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2008-01-28_REVISION - C1981008
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2008-01-28_REVISION - C1981008
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Entry Properties
Last modified
8/24/2016 3:21:43 PM
Creation date
4/17/2009 10:00:13 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981008
IBM Index Class Name
REVISION
Doc Date
1/28/2008
Doc Name
Adequacy Review
From
DRMS
To
Western Fuels Colorado
Type & Sequence
TR56
Media Type
D
Archive
No
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Mr. Ross Gubka, P.E. <br />Western Fuels-Colorado <br />January 28, 2008 <br />Page 3 <br />As stated in our inspection report the principal spillway was built differently (two gated <br />valves connected to a drop inlet riser), and the modeling and As-Built Certification report <br />submitted with TR-56 are inconsistent with the approved design. From the As-Built <br />model and Map 2.05.3(3)-18 it shows that the valves below the principal spillway acting <br />as weep hole(s) will be left open instead of normally remaining shut. The Pond As-Built <br />report states that the permanent pool elevation is at the weep hole elevation and the <br />model shows the top of sediment storage only .05 feet below the weep hole/gated valves. <br />As constructed and if operated according to the configuration shown in the As-Built <br />Certification report, there does not appear to be adequate sediment storage and treatment <br />capacity for Pond 013. <br />2. Pond 013 was built significantly different from the approved design and there are <br />inconsistencies noted between the As-Built model and the As-Built Map <br />2.05.3(3)-18. On Map 2.05.3(3)-18 (plan view) the bottom of the pond is labeled <br />at an elevation of 5549 feet, yet the Stage Storage Curve on the map shows the <br />bottom of pond at 5548 feet. The Stage Storage Curve also shows a Clean Out <br />Level (5550.00 feet), which is not consistent with the SEDCAD model showing a <br />Top of Sed. Storage at 5551.95 feet. <br />According to the 10-year, 24-hour SEDCAD demonstration, there is only.05 feet <br />between the top of sediment storage and the low-hole spillway. As configured in <br />the As-Built report and model there does not appear to be adequate sediment <br />storage volume or sufficient treatment capacity. A more prudent design and to <br />avoid resuspension of sediment would be to allow for additional space between <br />the top of sediment storage and the lowest spillway elevation. In the SEDCAD 4 <br />User's Guide (page 64) it is suggested that a minimum two foot elevation <br />difference exists between the invert of the principal spillway and the top of the <br />sediment storage area. If a slow passive dewatering system is employed such as <br />the low-hole spillway of Pond 013, the elevation can be reduced to 0.5 to 1.0 ft, <br />depending upon the size and flow rate of the dewatering hole. From the <br />information provided it is unclear what the size and flow rate of the dewatering <br />hole will be since there are two adjustable valves and the SEDCAD model shows <br />one low hole-spillway/weep hole. <br />From the inconsistencies noted in the As-Built information, it is unclear how the <br />pond will be operated (manual versus passive dewatering). If the bottom of the <br />pond is at 5549 feet and the permanent pool elevation is at the low hole spillway <br />elevation of 5552.00 then there would appear to be sufficient sediment storage <br />and treatment capacity depending on the cleanout level. However, as shown in <br />the model there is insufficient space (.05 feet) between the top of sediment storage <br />and the low hole-spillway to provide sufficient sediment storage volume. <br />Please provide a revised As-Built Certification report for Pond 013 to <br />address the discrepancies identified above for the As-Built information. <br />Please also reconsider the configuration/operation of Pond 013 to allow for a
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