DRC-2009-003937 - 0901a068801403e0

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From: Loren Morton
To: Harold Roberts
CC: Dane Finerfrock; Dave Rupp; David Frydenlund; Doug Oliver - MWH; Ed ...
Date: 9/3/2009 7:06 PM
Subject: Denison Mines: Further Thought on Meeting Yesterday - Radon Control Issues
Harold,
As I mentioned on the phone today, a few other thoughts came to me last night, that I don't think we explored yesterday. I bring
these to your attention, so you will be aware of them, and can then decide if you want tackle them in the upcoming Modeling
(ICTM) Report, or at another time. In either case, the Reclamation Plan won't be ready for approval until a second demonstration is
made and approved - that being the issue of proper control for radon emanation. If we already addressed any of this, I apologize,
but I wanted to get it all out on the table, so as to avoid any surprises for you. My preliminary thoughts were as follows:
1. Conflicting Philosophy - we spent a lot of time yesterday talking about the infiltration model. MWH made several points
about how many of their assumptions were conservative, in that they would over-predict infiltration and over-predict moisture
storage in the cover materials above the tailings. We agreed yesterday that this appeared conservative for purposes of protecting
ground water resources. However, after further thought it is clear to me that this is not conservative for radon control, in that
radon emanation is inversely proportional to cover soil moisture content. In other words, when cover soils are wet, less soil
thickness is needed to control radon gas. As a result, DUSA needs to give.some thought to how to resolve these competing
concerns. On the phone today, we agreed that DUSA has the option to submit one infiltration model that meets both needs, or to
submit 2 models to address these different purposes. The choice is yours. What Is important is that what you ultimately build in
the field must be representative of the analyzed condition, or is more protective of the analyzed condition - for both radon control
and water resources protection.
2. Burrowing Animal Reference - yesterday Ed said he believed the "basement" of burrowing depth in a soil profile would be
on the order of 4 - 5 feet. Please provide supporting technical documentation for this conclusion with the upcoming report.
3. Burrowing Animal Implications - if animal burrowing will or could invade the radon barrier layer, then appropriate soil
permeability and moisture storage characteristics need to be assigned to that layer in both models (infiltration and/or radon
control). This would include higher water permeability (lower gas-entry pressure), and perhaps lower moisture content. However,
if engineered a bio-intrusion layer is included in the design above the radon barrier, then such a need in the radon model would be
mute.
4. Frost Heave Effects / Implications -1 don't recall if this was covered yesterday. If not, this phenomenon needs to be
addressed, including either design and construction to prevent it, or modeling to show that even if it happens, that the infiltration
and radon barrier models still work for their respective purposes.
If we need to discuss this further, I will be back in the office on Tuesday. If we need to re-convene the group, we can do that too,
just let me know.
Thanks,
Loren