Banda Group International, LLC

Implementation of The Material Disposal Area T Moisture Monitoring Pilot Study

LOCATION: Los Alamos National Laboratory, NM

CLIENT: Newport Nuclear News BWXT – Los Alamos (N3B)

Material Disposal Area T (MDA T) is located within Technical Area 21 (TA-21) at Los Alamos National Laboratory (LANL). MDA T is a 2.2-acre radiological waste disposal site consisting of four plutonium-contaminated absorption beds used to dispose of liquid wastes from the plutonium-processing laboratories at TA-21 from 1945-1952; a retrievable waste storage area; a series of disposal shafts containing radioactive elements; an acid holding tank and acid sump; a caisson built in 1959 at the northwest corner of Absorption Bed 1; an inactive container storage area for alcohol, acetone, and freon; and two surface spills of radioactive waste. The MDA T Moisture Monitoring Pilot Study took place west of MDA T proper, partially on the footprint of the former filter house (SWMU 21-020(a)).

BGI conducted a pilot study to evaluate three monitoring instrumentation scenarios for the detection of vertical migration of moisture within the subsurface lithology at MDA T. The goal of the project was to determine the most effective combination of monitoring well design and equipment for detecting moisture in the subsurface for the eventual large-scale implementation below the MDA T Nuclear Environmental Site (NES). Conducting this pilot test outside of the NES (a Category II Nuclear Facility) provided an opportunity for a “dry-run” to reduce some of the testing complexities and uncertainties in an area with fewer health and safety concerns.

The BGI Team drilled and installed three moisture monitoring wells with varying monitoring equipment and annulus materials using hollow stem auger drilling methods. Heat dissipation probes were installed within two monitoring wells with different backfill materials (SiLiBeads® and crushed tuff). The third monitoring well was constructed to facilitate neutron logging instrumentation for the detection of moisture within the subsurface. During advancement of each monitoring well, continuous cores were collected for laboratory analysis to obtain baseline moisture concentrations for comparison of data collected during water application.

BGI installed a data logger and remote monitoring systems for data collection download from the sensors. A trench was constructed at the surface and vertically positioned over the sensors installed within each well. BGI introduced water within the trench, maintaining a baseline depth while simultaneously monitoring the sensors for detection of the moisture front during application. Neutron logging was performed at the third well, daily, for the entire duration of the study.

The moisture monitoring data collected from all three wells was used to determine which of the three scenarios was most effective in moisture detection and for selecting the appropriate system for full scale monitoring at MDA T proper.