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• 6.0 CONCLUSIONS <br />The data presented in this report shows that the exceedances of the potentially dissolved 30-day <br />average and daily maximum zinc concentrations in flows from the Carlton Tunnel aze <br />attributable to the heary precipitation received since April 1999. The hydrologic analyses <br />presented above indicate that the high precipitation rates in late spring and early summer were <br />not typical of a normal water year. In fact, the precipitation total for the month of April is <br />greater than any monthly total ever measured locally and as such represents an upset condition. <br />The unusually heary precipitation rates in tum led to the increased flow rates in the Carlton <br />Tunnel that were observed over the months. The Carlton Tunnel flow rates measured in June and <br />July were some of the highest flows recorded in the past 10 years. The prolonged dry conditions <br />prior to this record event combined with the intensity of the April and May 1999 precipitation <br />events resulted in a unique geochemical rinsing that led to the upset condition. <br />As the record precipitation caused flow rates within hydrologic system to increase, fractures that <br />• were typically dry became saturated and carried more water. During the dry season or during <br />low-flow conditions, these dry (or partially dry) conduits accumulate secondary zinc-bearing <br />minerals due to evaporation and mineral precipitation processes. These precipitates represent <br />mineralogical sources of zinc-containing material that can be mobilized and ultimately drained <br />from the Cazlton Tunnel. As flow rates through the hydrologic system increase, the secondary <br />zinc precipitates dissolve, causing zinc concentrations in the Carlton Tunnel to increase. The <br />unique antecedent moisture conditions and the record rainfall in April and May 1999, combined <br />to produce unusually elevated zinc concentrations that clearly represent an upset condition. <br />• <br />Cnpple Creek & Victor Gold Mining Compnny Shepherd hfi(lrr, lnc. <br />IIDI.IMONDiP~oxlYlIIOOJ1nRgonunndwrn~J Jm 11 Narember 32. 1999 <br />