State seeks source of W. Valley nitrate

About three dozen wells in the West Valley area were sampled last week in an

effort to identify the source of a major nitrate plume.

About three dozen wells in the West Valley area were sampled last week in an effort to identify the source of a major nitrate plume.

Nitrate is a common groundwater contaminant that, in high enough concentrations, can cause significant health problems, particularly in infants.

During the last several years, a number of wells in the shallow Lost Creek aquifer have tested as high as 20 to 40 parts per million for nitrate in drinking water.

The federal standard is no more than 10 parts per million.

Officials with Flathead County's Environmental Health Department say this is the only place in the county where nitrate concentrations of this magnitude have ever been found.

The Lost Creek aquifer is located in the vicinity of Farm to Market Road, Church Drive and Clark Drive.

Laura Alvey, an environmental specialist with the Montana Department of Environmental Quality, said the aquifer is an "ideal" place for groundwater contamination to occur.

"It's very gravelly, so contaminants can easily be transmitted from the surface to the subsurface," she said. "The area lends itself to having this kind of problem."

At least five wells in the area currently have elevated nitrate levels, Alvey said. Others have had to be drilled deeper, down into the valley's deep artesian aquifer, which currently shows no signs of being polluted.

In many cases, nitrate plumes have an identifiable "point source," such as a chemical spill or broken septic tank.

However, Alvey said the origin and even the full extent of the Lost Creek plume still haven't been identified.

Potential sources include faulty septic systems, septic dump sites, agricultural and residential fertilizer, and concentrated manure piles - all of which can be found in the rural West Valley.

"We have multiple potential sources in a large area, so it might be difficult to tease apart" the cause or causes of the plume, Alvey said. "The most important thing for us is to try and figure out where the problem starts and stops. Then we can look at what's going on there" and possibly determine the cause of the pollution.

To that end, Alvey and local environmental health officials recently took samples from about three dozen wells in the West Valley.

The samples will be tested for a variety of contaminants, she said, including nitrate, nitrite, coliform bacteria, chloride and sulfates.

Some samples also have been sent to a lab to measure nitrogen isotopes.

"Given the ratio of heavy to light isotopes, it's sometimes possible to see a 'signature' that would help us identify the source," Alvey said.

Well owners will be notified about the results of the tests, she said. The information also will be plotted on a map to see if any patterns emerge.

A formal report will be released in four to six months, Alvey said, highlighting the results and any remedial actions that are necessary.

The nitrate plume and fragile nature of the Lost Creek aquifer have come up repeatedly in the last few months during the debate over a new, 320-acre gravel pit near the intersection of Farm to Market and Church Drive.

Given the uncertainty regarding the source of the pollution - and the possibility that a gravel mine would worsen the area's water-quality problems - opponents suggested that a conditional-use permit for the pit be denied.

The permit was approved in June and is now in litigation.

Alvey, who runs the state's groundwater mediation program, said she oversees about 80 sites that have groundwater issues. None of them are gravel pits.

"If you have a fuel spill, certainly a gravel pit is about as bad a place as any to have one, because it's hard to capture the spill before it gets into the water," she said. "But a pit alone? I don't know how it would be a source or cause of contamination. It's just gravel and water."

Alvey also noted that, under current conditions, it would be difficult for the deep artesian aquifer to be polluted, whatever the source of the nitrate in the shallow aquifer.

"It's always possible that contamination from the upper aquifer could find a way to the deep aquifer," she said. "But the deep aquifer is under pressure. That would typically prevent water from filtering down into it.

"We did sample several deep wells last week. We don't anticipate seeing anything in them, but it's always good to check."

Reporter Bill Spence may be reached at 758-4459 or by e-mail at bspence@dailyinterlake.com