2014-11-14_PERMIT FILE - M2014043 ‎(3)‎

• Permit No: M2014043
• IBM Index Class Name: Permit File
• Doc Date: 11/14/2014
• Doc Name: Adequacy Review 01
• From: Environment, Inc.
• To: DRMS
• Email Name: TOD
• Media Type: D
• Archive: No

ENVIRONMENT, INC.
NOVEMBER 14, 2014
PAGE 2
perimeter in Phase 2. As mining approaches the perimeter of the mine a 25 foot mining
setback will be staked from the permit line to establish the mining limit. An additional safety
setback of 25 feet will be staked from the mining setback line to establish the limit, where
mining with a near vertical face will stop. In the Geotechnical Analysis we show that by using
the setback proposed in this text the safety factor for the closest structure will be 1.52, so by
reason, as you move away from the mine face the greater the safety factor would be for any
structures within 200 feet of the permit line.
4) The mining plan states that mining slopes near adjacent structures will not exceed 3H:1 V during
mining; however, the mining plan map C -1 shows slopes of phase 1 steeper than 3H: I V. Please describe
in more detail the pit slopes of mining phase 1 during mining operations and use as a recycled water pond
for the wash plant. Will the western and southern pit slopes of mining phase 1 be mined at a 3H:1 V
slope?
Here again the plan is to have the mining face worked at a near vertical slope as mining
progresses thru the area. Albert Frei & Sons, Inc. has decided to not mine within 200 feet of
the Thornton Reservoir complex slurry wall /dam. This new setback is shown on the following
revised Map Exhibits; C -1 - Mining Plan Map, F - Reclamation Plan Mip, Figure E -2 and
Figure E -3. Please see the attached Geotechnical Analysis prepared by Deere and Ault
Consultants for the Thornton structures. Along the south side the mining setback will be 25
feet but that slope will be mined 2:1 or flatter then the natural angle of repose.
5) The mining plan states the applicant plans to mine pit slopes at a 3H:1 V slope near adjacent structures.
Please illustrate on the Mining Plan Map which slopes will be mined at a 3H:1 V slope.
As noted above the plan is to leave a safety buffer around the mine if the 1/2:1 slopes proves
to be prone to failure. This 25 foot safety buffer is shown on the north .and south sides of
Phase 2 on the revised Map Exhibit C -1 - Mining Plan Map. In addition, no mining will take
place within 200 feet of the Thornton structures.
6.4.4 EXHIBIT D - Mining Plan
6) Please describe the nature of the stratum immediately beneath the material to be mined.
According to the USGS Geologic maps for this area the material underlying the gravel to be
mined is a part of the Denver Formation. It is a dense grey shale, silty claystone and
interbedded siltstone formation of the Upper Cretaceous age that is from 800 to 1000 feet
thick.
7) Please specify if explosives will be used in conjunction with the mining or reclamation
operations.
Explosives will not be used during mining or reclamation at this sand and gravel mine.
8) Please commit to salvaging enough growth medium to spread 8 inches over all of the affected lands.
Albert Frei & Sons agrees to salvage enough growth medium to resoil--the affected lands with
a minimum of 8 inches average.
9) The installation of the slurry wall around the Hatchery Pit would direct groundwater flow between the
pit and the lined reservoir to the west. DRMS believes the applicant may reduce the cross sectional area
of the alluvial groundwater flow between the reservoir to the west and the shale by as much as 80 %.
DRMS believes the installation of the slurry wall around the Hatchery Pit would further constrict the