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• 5.0 HYDROGEOCHEM[CAL RESPONSE OF THE CARLTON TUNNEL The peak flow for 1999 from the Carlton Tunnel was 1,887 gpm recorded on June 1, 1999. The peak zinc concentration was measured on May 19, 1999. As discussed above, April 1999 was the wettest April on record. Wet conditions prevailed through the summer of 1999, as well, generating conditions that likely maximized the amount of infiltration into the diatreme and caused increases in flow rate and zinc concentrations for the Carlton Tunnel. The snowstorms that occurred before [he April events generated snowmelt that began to increase the amount of water saturation in the fractures, fissures, and other flow paths. This increase in saturation shifted flow from the smaller fractures and pores to the larger ones. Capillary tension dictates that the smallest fractures/pores will retain the highest degree of saturation following an extended dry period (e.g. winter). By having a higher degree of saturation than larger fractures and pores, these small fractures are able to transmit water and provide the base flow to the Carlton Tunnel. • Following the relatively dry winter months of 1998/1999, the initial spring snowmelt period in April 1999 likely resulted initially in an increase in the degree of saturation in the fractures and pores of the unsaturated parts of the diatreme. As the degree of saturation increases, the hydraulic conductivity also increases. Thus, initially, the smallest fractures would have had the highest hydraulic conductivity and transmitted more water than the larger fractures (given the sanre gradient). As the degree of saturation continues to increase, the hydraulic conductivity of the larger fractures rapidly exceeds the smaller fractures and they begin to transmit more water. According to tritium age-dating techniques, the water flowing from the Carlton Tunnel is likely composed of a mixture of old water and young water. The older portion is attributed to the water retained in the small pore spaces and small fractures that continuously supplies water to the base flow in the Carlton Tunnel. This water is likely following the smaller fractures and pores toward the [camel. The young water in the Carlton Tunnel is the result of fresh infiltrating water following the most permeable conduits (larger fractures) to the tunnel. These large fractures contain deposits of soluble sulfate salts of zinc and other metals that have • precipitated during periods when these large fractures were dry. Historical accounts of efflorescent salts on the surfaces of underground workings confirm that soluble minerals form in Cripple Crcek & Mirror Gald ,timing Company Shepherd Aliller, Inr. iiDI.IMO,VDiP-OR/Vlll00fb:VleynUnnrhmnrl Jor 9 No~•ember ll, /999