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Suggested Method to Calculate NPLs and EWIs for Approval of TR-004: <br />The Division suggests use of the 15-month baseline data set and the Dixon calculation to <br />determine the cutoff concentration for what would or would not be an outlier, and <br />establish the EWIs and NPLs at that cutoff concentration for the pazameters selected for <br />on-going monitoring. <br />2. American Soda has been collecting BTEX samples in the production lines during the <br />active solution mining operations. The Division concurs that BTEX can be eliminated <br />from the monitoring program during the interim operating status. However, once <br />American Soda resumes commercial production BTEX sampling should be resumed on <br />the production lines. <br />3. American Soda proposes to remove Barium from the list of parameters monitored. <br />Barium has exceeded the NPL and EWI on a number ofwells (21-3U, 29-3, and 19-2). <br />Please further explain the reasoning to eliminate Barium from the monitoring program. <br />Upon review of the data, there appeazs to be some sort of trend between baseline and <br />production values (in Wells 21-3d, 19-2, 21-4b). <br />Please be advised that Division's decision due date is set for October 18, 2004. If you feel more <br />time is needed to complete your reply, the Division can grant an extension to the decision date. <br />This will be done upon receipt of a written waiver of your right to a decision by October 18, <br />2004 and request for additional time. This must be received no later than the deadline date. If <br />you have any questions, please contact me at (303) 866-4943. <br />S ~ cere y, /~~/~/~ <br />nca . Cro(J/sby" " " <br />Environmental Protection S cialist <br />cc: ~Cayl Mount; DMG <br />len Sorenson; DMG <br />