Tritium Transport from a Solid Radioactive Waste Burial Ground Whose Heterogeneous Conductivity Field is Based on Site Lithologic Data
L. L. Hamm, G. P. Flach, M. K Harris, P. A. Thayer, and J.
S. Haselow
Variability in hydraulic conductivity can dominate regional scale groundwater
(GW) flow patterns and dispersive transport. An approach for generating
heterogeneous conductivity fields from sediment lithologic descriptions is
employed. The approach involves creating a fine-scale representation of mud (silt+clay)
fraction using "stratified" interpolation that is translated into horizontal and
vertical conductivities using direct correlations. The fine scale conductivity
fields are then scaled-up to a coarser grid for use in GW modeling. The approach
is demonstrated using a 3-D
model for tritium
migration
from a Savannah River
Site solid radioactive waste burial ground. The site area contains a significant
number of core logs for defining lithology, has complex vertical heterogeneity
in the upper aquifer units, numerous monitoring wells for hydraulic heads, and
several tritium sources (ideal tracer) for assessing the model's accuracy. This
study demonstrates that detailed lithologic information can be successfully
incorporated directly into the models. A more defensible method of addressing
aquifer heterogeneities (than the traditional layered approach) is achieved
because the model more closely reflects the actual lithologic data. For the
burial ground field-observed preferential pathways for tritium transport occur
without the need to resort to the artificial creation of locally high
conductivity zones. A comparison to measurements is presented for tritium
breakthrough at the down-gradient seepage face of Fourmile Branch Creek.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California