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INTEROFFICE MEMORANDUM TO: FROM: SUBJECT: R.A. Mills DATE: Yampa Valley Coal Co. October 21, 1986 J.G. Nalven ~~ _ ~~ ~~ YVCC - Aquifer Testing, Well 026-SP-2 On September 16, 1986, a pumping test was performed on Well 026- SP-2. The well was pumped for approximately 500 minutes at a constant rate of 99 gpm. The pump was set at approximately 54 feet below ground surface. Other than an initial water level for calibration purposes measured with an electric water level indicator, all water level measurements were made with a pressure transducer which measures to the nearest 0.01 feet with an accuracy of 0.03 feet. The pumping rate was measured with a 3 inch by 2 inch orifice. The estimated accuracy of the orifice was +/-2%. The maximum drawdown during the test was 0.62 feet. The water level recovered approximately 100% shortly after the end of the test. The data from the test on Well 026-SP-2 was analyzed to estimate aquifer properties. The data and results ire presented in Appendix A. The test data indicates that the aquifer is unconfined (water table) and that the transmissivity is approximately 33,000 gallons/day/foot and the permeability is approximately 2200 gallons/day/square foot (gpd/ft ). This is approximately 100 times the permeability measured in Well 008-SP- 5 at Mine 3. Due to the very small drawdown the permeability is estimated to be only accurate to +100% and -50°s. No barrier or recharge boundaries were detected in the test data, 'but the aquifer is believed to be bounded (of limited areal extent) by the limits of the spoils. The measured drawdowns were not corrected to the theoretical artesian drawdowns because the maximum correction was only 0.01 feet. The aquifer was assumed to be 15 feet thick under static water level conditions. This value is derived frm the well depth and the static water level. The actual aquifer thickness is larger; however, the bottom of the well is approximately 16 feet above the bottom of the aquifer. The specific yield could not be calculated because no observation well was available. However, the specific yield is estimated to be 0.15 (unitless). Summary and Recommendations: 1. The permeability of the spoils ir~ the vicinity of well 026- SP-2 is approximately 2200 gpd/ft +100°s, -50%. 2. The spoils behave as an unconfined aquifer.