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~! <br />~SED ~~ <br />~m~~ <br />~, ~/ ~ <br />F,~ <br />Ref: 8EPR-EP <br />~ III IIIIIIIIIIIIIIII ~- ~~ <br />UNITED STATES ENVIRONMENTAL PROTECTION AGENCY <br />REGION 8 <br />99918'" STREET -SUITE 500 <br />DENVER, CO 80202-2466 <br />http://www.e pa. gov/reg i on08 <br />~~~° <br />~~GE <br />a r~pp0 <br />n~o~M~~ <br />;; <br />Ms. Kathleen Reilly <br />Outreach and Assistance Unit <br />F E B 1 7 2000 <br />Water Quality Control Division <br />Colorado Department of Public Health and Environment <br />4300 South Chevy 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 lever to you dated January 18, 2000, I provided an evaluation of ground-water flow <br />in the azea azound the Town of San Luis with a simplistic analytically estimated time of travel <br />from the Battle Mountain Gold facility to the town's drinking water-supply wells. The approach <br />used for this estimate follows the methods of the State's Wellhead Protection Program which <br />uses simplistic, ultraconservative analytical methods for drinking water protection. 1 would like <br />to clarify the approach and purpose ofthis 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 \~Jellhead <br />Protection and Source Water Assessment and Protection programs 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 />that may not be entirely representative of the most probable pathway that the contaminants might <br />take to a well and no consideration of dilution, dispersion, or other contaminant atterfuation <br />mechanisms). The methods employed for WHPA/SWAA delineation use simple equations based <br />either on volumetric flow concepts or on Dazcy's Law. State policy is to use a 5-year time of <br />travel in the determination of WHPAs/SWAAs for use in these programs. The 5-year time of <br />travel is used by the State and locals in order to determine those potential sources of <br />~Prinfed on Recycled Peper <br />