INSPEC29787

• Permit No: M1977215
• IBM Index Class Name: Inspection
• Doc Date: 3/28/1994
• Doc Name: HYDROLOGIC EVALUATION BULLDOG MINE FN M 77-215
• From: DMG
• To: HOMESTALK MINING CO
• Media Type: D
• Archive: No

~ I II I IIII II IIIII I II I ~

STATE OF COLORADO '
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
1313 Sherman St., Room 215 I{y

Denver, Colorado 80203 ~~~

Phone: [phone] III
FAX: [phone]
DEPARTMENT OE
NATURAL
RESOURCES
March 28, 1994 aoy ROmer
Governor
Mr. Luke Russell Kensa'a:a.
Homestake Mining Company E.er~~weD~re<~n~
650 California Street A1lc hael B. Gmg
Drviuon Dvccmr
San Francisco, CA 94108
Re: Hydrologic Evaluation, Bulldog Mine, File No. M-77-215
Dear Mr. Russell:
This letter will serve as notification of acceptance of the revised
Bulldog Mine hydrologic evaluation, and the appurtenant windy gulch
design criteria and riprap gradation requirements, included in your
letter and attachments dated March 23, 1994. Some explanation is
necessary regarding the Division's assignment of a Curve Number
(CN) in the range of 75-82 in previous correspondence, and our
acceptance now of a CN of 68. The assignation of a CN in the range
of 75-82 was a result of duplicating the methodology used by Scott
Benowitz as detailed in his letter dated January 22, 1994. Using
the TR-55 tables and soil information available to him at that
time, Mr. Benowitz had selected a CN of 41 for the basin, then
increased this to a CN of 55 to allow "for small areas of fair and
poor hydrologic condition and a safety factor". In specifying a CN
in the range of 75-82, I had used the TR-55 tables to select a CN
of 61, a selection verified in Scott Benowitz most recent
evaluation, then added 14 to come up with a CN of 75 (14 being the
numeric value added to the TR-55 table value in Scott Benowitz
original evaluation). Thinking that an addition for "small areas
of fair and poor hydrologic condition and a safety factor" might
more appropriately be determined as a percentage increase, I
increased the table value of 61 by 34 percent (the same percentage
increase utilized in the original evaluation) to come up with a CN
of 82. Hence the assignment of a CN in the range 75-82 in my
letter dated February 23, 1994. The Division's acceptance of a CN
of 68, rather than requiring an evaluation using a minimum CN of
75, is based on the reduced necessity of a safety factor due to the
relative increase in confidence regarding soil type information for
the Windy Gulch drainage basin.
The effectiveness of the proposed Windy Gulch channel upgrade is
partly dependent upon the quality of the riprap utilized, which
must be durable and chemically inert. The Division understands
that the riprap source for the project will be talus from the 9700'
portal area. Homestake should assure that only non-mineralized and