HYDRO30853

• Permit No: M1981165
• IBM Index Class Name: Hydrology
• Doc Date: 9/13/1996
• From: LABORATORIES
• To: MINE DEVELOPMENT CORP
• Media Type: D
• Archive: No

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L A B O R A T O R I E S
A DIVISION OF CASA DEL SOL. INC.
September 12, 1996
QENVER
OFFICE
Received
Mine Development Corp
Tray Scofield
7026 Fuchsia Lane
Humble, TX 77346
Dear Mr. Scofield,
SEP 1 3 1996
[phone]
FAX [phone]
1-800-553-6266
F)urango Field 0flice
4ivision of Minerals & Geology
In answer to our discussions of yesterday please accept the following as
documentation for the "detoxification" of the waste ore pile that was left over
from past cyanide leach operations at your operation in La Plata County Colorado
known as the Neglected Mine. As the attached graph and its accompanying table
demonstrate the cyanide levels at the mine opening just below the abandoned heap
leach pad have dropped dramatically over the past three quarters. The total
cyanide has dropped over 70%. The most dramatic drop was after the first
sampling event. This dramatic drop was due to the extensive detoxification using
hydrogen peroxide. In this process, the peroxide was diluted and sprayed over the
pile while it was mixed using a track doser. The pile was mixed several times to
within one foot of the liner while the peroxide was sprayed on the moving waste
ore. The ore was shaped and allowed to remain in storage.
During the past thrE:e quarters tested, the pH of the pile slowly became more
acidic (7.50 to 7.09 to 6.18]. This small increase in the acid levels allowed the
production of low levels of ferrous iron which will complex cyanide [along with
other metals] to form an unreactive chelate of cyanide [ Fe (CN}x }. The attached
Table shows that the total iron increased from 0.190 to 0.198 to 0.220 mg/L
during the same time period. This iron chelate is not available to the WAD cyanide
test.
When the data from the third quarter is analyzed, with consideration of the
iron levels of 0.22 mg/I this total cyanide would be almost completely attached to
the iron atoms. Since this iron bound cyanide is not available to the WAD Cyanide
reaction, this unreactive value must be removed from the values found in the water
passing through the abandoned heap leach pad into the surface water below. The
iron level of 0.22 mg/I would bind [chelate] with over 90% of the total cyanide [at
the pH of 6.13]. This calculation would remove at least 0.034 mg/I of the total
cyanide and leave a WAD Cyanide value of about 0.0038 which is well below the
esu 75 Suttle Street .Post Office Box 2605. Durango Colorado 81302 ~~