2014-01-06_REVISION - M2000041

• Permit No: M2000041
• IBM Index Class Name: REVISION
• Doc Date: 1/6/2014
• Doc Name: Response to Adequacy of October 7, 2013 AM01
• From: Environmental Alternatives, Inc
• To: DRMS
• Type & Sequence: AM1
• Email Name: TC1
• Media Type: D
• Archive: No

determined, h can be calculated for any radial distance
from the pit, and drawdown can be calculated as
ho — h. In addition, the inflow rate, Q [L3/T], through
the pit wall can be calculated as:
Q = W7t(ri2 — ri2 ) (3)
The analytical solution of Marinelli and Niccoli
(2000) is valid for ground -water flow systems that
meet the following assumptions:
• The geologic materials are homogeneous and
isotropic;
• Ground -water flow is steady state, unconfined, hori-
zontal, radial, and axially symmetric;
• Recharge is uniformly distributed at the water table
and all recharge within the radius of influence is
captured by the pit;
• Pit walls are approximated as a right circular
cylinder;
• The static premining water table is approximately
horizontal; and
• The base of the pit is coincident with the base of the
aquifer, and there is no flow through the pit
bottom.
Marinelli and Niccoli (2000) also present an
analytical solution for upward ground -water flow
through the bottom of a pit that partially penetrates an
aquifer.
However, inflow to the bottom of a pit is not
considered in this report because (1) analytical solu-
tions are used only to calculate hydraulic head at the
water table, which is independent of ground -water
flow through the mine bottom in the solution, (2) the
bottom of aggregate mines in sand - and - gravel aquifers
in the Front Range area generally are near the base of
the aquifer, and (3) hydraulic conductivity of fractured
crystalline -rock aquifers generally becomes exceed-
ingly small with depth, which limits inflow to the mine
bottom. For pits that do not meet these conditions,
consideration of flow to the mine bottom may be
important.
A steady- state, one - dimensional analytical solu-
tion is derived for ground -water flow to a mine exca-
vated into a steep hillside such as in the mountainous
part of the Front Range area. The derivation of the
one - dimensional solution is similar to the Marinelli
and Niccoli (2000) solution, but the mine is repre-
sented as a straight line along a hillside rather than a
circular pit. The mine in this situation intercepts only
the upgradient ground water within the hillside.
Ground -water flow toward the mine at distance x
upgradient from the mine wall can be expressed as:
Q = Khh A (4)
where
Q is flow per unit Iength of the mine [L2/T],
Kh is horizontal hydraulic conductivity of
surrounding geologic materials [L/T],
h is saturated thickness above the mine base at
distance x from the mine wall [L], and
x is distance upgradient from mine wall [L].
If all ground -water flow to the mine is assumed
to originate from uniform distributed recharge (W)
within the drawdown distance of influence (x;) of the
mine, then flow toward the mine also can be expressed
as:
Q = W (x; — x) (5)
Substituting equation 5 into equation 4 and inte-
grating from the mine wall to distance x gives:
X h (6)
W f (xi — x)dr = f hdh
Kh 0 h.
where
hm is saturated thickness above the mine base at the
mine wall [L].
Carrying out the integration leads to an analyt-
ical solution for head in the aquifer adjacent to a linear
mine that is given as:
h =�hn,2+ W [2x,x —x2] (7)
Kh
S Analytical and Numerical Simulation of the Steady -State Hydrologic Effects of Mining Aggregate in Hypothetical Sand - and - Gravel
and Fractured Crystalline -Rock Aquifers