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Exhibit 4e-3, Northern Mining District, AVF Subsidence Prediction, provides the cross-section for the Fish Creek <br />and its profile though the nursing area wvered by Panel 13 Right through 16 Right. This data was developed <br />• through an extensive survey of Fish Creek and its valley floor. As stated in the exhibit, approximately 2,000 cross <br />sections were generated through the mine azea. The longitudinal profile of the pertinent segment of Fish Creek is <br />presented in Exhibit 4e-3, Figure l . <br />During the summer of 1999, TCC enlisted the services of lames G. Nalven Consulting, to perform slug testing on <br />two alluvial wells in and adjacent to the mine area. The testing was done to determine the hydrologic characteristics <br />of the Fish Creek and Trout Creek alluvium. The results are presented in Exhibit 4e-6, Slug Testing of wells FI-1 <br />and 008-AT-1. In 1983 slug tests were preformed on two alluvial wells in the Fish Creek alluvium (Exhibit 4e-8). <br />The permeability ranged from 0.8 gpd/R'to 300 gpd/ftZand the transmissivity ranged from 7.8 to 1700 gpd/ft. These <br />values are typical for a poorly to moderately developed aquifer in silty to clean sands. <br />The data presented on Table 74, Summary of Water Depths in Alluvial Wells was used to develop the peizometric <br />surface maps presented on Figure 3i. As shown on the figure, the water elevation in the wells follows the same <br />seasonal pattern as exhibited by other alluvial wells in the area. <br />Aquifer Thickness/Aquifer Properties: <br />The thickness of the Fish Creek alluvium in the area to be flooded by subsidence by Panels 12 to 16 ranges from <br />approximately 10 to 14 feet thick. This is based upon drill hole data presented on cross-sections shown on Exhibit <br />4e-9, Fish Creek AVF cross-sections. These sections were prepared by P&M in 1983. The location of the cross- <br />section is shown in the map titled Location of Hydrologic Monitoring Stations, as prepared by P&M. The alluvium <br />upstream of this area can be thicker. th the deepest part of any cross-section of the alluvium, the saturated thickness <br />averages 3 to ]0 feet. The saturated thickness at any point can vary over the year an average of 4 feet due to the <br />• seasonal variation (see 1998 Annual Hydrology Report). Generally, the depth to groundwater is about 2 to 4 feet <br />below ground surface but ranges from at the surface during the spring and early summer of high run-0ff years to over <br />eight feet in the fall of low run-off years. <br />Tn the area to be flooded the Fish Creek alluvial valley averages approximately 1500 feet wide. It does narrow to <br />approximately 500 feet wide at the downstream end of the area to be flooded for approximately two-thirds of a mile <br />before widening again. <br />Based upon water levels measured in September 1983, the average longitudinal gradient of the alluvial aquifer was <br />0.4% (see Table 76). This is equivalent to the gradient of the stream. Tn general during periods of recharge to the <br />alluvium the lateral gradient is away from Fish Creek and during periods of discharge from the alluvium lateral <br />gradient aze towards Fish Creek. <br />Based upon drill logs and test pit logs, the saturated portion of the Fish Creek alluvium is primarily silty sand, sand, <br />and silty to clean sand and gravel. Porosity and specific yield were not measured, but based on the descriptions of <br />the material and the measured permeability the porosity should range from 25 to 50 percent of clean to silty sands <br />and gravels and the specific yield should range from 10 to 25 percent for silty sands to clean sands and gravels <br />(Todd, David Keith, 1960, "Ground Water Hydrology", John Wiley & Sons, Inc.). <br /> <br />l;..~r1=L'.~'Wc~D JUN 2 S 200D <br />PR 99-OS 2.06-13.1 11/17/99 <br />