Laserfiche WebLink
CG <br />December 14, 2009 <br />Mr. Michael Cunningham <br />Division of Reclamation, Mining and Safety <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />RE: Varra Heintzelman Project <br />Response to Division Letter <br />DRMS File No. M-2009-018 <br />CGRS No. 1-135-10807ab <br />Dear Mr. Cunningham: <br />ENVIRONMENTAL 09G°QW0@9@ <br />This letter addresses your comments presented in our letter of December 2, <br />2009, to Mr. Brad Janes regarding dewatering operations at the proposed mine <br />site referenced above. <br />Item 1 - We concur that baseline data should be obtained prior to commencing <br />dewatering activities to verify the dewatering analysis. Varra Companies has <br />collected 1 month of data from wells adjacent to the proposed mining operations. <br />Our firm has conducted groundwater investigation within the mine area since <br />2000 and is familiar with local groundwater hydrology. However, once <br />dewatering commences it will be difficult to determine the effects of seasonal <br />fluctuations compared to the induced drawdown. We recommend collecting <br />monthly data from this point forward which will provide an adequate baseline for <br />determining the influence of dewatering operations. As such we propose that <br />the 5 quarters of water level data be waived in lieu of proposed monthly data. <br />Item 2 - It is our opinion that assigning a drawdown at a specified point as the <br />trigger for mitigation may not be the best technical or practical approach prior to <br />assessing the validity of the groundwater model. As dewatering occurs and data <br />are collected they will be compared to model predictions and decisions made <br />from data comparisons. Transient model simulations will compare predicted <br />heads to measured heads at early times in the mine life - these data will be used <br />as a calibration tool if required. We then recommend that the model predictions <br />be used to determine what if any mitigation will be required - this can be <br />accomplished many months in advance of any adverse effect. Other influences <br />such as domestic well use, irrigation returns and ditch seepage should be taken <br />into account when assessing mine dewatering operations. <br />P.O. Box 1489 Fort Collins, CO 80522 T 800-288-2657 F 970-493-7986 <br />www.cgrs.com