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Post Grout Crimp Elevations remaining are <br />32.94' 424.21' 819.49' <br />97.53' 490.09' 885.10' <br />163.53' 556.01' 950.07 - <br />229.6' 622.05' 1000.00' Short in cable <br />295.14' 687.69' <br />359.85' 753.56' <br />A reading taken on July 1, 2004 showed the crimp elevations to he the same as the June 17, 2004 readings. A slight change <br />in the waveform was detected between the Pre Grout and Post Gmut readings taken on June 17, 2004. The waveform did not <br />vary between the Post Grout reading on June 17, 2004 and the Post Grout reading on July 1, 2004. The elevations remained <br />the same in al{ readings. <br />The readings on September 2, 2004 show the crimp elevations are the same but the Waveforms are reduced by as much as <br />.OS units at the 950.07' elevation with a lesser reduction at each ascending elevation up to elevation 295.14' where the <br />Waveforms match the previous readings. <br />The instrument used to read the TDR cable was calibrated and a diode was replaced prior to the December 16, 2004 <br />readings. This change in the instmment might explain the drift in the Waveform readings of earlier tests. The December 16, <br />2004 readings show the same crimp elevations as all eadier readings but the Waveforms less than .01 between elevation <br />950.07' and 32.94' where alt of the eadier readings had shown a nonlinear increase of approximately .08 units from elevation <br />950.07' to 32.94' for the June 17 and July 1, 2004 tests and approximately .13 units for the September 2, 2004 test. <br />If the next quarterly readings of the TDR cable duplicate the Waveforms of the December 16, 2004 readings that should <br />confirm that the Waveform variations were from a weakening diode in the instrument. <br />The TDR data gathered on March 9, 2005 is basically idermcal to the data from December 16, 2004. There are no indications <br />of ground movement at well 20-12. <br />Since many of the wells in the lower well field including well 20.12 have been plugged American Soda has reclaimed the <br />surface area on and around the plugged wells. Gamba and Associates has surveyed points around well 20-12 to establish <br />new surface elevations. These measurements have been compared to aerial surveys of this site and the findings are that <br />within the accuracy of the aerials which is plus or minus 1 fooCand the elevation difference of any given location was less than <br />0.6 ft., there is no indication of surface subsidence. The newly established ground elevations will be used for comparison with <br />future measurements for subsidence monitoring. <br />Attached with this letter are the folbwino documents: <br />Graphs of TDR Cable readings for Well 20-12 from 6-17- 04, 7.01-04, 9-02-04,12-16-04 and 3-09-05. <br />Agapito Associates Inc. March 11, 2005 communication verifying March 9, 2005 TDR Readings on Well 20-12. <br />Gamba & Associates April 7, 2005 communication verifying the accuracy of the field survey of surface elevations around Well - . __ <br />20-12. <br />Gamba S Associates Apri17, 2005 communication identifying the Excel spread sheet showing three general areas of surface <br />measurements around Well 20-12. <br />Spread sheet showing elevation readings from Areas 1, 2, and 3 at Well 20-12. <br />Should you have any questions or require more information concerning this matter please contact me at 970-285 -0407. <br />Sincerely, <br />Gn ~ i~ <br />E~o ey ' ~ <br />Environmental Health and Safety Manager <br />cc: Kent Walter/BLM <br />Erica Crosby/CDMG <br />