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J&T Consulting, Inc. ? <br />c?ba, qj 'VO <br />November 30, 2007 <br /> <br /> <br />Mr. David Bird <br />Environmental Protection Specialist, Senior Geochemist <br />State of Colorado <br />Division of Reclamation, Mining, & Safety <br />1313 Sherman Street - Room 215 <br />Denver, CO 80203 <br />&Np <br />RiECIFrveo <br />DEC 0 3 2007 <br />Division or Kec,amarion, <br />dining and Safety <br />RE. Northern Colorado Constructors, Inc. - NCCI Pit #1, 112(c) Amendment Application - <br />Permit No. M-2001-107 Weld County- Adequacy Review 01 Response <br />Dear Mr. Bird, <br />We have received the Division's Adequacy Review 01 request for additional information relating <br />to Northern Colorado Constructors amendment application for permit number M-2001-107. <br />NCCI offers the following additional information addressing the Division's questions and <br />requests. <br />Rule 3.1.6 Water - General requirements <br />1) Permanent impoundments have the potential to affect regional ground water quality through <br />evapoconcentration. Although the reservoir will be lined, the specifications detailed in the State Engineer <br />Guidelines for Lining Criteria for Gravel Pits (0.03 filday/f? for the perimeter wall and 0.0015 filday/ft2 <br />for the bottom) still allow for the potential of steady-state through flow, in the range of tens to hundreds of <br />gallons per minute. Please provide an estimated post-mining water balance (surface and ground water <br />inflow/outflow and evaporation) that the Division can use to assess the potential for evapoconcentration. <br />The water balance that will occur during post-mining conditions for the approximately 2,300 <br />acre-foot reservoir has been estimated for the 3 steady state cases shown below. Please <br />reference the attached calculations for details on the assumptions used for reservoir perimeter <br />length, average reservoir depth, reservoir water surface area, groundwater inflow/outflow <br />rates, precipitation rates, and evaporation rates, and the methodology used to determine the <br />water balance conditions. <br />Case 1 - Unlined water storage reservoir with no surface diversions other than <br />precipitation and evaporation. <br />The approximate water balance for an unlined water storage reservoir was found to be the <br />following: <br />• Groundwater inflow: 123,543 gpm <br />• Groundwater outflow: 123,383 gpm <br />• Precipitation: 70 gpm <br />• Evaporation: 230 gpm <br />2 1400 W 122nd Avenue - Suite 120 • Westminster CO 80234 • Ph: 303-457-0735 • Fax: 303-920-0343