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G~~t /c gam! GeoScience Services l/ n, tfi 11631thigsron Road ~~~~~ GrandJund~on,C081503 (970) 311-3356 MAR 1 6 20Q7 "~ GRAND JUNCTION FlELO OFFICE Date: Mazch 12, 2007 DIVISION OF RECLAMATION MINING & SAFETY ~/ To: Colorado Department of Minerals and Geology (DMG), Grand Junction Office ..~' Re: Update on the installation of a monitoringwell at the JD-9 mice s-ter f'1-Ig77~3o6 This letter provides technical information regarding the installation of a monitoring well's at the JD-9 mine site as requested by the Colorado Department of Minerals and Geology (DMG). The intent of the monitor well is to intersect perched groundwater in the upper sandstone unit of the Salt Wash Member of the Morrison Formation downgradient from the JD-9 mine. Groundwater in the mine provides a potential pathway for the movement of chemical species of concern. The monitoring well will provide water-level measurements for detennining groundwater flow directions and rates plus water samples for delineating background water quality and mining impacts to the environment. Drilling began on the 21 ~` of December at a location downgradient from the mine to a depth of 250 ft below ground level (BGL). Landslide deposits were encountered from land surface to a depth of 33 feet where bedrock was located. At this depth, drill cuttings were moist and the borehole made small amounts of water indicating that groundwater occurs at the landslide/bedmck contact. Water moves in the unconsolidated landslide deposits and the bedrock acts as an aquitazd restricting downwazd movement. The upper sandstone unit was encountered at a depth of 153 ft ($GL) to 243 $ where a dark-gray mudstone was encountered. This 90 ft-thick sandstone showed mineral alterations at several intervals and is consistent with the sandstone being Honed in JD-9, hence the target zone for the monitoring well. Since the purpose of the monitoring well was to determine the impact of mining on the water quality of the perched groundwater located in the upper Salt Wash sandstone unit, it is important to isolate groundwater in the landslide deposits and prevent potential dilution of bedrock groundwater samples. Consequently, it was decided to offset the first boring, drill an additional boring, and install surface casing through the landslide deposit to the bedrock in order to prevent possible cross contamination.and ensure-the overall integrity of the monitoring well. The second boring was drilled to a depth of 240 feet with 6-inch PVC surface casing extending from land surface to a depth of 40 feet. Two-inch well casing was installed to a depth of 238 ft with the bottom 30 feet (208 to 238 ft) screened with 0.020-inch slotted well screened. The screened interval is located at the base of the upper Salt Wash sandstone unit and will provide water quality information for this unit. A sand pack was installed to a depth of 205 feet or three feet above the top of the well screen. To prevent possible cross contamination from groundwater in the overlying landslide deposits, 12 feet of bentonite pellets were placed on the sand pack. Drill cuttings were used to fill the remainder of the annular space of the well to a depth of three feet and then cemented to the surface. RECE14`LD MAR 12 ~'uU7 Division of Reclamation, Mining and Safety