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Mr. Gregg Squire • • <br />Page 5 <br />December 20, 2000 <br />6. In ] 999, the portion of the main channel on the south side of the island is no <br />longer part of the main channel. <br />7. The island in the river has changed shape significantly. <br />8. Observations 2 and 3 from the 1982 topographic map review are still valid. <br />Based on the above observations the West End mining area is separated from the other mining <br />areas to the east by approximately 30.55 acres that are out of the 100 year floodplain and as such <br />will be discussed separately from the other pits to the east. The potential fora ] 00 year flood to <br />capture the west end pit is limited since only the northwest end of the pit is in the 100 year <br />floodplain. The estimated depth of flooding is approximately 1 foot. Even if the river did connect <br />directly to the pit by eroding the 100 feet barrier, this pit would likely become a backwater area. <br />The pits in the West Property Line to Horse Fence, Slough to East Property Line and Dry Creek <br />mining areas contain a drop of ib feet in water surface elevation. The pits are incised in nature <br />and utilize natural ground as a barrier. The post mining 3:1 slopes start at the top of the pit crest <br />at existing ground elevation and are projected to the pit bottom. Based on the estimated water <br />surface elevations of the ponds, there is approximately four feet of freeboard from the existing <br />ground to the water surface. If the Colorado River rose to a 100 year flood stage these pits <br />would be covered with approximately 0.3 to 4 feet of water using the surrounding ground as a <br />reference. The portion of the Dry Creek and West End mining areas that are out of the 100 year <br />floodplain will direct the Flows back into the main river channel at the same point that the flood <br />has historically entered the river. <br />The potential for the river to capture the pits is lessened considerably by the fact that the <br />freeboard space greatly increase the cross sectional area of the flood area which will slow down <br />the floodwater velocity and lessen its erosive potential. As the velocity slows, material will be <br />deposited into the pits near the entry point thereby beginning to replace lost material in the <br />barrier. This deposition of material in the pit on the inside edge of the barrier and the fact that the <br />pits are filled with water to within 4 feet of the ground is expected to limit the depth of erosion in <br />the barrier. As the floodwaters recede, the breach, if one occurced, can be backfilled or a <br />reinforced inlet can be installed to stabilize the breach area. This aspect will be covered more fully <br />in item 10. <br />The operator will also leave additional fill material in the northeast corner of the west property <br />line to horse fence area during potential high flows to provide an additional barrier to the pits <br />being captured by the river. This is the area that the river is expected to breach the 100 feet <br />barrier along the river bank first. <br />Item 8 -The utility on the west property line is a high pressure gas line owned by Questar. The <br />mining plan has been sent to Questar and several phone conversations have been held with <br />Questar's Land and Engineering Departments. Questar appears to be comfortable with the 2;1 <br />setback to the right-of--way. Questar has indicated that the gas line is near the center of the <br />