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2018-06-25_REVISION - M2011001 (2)
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2018-06-25_REVISION - M2011001 (2)
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Entry Properties
Last modified
1/28/2021 3:29:58 AM
Creation date
6/25/2018 4:15:27 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M2011001
IBM Index Class Name
Revision
Doc Date
6/25/2018
Doc Name Note
Evaluation of Reclamation Improvements
Doc Name
Formal Complaint
From
Timothy Iverson
To
DRMS
Email Name
PSH
Media Type
D
Archive
No
Tags
DRMS Re-OCR
Description:
Signifies Re-OCR Process Performed
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April 5,2018 <br /> Page 4 <br /> Adequacy of Flood Hazard Mitigation Measures <br /> The reclamation improvements were evaluated for conformance to the UDFCD Guidelines per <br /> Comments 14 and 16 of the DMRS First Adequacy Review dated 4-1-2011. The evaluation was based <br /> on the As-Built Survey dated 12-19-17 and hydraulic modeling described in the previous sections. The <br /> following items do not adequately address the DMRS concerns in Comments 14 and 16. <br /> • The UDFCD Guidelines require riverbank protection in areas where river currents will have a <br /> tendency to erode the river banks and the riverside berm is less than 400 feet in width. The <br /> hydraulic model indicates river velocities along the riverside berm are erosive ranging from 5 <br /> to 8 feet per second during the flood events. The Cache La Poudre river at this location clearly <br /> has the potential for eroding the banks, altering the channel location and capture of the mining <br /> pit. The existing berm has widths as narrow as 150 feet on the west side, 95 feet on the north <br /> side and 180 feet on the east side. The UDFCD Guidelines require the both the riverbank and <br /> the pitside to be protected with riprap for riverside berm widths of 150 feet in areas of unstable <br /> (erosive)river conditions. The lack of erosion protection for the riverside berm is a major factor <br /> in the repeated breaching of the berm. <br /> • The spillways do not meet the size requirements of the UDFCD Guidelines for a 27.2 acres <br /> impoundment with a riverside berm 5,400 feet in length. The UDFCD requires a spillway width <br /> of at least 100 feet for the conditions at the Iverson Mine reclamation site. The existing trapezoid <br /> spillways have a bottom width of 34 feet on the inlet spillway and 26 feet on the outlet spillway. <br /> The discharge through the spillways as shown in Table 1 during flood events up to the 50-Year <br /> Flood are inadequate to equalize the water levels between the river and the lake in a reasonable <br /> amount of time. High differential heads between the river and lake result in erosive velocities <br /> of flows overtopping the riverside berm and possible breaching of the berm. <br /> The quality of the construction of the reclamation improvements was evaluated in view of the long term <br /> stability of the site. John Allis PE,of TZA Water Engineers,Alan Hill of Hill&Pollock,LLC and Tim <br /> Iverson, landowner, visited the project site on November 8, 2017 and observed the existing spillway <br /> structures and the site grading completed to date. A topographic survey was completed by Lamp <br /> Rynearson & Associates on December 19, 2017 to document the as-built condition of the site. The <br /> topographic survey is attached as Exhibit A. The following observations are made as a result of the <br /> inspection and survey. <br /> • The grading of the riverside berm at the northwest corner of the lake is not uniform and has <br /> several low areas. The general location of the low areas is shown in Figure 1. The low areas <br /> range in elevation from 4685.1 to 4685.4. This area was reported to have been breached during <br /> the floods of September 2013 and May 2014 and is highly subject to erosion during flood events. <br /> The 2-Year Flood elevation at this location is 4685.3 which is approximately equal to the ground <br /> elevation at the low points. Flood events greater than the 2-Year Flood will overtop the <br /> riverside berm and could result in additional breaches at the northwest end of the lake. <br />
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