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these precipitates as being comprised of sulfate salts of magnesium, sodium, calcium, manganese, and zinc. Denny and others (1930) make similar observations of the presence of secondary sulfate salts comprised of variable mixtures of calcium sulfate, magnesium sulfate, iron-aluminum sulfate, manganese-sulfate, manganese-silica, and aluminum-silica. The precipitation of efflorescent salts along flow paths through the diatreme is expected to be a yearly or seasonal occurrence, with the amount of salts that can accumulate being dependent on the duration of the dry season. In all likelihood, these various salts also incorporate substantial amounts of zinc into their crystal structure (Keith and others, 1999). These salts are potentially the most important sources of zinc in the Cazlton Tunnel water because they are readily soluble and may be rinsed from the subsurface during periods of high infiltration and flow through the flow paths that lead to the Carlton Tunnel. 2.3 Hydrology ABC (1998) provided a detailed evaluation of the water balance for the Carlton Tunnel. The Carlton Tunnel was constructed between 1939 and 1941 for the purpose of draining underground mine workings in the diatreme. The Carlton Tunnel also drains the granitic rock through which it was constricted. At the current time, [he diatreme is largely unsaturated at elevations above the Carlton Tunnel. Saturated conditions are believed to occur a[ elevations just above the Carlton Tunnel (approximately 3,100 feet bgs), although the exact elevation is probably variable, depending on localized occurrences of fractures. Given the area of the diatreme and the calculated average annual infiltration rate, the amount of water that enters the diatreme has been calculated at 1184 gpm (ABC, 1998). The diatreme is much more permeable than the surrounding granite, hence it acts as a large well that receives flows from the surrounding granite. The rate of inflow to the diatreme and ultimately to the Cazlton Tunnel from the granite is estimated at 322 gpm (ABC, 1998). An additional 92 gpm is estimated to infiltrate to the Carlton Tunnel from the surrounding granite. Considering these sources, the total amount of water entering the Cazlton Tunnel has been estimated at 1593 gpm (ABC, 1998), which is slightly greater than the average flow rate of 1585 gpm from the tunnel. Cripp/c Crcck rY Viaar Gafrf rNining Compnn}' ShephcrA,Ni(lcr, lrtc. IIDI.{M0.1'DIP-OR/VEl/pJ{bT.RrpnUttn[Amcnrl Ja 3 November?I, 1999