2005-12-16_REVISION - M1999069

• Permit No: M1999069
• IBM Index Class Name: Revision
• Doc Date: 12/16/2005
• Doc Name: Response to Adequacy Review Comments
• From: Applegate Group Inc
• To: DMG
• Type & Sequence: AM1
• Media Type: D
• Archive: No

Ms.~EricaCrosby-- --= ~ - - - ~ ~~
RE: Jake Kau/jman & Son'Inc Wagner/Kauffman Pit #3 Amendment AM Ol '
. 'Dece»ilienl5, 705'
Page 4 of 6 ~ . _
dewatering operation."s-will-continue to,,take place~.for.both:Phase II-and Phase IIL '
operations:
The'.perimefer for.the Phase-II mining area is approximately 9;700 feet. Dewatering
.is being performed with the construction of a perimeter trench that fully penetrates "
the alluvium: The: bottom of the trench is sloped to one or-more sumps where the , , • ; -
_ water is collected and pumped from the site: Although the 'average depth 'of
- overburden and alluvial material at the proposed -site is approximately 12 to 18 feet, ,
on average.only the,bottom 5 feet is saturated with'alluvial ground water. Therefore;.
the: surface 'area of he alluvial aquifer exposed by the' fully developed =trench
` (extending the entire perimeter of the pit) in the .Pliase II-mining azea is 48,500 ft
Darcy's Law approxirriates flow into the renches"based on the exposed surface' area'
acid the hydraulic properties of the aquifer. Using Darcy's Law, the e"stimated flow
- into the folly developed trench from thesurrounding alluvial.aquife`r is approximately _
190 gallons per minute.(gpm): Flow within the. trenches will actually be gss since the,
3
dewatering->trenches'do not typically :cover the entire perimeter of the pit, but the fully
developed trench can be used as a worst case scenario.
~

Irr order to estimate -the pit' dewatering affects, .the- Theis assumptions were extended ~
''
- to the alluvial aquifer at the site. The mathematical approaches developed with the

use.of these assumptions can approximate the response of the alluvial aquifer near the '
mining azea. -Among other- aspects;`the saturated alluvium at the site is- fairly

consistent iri material and thickness; the hydraulic gradient is low, and the specific '
"Yield is high. ° _ I
.:Additional simplifying assumptions were made in estimating the' pit dewatering ';
- affects. -Although the Big-Thompson River-wi111ikely. reduce dewatering affects neaz - ,
boundary of the site, the, influence of the" river was neglected ,for the
the southern ~
.
estimate. Surface- recharge -was- also„neglected since <values would _flixctuate,
ii'
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gatro
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considerably throughout the yeaz. For instance; surface recharge-.from
` x =
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would likely reducette affects of dewatering significantly during the.growing season.' ;~
In addition; calculations were made assuming the entire pit area would be exposed-.' ':., ~'
and: dewatered continuou§ly: _ In reality,-with phased :`mining. and concurrent - _
d
w
t
ill b
d
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ere
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pif are
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reclamation; it is anticipated. that only a-fraction: of the tota
of any one time.. The reduced dewatered pit area and rechazge from the rivers and
imgation are expected to reduce the affects of dewatering. The"refore, the calculation - '
is considered to be.a worst-case estimate.. _ i
The approach that was used. to estimate the extent of drawdown from dewatenng is
referred to as "flow.to a drainage trench from.a line source" and :is referenced iri i
1992 (Construction.Dewatertng, New. Methods and Applications; John Wiley
Powers
,
and Sons, New York; N:Y. 2ap Edition).. Results were checked with -additional= ; '
'approaches a presented. in Freeze and Cherry, 1979 (Groundwater; Prentice-Hall).
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