PERMFILE64785

• Permit No: C1980001A
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: pages 2.5-1 to 2.5-107
• Section_Exhibit Name: 2.5 HYDROLOGY
• Media Type: D
• Archive: Yes

Topsoiled are expected to have a potential maximum surface retention somewhat
• greater Thon 10 inches due to their apparently high infiltration capacity, numerous
small closed depressions, and poorly developed surface drainage. On the other hand,
the graded and topsoiled and graded spoils that occupy a portion of the permit area
and the undisturbed portion in the Moffat Area are believed to have a potential
maximum retention less than 10 inches. The value of 10 in used for the potential
maximum retention is believed to be a reasonable mean or the entire lease area as
iT now exists. The manner in which this number is expected to be modified as a
result of mining and subsequent reclamation is discussed in Section 2.5.3.
Using S = 10 inches, values for qk were computed. As an example, the value
of qk for k = 6, corresponding to a precipitation of 3.25 inches is:
q6 = 0.01 [3.25 - 0.2 (10)]2 = 0.0014.
3.25+0.8(10)
A similar computation was made to obtain the remaining values shown in the fourth
column of Table 2.5-22. Note That this procedure yields no surface runoff for 24
hour storms less than 2 inches in magnitude.
• The summation of the qk in Table 2.5-22, multiplied by the mean number of
rainfall events, yields the mean annual surface runoff from rainfall. Precipitation
records at Pyramid show that over the period 1951 - 1970, the mean number of days
per year that rainfall exceeded 0.1 inches was 36.5 days. Therefore, 36.5 was used
for N, yielding an average annual surface runoff from rainfall equal to 0.15 inches.
At first glance, This value for surface runoff appears to be less than one would
expect. However, much of the flow that is observed in the numerous drainages on
the Edna Mine is due to subsurface runoff seeping into the surface channels. Further
discussion of the reasonableness of the calculated overland flow runoff is presented
after the remainder of The hydrologic budget is calculated.
The final step in the computation of the surface water budge is to distribute
the mean annual surface runoff by months. This is accomplished by determining the
distribution coefficients Ri based on the fraction of the Total available precipitation
that is available in each month. The data used to determine the Ri are from the
20 year records at Pyramid. The computations are shown in Table 2.5-23. The
difference between the precipitation available for infiltration or runoff given in
Table 2.5-20 and Q given in Table 2.5-23 is the infiltration, I, used as input to the
• subsurface balance.
Revised 7-81 2.5-84