2005-03-01_REVISION - M1978314 - Laserfiche WebLink

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Erica Crosby Division of Minerals and Geology March 1, 2005 Page 2 of 5 application (see attached seed mix copy). If additional seeding is necessary, the seed mix approved in this conversion application will be used. 7) Surface Water: In response to your concern about surface water drainage, we requested that an engineer estimate runoff volumes for the area that would naturally drain into the pit. By studying the surrounding drainage patterns, he determined that the amount of runoff likely to enter the pit is very small, even during large storm events, and that the potential for ponding in the pit is very low. The engineer also found that breaching of the pit wall would be virtually impossible (see attached memo from Ramsay M. McDermid, P.E. to Banks and Gesso, LLC, dated February 21, 2005.) Secondly, we have researched the issue as to whether the Division of Water Resources (DWR) requires an augmentation plan or water court decree when stormwater is retained for a period exceeding 72 hours. According to our research, there are no water rights issues when a retention basin is always dry within 72 hours of a storm event, and infiltration is an acceptable manner of ground water recharge if a basin has no outlet. If the basin is not always dry within 72 hours, the DWR may require further analysis, but augmentation is not definitively required. It is our opinion, based on the operator's experience and engineering analysis of surface water runoff potential, that it is highly unlikely that the site will retain surface water for periods exceeding 72 hours, both during mining and after reclamation is complete. Rule 6.4.7 Exhibit G -Water Information 8) Monitor Well Elevations: The locations and elevations of the 5 monitor wells have recently been re-surveyed and tied to local benchmarks. The previous survey was apparently done using an un- calibrated GPS, resulting in a large vertical margin of error. The revised survey data is as follows: Survey Point Surveyed Elevation (ft) GW Elevation (ft) (measured on Jan. 28, 2005) Measured GW depth below ground surface (ft) Well Depth (ft below ground surface) Difference between survey and USGS contours ft MW #1 8657.0 8611.8 45.2 60 +1.7 MW #2 8548.5 8548.3 .2 19.5 -6.4 MW #3 8601.4 8565.7 35.7 43.5 +1.4 MW #4 8536.6 8525.4 11.2 26.8 -9.5 MW #5 8574.2 D < 8529.2 45+ 45.0 +13.9 Pit Floor 8572.1 Dry N/A S rin 8462.0 8462.0 0 N/A -7.0 The existing pit floor was also surveyed, and the lowest point was found to be at 8572 feet elevation. Please refer to the newly-created Exhibit G: Ground Water Information for locations of the monitor wells and ground water table contours based on recent measurements. You will note on Exhibit G that there is still some discrepancy between the surveyed well elevations and the topographic contours. The elevation of wells 1 and 3, which are located on relatively flat ground, are within 2 feet of the contour elevations. Wells 2, 4, and 5 are off by 6, 9 and 14 feet, respectively. We believe these discrepancies are the result of interpolation of the USGS 40 foot contours, and that interpolation errors are more pronounced on steeper (predominately non-mined) areas.