Successful remediation of four uranium calibration pits at Technical Area II, Sandia National Laboratories, Albuquerque, New Mexico, USA Page: 3 of 15
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INTRODUCTION
The UCPs were used between 1978 and 1984 for geophysical instrument calibration. Remediation
of the UCPs was conducted in the summer of 1994 as a VCM. The decision to perform the VCM
was made for several reasons; the UCPs were no longer being utilized, known radiological and
possibly hazardous material remained, the final remedy was obvious, and reductions in cost and
schedule could be achieved. The objective was to eliminate risk to human health and the
environment.
HISTORY OF THE UCPs
Construction Details of the UCPs
The UCPs were located in the western portion of TA-Ili (Fig. 2). The site consisted of four concrete
culvert pits that were managed by the DOE. The UCPs were used to test and calibrate down-hole
radiometric logging tools for the National Uranium Resource Evaluation (NURE) Program. The pits
were constructed in 1978, and were used until 1984; the site has been inactive since 1984.
Between 1978 and 1984, the site was enclosed with a chain link fence and contained a mobile
office. The chain link fence and mobile office were removed in about 1989.
From west to east, the four UCPs were numbered sequentially 1 through 4 (Fig. 3). The distance
between the centers of each pit was approximately 1.8 m. The four UCPs were constructed by
excavating 1.2 m diameter pits to 2.4 m BGL. An 11.5-cm diameter borehole subsequently was
drilled beneath each pit. Three of the boreholes were drilled between 4.5 and 5.8 m deep (UCPs 1
through 3). The UCP 4 borehole was drilled to an approximate depth of 64 m. Ten-centimeter
diameter polyvinyl chloride (PVC) pipe was then installed into the UCP-2, -3, and -4 boreholes. A
ten-centimeter diameter steel pipe was installed in the UCP-1 borehole. The pipes were not grouted
in place. A 1.2 m x 2.4 m concrete culvert (i.e., hollow concrete pipe) subsequently was lowered
into each of the four open pits. After the culverts were in place, a 15.2-cm concrete plug was
poured at the base of UCPs -1,-3, and -4. UCP-2 did not have a concrete plug base. Although the
cement plugs were poured in the culverts, a water-tight seal was apparently not created between
each plug and culvert. A circular steel plate was placed upon, but was not sealed to, the top of
each UCP and served as a pit cover.
Historical Use of the Uranium Calibration Pits
Although basic construction details were similar for the four UCPs, the pits were used for different
calibration operations. Reported materials used at each pit are described below and are shown in
Fig. 3.
UCP-1 was used to simulate a water-saturated, uranium-bearing sand. The pit was filled with silica
sand and subsequently was saturated with a solution of uranyl nitrate. The original specifications
for the uranyl nitrate solution indicated that about 9 kg of uranium oxide was planned to be used,
although a memorandum indicated that only 4.5 kg of uranium oxide was actually used. The
uranium oxide was dissolved with a minimal amount of nitric acid which then was diluted with
distilled water to form the uranyl nitrate solution. The total volume of uranyl nitrate solution was
approximately 852 L. After the UCP was filled, the solution leaked out overnight into the soil
beneath the pit where it precipitated in the alkaline soil; the leak was not anticipated.
Contaminated soil, which was removed during the recent VCM, was found within approximately
1.8 m beneath the bottom of the concrete plug.2
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Conway, R.; Wade, M.; Tharp, T. & Copland, J. Successful remediation of four uranium calibration pits at Technical Area II, Sandia National Laboratories, Albuquerque, New Mexico, USA, article, December 31, 1994; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc717033/m1/3/: accessed June 8, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.