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NF-03, indicates that clay or clay-shale strata in the immediate roof and floor are present <br />only at NF-02 in the floor strata. Recent core sampling from twin holes at the three sites <br />confirmed that the immediate roof and floor at the NF-Ol and NF-03 sites consists of <br />stable strata including sandy mudstone, siltstone, and sandstone. <br />Northfield commits to sampling for and presentation of engineering properties as <br />appropriate during construction of the mine, prior to coal extraction. Northfield <br />understands the importance of the information for a safe and stable underground mine. <br />Permit text on page 2.04-14 is revised to reference the commitment to obtain engineering <br />properties data. <br />Item 12 (BB): The DRMS requested pumping test data referenced in our report, which <br />support low hydraulic conductivity values in sandstone units of the Vermejo Formation. <br />The pumping test data referenced aze based on reported test data from residential water <br />supply wells in well driller and pump installation reports. These test data aze informal but <br />specific capacities determined from these test data provide an indication of the low <br />aquifer transmissivity and hydraulic conductivity of these formations. The table below <br />presents a summazy of representative well data, including specific capacity values. The <br />average specific capacity value from these wells is 0.006. Based on an industry standazd <br />rule-of--thumb methodology of multiplying the specific capacity in a confined system by a <br />factor of 2000, the estimated transmissivity of the formation material is 12 gpd/ft. <br />Assuming a conservative low saturated thickness value of 50 feet, the estimated hydraulic <br />conductivity value is 0.024 gpd/ ftz. This value is low and is in line with values of tight <br />silt and cemented sandstone. For the purposes of comparison, we note that the hydraulic <br />conductivity of productive aquifer sands is on the order of 1000 to 5000 gpd/ftz, or four <br />orders of magnitude higher than the estimated hydraulic conductivity of the formation <br />material. <br />Permit <br />No. Pumping <br />Rate <br />( m) Static Water <br />Level (ft) Pumping <br />Water Level <br />(ft) Drawdown <br />(ft) Specific capacity <br />(gpm/ft of <br />drawdown) <br />248244 1 380 540 160 0.006 <br />243372 1 357 460 103 0.010 <br />248451 1 303 460 157 0.006 <br />248242 5 370 510 140 0.007 <br />222887 1 305 600 295 0.003 <br />Because of the low hydraulic conductivity values, and because the mining operations will <br />not introduce contaminants into the formation there will be little to no potential for water <br />quality changes to occur in the bedrock formations. The minimal changes in water <br />quantity (ground water levels) that have potential to occur are addressed in our April 25, <br />2007 letter report. <br />Item 13 (BB): The DRMS noted that some of the information presented in our well <br />inventory did not include information now available in the State Engineer's Office well <br />records, which was not available at the time we prepared our April 25, 2007 letter report. <br />402 Valley Rd, Suite G, Canon City, CO 81212 %0 81212 <br />asnan.net <br />Phone: 719-275-8951 • Cell: 719-429-8950 <br />