Page 804 - The Toxicology of Fishes

784 The Toxicology of Fishes

the litigation. In 1998, the State of Montana was awarded $260 million to clean up the primary waste
deposits in the 40-km reach of Silverbow Creek between the mine and the smelter. In the early
remediation, tailings were removed, and streambeds were reconstructed from experimental segments of
the creek. By 2005, a massive effort was underway to reconstruct the creekbed over large areas and to
move all the major tailings deposits from the Silverbow floodplain to the large, historic tailings ponds
near Anaconda. The slickens were replaced with uncontaminated fill. Today, metal-tolerant grasses are
becoming established over many of the former slickens, changing both the appearance and the ecology
of the riparian zone. Anecdotal evidence indicates that invertebrate communities are gradually increasing
in diversity and abundance in the creek, and anecdotal reports of fish in the stream have also appeared
in recent years. It is not yet clear whether or not tailings left behind under some of the fill will cause
problems in the future, and there are questions about the stability of the remediated creekbed during
floods. Most important, however, systematic and detailed studies documenting successes and failures
are not yet a part of the remediation effort. Nevertheless, improvements are obvious as a result of one
of largest remediation efforts in any mining region in the world. Limits to progress reflect the massive
extent and complexity of the problems, and the short period of the restoration effort (a decade) compared
to the 15 decades of damaging activity before it began.

Warm Springs Ponds

Modern, well-run mining operations capture and contain tailings in (sometimes extremely large) pond
systems, although well-known exceptions also exist (e.g., the OK Tedi mine in Papua New Guinea is
built on extremely steep terrain and releases tailings directly into the Fly River). Between the 1870s and
1950s, little effort was made to capture contaminated soils, sediments, or waters from the Clark Fork
mining and smelting operations. Historically, the Clark Fork River was turbid with sedimentary mine
waste for over 200 km downstream, at least periodically into the 1950s. Before the 1900s, Evermann
(1892) seined the Clark Fork River near Deer Lodge (Figure 19.1) and found no fish. He stated that the
river “is said to have been well supplied with trout and other fish, but none has been seen since the
concentrators began operations.” In the 1950s, ponds were completed that contained smelter wastes and
mine tailings. Another set of ponds attempted to capture Silverbow Creek near its terminus and settle out
contaminants. Through the next three decades the pond systems were upgraded, and water treatment (e.g.,
liming) was added; however, sedimentary wastes bypassed the ponds during high flows until the extensive
upgrades were complete in the 1990s. As much as a meter of tailings was removed from stream channels
external to the ponds as a part of the remediation efforts in the mid-1990s. Releases of zinc and arsenic
increase during high discharges into the ponds, but most anecdotal signs are that the contaminated
sediments from Silverbow Creek are now efficiently captured in the pond system. The system has not
been tested by a large flood. Presumably, progressive improvement of the containment system (tailings
ponds) was a major factor in improvement in biological quality of the Clark Fork River. Some trout began
to reappear in the river below Deer Lodge in the late 1950s (Spindler, 1959). Virtually no trout were
present immediately below the ponds until 1973, one year after some major improvements in waste
treatment capabilities were installed. Since 1973, brown trout (Salmo trutta) have been the most abundant
trout at the site, but their numbers have fluctuated widely. A few rainbow trout (Oncorhynchus mykiss)
are found below the ponds, but native trout (bull trout and cutthroat trout) are rarely, if ever, observed.

The Environment within 2 km of the Warm Springs Ponds
The environment in the first 2 km from the Warm Springs Ponds is a unique habitat in the river. It is
worth mention because its characteristics have confounded attempts to relate mining activities to con-
tamination and ecological change in the river. Sediments and benthos adjacent to the outlet from Warm
Springs Ponds were first sampled for metal contamination in the mid-1990s. Concentrations of copper,
cadmium, and zinc were as low as stations subjected to much more dilution downstream (Table 19.1).
The waters of Silverbow Creek are treated with lime and progressively settle into an anoxic bottom as
they move through the ponding system. This appears to be effective in reducing metal inputs to the
stream just below the ponds, at least during low-flow periods of the year, although arsenic inputs have