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0? 09.00 WED 1J-53 FAS (~pp~ <br />~ ~ UNITED STATES ENVIRONMENTAL PROTECTION AGENCY <br />~~ REGION 8 <br />Y 99918'" STREET -SUITE 500 <br />DENVER, CO 80202-2466 <br />http:t/Www.epa.govlnvgion08 <br />DRAFT <br />Ref: 8EPR-EP <br />Ms. Kathleen Reilly <br />Outreach and Assistance Unit <br />Water Quality Control Division <br />Colorado Department of Public Health and Environment <br />4300 South Cherry Creek Drive <br />Denver, Colorado 80246-1530 <br />RE: Clarification on Recotnmendations for <br />Grouad-Water Monitoring is the San Luis <br />Area <br />Dear 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 Battle 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 regard 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 ptograrns calls for the delineation of <br />wellhead protection azeas (WHPAs) /source water assessment azeas (SWAAs) using analytical <br />methods based on ultraconservative assumptions (ie., single input values for aquifer properties <br />and no consideration of dilution, dispersion, or other conrarr,;~a~t attenuation mechanisms). <br />State policy is to use a 5-yeaz time of vavel in the determination of WHPAs/SWAAs for use in <br />these programs. The approach used in my work was an ultraconservative ground-water velocity <br />calculation which is scientifically 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 compazison versus the existing State policy of 5 years to show <br />whether or not the facility in question would be located within the WHPA/SWAA roar would be <br />delineated based on ground-water flow time of travel determinations. <br />O L ~ ~Pmbd on Recycled paper <br />