UNIVERSITY OF COLORADO AT DENVER

PLACE: Mathematics Conference Room 626 UCD Building, 1250 14th St., Denver

TIME: NOON (Refreshments served at 11:45 am)

DATE: Nov. 6, 2000

Title:
On the Evaluation of Groundwater Contamination from Underground Nuclear Tests

Speaker:
Andrew F. B. Tompson
Geosciences and Environmental Technologies Division
Lawrence Livermore National Laboratory, Livermore, California 94551



Abstract:
Increasing concern about radioactive contamination of groundwater
from underground nuclear tests has reinforced the need for a basic
understanding of how the radionuclide inventories of such tests enter
and migrate through groundwater. As a basis for studying these processes,
the physically and thermally disturbed geologic environment produced by
such tests and its relation to the post-test distribution of radionuclides
is discussed from a conceptual perspective. These concepts are used to
support the development of a reactive transport model to evaluate the
nature and extent of radionuclide contamination within alluvium surrounding
a specific underground nuclear test at the Nevada Test Site. Simulations
are focused on determining the abundance and chemical nature of radionuclides
that are introduced into groundwater, as well as the rate and extent of
radionuclide migration and reaction in groundwater surrounding the working
point of the test. Transport simulations based upon an efficient,
streamline-based numerical model are used to illustrate the nature of
radionuclide elution out of the near-field environment and illustrate the
conceptual modeling process. The numerical approach allowed for relatively
complex 3D flow and chemical reactions to be considered in a computationally
efficient manner. The results are particularly sensitive to the rate of
melt glass dissolution, spatial distribution of reactive minerals in the
alluvium, and overall groundwater flow configuration. They provide a rational
basis from which defensible migration assessments over larger spatial and
temporal scales can proceed.