by Carol Flaherty
6/5/96 BOZEMAN -- The condition of Montana's water resources resembles the proverbial riddle: Is the glass half-full or half-empty?
Montana has some of the best water and some of the worst, and both occur naturally. Assuming you choose not to worry about the wildlife-deposited giardia, you could drink safely from many streams, or you could drink from a stream with magnesium sulfate levels so high-- naturally high--that it would act as a laxative.
But talking about "Montana" water quality can be misleading. The quality of water varies not only with local land use but also with the geologic history of the earth it flows through. Of 50,000 miles of Montana rivers, about 14,000 miles do not meet Montana water quality standards, says Loren Bahls of the state's Water Quality Division.
Changes in water quality begin before rain or snow touch the ground. Rain picks up airborne dust, which can be a significant pollutant. Rain and snow melt that do not evaporate flow over and into the land, picking up pollutants.
One element Yellowstone Park's geothermal waters pick up is arsenic, and that accounts for the Madison River's high arsenic concentration. The river's arsenic is highest near the park, but the ground water's arsenic is highest at Three Forks, where the Jefferson and Gallatin rivers join the Madison to form the Missouri. Ground water arsenic near Three Forks varies from acceptable levels to more than three times the Environmental Protection Agency's drinking water maximum of 50 parts per billion. Proposed changes could lower the allowable level to 15 ppb.
Ground water arsenic at Three Forks probably is due to some ancient geologic occurrence, say Jim Bauder and Bill Inskeep of Montana State University's Department of Plant, Soil and Environmental Science. Some people thought crop irrigation contributed to Madison and Missouri river arsenic levels. Actually, Bauder and Inskeep's studies show that irrigation removes arsenic from river water, because soil will hold arsenic.
Madison/Missouri River arsenic concentrations steadily decrease with dilution by tributaries. It goes from about 280 ppb above Hebgen Lake to less than three ppb at Fort Peck Reservoir. At Helena, which uses Missouri River water during part of the summer, the arsenic is 15-20 ppb, says Jim Melstad of the state Department of Environmental Quality (DEQ). At Great Falls, which uses the Missouri as its major source of drinking water, the arsenic level averages about 10 ppb, says Melstad.
As measured by the U.S. Geological Survey, the Madison also has a relatively high phosphorus level. Though not dangerous to people, phosphorus contributes to algae growth, and decomposing algae reduces the water's oxygen that is available to fish and other aquatic life.
Ninety percent of Montana's surface water pollutants are sediment, says John Arrigo of the DEQ. Sediment can silt-up rivers making them poor spawning grounds for fish. It also carries minerals and organic matter that cause other problems.
Some sediment comes from natural erosion. For example, when melting snow and rain run into the Madison River near the Bear Trap south of Three Forks, it makes the water muddy even though there is no human-caused land disturbance upstream. Distinguishing between natural sediment levels and those due to human activity is a challenge for water regulators.
Humans add to natural sedimentation by farming, constructing roads and buildings, logging, mining--anything that disturbs the landscape. What agriculture adds is a primary concern, not because management is bad, but because farming uses by far the most water--about 98 percent of the water withdrawn from surface sources. Agriculture puts 78 percent of the water back immediately, says Bauder, but 22 percent either is used by plants or evaporates.
Most Montana rivers begin in the western mountains. As they flow from their headwaters, they steadily pick up more dissolved minerals and sediments. Consequently, surface waters in eastern Montana generally have more dissolved solids than in western Montana, according to the USGS. MSU studies of well water also show that eastern Montana ground water tends to have more dissolved solids than that in western Montana.
The Musselshell, the only continuously flowing river that begins east of the mountains, has the highest concentration of dissolved solids in the state, according to the USGS. It flows through shale, siltstone and sandstone that dissolve easily. The Powder and Tongue rivers in southeastern Montana and the Milk River in the north are not far behind in dissolved solids. The solids are predominantly salts, according to the 1990 National Water Summary for Montana.
The Milk River flows through glacial moraines that also add salts and sediment to its water. The Milk River's phosphorus concentration is the highest of the 10 river basins tested. Phosphorus comes from municipal and private sewage disposal, detergents and eroded soils. The USGS reports that upstream of its Milk River test site at Nashua are 140,000 acres of irrigated cropland and a dozen communities discharging waste water.
The St. Mary River by the Canadian border of Glacier National Park and the Sun River flowing from the park to Great Falls have the least phosphorus of any Montana rivers. The Sun River, however, picks up minerals and sediment from shale and glacial deposits and nitrates from fertilizer runoff as it travels through the Sun River Irrigation project. Though the USGS has said that the Sun River's nitrate levels are "moderate" compared to other U.S. rivers, they are the highest for any of the Montana river basins measured by the USGS.
Human sewage also contributes to surface and ground water nitrate and phosphorus. Nitrates are a concern, because in high quantities they cause human health problems. Both nitrate and phosphorus contribute to algae growth.
Even good sewage treatment plants and septic systems discharge some nitrate and phosphorus into the water. The better the treatment, the less of these minerals in the discharge.
In ideal soil, septic systems filter human sewage beautifully, says Bill Woesner, a University of Montana hydrogeologist who has studied the water under septic systems. However, in the sandy and gravelly soils common to Montana river valleys, septic effluent may allow a large portion of dissolved waste to "pass right on through."
"There are lots of ifs, ands and buts," he says. "Things are very site specific, but you have to have at least four feet between a septic field and the ground water," or your system probably is leaking raw sewage into the water.
Though few would guess it, dust and smoke add significantly to water pollution. "Almost 40 percent of the phosphorus load in Flathead Lake comes from atmospheric deposition," says Bahls. This includes phosphorus from fireplaces, road dust, slash burning, pollen and forest fires. The phosphorus feeds algae and plankton, which are visible as "ring around the lake."
Phosphorus is the most critical element in algae growth, because algae that feed on phosphorus can make the nitrate they need, says Bahls. Flathead Lake had major algae blooms in 1983 and 1993. The 1983 bloom prompted action that has led to many improvements.
In 1986, about 20 percent of the lake's phosphorus came from sewage treatment plants. By 1993, less than five percent of the phosphorus came from that source, says Bonnie Ellis, a researcher with UM's Flathead Lake Biological Station. In addition, an area ban on phosphorus detergents has helped reduce phosphorus in the lake.
"The cities really have done their part," says Ellis. However, she says she is still concerned about the future of Flathead Lake water quality. Scattered sources of nitrogen and phosphorus usually increase as population and economic activity does, says Ellis. These diffuse sources and increasing volume of sewage reaching the plants could offset the conservation gains made by improvements in sewage treatment, she says.
Even well-intentioned changes in wildlife biology may contribute to degrading water quality, says Ellis. From 1968 to 1975, Montana Fish, Wildlife and Parks introduced opposum shrimp upstream from Flathead Lake as a food source for kokanee salmon (whose introduction in 1916 triggered the decline in native cutthroat trout). The shrimp migrated to Flathead Lake. Instead of being food for kokanee, the shrimp ate the kokanee's primary food: microscopic animals called "zooplankton." The population of both kokanee salmon and some zooplankton species plummeted, which contributed to algae growth, because zooplankton eat algae.
Whether caused by sewage, fertilizer or wood smoke, too much decomposing algae and other organic matter decrease the oxygen that fish and other aquatic life need, says Bauder. The symptoms of this include eight-foot long tendrils of algae in the Clark Fork River between Butte and Missoula and algae blooms in the Madison Reservoir and Flathead Lake, says Bahls.
In one way, the long tendrils of algae in the Clark Fork are a sign that Montanans are improving water quality, says Bahls.
"Prior to 1970, there were no algae blooms in the Clark Fork, because the water was toxic," he says. In recent years, enough old mine tailings have been cleaned up or immobilized that algae began to grow again, which drew attention to the river's excess nutrients, says Bahls.
That's not to say metals in the river are gone, adds Scott Brown of the Helena EPA office. Average copper levels in Silver Bow Creek before treatment in the Warm Springs Ponds range from 100 to 200 ppb. The Ponds knock that down to about 20 ppb, says Brown, but the creek picks up more metals from old tailings as it flows toward Deer Lodge, where the copper averages about 80 to 100 ppb.
As we enjoy Montana's water resources, most of us would conclude that Montana'.s water glass is "half full." However, water quality trends already show us that for each additional person and each additional use of water it takes a little more work to maintain water quality.
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