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direct relationship between potentially dissolved zinc concentrations and precipitation (Figure G), <br />and the corresponding increase in flow from the Carlton Tunnel (Figure 5). The elevated zinc <br />concentrations that coincided with increases in flow, represent the upset condition for the Carlton <br />Tunnel. <br />4.3 Lag Times <br />The increases in flow and potentially dissolved zinc concentrations at the Carlton Tunnel in <br />response to precipitation events indicate that the lag time could be as long as 33 days (from <br />snowmelt after April 1) or as short as 8 days from rain and/or snowmelt on April 28 (Figures 4 <br />and 6). <br />The most dramatic rise in flow and zinc in the Carlton Tunnel was observed between May 12 <br />and May l9, 1999. The most likely storm event causing this increase of flow and zinc in the <br />tunnel is [he near-record snowstorm that began on April 28. Given this date, the lag time can be <br />estimated to be between 14 and 21 days. <br />4.4 Age of the Water in the Carlton Tunnel <br />The lag time between a precipitation event and the corresponding change in flow in the Carlton <br />Tunnel is only part of the characterization. Although rainfall and/or snowmelt are the driving <br />forces behind the flow response in the Cazlton Tunnel, the infiltrating precipitation is not <br />necessarily the same water that flows from the tunnel. <br />Measurements of tritium concentrations in water from the Carlton Tunnel between November <br />1997 and August 1998 yield an average value of 5.4 tritium units (TU; one TU is one tritium <br />atom per 10'g hydrogen atoms). Tritium concentrations in water from near-surface monitoring <br />wells and the drinking water supply for the town of Victor, Colorado, collected during the same <br />time period, yield a range of 14 to 2l TU for water samples (Table 9). <br />Based on the difference in tritium concentrations behveen the Carlton Tunnel and the shallower <br />waters, a time of about 2 half-lives for tritium (t'/Z = 12.43 years) or about 25 years, would be <br />needed [o achieve the measured decrease in tritium levels measured at the Carlton Tunnel. <br />However, not all of the water flows through the diatreme and into the Carlton Tunnel at the same <br />rate. ABC (1998) estimated that the water in the Carlton Tunnel is comprised of approximately <br />Cripple CreeA ~ yiROr Gold ,4)ining Compnny Sheppard .4111/cr, /nr. <br />uDl.1AIONDiP.OR/VEilOpfbnRmortt~rrnrAmurJ /z 7 Na~~embcr ll. 1999 <br />