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MEMORANDUM At Adrian Brown elevation of the post-drainage water table (the top of the zone where there is positive water pressure) is presented in Plate 12. 4. The water levels in southeastern Grassy Valley are elevated today.The water table at GVMW-24 is at elevation 9,780 ft amsl, some 30 feet higher than the Grassy Valley overflow point located approximately 2000 feet to the northeast(Plate 12).This well indicates that there is some potential for groundwater in this segment to discharge into Grassy Valley and flow in the alluvium or on the surface to Beaver Creek. Note that at this location,the water level is approximately 131 feet below ground surface(in Well GVMW-24A-250), and the (pumping) hydraulic conductivity of that well is 4x10.8 cm/sec, which limits deep vertical infiltration. Well GVMW-246-100 is a shallower well at this location, is dry, and has an (injection) hydraulic conductivity of 3.5x10-4 cm/sec, four orders of magnitude higher than the deeper well. This assemblage essentially prevents vertical flow, and infiltration is diverted laterally, likely both to the west and to the east,as GVMW-24 is located in a groundwater "saddle"with heads reducing to both the east and the west,while increasing to both the north and the south.The low permeability at depth explains the high water table, and results in the surface infiltration being diverted. It is unlikely that the water level and the water infiltration in this area have been affected by the drainage tunnels.The elevated head at GVMW-24 demonstrates that there is groundwater flow to the east out of Grassy Valley into Beaver Creek, from the 106 acre area shown double hatched in Plate 12. 5. There are also a number of locations within the diatreme where there are shallow wells which currently exhibit water levels at or close to the ground surface.These water levels are considered to be representative of generally perched conditions in shallow, low permeability cover materials, particularly in the eastern overflow apron. Generally these wells are paired with deeper wells or piezometers, which currently show a much deeper current water table, which is used in this study. In particular, VIN-02-140 in the southern part of the diatreme shows a water level of 9,981 ft amsl, yet it is located almost directly over the Carlton Tunnel 3,000 feet below, in which the water level is 6,985 ft amsl, some 3,000 feet lower.This water level is clearly perched, and is not used to develop the post-mining contours presented in Plate 12. 6. The hydrologic information has been assembled to create a post-drainage piezometric surface for the diatreme and the surrounding Precambrian rockmass,which is presented in Plate 12. When compared with the pre-mining piezometric surface, it is observed that there is a 0.81 square mile (516 acre) area on the eastern fringe of the Eastern Overflow Apron of the diatreme in which there has been no observable change in head due to the long-term drainage of the diatreme by the drainage tunnels.This condition is the result of a combination of the rapid thinning of the diatremal material to the east(Plate 2), and a significant reduction in the hydraulic conductivity(permeability) of the diatremal material in this area due to its emplacement as an overflow deposit(ABC, 2015). In this area the direction of flow of infiltration is unchanged by post-mining drainage, both for water which flowed—and flows—east and for water that flowed—and flows—west. 7. This unaffected area includes the Grassy Valley capture zone(double hatched area),with the result that there has more probably than not been no change in the groundwater flow to Grassy Creek from the diatreme as a result of the diatremal drainage. Page 8 Adrian Brown Consultants, Inc. 130 W.4th Ave., Denver CO 80223 303-698-9080 www.abch2o.com