2004-10-06_REVISION - M1999002

• Permit No: M1999002
• IBM Index Class Name: Revision
• Doc Date: 10/6/2004
• Doc Name: Review of the Proposed Ground Water Monitoring Plan
• From: DMG-acs
• To: DMG-esc
• Type & Sequence: TR4
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
1373 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
COLORADO
DIVISION O F
MIN ORALS
GEOLOGY
RECLA MAiION•MIN ING
SAFETV•SCIEN<E
Bll QWPns
Governor
DATE: October 6, 2004 Russell George
Executive Direaar
TO: Erica Crosby Ronald W. Cattany
Division Director
Natural Resource Trustee
FROM: Allen Sorenson
RE: Review of the Proposed Ground Water Monitoring Plan, American Soda, L.L.P., Yankee
Gulch Sodium Minerals Project, Technical Revision TR-004, Permit No. M-1999-002
In establishing the original Numeric Protection Levels (NPL) and Early Warning Indicators (EWI)
through technical revision TR-002, American Soda used the Dixon method to identify outliers at the
upper end of the data sets. If outliers were present, they were rejected and the NPL or EWI was
established at the highest detected level that was not an outlier (unless that highest detected level was
below a table value standard (TVS), in which case the TVS was selected as the NPL or EWI). This
practice has not been regulatorily effective; review of appendix B to TR-004 shows that numerous NPLs
and EWIs have been exceeded during the production period, even though there is little reason to think that
process water has contributed contaminants to the water being sampled. In other words, the natural
fluctuations in ground water chemistry result in concentrations of certain constituents that are higher than
the NPLs and EWIs for those constituents. DMG and American Soda must establish NPLs and EWIs in a
way that if exceeded, it will be a rather more clear indication of process water influence.
Suggested Method to Calculate NPLs and EWIs for Approval of TR-004:
Use the 15-month baseline data set and the Dixon calculation to determine the cutoff concentration is for
what would or would not be an outlier, and establish the EWIs and NPLs at that cutoff concentration for
the pazameters selected for on-going monitoring.
ca Carl Mount, DMG (via email)
c:~acs\LOANER MACHME\My Documentslam soda tr4.doc
Office of Office of Colorado
Mined Land Reclamation Active and Inactive Mines Geological Survey