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. 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 determine the progression of moisture within the subsurface lithology of MDA T. The goal of the project was to determine the most effective methods for conducting similar studies within 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 three angled boreholes without drilling fluids and collected core. Borehole drilling was followed by the installation of delicate moisture sensors (heat dissipation probes) down the boreholes with two different backfill materials (SiLiBeads® and crushed tuff) around the sensors to ensure good hydraulic contact with surrounding tuff and to avoid bridging of backfill. Water was ponded in a nearby trench so that a wetting front propagated through the moisture monitoring zone. In addition to downhole sensors, BGI utilized neutron logging to compare of the pros and cons of moisture monitoring with neutron probe versus using installed sensors.