickly in the field by a simple pH test (1:1 by weight or
enough to permit measurement). The soil will be said to contain sulfidic
materials if it shows a rapid drop in pH of 0.5 or more units to a pH
value of 4.0 or less within 8 weeks. For soils showing a rapid drop in
pH, the candidate soil should be incubated under moist aerobic
conditions (field capacity) at room temperature. Decisions should then be
made as to whether the soil should be avoided or used with amendments
to the cap design.
Date: Friday, September 23, 1994
Time: Noon - 1:30
Place: Room 213, Steinberg Hall-Dietrich Hall
University of Pennsylvania
NO REGISTRATION REQUIRED
Direct questions to:
Arlene Mand
tel. 215-573-3164
email. am...@mail.sas.upenn.edu
fax. 215-898-0964