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20-30% water younger than 50 years old and 70-80% water older than 50 yeazs, using other <br />estimation methods based on water balance. <br />The time estimates of groundwater movement likely represent a composite age for the mixture of <br />young water (recent rainfall that reaches the Carlton Tunnel via interconnected fractures and <br />historic underground mine workings) and old water (slowly infiltrating water through the <br />mineralized complex). Following unusually lazge precipitation events, it might be anticipated <br />that a higher tritium (younger) value would be determined for the Carlton Tunnel water because <br />of increased infiltration rates of rainwater (young water) through fractures and interconnected <br />underground workings. <br />During the very high flow period in AugusdSeptember of 1999, a water sample from the Carlton <br />Tunnel (collected on September 8, 1999) was determined to have a tritium content of 6.26 TU <br />(Table 10). This tritium value is slightly higher than the previously determined average value of <br />5.4 TU (Table 9), indicating that a larger proportion of yomtger water is making its way to the <br />Carlton Tunnel during periods of high precipitation and infiltration. <br />Although the tritium analyses indicate that the bulk of the water flowing from the Cazlton Tunnel <br />is more than 25 to 50 years old, it would take a relatively small amount of young water with <br />elevated zinc concentrations to produce a significant effect on the concentration in [}te Carlton <br />Tunnel flow. For example, to account for the peak zinc concentrations observed in May and <br />June 1999, an increase in flow (of young water resulting from precipitation) of only 10% with an <br />accompanying zinc concentration of 7 mg/L would be required. Both of these assumptions (flow <br />increases and zinc concentrations in rinsing solutions) are reasonable estimates, based on the <br />hydraulic investigation presented above and knowledge of the effects of seasonal dissolution of <br />soluble salts in mining systems (Bayless and Olyphant, 1993; Alpers and others, 1994; Keith and <br />others, 1999). <br />• <br />Cripple Crcek & Virmr Gold hlinirtg Company Shepherd Mdlcr. lnr. <br />nD/.1.NONDIP-OR14'EV°°JJTRrryrtNnndnaJ dx 8 NovemLcr??. 1999 <br />