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21 <br />Schwartzwalder Mine -Hydrologic Evaluation of Mine Closure and Reclamation <br />Table 11. Completion Data for Alluvial Monitoring Wells <br /> <br /> <br />Well <br />ID <br /> <br />Completion <br />Date <br />Total <br />Depth <br /> <br />(ft) <br />Depth to <br />Bedrock <br /> <br />(ft) <br /> <br />Well <br />Construction Screened <br /> <br />Interval <br />(ft) Completion <br />De th to <br />Water <br /> <br />ft <br />MW00 11/4/98 27.3 25 4"PVC 16.9 - 26.9 10.25 <br />MW 1 11/12/81 25.5 23 2 1/2"PVC 17 - 22 7 <br />MW2 11/12/81 15.4 21 2 1/2" PVC 8.4 - 13.4 10 <br />MW3A 6/19/89 14 Not Penetrated 4" PVC 8.6 - 13.6 10.0 <br />MW4 6/16/89 38.9 36.3 2"PVC 25.9 - 35.9 31.4 <br />MWSR 1/19/99 20 17 4" PVC 9.5 - 19.5 15.5 <br />MW6 6/20/89 15 13 2" PVC 5 -15 40 <br />3 <br />5 <br />MW7 6/20/89 11 8 2" PVC <br />" 5 -10 <br />7 - 12 . <br />Dry <br />MW8 12/8/90 12 10 PVC <br />4 <br />" 19 <br />9 10 <br />MW9 1/19/99 19.2 16 PVC <br />6 - <br />4.2.1 Thickness and Extent of the Alluvium <br />Alluvium along Ralston Creek ranges from 5 to over 30 feet thick in the vicinity of the mine. In general, <br />the alluvium is confined to the valley floor along Ralston Creek and pinches out at the eastern edge of <br />Section 25, near the property boundary, where a natural constriction in the valley occurs (Figure 4). This <br />"choke point" in the alluvium occurs where the valley narrows and its walls rise steeply from the creek bed. <br />Bedrock is exposed along the width of the valley floor and groundwater previously flowing in the alluvium <br />is forced to the surface where it enters Ralston Creek. Alluvium thickens again downstream from the <br />choke point. Monitoring Well MW8 which is installed in the alluvium on the downstream side of the <br />choke point has always been dry. <br />Alluvial monitoring well MW4 is also frequently dry as a result of its distal location on the southwestern <br />fringe of the alluvial system. <br />4.2.2 Alluvial Permeability Tests <br />Hydraulic conductivity data for alluvium are available from single well permeability tests (Geo-Hydro <br />Consultants, 1982), laboratory permeability tests (Geo-Hydro Consultants, 1982), and a 72 hour pumping <br />test performed in 1999 in monitoring well MW9 (Appendix D). <br />Geo-Hydro performed falling head (MW 1) and rising head (MW2. MW3) permeability tests to characterize <br />the hydraulic conductivity of alluvium adjacent to Ralston Creek. The results (Table 12) varied from 2.8 x <br />10"4 cm/sec to 1.7 x 10"2 cm/sec, with an average value of 1.1 x 10_z cm/sec (28.6 ft/day) and a geometric <br />mean of 3.96 x 10"3 cm/sec (11.2 ft/day). Laboratory testing indicated lower permeabilities than field <br />testing, which is typical because the laboratory samples contained only the smaller grain size particles, <br />rather than the complete distribution of particles in the sandy gravel. <br /> Table 12. Summary of Single Well Permeability Tests in Alluvium <br /> Total ~ Field Hydraulic Hydraulic <br />Monitoring :Installation depth of ;Perforated Permeability Conductivity ~ Conductivity <br />Well Date PVC Interval Test Method I <br />s ft/d <br /> <br />(ft) <br />(ft) ec <br />cm <br />/ a <br />MW 1 ~ <br />11/12/1981 <br />: 24.0 ~ 17.0 - 22.0 ~ Falling Head 2.80E 04_ Y___ _~ 79 ._ <br />MW2 _ <br />_. <br />~ <br />11/12/1981 15.4 8.4 - 13.4 ~ Constant Head ~.___ <br />_ _ 1.70E-02 ~ 8.19 _. <br />4 <br />MW3 _ <br />=~ 11/13/1981 ~ 14.6 8.6 -13.6 Constant Head 1 8 <br />3 <br /> E-02 <br />1.0 6 <br />8 <br />Mean 3.96E-03 11.2 <br />Geometric Mean <br />Whetstone Associates <br />4109B.071116 <br />