2008-10-17_PERMIT FILE - M2008017

• Permit No: M2008017
• IBM Index Class Name: PERMIT FILE
• Doc Date: 10/17/2008
• Doc Name: Adequacy Review Response
• From: J&T Consulting, Inc.
• To: DRMS
• Email Name: MAC
• Media Type: D
• Archive: No

Broken Arrow Investments, LLC Derr Pit, Adequacy Review Comment Responses, File No. M-2008-017 10117108
-5-
Response:
The mining will progress in each phase beginning at the outer edge of the phase
where material will be moved toward the interior of the phase such that a 3H.• 1 V
mining slope can be established on the exterior of the phase. The mining slope will
be established for the entire perimeter of the phase in 3 to 6 feet intervals. The
dewatering trench around the perimeter will be placed at the toe of the 3H:1 V mining
slope. As the phase is mined deeper the dewatering trench will be lowered and
moved laterally along the 3H:1 V mining slope toward the center of that phase. Once
the interior footprint becomes small enough where the 3H:1 V mining slopes from
three to four sides are encroaching upon the portable plant and haul roads another
phase will be opened to continue mining. Please refer to the revised Exhibit D.
15. The mining plan map shows that a portion of the affected acreage lies within
the 100 year floodplain of the Poudre River. There is the possibility that water
could enter the pit during a 100 year flood event, resulting in headcutting of
the headwall. The Division asks that you consider implementing measures to
keep water from entering the pit during such an event.
Response:
Best management practices in regard to on-site drainage are part of the proposed
Weld County Use By Special Review Permit drainage plan and report. Measures
such as creating berms to re-direct, block, or impede 100 year flood flows are not
allowed in the 100 year flood plain as the fill placed within the floodplain would cause
a rise in the 100 year base flood elevations. The proposed stockpiles for topsoil and
overburden have been placed outside the 100 year floodplain for this reason.
16. The mining plan states that a perimeter drain will be installed, "...if needed to
convey groundwater around the lined reservoir after the slurry wall is
installed". The applicant should identify the trigger(s) that will determine
whether the installation of the drain is needed.
Response:
The depth to groundwater has been measured on a monthly basis in piezometers
located on the interior and exterior of the proposed sluny wall alignment since
October 2006. Groundwater depths will continue to be measured and recorded at
monthly intervals in each piezometer to establish what the seasonal groundwater
levels are. These measurements will be used as a benchmark for maintaining the
groundwater levels in subsequent years. The triggers that would require the drain to
be installed are as follows.
1. A three foot difference in the depth to groundwater from the seasonal
groundwater levels in two or more piezometers as observed in the previous
years monthly measurements for two consecutive months.
Please refer to the revised Exhibit E.
17. Specify whether explosives will be used during mining per Rule 6.4.4(1).
Response:
Explosives will not be used during mining. Please refer to the revised Exhibit D.
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