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2004-08-27_REVISION - M1989029
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2004-08-27_REVISION - M1989029
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Last modified
6/16/2021 6:21:21 PM
Creation date
11/21/2007 8:28:56 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M1989029
IBM Index Class Name
Revision
Doc Date
8/27/2004
Doc Name
Technical Revision
From
Hart Environmental
To
DMG
Type & Sequence
TR4
Media Type
D
Archive
No
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well as water from the Bonus and Coffin-Davis irrigation ditches. Bonus Ditch water <br />will flow into the Peschel Property at points along the western edge of the property. <br />Also, water from the Coffm-Davis irrigation ditch will flow into the Bigelow property. <br />The entire reclaimed azea will dischazge water to St. Vrain Creek, to the northeast of <br />the Longmont property, via an existing reclaimed pond and outfall. <br />The rate of inflow to the system from the Coffin-Davis and Bonus lateral ditches will <br />be controlled by diversion structures. The Coffm-Davis Ditch diversion structure is <br />located on the Bigelow property and includes a bypass to St. Vrain Creek, along the <br />original imgation ditch, that will allow the flow into the wetlands to be controlled <br />during periods of high flow. An additional flow control box may be constructed on the <br />Coffin-Davis ditch to supply a lateral ditch that will be used to feed the post-mining <br />pond on the Bigelow property. The flow control boxes are designed to operate in the <br />same manner as existing flow control structures currently in place in irrigation ditches <br />in the azea. <br />The location of the wetlands and ponds is shown on the revised Reclamation Plan <br />(Exhibit F.1). The final location of all wetlands, channels and ponds is dependent on <br />the topography of pit floor at the completion of mining; where feasible, wetlands and <br />ponds will be positioned in topographic low areas to minimize material movement and <br />excavation of the bedrock. The final drainage pattern and shape of the ponds and <br />wetlands will be constructed by the placement of overburden fill and grading of the pit <br />floor. <br />The depth of water in the wetlands will be controlled by a series of check dams (see <br />Exhibit F.1). The depth of the substrate in these wetlands typically varies from 0 to 3 <br />feet. The check dams will be constructed of logs and overburden material. The design <br />of a typical check dam is illustrated in Exhibit F.1. <br />As stated in the current DMG Permit, channels and spillways will be sized to pass <br />surface runoff from a 25-yeaz storm event plus the baseline groundwater flow. <br />Hydmgeologic modeling completed in May 2001, indicates that baseline groundwater <br />flow in the Peschel, Bigelow, Distel, and Longmont pits will be approximately 104 <br />gpm. Therefore, channels and spillways will be conservatively sized to pass a 25-yeaz <br />storm event surface flow plus a 130-gpm groundwater inflow into the reclamation <br />area. The majority of the reclaimed areas are in the FEMA flood plain of St. Vrain <br />Creek and Boulder Creek. However, the reconstructed drainage pattern is confined to <br />the excavated pit azeas. All flow control structures aze constructed below the current <br />ansnooa <br />
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