GENERAL48692

• Permit No: C1981019
• IBM Index Class Name: General Documents
• Doc Name: Proposed Decision & Findings of Compliance
• Permit Index Doc Type: General Correspondence
• Media Type: D
• Archive: No

-24-
This is a temporary condition, and over an extender period of time, these
surface soils will consolidate to approximate pze-mining condition.
Nevertheless, the short-term effects-of mining will be an incr~se in the
infiltration rate and moisture-holding capacity of the surface soils,
This will result in an increase in evapotranspiration and a net decrease
in surface runoff.
The EMRIA Report Number 3-1975 indicates the premeability for surface soils
before mining were slow to moderately slow, 0.20 to 0.60 inch per hour.
Mosi tore retention or water-holding capacity for these soils was rates good,
ranging between 4 and 6 inches per effective soil depth. In studying the
infiltration rate of reclaimed lands at Colowyo, Striffler, and Rhodes
(1981) calculated a mean final infiltration capacity of 5.5 cm per hour
at the Colowyo mine site (2.17 inches per hour).
Estimating composite Runoff Curie Number of 67 and 63 for the pr:e-mining
and post-mining conditions respectively results in maximum potential
differences of 4.93 inches for the pre-mining condition and 5.87 inches
for the post-mining or reclaimed condition. Utilizing these relationships
results in an estimated mean annual runoff of 0.35" and 0.24" for the
pre-mining and reclaimed post-mining conditions respectively. These
relationships are tabulated below:
Ztem
Pre Mining
Post lining
Curve Number, CN 67
Runoff, Q, in inches 0.35
Potential difference, S, in inches 4.93
Initial abstraction, Ia, in inches 0.99
63
0.24
5.87
1.17
During the Life-of-the-mine, it is anticipates that a total of 1,433 acres
will eventually be disturbed in Streeter Gulch and other areas tributary to
Good Spring Creek. Another 595 acres will be disturber in areas which are
included in the II'aylor Creek-Wilson Creek drainage basins. Mean annual
runoff from these reclaimed areas are estimates to be as follows:
Drainage Basin Pre Mining Post Mining Difference
Good Spring Creek 42 ac. -f t. 29 ac.-f t. 13 ac. -f t.
Taylor Creek 17 ac. -f t. 12: ac.-f t. 5 ac. -f t.
The Hydrologic consequences of mining on the various drainage basins
downstream of the Colowyo mine site are summarized below.