=======================Electronic Edition========================
RACHEL’S HAZARDOUS WASTE NEWS #116
—February 14, 1989—
News and resources for environmental justice.
——
Environmental Research Foundation
P.O. Box 5036, Annapolis, MD 21403
Fax (410) 263-8944; Internet: erf@igc.apc.org
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ANALYZING WHY ALL LANDFILLS LEAK.
The U.S. Environmental Protection Agency (EPA) has paid for a
series of engineering studies to find out the best way to make a
landfill. They wanted to know what was the “best demonstrated
available technology” (BDAT) for making landfills. These studies
reach some surprising conclusions.
Landfills are bathtubs in the ground; the bottom of the bathtub
is called a liner and it can be made of compacted clay soil, or
it can be made of a huge sheet of plastic underlain by ordinary
soil, or it can be a huge sheet of plastic underlain by a layer
of compacted soil (usually clay soil). The third combination,
plastic liner and compacted soil, is called a “composite liner.”
(A composite liner is not a double liner; it is a single liner
made up of two parts; to create a double liner, you would use two
composite liners together, separated by a layer of sand or
gravel.) Geoservices did not examine the second type of liner
(plastic sheet on ordinary soil) because ordinary soil provides
poor support for a plastic liner carrying many tons of weight, so
they restricted their analysis to compacted clay liners vs.
composite liners.
The EPA wanted to know which liners were the best ones available:
compacted clay liners, or composite soil liners? So they hired
Geoservices (of Boyton, Florida) to tell them. The resulting
study makes dull reading because it is filled with technical
details, but the conclusions are fascinating. All liners perform
worse than anyone suspected.
Clay liners
Geoservices didn’t have much good to say about clay liners. The
flow of liquids through a liner (the liner’s permeability) is
measured in centimeters per second (cm/s). The EPA’s current
requirement for a liner for a hazardous waste landfill is that it
pass liquids through it no faster than 10-7 cm/s (read ten to the
minus seven centimeters per second, or one ten millionth of a
centimeter per second). However, based on actual experience in
the field, Geoser vices concludes that this ideal permeability is
often not achieved for a variety of reasons. (See pgs. 3-3
through 3-8; case studies of clay liners appear in Appendix A.)
Therefore, they assume that the actual permeability in the real
world lies between 10-7 and 10-6 cm/s. Geoservices concludes,
“Possibly the most significant observation is that with
compacted [clay] soil bottom liners, leakage out of the
[landfill] will be large (if there is leakage through the top
liner)…. even in [landfills] meeting current EPA design
requirements” including permeability of 10-7 cm/s (pg. 3-18). By
“large” leakage, Geoservices means 90 gallons of fluid leaking
through each acre each day, or 900 gallons per day leaking from a
10-acre landfill. Their calculations show that, with 3 inches of
water standing on the bottom liner, it will take 15 years for
leakage to break through a 3-foot-thick compacted clay bottom
liner, but once breakthrough has occurred, 90 gallons per acre
per day will pass through the liner continuously thereafter. (See
pg. 3-16, and Table 3-3 on pg. 3-40.) It won’t take very long to
contaminate a large drinking water supply if you pour 90 to 900
gallons of toxics into it day after day, year after year. Thus
Geoservices has shown that clay liners are an environmental
disaster.
Composite liners
Geoservices reports that all plastic liners (also called Flexible
Membrane Liners, or FMLs) always have some leaks. “A common
misconception regarding FMLs is that they are impermeable, that
is, no fluid will pass through an intact FML. However, it is
important to realize that all materials used as liners are at
least slightly permeable to liquids or gases and a certain amount
of permeation through liners should be expected. Additional
leakage results from defects such as cracks, holes, and faulty
seams.” (pg. 4-2)
FMLs often develop defects called “pinholes” during manufacture;
these result from thin places (“fish eyes”), bubbles, foreign
material, or lumps of carbon in the raw molten plastic from which
the FML is rolled (“calendered”) into sheets. Furthermore, when a
large landfill liner is created by joining strips of FML together
with glue or by welding, the resulting seams often leak.
Geoservices provides some data on typical seam defect rates. They
look at six case studies (pgs. B-7 thru B-11). Based on the six
case studies, they draw the following “tentative conclusions:” an
average of one leak per 30 feet of seam can be expected if there
is no quality assurance program (quality assurance being a third
party coming along behind with special equipment to check the
adequacy of the seams). Even with good quality assurance, “an
average of one leak per 1000 feet of seam can be expected with
reasonably good installation, adequate quality assurance, and
repair of noted defects.” (pg. B-11) That is to say, under the
best of circumstances, you’ll get one leak per thousand feet of
seam. If the landfill liner is made by welding strips of FML that
are each 20 to 30 feet wide, you can expect one to two defective
seams in each acre of landfill.
Based on actual data, Geoservices concludes that a “standard”
(typical) leak in an FML has an area of one square centimeter
(1/16 of a square inch) and that the “standard” (average) number
is one hole per acre. They point out that this “standard” hole
size and standard number per acre are based on the assumption
that “intensive quality assurance monitoring” will be performed
during liner installation, so clearly we are talking about the
best case, not the worst case here. Design flaws, poor
construction practice, or poor quality assurance would result in
larger holes, greater numbers of holes, or even large tears. (pg.
B-13)
Geoservices then goes through an elaborate mathematical analysis
to figure out how much fluid will pass through a composite liner
under the best possible conditions and under less ideal (but
still optimistic) conditions. They conclude (pg. B-41) that the
“best demonstrated available technology” (BDAT) for composite
landfills liners will allow leakage rates somewhere between 0.02
and 1.0 gallons per acre per day. (See Table B-10 on pg. B-51.)
Thus they conclude that a 10-acre landfill will have a leak rate
somewhere between 0.2 and 10 gallons per day, or between 73 and
3650 gallons of fluid per year; over 10 years, such a landfill
will allow the leaking of 730 to 36,500 gallons of fluid. And
this is the “best demonstrated available technology”–the very
best we can do when everything goes right.
Next week we will show that leaking 730 to 36,500 gallons of
toxics into a water supply during a 10-year period guarantees
destruction of the drinking water resource.
We will also show that the Geoservices study is unduly optimistic
because, as they say themselves (pg. B-7), “Many tupes of FMLs
swell when placed in contact with chemicals. As a result, the
distance between polymeric chains increases and permeability
increases. Therefore, an FML can have a low permeability for
water and a high permeability for some chemicals.”
If you’re interested in technical details, get: Geoservices,
Inc., BACKGROUND DOCUMENT ON BOTTOM LINER PERFORMANCE IN
DOUBLE-LINED LANDFILLS AND SURFACE IMPOUNDMENTS. Springfield, Va:
National Technical Information Service, April, 1987. Order from
National Technical Information Service, Springfield, Va 22161;
phone (703) 487-4650. Order No. PB87-18229-1. $36.95.”
–Peter Montague, Ph.D.
Descriptor terms: landfilling; landfill design; clay liners;
fmls; epa; geoservices, inc; bdat; composite liners; leaks; leak
rates; statistics; leakage;