2008-09-04_HYDROLOGY - M2007044 (2)

Home Browse Search

Page 2 September 2, 2008 Field notes, photographs, and global positioning system (GPS) coordinates were collected as needed at selected locations. A summary of key observations follows. Figures 1 and 2 show the locations of key observation and sampling points. Whirlwind Mine Workings A tour of the Whirlwind Mine workings provided a qualitative hydrological inspection of the main decline, the mine sump (under construction), and the exploration drift areas beyond the sump location at the bottom of the decline. Seepage into the mine workings was observed at four general locations: 1) Upper Decline, 2) Lower Decline, 3) Sump Area, and 4) Drift Area. It is important to note that seepage observed in the Sump and the Drift Areas may be due to storage of groundwater in surrounding rocks from the flooded decline and nearby workings while the mine was closed from 1982 to 2007. The long-term status of this seepage will require further evaluations. Upper Decline Seepage at the upper decline area is considered minor and is characterized by moist to wet deteriorated shale and road base materials on the floor of the decline, located approximately 200 ft from the portal. The moist to wet material was limited in extent and did not continue down the decline for more than approximately 40 ft. No channelized flow was observed on the decline floor. It is possible that this groundwater is related to infiltration from colluvium at the contact with bedrock (Brushy Basin Member). Lower Decline Seepage in the lower decline area is associated with a sandstone bed or lense that intercepts the decline at an elevation of approximately 6,940 ft. The sandstone unit is <5 ft thick and interpreted as a lower sandstone lense (channel sand) within the Jurassic age Brushy Basin Member of the Morrison Formation. Characteristic to the Brushy Basin, the channel sand is over and underlain by sequences of maroon-colored mudstone with light gray to green mottling. The point of highest elevation where seepage was observed is covered by timber supports on the right rib (Attachment A, Photo 1). Further down the decline the sandstone unit and contact with the lower mudstone is visible (Photo 2). Seepage in the decline at this sandstone intercept is somewhat diffuse and is only partially channelized on the decline floor along the right rib. Observed flow was estimated to be 1 to 2 gallons per minute (gpm). Several areas of point source flows were observed on the sandstone face, at the base of the sandstone, or near the contact with the underlying mudstone (Photo 3). These seepage points maintained a thin film of free water on the rock surfaces that resulted in drips in places, but no distinct running rills were observed. Measuring the combined flow from this area would be difficult using conventional techniques. With systematic operation, the sump pumping system being constructed (see below) will allow better quantification of discharge into the mine from surrounding water-bearing units. Sump Area During the mine visit, EFR was installing a French drain system on the decline floor, across the decline's floor just down structure of lower sandstone and along the right rib, to collect water from the lower sandstone seepage in the lower elevation of the decline (described above). The system consisted of a -3-inch perforated polyethylene pipe embedded in washed imported gravel (Photo 4). The French drain system is to be connected to a vertical, perforated corrugated metal pipe (CMP) system that will act as the main pumping sump in this area of the mine. The sump consists of two CMPs one inside the Weans090108.doc