ISFAPPC04246

• Case Number: 00CW0101
• Stream Name: Fourmile Creek
• Watershed: Fourmile Creek
• Water Division: 2
• Water District: 12
• County: Fremont
• Instream Flow App - Doc Type: Supplemental Data

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1.0 INTRODUCTION

In 1987, the Federal Clean Water Act was reauth(>rized and Section 319, a new section, was
introduced and added. Under this new section, th'e Colorado Water Quality Control Division
(wQCD) developed a statewide program to determine sources of nonpoint pollution. Section
319 established a federal matching fund for cleanup of nonpoint pollution sources where drinking
water or fish populations are directly affected. As ,part of this program, waters are surveyed to
determine if nonpoint pollution impacts are present; The Colorado Division of Wildlife (DOW)
conducted a stream survey of Fourmile Creek in October, 1988. Fourmile Creek is a tributary
of the Arkansas River located in Fremont and Teller counties (Figure 1).

Nonpoint pollution is defined as the contamination of water by any source that does not enter
the water through a discreet conveyance. Agriculture, mining, and urban construction are
several of the possible causes of nonpoint pollution. In the case of Fourmile Creek, the
suspected source of contamination was the result qf the mining activity in the towns of Cripple
Creek and Victor. From the 1880's and on, manyiflows from mine tunnels, tailings, and waste
rock piles have increased the possibility for contamination. The purpose of this study was to
provide a biological assessment of Fourmile Creek to determine whether or not a 319 project
is feasible.

The metals that commonly impact trout populations in Colorado are zinc, cadmium, and copper.
Other metals including those of lead and silver impact a minimum number of rivers and creeks
in the state. The toxicity of a given concentration of metal is dependent on the instream
alkalinity and hardness concentrations. When values of alkalinity and hardness are less than 100
mg/L, lower concentrations of metals may cause acute or chronic impacts to aquatic life. If zinc
concentrations are less than 50 ug/L, cadmium less than 0.4 'ug/L, lead less than 4 ug/L, and
copper less than 10 ug/L in waters of low hardnesS, sensitive species will be unable to complete
entire life cycles (Colorado Water Quality Standards).

Many species can tolerate higher concentrations qf metals. In the waters of Colorado, where
brook trout are capable of surviving, metal conce~trations may be elevated to a level where the
more sensitive species such as rainbow and cutth~oat trout cannot survive. Chronic impacts to
brook trout for zinc levels occur somewhere b~tween 500-1300 ug/L, for cadmium levels
between 1.7-3.4 ug/L and for copper betweqn 10-17 ug/L. In waters where metals
concentrations exceed the chronic levels for sensitive species and are less than the high levels
for brook trout, various species combinations and numbers of trout are present. For the most
part, as metals continue to increase, first the numqer of species then the number of trout present
decrease (Davies and Woodling 1980). When met1U concentrations reach the maximum endpoint
of the range, causing chronic impacts, the number of brook trout decreases. Further increases
in metal concentrations can result in the complet~ elimination of the brook trout.

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When a stream or cr~k is impacted by metals, a!reclamation project does not have to result in
metal concentrations that are equal to the values for the sensitive species to be altogether
worthwhile. When metal concentrations can be reduced to levels less than that of the maximum
endpoint of the range which causes chronic impacts to brook trout, reproducing brook trout

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