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I <br />• III IIIIIIIIIIIII III • <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Deparlmem of Natural Resources ~~~~~ <br />1 ~ I i Sherman Si.. Room 21 5 <br />Dem~er, Galorado AO'_03 <br />Phone 11113 1 116 6-3 5 6 7 <br />E,~x:13o3~ A3z aio6 DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Ruy Rumrr <br />ME]\ZO Gueernor <br />~amcs 5. Luchhead <br />E eeutlrve Direr for <br />M¢hael B Long <br />TO: James Stevens Division Dnector <br />James Peudletou <br />FROM: James Dillie ~~- <br />DATE: January 26, 1996 <br />RE: GROUNDWATER MODEL REVIEW-Santa FeForTnationUndCrlyingTailings <br />Facility -San Luis Project - Permit No. M-88-112 <br />During the December 8, 1995 meeting, the Division requested that BMRI evaluate fluid travel times <br />in the saturated portion of the Santa Fe Formation beneath the tailings facility to the closest existing <br />Santa Fe Formation monitoring well (M-14). The fluid travel time model is to be based on a range <br />of actual data and a set of hypothetical assumptions proposed by the Division. <br />The proposed assumptions were: 1) a leak occurred in the tailings pond during the 1991 excursion <br />when cyanide was at elevated levels (200+ ppm total cyanide), 2) the leak occurred when the water <br />level in the tailings pond created maximum head (the lower pond had the highest water level during <br />the excursion, so it was selected as the worst possible case), 3) the distance from the lower pond <br />to the M-14 monitoring well is 1,400 feet, 4) leaking fluids are input directly to ttrre groundwater <br />under saturated flow, 5) the leak is of sufficient volume to create flow to the groundwater, 6) the <br />minimum porosity value is 20 °k (.20) and 7) the groundwater hydraulic gradient in the Culebra <br />Creek drainage is .052 ft/ft. <br />BMRI was asked to evaluate a range of fluid travel times based on permeability data from actual <br />test results obtained from falling-head tests conducted during 1988 in nine (9) bore holes which <br />penetrated the Santa Fe Formation. <br />BMRI determined that the maximum hydraulic conductivity (2.1 x 10-' cm/sec) would produce a <br />seepage velocity of 1.55 ft/day or 565 ft/year. At this seepage velocity, it would take about 2.5 <br />years for the leaking contaminant to reach the M-14 well. <br />