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WATER 0 EnVIROt1MCATAI IYfTEMI TECHnOIOGY, U1C. <br />Catherine Kraeger-Rovey, Ph.D., P.E. Ed Rovey, P.E. <br />(303)480-1579 (303)433-9125 <br />MEMORANDUM <br />TO: Connie Davis i fj <br />FROM: Catherine Kraeger-Rovey <br />DATE: May 15, 2015 <br />SUBJECT: Monitoring plan for water level monitoring - east Hazeltine Mine, Permit No. M- <br />2004-031 <br />This memo puts into writing some of the ideas you and I discussed about a monitoring plan for <br />the high water areas between the east slurry wall of the Hazeltine Mine and the Fulton Ditch. <br />I recommend that monitoring stations 3, 4, and 5 not be included in the temporary, and also the <br />permanent, monitoring plans. The detailed cross-section of the lined Fulton Ditch shows that the <br />ditch operates as a hydraulic barrier much of the time. Whether or not the ditch is flowing, <br />ground water at the east bank of the ditch cannot be higher than the level in the ditch and <br />adjacent lateral drains. When the ditch is flowing, ground water levels below the ditch are <br />maintained between the levels of the lateral drains and the drains below the ditch channel invert <br />under most conditions. If the ditch is dry and ground water levels fall below the sub -invert <br />drains, water level measurements from monitoring stations 6 and 11 will provide sufficient <br />information about ground water levels between the ditch and slurry wall. <br />Also, wells 3, 4, and 5 are sufficiently distant from the slurry wall that, even without the <br />presence of the Fulton Ditch acting as a hydraulic barrier, the data from these up -gradient wells <br />is not sufficiently useful to warrant maintaining and monitoring them. <br />Monitor well 1 is intact, fully operational, is currently being accessed for water level <br />measurements, and can be accessed to measure water levels at monthly intervals for both the <br />temporary and permanent monitoring plans. <br />Monitor well 2 is located on Aggregate Industries property between the slurry wall and the <br />Fulton Ditch property that lies between the mine and the Orr property. The aerial photo you sent <br />me, with monitoring station locations shown,. will be helpful for locating this well. When we <br />visited the site on April 30, it appeared that this area was inundated, and we did not see any sign <br />of this monitoring station. This monitoring station is near the site of the proposed drain that will <br />be used to lower the water levels outside the slurry- wall, including the Orr property. Periodic <br />readings (as needed based upon on-site observations) from a temporary staff gage following the <br />installation of the drain will be useful for determining the effectiveness of the drain. After the <br />initial period following the installation of the drain, monthly monitoring is recommended for this <br />station. <br />2914 W. 29th Ave. P.O. Sox 11216 Denver, Colorado 80211-0216 Fax (303) 480-1915 <br />