GENERAL31667

• Permit No: M1988112
• IBM Index Class Name: General Documents
• Doc Date: 3/9/2000
• Doc Name: RECOMMENDATIONS FOR GROUND WATER MONITORING IN THE SAN LUIS AREA COST ILA COUNTY
• From: COLO DEPT OF PUBLIC HEALTH AND ENVIRONMENT
• To: ECOSYSTEMS PROTECTION PROGRAM
• Media Type: D
• Archive: No

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Bill Owens, Governor
Jane E Norton, Eeecutive Director
Dedicated to protecting and iml
4}00 Cherry Creek Dr. S.
Denver, Colorado BO24G1530
Phone [phone]
TDD Line [phone]
Located m Glendale, Colorado
hap'/hvwsecdphe sta[e.co.us
^~'E. ~ ~^ 200
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March 8, 2000
Mr. Rich Muza, Hydrologist
Ecosystems Protection Program
Office of Ecosystems Protection and Remediation
U.S. Environmental Protection Agency, Region 8
999 Eighteenth Street, Suite 500
Denver, Colorado 80202-2466
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Colorado Department
of ('ublic Healrh
and Environment
RE: Recornmendations for Ground Water Monitoring in the San Luis Area, Cost lla County
Dear Mr. Muza:
We have received your report, dated January 28, 2000, and the follow up clarification letter of
February 17, 2000, on the recommendations for ground water monitoring in the San Luis area. We
have also received the draft questions and answers on this situation that you prepared to explain the
approaches and terms used in the report and have received copies of the letters from the state Division
of Minerals and Geology (DMG) written in response to your report and clarificatior letter.
You will recall that, pursuant to a request from the San Luis Water and Sanitation E istrict (District),
we requested your assistance in determining the best location for a drinking water monitoring well for
the District. A representative of the District had contacted us expressing concern at~out possible
contamination from "a nearby gold mining operation." The District had decided that they wanted to
monitor the situation and asked for assistance in determining the best location to drill a well.
The report and follow up clarification describe the assumptions used and research undertaken to
complete an analysis using the wellhead protection assessment (WHPA) model dest;ribed in
Colorado's wellhead protection plan. The model results indicate that it would take art estimated 15
years for a contaminant to move through the Alamosa aquifer from the southwest comer of the Battle
Mountain Resources, Inc. ($MRI) mining site to the District's noRhem well. Under Colorado's
wellhead protection plan, technical assumptions and a modeling approach are estab.ished to generate
very conservative results in order to identify potential risks to drinking water supplies. If, after
implementing such conservative assumptions, the predicted time of travel (TOT) to the drinking water
supply well exceeds five years then no real threat has been identified and no further action is taken.
The Division agrees with the EPA that the methods and assumptions used to amve at your conclusions
predict a significantly shorter time of travel than would more sophisticated models :hat account for a
number of additional factors. The Division believes that, where such models and data to calibrate them
are available, we should take advantage of them to develop a more accurate prediction of TOT.
STATE OF COLORADO
aroving the health and environment of the people of Colorado
Laboratory and Radia4nn Services Drvrsion
8100 Lowry Blvd.
Denver CO 110230-6920 s, I VE D
1703169?-3090