PERMFILE127679

• Permit No: C1981023
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: EXHIBIT 7 SEDIMENT CONTROL DESIGN CRITERIA
• Media Type: D
• Archive: No

• EXI-IIBIT 7
(Midterm Review, January 1996)
7-1 Preface
This review and analysis is made using the Sediment, Erosion, Dischazge by Computer Aided
Design (SEDCAD+ Version 3) developed by Ms. Pamela J. Schwab of Civil Softwaze Design
and Dr. Richazd C. Warner, Agricultwal Engineering Department, University of Kentucky..
Design criteria is promulgated by Colorado Division of Minerals and Geology Rule(s)
4.05.6(3)(a) (10-year, 24-how precipitation event); 4.05.6(3)(b) (3 yeaz storage volume, cleaning
scheduled at 60% of design capacity), and Peak Settleable Concentration in pond dischazges not
to exceed 0.50 mlll); 4.Q5.6(3)(c) (conduit spillway); 4.05.6(3)(d) (combination of principal and
emergency spillways)(25-yeaz, 24-how precipitation event); and 4.05.6(4). This midterm review
acknowledges that Ponds 002, 004, and 005, as constructed, do not meet the criteria of Rule
4.05.6(11)(f), and that Pond 002, in part, does not meet the criteria of Rule 4.05.6(I1)(h).
However, demonstrated embankment stability and structwal integrity, low risk to life and
property, and negligible impacts to water quality from catastrophic failwe, and diminishing
usefulness as these temporary structwes neaz their time of removal, develop a relevant showing
that structwal modifications to correct criteria deficiencies aze not warranted. See Map 8,
• Drainage Control, last revised 5/2/96, for locations described in the following sections of this
Exhibit. The Storm Type selected is Soil Conservation Service (SCS) Type II. Rainfall depths
selected aze 2.10 inch for the 10-yeaz, 24-how event, 2.50 inches for the 25-yeaz, 24-how event,
and 3.4 for the 100-yeaz, 24-how precipitation events (Precipitation-Frequency Atlas of the
Western United States, Volume III -Colorado, National Oceanic and Atmospheric Administration,
1973). Soils information was taken from Map 5. Erodibility and Hydrologic Profile information
was obtained from Soils of Colorado, Loss Factors and Erodibility Hydrologic Groupings, 1983,
Soil Conservation Service. SEDCAD+ pazameter values were selected from SEDCAD+ user's
manuals. Particle size information was derived from sieve analysis information presented in the
Phase II Release Analysis of Pre-Mining and Post-Mining Erosion at the Chimney Rock Mine,
Archuleta County Colorado, September 1992 (Phase II 92). Vegetative and Ground Cover
information was from the same document and the Request for Partial Phase II Bond Release at
Kaiser Resowces, Inc. Chimney Rock Mine Permit No. C-81-023, September 1993 (Phase II 93).
Curve Numbers aze correlated in the following table.
Table 7-1-1 Curve Numbers

Soil Type Location Land Use Description and Hydrologic Curve
Soil Group Number
Nunn Loam, Alluvial Valley Other Agricultwal Lands, Meadow', C 71
Soil Floor soil

Number 1
Other Agricultwal Lands, Pastwe,
74
good', C soil
7-1 8 May 1996