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

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

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.

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