By Stephanie Lynn EBS CONTRIBUTOR
Elevated
levels of nitrate, a nutrient that can impact river health and drinking water
quality, have been found in a groundwater monitoring well above the Big Sky Resort
Golf Course, according to a collaborative groundwater study in the Big Sky
meadow area.
The
study, which took place in June and August this year, sampled six existing
monitoring wells and one spring in Big Sky. This data collection resulted from
a collaboration between the Montana Bureau of Mines and Geology, Big Sky Water
and Sewer District, Gallatin Local Water Quality District, and Gallatin River
Task Force.
A
well that is located between Two Moons Road and the Town Center stoplight
revealed the highest groundwater nitrate levels of 6 to 7 mg/L. Similar nitrate
concentrations were measured across Highway 64 in a well near Roxy’s Market a
few years earlier.
“We
did not expect to see nitrate in the 6 to 7 mg/L range in the Two Moons well,”
said Christine Miller, a water quality specialist with the Gallatin Local Water
Quality District. “Although the U.S. Environmental Protection Agency Maximum
Contaminant Level for nitrate in drinking water is 10 mg/L, 2 mg/L is usually
considered background for groundwater. Levels above 6 mg/L, like we saw this
season, indicate there are one or more nutrient sources negatively impacting
groundwater quality.”
Groundwater
can be influenced by human activities on the surrounding landscape when rain
and snow carrying pollutants soak into the ground. Human-caused sources of
nitrogen include wastewater from septic or sewer systems, household uses such
as fertilizer and pet waste, and agriculture.
Once
underground, water is directed “down gradient” by elevation, pressure, and
impermeable layers of rock. Researchers must consider human activity and the
direction of groundwater flow in tandem to determine the cause of
contamination.
“The
Two Moons well is above the Big Sky golf course and at this location
groundwater flows from the southwest to the northeast,” said Mike Richter, a research
specialist with the Montana Bureau of Mines and Geology and Task Force board
member. “This flow direction suggests a source of nutrients entering the Meadow
Village aquifer up gradient from the golf course and southwest of the Town
Center.”
Groundwater
from the Two Moons well eventually flows to the West Fork of the Gallatin
River, a stream already impacted by nitrogen pollution. Elevated nitrogen affects
river health when it triggers algae blooms, such as the one observed this
summer, which alter aquatic habitat and reduce the high oxygen levels required
by aquatic insects and trout.
Regular
groundwater sampling by the collaborative group will continue in order to pinpoint
this source, and other potential sources, of nitrate to safeguard the
community’s drinking water supply and protect local fisheries.
“Long-term
water level and water chemistry monitoring will let us know if there are
changes over time,” said James Rose, a hydrogeologist with Montana Bureau of
Mines and Geology and an associate Professor at Montana Tech. “Concerns about
climate change, development, and drought can be evaluated and any impacts can
be determined.”