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• 02~:02100 WED 15:08 FAb • • C~J OOJ <br />~~~' UNITED STATES ENVIRONMENTAL PROTECTION AGENCY <br />~~j REGION 6 <br />YY 9991aTMSTREET -SUITE 500 <br />DENVER, CO 80202-2466 <br />http:l/www.epa. govlreg1an06 <br />Ref: 8EPR-EP FE° -2 2000 <br />MEMO_ ALUM <br />DATE: February 2, 2000 <br />FROM: Rich Muza <br />T0: Kathleen Reilly, CDPI-IE <br />SUBJECT: Clarification on Recommendations for Ground-Water Monitoring in the San Luis <br />Area <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. This time of travel <br />determination was performed for the sole purpose of providing an ultraconservative estimated <br />value for ground-water flow in the area to aid the San Luis Water end Sanitation District <br />(SLWSD) monitoring project. I would like to clarify the approach and purpose of this work and <br />provide in writing an additional recommendation for this project based on this infonnation- <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 areas (WHPAs) ! source water assessment areas (SWAAs) using analydcal <br />methods based on ultrawnservative assumptions (ie., no dilution, dispersion, or other <br />contaarinant attenuation mechanisms). State policy is to use a 5-yeaz time of travel in the <br />determination of WIiPAs/SWAAs for use in these programs. The approach used in my work <br />was an ultraconservative ground-water velocity calculation using Dazcian principles which is <br />scientifically consistent with the recommended methods for WPHA/SWAA delineation within <br />the State's programs. The resulting value of time of travel was presented for compauison versus <br />the existing State policy of 5 years and is presented to show whether or not the facility in <br />question would be located within the WHPA/SWAA that would be delineated based oa ground- <br />water flow time of travel determinations. <br />The calculation of time of travel from the southwestern mine permit boundary to the <br />town's nearest drinking water-supply well was performed using values for hydraulic parameters <br />~Pringd 0f1 Recycled Paper <br />