C153705 Feasibility Study - Laserfiche WebLink

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I I I I I I I I I I I I I I I I I I I ~'0 -r Beaver Reservoir Company Attention: Mr. Neil Thompson February 4, 1993 Page 9 Bedrock at the ground surface was observed to be moderately jointed with the joints having strikes of approximately N50W and N50E with both sets dipping very steep to near vertical. The joints were primarily observed within the harder sandstone outcrops. Subsurface faulting has been indicated in the immediate project vicinity on regional geologic maps (Ellis et aI. 1987). This map indicates an inferred fault trending approximately north-south along the trend of the creek along with two. additional faults in the left abutment area. These faults are noted as representing offset at depth of the Rollins Formation, the lowest member in the Mesaverde Formation, interpreted from test hole information, mine workings, and outcrop data. Permeability tests were completed in the test holes, during both the investigation by Reclamation and the WCC investigation. These tests were completed to determine the mass permeability of the rock. Several zones 'within the test' holes could not be tested as it was not possible to properly seat the packers. TIlls probably is the result of washing and eroding of the test hole waIls in areas of soft bedrock. Analysis of the permeability test data indicates that the permeability coefficient (K) is general on the order of 1 x lO.3 and 1 x 10" cm/sec with a few zones indicating (K) as low as 1 x lO.5 and 1 x 10-6 cm/sec. The values of 1 x lO.3andl x lQ-4 cm/sec indicate that sections of the foundation rocks have permeabilitiessimilar to clean fme sand to silty sand. Permeability results are summarized in Table 2. At the time of this fuvestigation, the reservoir had been drained and no water was being impounded. .With-no impoundment of reservoir water there was no observed seepage downstream ofthe.dam structure. We contacted the State Engfueer's office (Norfleet 1992) and they fudicated that when the reservoir is impoundfug water, seepage is observed downstream of the dam on the left and right abutments. On the left abutment area seepage is heard beneath the surface riprap a short distance above the break fu slope at an estimated elevatiOli'of approximately 8060 feet. This location corresponds with the western end of geophysical line I50N. Mr. Norfleet fudicated seepage is heard at this location when the reservoir level reaches a gage height of 51 to 52 or elevation 8071 to 8072 feet. Gage level zero is equal to the fuvert of the upstream end of the outlet pipe. Seepage is described as occurring at several locations along the right abutment along the steeper slopes. The most upstream seepage was described by Mr. Norfleet as occurring in the vicinity of a grove of trees about midway down the flatter downstream portion of the dam embankment at approximate elevation 8022 feet. This location corresponds with the east end of geophysical line 2ooN. Additional seepage occurs downstream along the right 23067!LEIO 02.04.93(4:24pm)/RPT