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of the time of day the measurement was conducted, and thus do not have a spatial pattern, '. The pH in Fourmile Creek was relatively basic, reflecting the geology and morphology of the basin. In the smaller, colder headwater reaches of Fourmile Creek above the town of Cripple Creek, the pH is closer to a neutral pH of 7. As the stream travels downstream, COllecting more ground water and surface runoff, the pH increases to around 8.3 to 8,5. Hardness (calcium and magnesium). mitigates metal toxicity, As hardness increases, the toxicity of a metal concentration usually decreases. The hardness in the Fourmile Creek Drainage was increased by Ariqua Gulch (via Cripple Creek) and the Carlton Tunnel. The hardness levels of Ariqua Gulch and the Carlton Tunnel are higher than in most Colorado mountain streams. ~,..) ;;. Metal concentrations in Fourmile Creek upstream of Cripple Creek were at or less than detection limits, although iron and manganese were present in the Fourmile Creek headwater reaches, Both Cripple Creek a'nd Carlton Tunnel increased the metal concentrations in Fourmile Creek (Table 3), The highest metal concentrations were found downstream of the Carlton Tunnel. Fourmile Creek metal concentrations were not at levels toxic to fish or macroinvertebrates. 3.1.2 Cripple Creek Cripple Creek and Ariqua Gulch were sampled for the first time in 1995. Ariqua Gulch influenced the water chemistry of Cripple: Creek (Table 4), For example, upstream of Ariqua Gulch, the pH of Cripple Creek was basic, 8.28 and downstream of Ariqua Gulch pH was 7,71. Ariqua Gulch was acidic (pH = 6,33) with a very low alkalinity (6mg/1 CaC03) indicating a low buffering capacity, Hardness and sulfate were very high in Ariqua Gulch compared to a "typical" Colorado mountain stream, Cripple Creek hardness and sulfate concentrations increased downstream, with the largest increase just downstream of Ariqua Gulch. Metals in Cripple Creek were higher d~wnstream of Ariqua Gl.Jlch compared to upstream (Table 5). However, metal levels decreased as Cripple Creek flowed downstream to the confluence with Fourmile Creek due to dilution and/or precipitation. Cripple Creek metal concentrations were lower at the confluence with Fourmile Creek than upstream of Ariqua Gulch, The copper concentration in Cripple Creek upstream of Ariqua Gulch (18 ugll) exceeded a level of 17.4 ugll known to cause 100% chronic (long term) mortality to brook trout (McKim and Benoit 1974). Downstream of Ariqua Gulch, the copper concentration of 14 ugll approached the ~rook trout chronic value for low hardness waters, However, hardness levels were elevateq so that copper was not toxic. Brook trout are the most sensitive trout species to copper. ' '''4'\'''' Metal concentrations in Ariqua Gulch were higher than any other location sampled in the Fourmile Creek Basin by the DOW in' 1995. Cadmium, ml'lnganese and zinc 4 I I I I I 'I I I I I I I I I I I I I I