1995-06-14_HYDROLOGY - M1977378

• Permit No: M1977378
• IBM Index Class Name: HYDROLOGY
• Doc Date: 6/14/1995
• Doc Name: Control Chart for Measurement of Animas River Water Quality.
• From: Sunnyside Gold Corp
• To: CDPHE-WQCD
• Permit Index Doc Type: Hydrology Report
• Media Type: D
• Archive: No

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AN iCXO 2"COMPANY
P.O. Box 177 .SIIVWon, CO 61433
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June 13, 1995ivi,>�
Ms. Patricia Nelson
Colorado Department of Public Health and Environment
Water Quality Control Division
4300 Cherry Creek Drive South
Denver, Colorado 80222-1530
ixe: Control Chart for Measurement of Animas River Water Quality
Dear Ms. Nelson:
Enclosed with this letter please find a technical memorandum entitled"Control Charting
of Water Quality Based on Classes of Flow at Station A72, Animas River." The memorandum,
authored by Mark Logsdon of Geochimica, Inc., sets out a discussion of the technical basis of
Sunnyside Gold Corporation's proposal to monitor water quality at Station A72 below Silverton.
Briefly, SGC intends to monitor dissolved zinc as an indicator of water quality, using a
statistical control chart for each of three flow classes. The control charts have been constructed
using the data population of flow and dissolved zinc measurements already gathered by the
Water Quality Control Division, Sunnyside, and others. The charts have upper and lower limits
based on the 95%confidence interval for their sample populations. Going forward, Sunnyside
will sample the Animas at A72 at agreed-upon frequencies, measuring flow and analyzing for
dissolved zinc. Should the concentration of dissolved zinc in the Animas exceed the upper limit
boundaries of the flow-based control chart for three successive sampling periods, water quality
will be deemed not to have been protected by Sunnyside's offsite mitigation work to date, and
Sunnyside will undertake additional mitigation work, negotiate new work commitments, or seek
some form of accommodation from the WQCD. Should such exceedences occur,they will not
form the basis of a citation, notice of violation or other enforcement action against Sunnyside.
Please review this information and provide your comments on the suitability of this
approach to monitoring water quality at A72. We propose to attach an abridged version of the
memorandum to the consent decree now being negotiated between Sunnyside and the Water
Quality Control Division, and wish to be certain that it reflects the thinking of both parties.