Laserfiche WebLink
Accordingly, the shallow alluvial aquifer is "connected" to the bedrock aquifer in a <br />• unidirectional way: water flows from the riparian area to the shallow alluvial aquifer, and <br />from the shallow alluvial aquifer to the bedrock. Flow cannot occur in the reverse direction, <br />because the water level in the alluvial aquifer is always below the root zone of the riparian <br />area, and the water level in the bedrock is always (far) below the elevation of the base of the <br />alluvium in Grassy Valley. <br />This geohydrology of the Grassy Valley riparian areas leads to the following conclusions with <br />respect to the potential for mining impact in the general vicinity on the vegetation in the <br />riparian areas: <br />1. Mining in bedrock adjacent to the riparian areas cannot change the rate of outflow of <br />water from the alluvium in the riparian areas of Grassy Valley. <br />2. Encroachment of mining onto the northern flanks of Grassy Valley cannot impact the <br />riparian vegetation because there is no runoff from these flanks, and any precipitation <br />that infiltrates into the hillside colluvium infiltrates into the underlying (unsaturated) <br />bedrock and does not report to Grassy Creek. <br />CC&V conducted a well drau*71)n pump test by pumping the shallow aquifer at GVMW- <br />15B and monitoring the resulting head changes in ?dells completed in the surrounding <br />bedrock. The test was run for a total of 329 minutes before being terminated due to the <br />• discovery of a problem with the deep well in the test array. The results of the test are <br />presented in Figure 6 included as Attachment 8. The significant response was that well <br />GVMW-12A responded slightly to the test. The test indicated the following: <br />1. There was an apparent significant hydraulic connection between the upper portion of <br />the bedrock (GVMW-15B) and the bedrock approximately 600 feet beneath (GVMW- <br />15A). This was later found to be due to faulty installation of the well casing in <br />GVMW-15A, and is therefore discounted. <br />2. There was an apparent response of 0.10 feet in GVMW-12A due to pumping GVMW- <br />15B at 4.29 gpm. GVMW-12A is located approximately 680 feet to the northwest of <br />the pumping well. The static water elevation in GVMW-12A is approximately 150 <br />feet lower than the static water level in GVMW-15B, so if this slight response is <br />caused by the pumping, it must be due to interception of infiltrating ground water by <br />GVMW-15B, consistent with the above discussion of Grassy Valley geohydrology. <br />3. There was apparently no response in GVMW-04A, located about 590 feet to the <br />northeast of GVMW-15B. This result supports that the rock structure in this area is <br />parallel to Grassy Valley, and that the hydraulic conductivity is higher in the <br />northwest-southeast direction than in the northeast-southwest direction. <br />0, 4. The computed hydraulic conductivity of the Precambrian rock in GVMW-12B was 2 x <br />10-4 cm/sec. This is a relatively high conductivity for granite, and may be due to a <br />high degree of fracturing of near-surface rock, or disturbed rock close to the alignment <br />of Grassy Creek, which may be a disturbed geologic zone. <br />?1