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'~~~'• UNITED STATES ENVIRONMENTAL PROTECTION AGENCY <br />~~ REGION 8 <br />,~ ~ 99B 18TM STREET -SUITE 500 <br />DENVER, CO 40202-2166 <br />http:/Iwww.epa.govlregion06 <br />DRAFT <br />Ref: SEPR-EP <br />Ms. Kathleen Reilly <br />Outreach and Assistance Unit <br />Water Quality Control Division <br />Colorado Departittent of Public Health and Environment <br />4300 South Chcrry Creek Drive <br />Denver, Colorado 80246-1530 <br />RE: Clarification on Recommendations for <br />Ground-Water Monitoring in the San Luis <br />Area <br />Deaz Ms. Reilly: <br />In my letter to you dated January 18, 2000, I provided a simplistic analytical evaluation of <br />ground-water flow in the area around the Town of San Luis with an estimated time of travel from <br />the $attle Mountain Gold facility to the town's drinking water-supply wells. I would Like to <br />clarify the approach and purpose of this work in regazd to the San Luis Water and Sanitation <br />District's (SLWSD) monitoring project. <br />Current State policy on drinking water protection within the EPA-approved Wellhead <br />Protection and Source Water Assessment and Protection programs calls for the delineation of <br />wellhead protection aeeas (WHPAs) /source water assessment areas (SWAAs) using analytical <br />methods based on ultraconservative assumptions (ie., single input values for aquifer properties <br />and no consideration of dilution, dispersion, oz other contaminant attenuation mechanisms). <br />State policy is to use a 5-year time of travel in the determination of WHPAs/SWAAs for use in <br />these programs. The approac)LUSed in my work was an ultraconservative ground-water velocity <br />calculation which is seieatly consistent with and applied based on the recommended <br />methods for WPHAISWAA delineation within the State's programs. The resulting value of time <br />of travel was presented for comparison versus the existing State policy of 5 years to show <br />whether or not the facility in question would be located within the WHPAlSWAA that would be <br />delineated based on ground-water flow time of travel determinations. <br />~ooz <br />~., <br />_ ,~ _, <br />V Pnnted on Recycled Peper <br />