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Mr. Ross Gubka, P.E. <br />Western Fuels-Colorado <br />January 28, 2008 <br />Page 2 <br />The As-Built Map 2.05.3(3)-17 shows two adjustable valve weep holes at different <br />elevations (5612.00 and 5613.00) and the As-Built model shows one low-hole spillway at <br />5612.00. It is unclear what the diameter of the low-hole spillway is in the model but <br />certainly this would appear to dewater the pond at a slower rate than two 6 inch <br />adjustable valves. The SEDCAD demonstration shows that the gated valves will be open <br />during the storm event and appear to remain open since the permanent pool elevation is <br />set at the weep hole elevation. The SEDCAD model doesn't accurately reflect the As- <br />Built configuration and it is unclear if the pond will be operated manually or by passive <br />dewatering. A major concern is the top of sediment storage is shown to be 5606.00 feet, <br />which is equivalent to the bottom of the pond elevation. This indicates that there is no <br />provision for sediment storage and according to the configuration shown in the As-built it <br />will be constantly cleaned out. <br />Pond 011 was built significantly different from the approved design. There <br />appears to be adequate sediment storage volume available in Pond 011, but the <br />As-Built SEDCAD demonstration shows the top of sediment storage to be <br />equivalent to the bottom of the pond thereby providing no sediment storage <br />capacity. It is unclear how this pond will be operated. Please provide a revised <br />As-Built Certification report and if necessary revised permit text which <br />clearly explains how Pond 011 will be operated (manually versus passively <br />discharged). The revised Certification report and permit text shall also <br />provide a demonstration of compliance with Rules 4.05.6(3) (b) and 4.05.2(7). <br />This demonstration should identify the maximum sediment storage volume, <br />cleanout level, and the estimated periodic sediment removal interval. <br />Compliance with these permit commitments shall be demonstrated and <br />documentation of the existing storage capacity shall be provided annually in <br />the Annual Certification for Impoundments required by Rules 4.05.9(14) and <br />(15). <br />Pond 013 <br />Pond 013 was originally designed by WFC and approved by the Division in 1999. <br />During the last Midterm Review, some problems were identified with the way in which <br />the pond was to be operated utilizing valves below the level of the principal spillway (see <br />Division letter dated November 13, 2006). This potential problem was rectified and <br />WFC revised the design details with TR-54. The text on page 2.05.3(3)-6-22 was revised <br />to state that during normal conditions the valve will be shut to provide 24 hour detention <br />time during large storm events. When a large event occurs, the operator will wait a <br />minimum of 36 hours after the storm has ceased to check the water still detained by the <br />pond. If an Imhoff cone shows that the water meets effluent standard of 0.5 ml settleable <br />solids per liter, the valve will be opened until the water has dissipated to the valve level. <br />It will then be shut to allow detention time for subsequent storms. Map 2.05.3(3)6-1 was <br />also revised with TR-54 to show that the one 6" valve on the straight-pipe spillway will <br />normally be left shut.