Escalating Threats of Contamination
147
these waste beds contain over 50 million cubic meters of tailings, and
most intersect or drain into streams. Water quality concerns were raised
in 1996 when it was discovered that livestock grazing on pastures bordering streams near the waste dumps developed symptoms that were
diagnosed as selenium poisoning. Subsequent monitoring studies revealed high concentrations of selenium in phosphate mine solid wastes
(up to 1040!!g Se/g, parts per million), seepage water (up to 1500!!g
SelL), tailings ponds (up to 1500!!g SelL), and streams (up to 474!!g
SelL) near the waste dumps (Desborough et al. 1999; Herring et al.
1999; Lemly 1999).
Most of the mining activity occurs within the Blackfoot River watershed, which contains a Class 1 fishery (highest valued) of Yellowstone
cutthroat trout (Oncorhynchus clarki bouveri). A preliminary hazard assessment of selenium in the watershed indicated that waterborne selenium concentrations in the Blackfoot River and in 14 of its tributaries
met or exceeded toxic thresholds for fish. Concentrations of selenium
in fish tissues exceeded toxic thresholds for reproduction at 1 location
and approached the threshold at 2 others. It was concluded that there
was a high risk of toxic impacts to Yellowstone cutthroat trout and
other fish associated with the Blackfoot River, its tributary streams
that receive drainage from mine spoil sites, and Blackfoot Reservoir
(Lemly 1999).
This selenium problem centers around surface disposal of mine spoils.
With the advent of more stringent environmental controls in the 1990s,
backfilling of mine pits has been used as a way to minimize the need
for surface disposal of tailings. However, because soil and rock expands when it is dug out of a mine pit, from 10 to 30% of the excavated material still requires surface disposal. Compounding this problem
is the presence of historic tailings dumps, many of which are huge
(> 1 0 million cubic meters) and contain a tremendous reservoir of selenium that has the potential to be mobilized and introduced into aquatic
habitats. Large mineral leases are awaiting development, both on and
off national forest lands (Desborough et al. 1999; Herring et al. 1999),
which suggests that continued expansion of phosphate mining is likely.
Phosphate mining has the potential to elevate selenium levels in aquatic
ecosystems across extensive areas of the intermountain West. The cascade of events leading to toxic impacts has already started at some
locations.
Constructed Wetlands
In the mid-1980s, a new selenium issue emerged in central California. Irrigation of crop fields in the San Joaquin Valley produced seleniferous drainage water that was disposed in the San Luis Drain and
147
these waste beds contain over 50 million cubic meters of tailings, and
most intersect or drain into streams. Water quality concerns were raised
in 1996 when it was discovered that livestock grazing on pastures bordering streams near the waste dumps developed symptoms that were
diagnosed as selenium poisoning. Subsequent monitoring studies revealed high concentrations of selenium in phosphate mine solid wastes
(up to 1040!!g Se/g, parts per million), seepage water (up to 1500!!g
SelL), tailings ponds (up to 1500!!g SelL), and streams (up to 474!!g
SelL) near the waste dumps (Desborough et al. 1999; Herring et al.
1999; Lemly 1999).
Most of the mining activity occurs within the Blackfoot River watershed, which contains a Class 1 fishery (highest valued) of Yellowstone
cutthroat trout (Oncorhynchus clarki bouveri). A preliminary hazard assessment of selenium in the watershed indicated that waterborne selenium concentrations in the Blackfoot River and in 14 of its tributaries
met or exceeded toxic thresholds for fish. Concentrations of selenium
in fish tissues exceeded toxic thresholds for reproduction at 1 location
and approached the threshold at 2 others. It was concluded that there
was a high risk of toxic impacts to Yellowstone cutthroat trout and
other fish associated with the Blackfoot River, its tributary streams
that receive drainage from mine spoil sites, and Blackfoot Reservoir
(Lemly 1999).
This selenium problem centers around surface disposal of mine spoils.
With the advent of more stringent environmental controls in the 1990s,
backfilling of mine pits has been used as a way to minimize the need
for surface disposal of tailings. However, because soil and rock expands when it is dug out of a mine pit, from 10 to 30% of the excavated material still requires surface disposal. Compounding this problem
is the presence of historic tailings dumps, many of which are huge
(> 1 0 million cubic meters) and contain a tremendous reservoir of selenium that has the potential to be mobilized and introduced into aquatic
habitats. Large mineral leases are awaiting development, both on and
off national forest lands (Desborough et al. 1999; Herring et al. 1999),
which suggests that continued expansion of phosphate mining is likely.
Phosphate mining has the potential to elevate selenium levels in aquatic
ecosystems across extensive areas of the intermountain West. The cascade of events leading to toxic impacts has already started at some
locations.
Constructed Wetlands
In the mid-1980s, a new selenium issue emerged in central California. Irrigation of crop fields in the San Joaquin Valley produced seleniferous drainage water that was disposed in the San Luis Drain and