Groundwater concentration limits

[Devane Clarke <DCLARKE@smtpgate.tnrcc.state.tx.us>]

Greetings:

I am looking for guidance/advice on setting
concentration limits for natural uranium,
thorium-230, and molybdenum in groundwater
near 11e(2) tailings impoundments. 
Background values in the uppermost aquifer
were not adequately determined prior to
construction.  I am particularly interested
in learning:

1.  What concentration values have been
used at other impoundments in the past.

2.  Would it be appropriate to use
"default" values (eg. EPA drinking water
standards, or perhaps, 10 CFR 20 effluent
concentrations).

Best regards and thank you in advance. 
Please reply directly to
dclarke@smtpgate.tnrcc.state.tx.us