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Corey Hoffmann <br />November 1Q, 2005 <br />Page 2 <br />• Black Hawk augmentation and exchange points, Case Nos. 92CW059 & 94CW036, at the <br />location of the W WTP effluent discharge. <br />Thomas Schreiner's September 7, 2005 3`d Adequacy Review Comments 6.4.13 Exhibit M -Other <br />Permits and Licenses provides the applicant the following alternative ways to protect senior water rights <br />when ground water is encountered in the proposed quarry. <br />1) Obtain prior approval from the State Engineer's Office to deplete the aquifer, or <br />2) Cover the exposed ground water with at least two feet of backfill within 24 hours. <br />Option 1 is acceptable because the State Engineer would require a we]] permit. This action would require <br />a Temporary Substitute Supply Plan and(or an augmentation plan [o prevent injury to senior water rights. <br />Option 2 is not acceptable as described below. <br />The applicant in its responses (October 24, 2005 letter to Tom Schreiner from Banks and Gesso and <br />October 24, 2005 letter to Tom Schreiner from Bjork Lindsey Little, PC) commit to the backfilling option <br />described above and would seek approval from the SEO only after ground water has been impacted. <br />The applicant's proposed approach, while apparently simple, has the following problems: <br />1) [t assumes that the quantity of ground water that will be encountered is very small. In our <br />opinion, the ground water inflow to the quarry will be too great to simply be covered by <br />backfill. We estimate that ground water may be encountered in all fractures below a <br />depth of 30 feet as shown on Cross Section A-A', Exhibit 15 (Lyman Henn, August 19, <br />2005 estimates a depth of 60 feet) and that the inflow will be about 16 acre-feet per year <br />(see above), <br />2) It assumes that the exposed ground water is as at atmospheric pressure. In reality, it is <br />more likely that ground water will be encountered in fractures at pressures greater than <br />atmospheric [n that case, backfill will have to be placed up to the potentiometric surface <br />of the fracture. This may mean that the entire quarry will need to be backfilled. <br />3) It assumes that injury is avoided if evaporation is eliminated. While the owner of a <br />senior water right (Black Hawk, Gilpin County, BHCCSD and others) is interested in <br />preventing an up gradient depletion caused by evaporation, he/she is also interested in <br />preserving the hydraulic connection between up gradient seepage and the water right. <br />Excavating a fractured aquifer will likely alter the flow path from the recharge area to the <br />discharge point. Depending upon [he density, orientation, and degree of interconnection <br />of the fractures, the impact of the altered flow path may significantly reduce the supply to <br />the senior water right regardless of whether or not two feet of fill is placed over the <br />exposed ground water. <br />4) It assumes that it is practical to place two or more feet of backfill over exposed ground <br />water. The only place where backfilling over exposed ground water is practical is where <br />ground water is encountered in the bottom of the quarry. It will not be practical to place <br />backfill on a water filled fracture encountered on the steep rock face of the quarry. <br />The problems with the second portion of the applicam's proposal are: <br />I) Impact to senior water rights occurs prior to the applicant obtaining a well permit. <br />LEONARD RICE ENGINEERS. INC. <br />