¹Department of Civil Engineering, University of Colorado at Boulder, Boulder, CO, 80309 and ²EG&G, Rocky Flats Environmental Technology Site, Golden, CO, 303-966-8583
Macropores can be significant paths of flow in the vadose zone and can transport water and chemicals at velocities much faster than predicted with conventional solute transport models. At the Rocky Flats Environmental Technology Site in Golden, Colorado, plutonium-contaminated oil leaked from deteriorated drums and was subsequently airlifted by winds and deposited on soils in a cast and south east-trending plume. Macropores have been shown to occur at that site and must be considered in a model predicting the fate of Pu-238-239. While macropore models exist, few studies have calibrated using field data. This study was conducted to determine the feasibility of using a 2-D finite element macropore model at that site to predict the fate of Pu-238-239.
A well-defined system will be used to determine the feasibility of modeling macropores and to calibrate the model. Presently, a column is being manually packed with sieved soil into a 80 cm long and 30 cm diameter column. A macropore will then be created in the column. The sample will be tested under a variety of rainfall rates and boundary conditions.
Field samples will also be used to evaluate the model. Two undisturbed soil columns (35 cm by 50 cm) were excavated from a structured clay soil near Boulder Creek. A rain simulator, which consisted of hypodermic needles attached to the bottom of a short cylinder, applied water at 6 cm/hr. A 49 cell grid sampling device collected the outflow. Tensiometers showed that no flow occurred until the sample was fully saturated. Most of the flow occurred within two grid cells, and conservative tracers exhibited breakthrough at 0.5 pore volumes which suggest some type of macropore flow.
macropore, model calibration, radio active waste, vadose zone modeling
This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.