Re: U-238 concentrations in soil

[Lawrence Fiske <lfiske@shepmill.com>]

At 11:46 AM 7/12/96 -0500, you wrote:
>Dear Radsafers,
>	Can someone tell me where I can find the soil concentration limits
>for various materials (U-238, Th-230,...)
>
>Thanks in advance
>
>David Rynders
>
>
>
We are currently working under approved plans for two uranium mill tailing
sites.  One plan was approved by NRC and one was approved by the Washington
Department of Health.  The soil concentration limit for these sites (for
Ra-226) is specified in 10CFR40 Appendix A, Criterion 6(c) as 5 pCi/g above
background in the top 15 cm and 15 pCi/g in 15 cm layers below the top 15 cm.  

For Th-230 we calculated the allowable Th-230 based on ingrowth of Ra-226.
That is, the Th-230 standard was calculated on a grid-by-grid basis such
that over the 1000-year design life the Ra-226 standard was not exceeded.
Therefore, for the top 15 cm, if a grid had background Ra-226 concentrations
(about 1 pCi/g), we could have up to about 15 pCi/g Th-230, but if a grid
had Ra-226 concentrations near the limit, the Th-230 limit would be about 6
pCi/g.

For U-nat (238+234) we used the unity rule based the limits set out in the
Policy and Guidance Directive FC 83-23.