Ra-226 contamination in soil

[Lawrence Fiske <lfiske@shepmill.com>]

We have conducted gamma-radium(226) correlations at two uranium mill tailing
sites to demonstrate radiological compliance in support of unrestricted
release of lands contaminated with byproduct material.  One site is in
Washington, and the plan was approved by the WDOH, the other site is in
Wyoming, and the plan was approved by NRC.  We used Ludlum 2350 data loggers
with Ludlum 44-10 probes (2" x 2" NaI(Tl)) shielded with a lead shield
3-inches high and 1.75-inches thick.

The techniques we developed were similar to those used in New Mexico by
Brian Rees.  Using approximately 75 grids, we correlated a scalar gamma
count taken while walking over a 10m x 10m grid during a counting interval
of 150 seconds to the average Ra-226 concentration within the grids as
determined by several cores composited for each grid.

Like Brian, we held the position that the proof was in the soil samples, not
in the MDA or the LLD.  At our site in Washington we have successfully
completed final verification this year.  We gamma surveyed approximately
4,000 10m x 10m grids and soil sampled 10% of those to demonstrate that the
gamma-radium correlation adequately identified areas above the cleanup
standard.  We selected the grids to be soil sampled using two criteria:  (1)
even spatial distribution; and (2) high gamma exposure rates.  The intent
was to get good coverage while sampling the grids closest to the action
level in order to maximize our potential of identifying false negatives
(grids which look clean based on gamma, but are really contaminated at
levels above the action limit of 5 pCi/g Ra-226 above background).

The results of the final confirmatory soil sampling demonstrated that we had
only one false negative out of approximately 4,000 girds.

In 1997 we will be conducting cleanup and verification surveys a one of the
Wyoming uranium mill tailing sites using the same techniques under a plan
which has been approved by NRC.  For reference, I have published pieces of
our work at the Bioassay meeting for the past 2 years.  If you would like a
reprint, let me know.

Lawrence E. Fiske
Shepherd Miller, Inc.



Standard disclaimers and personal opinion notices apply.