2010-12-17_REVISION - C1981019 (153)

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Groundwater 59 Water levels were monitored electronically in the pumping well and piezometers SP -1, SP -2, and SP -6 using Geokon 4500 pressure transducers and Geokon LC -1 data loggers. Data from VWP -1 through VWP -6, as well as battery condition and barometric pressure, were recorded on two Campbell Scientific multi - channel data loggers. Data from the data loggers were downloaded on a regular basis to a laptop computer for analysis. A GK 403 vibrating wire readout instrument was used to measure the pressure response in VWPC- 04 -17. The GK 403 is not a programmable data logger, therefore VWPC -04 -17 was visited periodically during the test. The GK 403 readout was used periodically throughout the test to double check the values obtained from the 18 VWPs connected to the data loggers. Manual water level measurements were made in the more distant wells and piezometers using electric water level sounders. Manual measurements were also taken at piezometers SP -1, SP -2, and SP -6 to double check the electronic systems. During both the pumping and recovery phases of the test, the frequency of water level measurements was adjusted to capture early data from the wells closest to the pumping wells. Hydrographs of all locations monitored during the pumping and recovery tests are provided in Appendix 5.H. The pumping phase of the pilot well test lasted approximately 35 days, from March 21 to April 25, 2005. Pumping started at 14 to 15 gpm, but was decreased steadily over the course of the test to keep the water level above the pump inlet. The pumping rate at the end of the test was approximately 11.5 gpm. Pumping rates were kept as constant as possible throughout the test. The only interruptions occurred during brief maintenance periods for the generator on March 31 and April 12. Figure 5.10 shows water levels in the pumping well relative to the pumping inlet and base elevations of the principal units of the Williams Fork Formation, as well as the pumping rate (instantaneous and average). On April 25th, the pump was turned off and the recovery phase started. The recovery was monitored until May 18, at which point, water levels in the pumping well had recovered to 84 percent of the static level. Water levels in the pumping well dropped in a step -wise manner. Water levels remained relatively constant or declined slowly within a major water producing unit until the drawdown in the well reached the bottom of the unit, whereupon the water level dropped more rapidly to the next major water producing unit (Figure 5.10). From the start of the test until April 3, the water level was mostly in the Fab coal. On April 4, the water level dropped suddenly to the bottom of the G7 /G8 /G9 coal sequence. After April 6, the water level dropped into the Gb coal. From then until the end of the test, the water level varied between the G9, Ga, and Gb coals, as the pumping rate was adjusted to maintain the water level above the transducer located at of 6,715 ft amsl. 2572 -R2 Colowyo Coal Company Water Management Consultants