ETL 1110-1-175
30 Jun 97
probability that the concentration at the points of
described in this document as appropriate. This is
estimation exceed the clean-up value or other stan-
particularly true during planning of large-scale site
dard. These kriging estimates can be contoured to
characterization efforts or when there are risk
define areas or volumes of material that have a
management or design decisions to be made that
certain likelihood of exceeding some cleanup value.
must consider the uncertainty of site characteriza-
The contour value is essentially the probability of
tion results. The same USACE elements should
exceedance. Lastly, the size of the area defined by
also encourage the use of geostatistics, where
different probabilities of exceedance can be deter-
appropriate, by their contractors.
mined and, using a unit cost or similar approach, a
cost-versus-risk curve can be developed. This can
b. USACE elements shall make every effort
be used in programming money for the project, as a
to familiarize staff members actively supporting
basis for negotiating cleanup levels with regulators,
HTRW projects with the fundamentals and poten-
or to help determine if the cost and time of addi-
tial benefits of the application of geostatistics.
tional characterization work will be offset by less
This letter is a good starting point for learning
risk during construction. Alternatively, rather than
about the use of geostatistics for HTRW projects.
transforming the data to ones and zeros, the actual
Users are encouraged to attend appropriate
values are kriged and the kriging variances can be
training.
used to determine prediction intervals on each esti-
mated value as described in section 2-6. In the
c. This letter sets out procedures for the tech-
vicinity of the point estimate, these prediction inter-
nically correct application of geostatistics which
vals can be used to define the spread of potential
are consistent with current practice, such as set
values expected within a given probability. This
forth in ASTM D-5922 and D-5549. The techni-
assumes the data are normally distributed or have
cal procedures outlined herein shall be considered
been transformed to be normally distributed.
when performing USACE in-house geostatistical
analysis or reviewing such analyses done by
USACE contractors.
6. Actions Required.
a. USACE elements identified in paragraph 2
shall consider applications of geostatistics as
FOR THE COMMANDER:
2 Appendices
KISUK CHEUNG, P.E.
App A - References
Acting Chief, Environmental Division
App B - Notation
Directorate of Military Programs
3
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