PERMFILE133896

• Permit No: C1981039
• IBM Index Class Name: Permit File
• Doc Name: Rockcastle 1/15/92
• Section_Exhibit Name: Reclamation Project Binder
• Media Type: D
• Archive: No

Rackcasile Company, Grassy Creek Mine ~ Adequacy Responeses ` 2
• D) Vegetative cover values on newly reclaimed sites must be documented with field sampling when
preparing hydraulics designs. It is unjustified to indicate that the canopy cover of the reclaim is 50%
while the ground cover is 80% without empirical data.
Response: Revegeta[ion monitoring for [he Pi[ 4 reclaimed area would normally be completed per
[he standard revegetation monitoring schedule. Since monitoring would not normally occur for at
leas[ two yeazs following reseeding, Rockcas[le based estimated canopy and ground cover values
for hydrologic calculations on duet[ visual observation. Applicable regulations do not specify a
required basis for hydrologic calculations so the concept of best engineering practice is appropriate.
Given the stage of reclamation, [he time and expense of a separate vegetation survey [o support
hydrologic assumptions is no[ justifiable. While the estimated cover values utilized are not
represented as being enact, they are within a reasonable range of accuracy for the purpose for
which they were used.
REVISION ADEQUACY CONCERNS
1) TJte inslopes of Pond No. 4 are ertraordinarfly steep along the top 9 feet of the pond (44%50%).
This will be a problem if the pond is retained on a pem=anent basis, and contradicts the
recommendation found in the October 1$ 1990ACZ submittal that the pond should have 3:1 slopes.
The aforementioned submittal also recommended that Ditch 4-1 enter the pond on a 4:1 Jivestock
ramp. While the Division understands that Rockcastle is withdrawing from their request to leave Pond
4 as permanent at this limy I believe that the company could accommodate reconfiguration concerns
quite easily while regrading the overlying slope. Please modify the plan view, capacity table, and
stage/storage curve on the Pond No. 4 Design Plate accordingly.
. Response: The Pond 4 Design Map, (Map 3t-3), submitted in November, 1991, graphically
illustrates the proposed regraded configuration of Pond 4 following backsloping of the east slope.
The regraded configuration includes relatively uniform 3H:1V slopes on the east side of the pond,
maximum 2H:1V interior basin slopes on the south and west sides of [he pond and a uniform
4H:1V interior embankment slope on [he north end of the pond. All hydrologic calculators,
including pond capacity and stage/storage relationships are based on the illustrated configuration.
The entire north end of Pond 4, which is approximately 40-50 feet wide, will be established at a
4H:1V slope providing effective access to impounded water for both livestock and wildlife. A copy
of Map R3 accompanies these responses for review and reference.
2) Rule 4.05.6(11)(f) indicates that the com6rned upstream and downstream side slopes of the
embankment shall be no steeper than S:l. 1 measured both the inslope and outslope at 2:I. Please
modify the upslope portion of the embankment to accommodate this regulatory requirement. When
modtJying the design ensure that Rute 4.05.6(11)(h), the regulation on minimum top width, is in
compliance.
Response: As described in the October 8, 1990 ACZ submittal, Pond 4 is an incised pond created
by partial backfilling against the fmal Pi[ 4 highwall. As an incised pond, under Rule 4.05.9(4),
sideslopes are required to be "... stable and shall not be steeper than O.Sh:ly.". The east inslope
will be 3H:1V with no outslope. Similarly, the north inslope will be 4H:1V with no outslope. The
south inslope varies from 2H:1V to 12H:1V with no outslope and the west inslope is approximately
2H:1V with a 2H:1V outslope.
The west side of the pond appears to be the source of this concern. For the west side inslope
- gradients aze well within the regulatory limits for an incised pond. The existence of an outslope
• is a reflection of the natural terrain in this area which sloped away from the final pit highwall. Any
attempt to modify [he outslope would result in unnecessary disturbance of [he existing established
vegetation. Modification of either the inslope or outslope would offer little or no potential benefit
relative [o long-term pond stability.
ACZ Inc. ` P.O. Box 774018 "Steamboat Springs, Colorado 80477 ` [phone]