This is a problem I am dealing with at work. I am a regulator for a
state environmental agency, and I have to decide how 3,000 tons of
waste wood contaminated with arsenic will be disposed of. After this
wood pile is taken care of, another one awaits.
The short version of the story is that we expect the 3,000 tons of
waste, comprising 12,800 bundles of pallets and crates, to be
extremely heterogeneous (between-bundles) in their arsenic contents.
If you want more details, see the end of the message.
Following is the data:
[As] Log10[As]
2.500 0.3979
0.784 -0.1057
0.015 -1.8182
3.540 0.5490
0.005 -2.3010
0.005 -2.3010
0.016 -1.7959
0.397 -0.4012
0.017 -1.7696
0.392 -0.4067
0.636 -0.1965
0.062 -1.2076
Max. 3.540 0.5490
Median 0.227 -0.8072
Min. 0.005 -2.3010
Avg. 0.697 -0.946
s.d. 1.139 1.036
Skew. 1.984 0.028
Kurt. 3.179 -1.629
The two 0.005 values were reported as <0.010 mg/L, which is the
detection limit of the analytical procedure.
Histogram of [As]
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Histogram of Log10[As]
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The question to be answered is:
What fraction of the 12,800 bundles of pallets/crates exceed the
regulatory standard of 5.0 mg/L for TCLP arsenic? (If TCLP As is >
5.0 mg/L, the wood is hazardous waste and cannot be placed in a
municipal solid waste landfill.)
If the regulations were to be read strictly, each pallet/crate bundle
with As > 5.0 mg/L would have to be handled as hazardous waste, not
sent to the MSW. As a practical matter, no one could afford to test
every bundle. If we can expect the large majority to be < 5.0 mg/L,
they will be allowed to send all 12,800 bundles to the landfill.
I'm inclined to allow the material to be sent to the MSW landfill.
What do you think? Are there any statistical analyses you would
suggest performing on this very small amount of data?
(Note: This project was not handled the way I would have wished, but
this is the real world, and this is what I have to work with.)
Bob the Bureaucrat
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251026473393872
DETAILS:
A Department of Defense conctractor demilitarizes old and surplus
ammunition. They receive the ammunition on pallets and in wooden
crates from where it was deployed, anywhere in the world.
The contractor was supposed to be disposing of the wood as the
ammunition was demilitarized. However, they didn't, and two large
piles of pallets and crates accumulated. The crates were bundled up
and placed on the pallets and stacked in a remote hollow. There were
lawsuits over this and other, more serious violations, and someone
went to jail.
The ammunition was manufactured under innumerable contracts that had
specifications on whether and how the wood was to be preserved,
depending on the expected climatic conditions at the place of
deployment. The pallets/crates of concern were treated with arsenic.
The age of the pallets/crates vary from one to another. Some were
manufactured in the last several years, while some is as old as 30 or
40 years.
The crates were then subjected to a variety of environments during
their deployment. Some were stored in warehouses for the full time;
others were exposed to the weather for various lengths of time. They
have been exposed to the weather for years at the contractor's, too.
The pile of waste pallets/crates took years to accumulate, and years
passed while the lawsuits were going on.
The lawsuits are settled now, and the first wood pile is being cleaned
up. The It is estimated to be 3,000 tons or 12,800 pallets/crates.
It was decided to sample 12 pallets/crates for aresenic. In selecting
the 12 pallets/crates, an attempt was made to select different-looking
ones. Each selected pallet/crate separately was ground into chips,
stirred, spread out, and a composite sample was collected. The 12
composites were tested by the TCLP protocol, which mimics the chemical
leaching that occurs in a landfill. (Assume that the grinding,
mixing, composite sampling, and TCLP analysis was done correctly.)
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