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iii iiiiiiiiiiiiiiii , Date: February I I, 2000 TO: Rich Musa, Hydrologist, EPA From: Jim Stevens, Environmental Protection Specialist, DMG ~~ RE: Suggested revisions in proposed clarification letter and QUESTIONS AND ANSWERS addendum. Paragraph 2, Sentence I: (Add the capitalized phrase.) Current Stale policy on drinking water protection within the EPA-approved Wellhead Protection and Source Water Assessment and Protection programs calls For the delineation of wellhead protection areas (WHPAs)/ source water assessment areas (SWAAs) using arts ytical methods based on ultraconservative assumptions (ie. single input values for aquifer properties and no consideration of dilution, dispersion, other contaminant attenuation mechanisms OR HYDRAULIC CHARACTERISTICS ENTIRELY REPRESENTATIVE OF THE MOST PROBABLE PATH THE CONTAMINANTS MIGHT TAKE.) Paragraph 2, Sentence 3: (Substitute the capitalized word.) The approach used in my work was an ultra~;onservative ground-water velocity calculation which is TECHNICALLY consistent with and applied based on the recommended methods for WPHA/SWAA delineation within the State's programs. Paragraph 3, Sentence 2: (Substitute the following sentence.) THIS HYDROLOGICAL ASSESSMEN']' WAS MADE EVEN THOUGH 1T 1S NOT THE ALAMOSA FORMATION BUT THE SANTA FE FORM/~TION, A LOW PERMEABILITY UNIT, THAT UNDERLIES THE SOUTHWEST PERMIT BOUNDARY AREA OF THE FACILITY AND EXTENDS WELL OUT INTO THE BASIN. Paragraph 3, Sentence 3: (Substitute the following sentence.) IT IS BETWEEN THE AREA OCCUPIED BY THE SANTA FE FORMATION AND THE TOWN THAT THE ALAMOSA FORMATION ACTUALLY ItECOMES A PART OF THE GROUND-WATER PATHWAY OF CONCERN. Paragraph 3, Sentence 4: (Substitute the following sentence.) NEVERTHELESS, BY USING THE ALnMOSA FORMATION IN THE ANALYSIS, THE APPROACH BECOMES ULTRACONSERVATIVE AND CONSISTENT WITH THE STATES DRINKBVG WATER PROTECTION PROGRAMS FOR THE DEVELOPMENT OF THE WHPA/SWAA FOR THE TOWN'S WELLS. QUESTIONS AND ANSWERS, Response to question I, Sentence 2: (Substimte the capitalized word.) In this case, the time of travel estimates look at how long it would take for any possible contaminants in the ground water under SIMPLIFIED conditions [o flow from the mine permit boundary to [he drinking water supply wells for the [own. QUESTIONS AND ANSWERS, Response to question I, Sentence 3: (Add the capitalized phrase.) There is no consideration of dilution, dispersion, other attenuation mechanisms within the system, OR HYDRAULI~~ CHARACTERISTICS ENTIRELY REPRESENTATIVE OF THE MOST PROBABLE PATH THE CONTAMINANTS MIGHT TAKE. QUESTIONS AND ANSWERS, Response to question 2, Paragraph 3, Sentence 3: (Omit the underlines and add the capitalized words.) Thus, the resulting 190 yeazs is a conservative contaminant transport value REPRESENTATIVE OF THAT AQUIFER.