2019-06-28_REVISION - M1977004 ‎(12)‎

• Permit No: M1977004
• IBM Index Class Name: REVISION
• Doc Date: 6/28/2019
• Doc Name: Request For Amendment To Permit
• From: Homestake Mining
• To: DRMS
• Type & Sequence: AM1
• Email Name: DMC
• Email Name: THM
• Media Type: D
• Archive: No

Homestake Mining Company May 10,2019
Regular(112d)Operation Reclamation Permit Application Package
500-year values appear to be similar to the data from Golder (1994). Other stations reported in
Table 2-1 have precipitation values for comparison.
Table 2-1. Precipitation data for 24-hour storm and recurrence intervals from various stations near
the Project site.
24-Hour Storm (inches)
Station (Source) Notes
50 year 200 year 500 year
NOAA Atlas 2, Volume III [Station used from Golder, 1994 2.8 3.2 3.6
(Golder, 1994) not specified]
Pitch Project Site Interpolated by NOAA from other 2.67 3.36 3.88
(NOAA, 2019) stations
Porphyry Creek Similar elevation, nearby, same side 2.72 3.43 3.97
(NOAA, 2019) of mountain
Sargents Much lower elevation, nearby, same 2.14 2.66 3.03
(NOAA, 2019) side of mountains
Pitkin Somewhat lower elevation,far, same 2.25 2.79 3.17
(NOAA, 2019) side of mountains
Cochetopa Creek Much lower elevation,far,out in large 1.86 2.31 2.64
(NOAA, 2019) valley
Salida Much lower elevation, far, other side 2.54 3.14 3.56
(NOAA, 2019) of mountains and in large valley
Data were collected from the Colorado Climate Center (2019) database for monthly data trends.
Several nearby stations (different than those in the NOAA (2019) data) were available, but the
Sargents station's data were used in Table 2-2 due to is close proximity and most complete set
of data over the last 50 years. Monthly precipitation data at the Project site are available, but only
from October 2013 to October 2017. This short range of data is not typically enough to sufficiently
estimate historical trends. Therefore, the data was compared to the Sargents Station's data
(Figure 2-1) to see if they are similar. The median values of both data sets are very similar
(1.60 inches for Pitch and 1.59 inches for Sargents) and along with visual observation Figure 2-1,
indicate the recorded values for other years (1959-2018) at the Sargents Station are likely
representative of the precipitation at the Project site during that same time.
Appendix A provides monthly precipitation values for every year at the Sargents station. Table 2-2
shows the average, maximum, and minimum monthly precipitation values for each month. The
new data from Colorado Climate Center (2019) appear to provide similar results to the Golder
(1994) data. However, two significant differences were noticed:
1. The average annual precipitation from 1959 to 2018 is 22 inches, which is greater than
the range of 16-20 inches reported in Section 2.0 by Golder(1994).
2. The maximum annual precipitation recorded between 1959 to 2018 was 43.5 inches as
compared to 22.85 inches in Section 2.1 by Golder (1994).
EXHIBIT K-RULE 6.4.11 (CLIMATE INFORMATION) Page 2
HOMESTAKE MINING COMPANY