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

Rockcastle Company, Grassy Creek Mine Adequacy Responeses * 3
• 3) Please commit to providing apost-grading certiftcation of the pond and the overlying slope upon
completion of the project.
Response: In compliance with applicable provisions of Rule 4.05.9(10) and 4.05.9(8), Rockcastle
will certify modification of Pond 4 with respect [o consistency with design specifications. Given that
[here aze no regulatory requirements far certification of backfilling and grading activities,
certification of the backsloping component of the proposed work is not appropriate.
4) The open channel emergency spillway shows riprap along the crest. The operator must provide
documentation that flow from the 25 year-24 hour event on the outslope is non-erosive, or submit
designs to amtor the spillway to protect the integrity of the embankment during a flood. (Rule
4.05.6(3)(d)).
Response: As shown on the Pond 4 Design Map, (Map R-3), the emergency spillway daylights to
natural ground. In this area, natural ground slopes off a[ approximately 2H:1V and there is heavy
ground cover consisting of existing natural vegetation. Any dischazge through the Pond 4
emergency spillway will be quickly dispersed by [he natural vegetation, moving downslope as
overland flow.
The calculated emergency spillway dischazge velocty as shown on Map R-3 is 4.7 feet/second.
Given the existing vegetative cover at the point where the emergency spillway daylights to natural
ground and the fad that flows beyond this point will be dispersed over the slope rather Wan
confined to a flow channel, We dischazge velocity should not be erosive and We need for armoring
or other pro[ec6ve measures is not indicated.
• 5) Provide designs for the Pit No. 4 intermediate ditch discussed on page 4 or commit to its removal
during the upcoming constmctian season to show compliance with Rules 4.05.3(4) and 4.05.36).
Response: Response 1C (Page'7) of the November, 1991 Adequacy Response submittal addresses
We Pi[ 4 intermediate ditch and commits to it's removal.
6) Barfield Wainer, and Haan's redbook indicates that fine sandy looms can tolerate velocities of 2.5
fps from sediment laden waters. Therefore, al! portions of the ditches except 4-1 A must be riprapped
to prevent erosion.
Response: Given We relatively steep natural terrain in this azea, riprapping of essentially the entire
Ditch 41 and 42 channels would be very difficu[[ and may not be necessary. Portions of Ditches
41 and 42 offer some natural armoring, with exposed cobble and gravel materials within the
existing flow channels. There aze also significant portions of Ditch 42 which have well established
vegetative cover. Flow velocities of up to 5 fps aze allowable for gravel and cobble materials
(Table 3-2, Bazfield, et. al., 1987) and allowable flow velocities for vegetated channels range from
3-5 fps (Table 3-4, Bazfield, et. al., 1987).
In conjunction wiW modification of Pond 4 and final reclamation work in We Pit 4 azea, Rockcastle
proposes to evaluate current conditions for boW Ditches 41 and 42 for individual channel
segments. Based on this information, Rockcastle will determine appropriate erosion control
measures for each segment and present a proposed erosion control plan and supporting
documentation for the Division's review and approval. Upon receipt of Division approvals,
appropriate erosion control measures will be implemented along with the required clean-up and
repair previously identified.
•
ACZ Inc. • P.O. Box 774018 'Steamboat Spdngs, Colorado 80477 * [phone]