United States
 Environmental Protection
 Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87/039  Nov. 1987
 Project Summary
 Design, Construction,  and
 Maintenance of Cover
 Systems for  Hazardous
Waste:  An  Engineering
 Guidance Document
R. J. Lutton
  This document emphasizes the spe-
cial characteristics of solid waste
management as they bear  on  cover
systems. Cover systems typically con-
sist of two to four layers of soil and
other materials and resemble a highway
pavement system in many  respects.
This similarity facilitates the prepara-
tion and use  of construction and
maintenance specifications. Example
specifications are in the appendices of
the full report.
  Criteria and methods are provided for
engineering analyses  of percolation,
erosion,  stability, flooding,  freezing,
and settlement. Techniques  are avail-
able for compensation for each of these
threats, again using recognized design
and construction methods. Finally,
guidance is included on methods of
maintenance and repair over the unusu-
ally long design life of a solid and
hazardous waste disposal facility.
  This  Project Summary was devel-
oped by EPA's Hazardous Waste Engi-
neering Research Laboratory. Cincin-
nati, OH, to announce key findings of
the research project that is fully doc-
umented in a separate report of the
same title (see Project Report ordering
information at back).

Introduction
  Regulations for the management of
hazardous waste disposal facilities have
been promulgated by the Environmental
Protection Agency (EPA) as directed by
the Resource Conservation and Recovery
Act (RCRA). New hazardous waste dis-
posal facilities must meet the require-
ments of Title 40, Code of  Federal
Regulations, Part 264 (40 CFR 264) in
order to receive a permit. RCRA  also
dictates actions for correcting old sites
presenting  endangerment. As a part of
its response to RCRA, the EPA has issued
technical documents to assist in the
complex and important task of planning
adequate disposal facilities.
  The  full  document of this project
provides technical guidance on design,
construction, and maintenance of cover
for hazardous waste facilities based
largely on waste management practice,
concepts in soil construction, and inno-
vations to encourage new designs and
practice developed by creative  and
competent engineers within the limits of
RCRA regulations. Suitable designs are
ultimately translated into construction
therefore, and some of the guidance is
formulated  directly as specifications.

Basis of Technical Design
  The physical characteristics of the site
and the configuration of its surface are
among the  most important factors upon
which cover design is based. Sometimes,
site  characteristics directly influence
design of the entire disposal unit or the
assemblage of disposal units; for exam-

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pie, it is necessary to  limit the size of
disposal  units or  waste cells  in  hilly
terrain,  and their orientation and  ar-
rangement may  also be restricted by
operational considerations. Broad,  flat
sites present fewer restrictions on size,
orientation, and  arrangement of  the
disposal units.
  The character of the waste can have
long-term impacts on the cover and its
performance in relation to  subsidence,
differential offset,  and soil particle
migration. It is even helpful conceptually
to regard the disposal unit as the lower
component or  foundation  of  the cover
with a transition to the backfill soil within
the waste cells. Influences follow either
from the voids and other physical con-
dition of the waste at the time of burial
or from chemical-related changes  that
take place over a  long period. Charac-
terizing the waste focuses attention on
unfavorable eventualities that in some
cases may be avoidable. Certain worth-
while limitations on waste character and
form as well  as placement procedures
may be  incorporated  in  the plan of
operations.
  The  chemical  constitution  and  the
reactivity of bulk and containerized waste
always deserve careful consideration in
cover design  and  the design of  the
disposal unit. A listing of wastes to go
into each  cell  is already  required in
Subpart B, 40 CFR 270. In large disposal
facilities, this undertaking may be com-
plicated or simplified by any operational
plan to  segregate wastes  into subcells
according to waste type. The eventual
deterioration and  breakdown  of initially
rigid elements such as steel barrels, bale
straps, and boxes will  have to be eval-
uated as to their expected histories  and
the ultimate  effects. Although  it is
frequently found that metals and some-
times even paper are  little affected by
burial in  the  short  term  (e.g., at  the
Savannah  River  Plant), the  long-term
effects over tens  of years and to  the
design  life of the facility  must be
addressed to the highest degree available
with  state-of-the-art  knowledge  and
practice.
  The potential for generation of gases
or liberation of volatiles should also be
considered in  cover and disposal  unit
design. It may be necessary to provide
diversions  and vents for gases blocked
from their upward pathways by the cover.
Vents to the  atmosphere  may be  ade-
quate for toxic  components  of   low
concentration that  will  be  quickly
dispersed in the air to acceptable levels.
In extreme cases  where  the  gas  or
volatile component may reach a harmful
concentration, it may be necessary  to
provide on  line or contingency features
for absorption filters or other means  of
reducing concentration of toxic  compo-
nents.  General categories  of reactive
wastes that can conceivably  affect the
performance of cover are volatile organic
chemicals,  inorganic acids,  materials
capable of  reacting with others in the
waste cell,  materials capable of under-
going volume  change,  and  saturated
materials.
  The  hydrological environment of a
disposal site  constitutes the  most
influential combination of related exter-
nal factors  in cover design  and mainte-
nance. The several aspects of climate,
particularly the precipitation regime have
direct impacts on the performance of the
cover in blocking  percolation into the
waste cell.  Besides being  foremost
among  general constraints to cover
design, the climate enters  into detailed
analysis and evaluation  of  proposed
cover designs.
  The  importance  of the  hydrological
system can be illustrated by considering
two  extreme cases. It is believed that
most of the low rainfall of a typical year
at the  arid  Hanford and Richland,
Washington,   LLRW disposal facilities
penetrates  no more than a few meters
of depth. Since the ground water is at
much greater depth, most radionuclides
carried downward by percolating water
stop well above the water  table.  Thus,
these facilities and another hazardous
waste facility to the south near Arlington,
Oregon,  benefit directly from  the  dry
regime. On the other hand,  uncontrolled
waste sites  in the relatively damp
midwestern and eastern United States
frequently exhibit ground-water contam-
ination  plumes of  serious dimensions
and concentrations despite the presence
of cover over the waste in  some cases.
Major storm  events must also  be con-
sidered, since even an  arid region can
be  subjected to  infrequent but  major
storms  that  cause anomalous ground
saturation  and percolation to a  depth
ordinarily  not reached. Accordingly, a
rather complete  review of expectable
storm  events and  their  frequencies
should  be required  in preparing the
background on the hydrological system.
  Other  aspects  of  the  hydrological
system that need to be reviewed are the
evapotranspiration  history, the  water-
retention  characteristics of  the  near-
surface soil, and surface runoff parame-
ters as well as available measurements
at gaging stations. In the broader sense
of hydrology, the ground-water system
constitutes an important part. Familiar-
ization with ground-water configuration,
flow directions, and velocities is essen-
tial, if for  no other reason than to plan
and  to  anticipate contingencies for
unexpected performance or even failure
of the containment system.

General Design Concepts
  Once  the functions of the cover  have
been established or  constrained  by
regulation  or standard or  by clearcut
technical objectives such as reduction of
percolation to insignificant  levels, ele-
ments of  the design are defined and
integrated  using conventional design
methods.
  A  key task of cover  design  is the
selection of suitable materials. The cover
usually  will  include  a synthetic mem-
brane and a large volume of soil or soil-
like  material, but other materials are
sometimes included  also: i.e., Portland
cement, bituminous concrete, seal coats,
and geotextiles.  Guidance on suitability
of various  types of soil for performing
cover functions  and for general  long-
term  service ranking for various engi-
neering functions has been developed
based on considerable experience in the
Bureau  of  Reclamation, Corps of Engi-
neers, and other construction and engi-
neering organizations. Classification is
according to  the Unified Soil Classifica-
tion System (USCS).
  Emphasis on the best soil for the cover
will occasionally be unfeasible, since the
soils available at or near the site will be
chosen  for reasons of  economy. The
strategy of cover design targets the most
effective use of those available materials,
usually  in  a layered construction. The
availability of material may extend off-
site. Fly ash available in the near vicinity
continues to be  an attractive possibility
for use because of its relatively fine  gram
size  which,  by  careful compaction or
addition of reactive  chemicals, can  be
brought to a strength  and  permeability
that may be  suitable for fulfilling cover
functions.

Example Designs
  The appendix in the full report provides
guidance on  preparing specifications for
four example designs. The preparation of
plans and specifications demands careful
attention  to  detail, and sometimes the
choice of wording can have costly legal
ramifications. Therefore, the specifica-

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tions  in the  appendix  as well  as the
designs themselves  are intended for
guidance rather than for direct applica-
tion at any facility.
Richard J. Lutton is with the U.S. Army Engineering Waterways Experiment
  Station, Vicksburg, MS 39180.
Robert P. Hartley is the EPA  Project Officer (see below).
The complete report entitled "Design. Construction, and Maintenance of Cover
  Systems for Hazardous Waste: An Engineering Guidance Document," {Order
  No. PB 87-191  656/AS; Cost: $18.95. subject to change) will be available
  only from:
        National Technical Information Service
        5285 Port Royal Road
        Springfield, VA 22161
        Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
        Hazardous Waste Engineering Research Laboratory
        U.S. Environmental Protection Agency
        Cincinnati, OH 45268

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