INSPEC03556

• Permit No: M1990098
• IBM Index Class Name: Inspection
• Doc Name: MINERALS PROGRAM INSPECTION REPORT
• Inspection Date: 10/9/2001
• Media Type: D
• Archive: No

MINE ID # OR PROSPECTING ID#: M-1990-098 PAGE: 3
INSPECTION DATE: 10-9-01 INSPECTOR'S INITIALS: ACS
• The approximately 350 foot setback from the point where the levee is likely
to overtop to the edge of the pit.
• The presence of a slight basin west of the levee spill point that would
provide storage for initial overtopping flows and would serve to attenuate
velocity of flood flows moving toward the pit.
• The fact that the likely spill point is well north of the outside of the
river bend, such that the erosive energy of the river has lessened along
the left bank and has moved back toward the center of the channel. The main
energy of the stream shifts to the right bank of the river at a location
to the north of the levee spill point as illustrated on the included
diagram.
As discussed above, the Operator has concluded, based on site conditions, that
capture of the river by the Perry Pit excavation is unlikely to occur during
a 100-year flood. In order for this conclusion to remain valid, the existing
historic levee must remain functional. The condition of the levee will be a
subject of future site inspections by the Division of Minerals and Geology,
and the Operator must conduct periodic inspections and perform needed
maintenance on the levee. In particular, the levee must be inspected by the
Operator during and following high flow events along the South Platte River.
Certain of the discussion in the Operator's adequacy response letter dated
9/21/01 requires clarification of the Division's position on minimization of
impacts to the prevailing hydrologic balance and prevention of off-site
impacts during flooding when mine permit areas are within a floodplain. The
9f21lOl letter states that the criteria for analysis of the need for flood
management measures when mining occurs within 400 feet of the South Platte
River or its tributaries is not do to the probability of flood influences.
This 400 foot setback, adopted by both the Urban Drainage and Flood Control
District in the area of their jurisdiction and by the Division of Minerals and
Geology throughout the river system, is used primarily because the likelihood
of flood related damage is minimized when mining is setback 400 feet or more
from the river. The potential for flood damage increases as pits are located
400 feet or progressively closer to the river. This is why flood control
measures are not required by either the District or the Division when
Operator's specify 400 foot setbacks, and why analysis of the need for
stabilizing measures is required for mining within a 400 foot setback to the
riverbank (see page D-6, "In-stream Aggregate Extraction and Reclamation
Guidance Document," Colorado Division of Minerals and Geology, August 1998).
The Operator further states in the 9/21/01 letter that the Perry Pit is not
an in-stream aggregate operation as defined in the above referenced manual.
It is true that floodplain gravel pits are not included in the list of types
of in-stream operations provided on pages 13-31 of the manual, but the manual
does provide guidance on floodplain pits in other locations within the
document. Appendix D to the "In-stream Guide" in particular provides