State officials plan to do more water-quality testing in the West Valley this summer, in hopes of identifying the sources of what they say is the largest nitrate plume in Montana.

An initial round of testing last summer failed to pin down either the sources or boundaries of the plume, which is contaminating parts of the Lost Creek aquifer.

"We were hoping to get a better handle on it," said Laura Alvey, an environmental specialist with the Montana Department of Environmental Quality's groundwater remediation program, which conducted the tests. "We knew the plume was fairly widespread. I think the testing changed our perspective from looking for one source to looking for multiple sources."

Nitrate is a common groundwater contaminant that, in high enough concentrations, can cause significant health problems, particularly in infants. Potential sources include agricultural and residential fertilizer, faulty septic systems, cattle feed lots and manure piles, and septic or dairy waste dumping sites.

Alvey said all of these activities can be found in the Lost Creek area.

The aquifer is northwest of Kalispell in the vicinity of Church Drive, Clark Drive and Farm to Market Road. It's in the alluvial fan where Lost Creek spills out from the Salish Mountains onto the valley floor.

Elevated nitrate levels were first documented in the area in 1996. By 2002, some wells there had nitrate readings as high as 40 milligrams per liter, or four times the state drinking water standard.

Water samples collected last summer found elevated nitrate levels in 11 of 21 shallow wells, including eight that exceeded the state limit of 10 milligrams per liter.

Several of the contaminated wells were in two small clusters - one located just northwest of the intersection of Farm to Market and Church Drive, and the other farther east, north of Church Drive.

Elevated nitrates also were found in individual wells near the intersection of West Valley Drive and Clark Drive, and on Lost Creek Drive and Fox Farm Road west of Farm to Market.

However, Alvey said there was no clear pattern of pollution.

"With multiple sources, you would expect to see high concentrations here and there [as these test results indicated]," she said. "But some of the stuff we were seeing made no intuitive sense. We had one shallow well with a high nitrate level right near a well that had the lowest nitrates. There's a lot going on out in this area that makes it very complex from a regulatory standpoint."

Alvey said this is the largest nitrate plume she's aware of in Montana.

"All of the other plumes I deal with are smaller and have an obvious point source," she said.

Water samples were also taken from 13 deep wells that were drilled down into the artesian aquifer below the Lost Creek fan. Only one of those sample had elevated nitrates (4.53 milligrams per liter), and it was a replacement well for a contaminated shallow well.

"Nitrate doesn't appear to be present at levels of concern in groundwater deeper than about 150 feet," Alvey noted in her report on last summer's tests. "In general, elevated nitrate levels were found in shallow wells and not in deep wells."

Testing was also done to try to discover the isotopic "fingerprint" of the nitrate contamination.

Different nitrate sources have specific isotopic signatures, based on the ratio of nitrogen-14 to nitrogen-15. Alvey's report indicated that "one would expect to see higher [nitrogen-15] values in nitrate from septic systems and animal wastes … In general, septic effluent and animal waste show values of 8 or greater. Synthetic nitrogen sources [such as fertilizer] generally have values less than 7."

The West Valley isotope results all ranged from 2.96 to 7.52, except for one value of 14.99. However, given the potential for mixing from different sources, no conclusion was reached regarding the source of the Lost Creek nitrates.

"Generally, we wouldn't want to make any statements based on one round of sampling," Alvey said. "If there's much mixing going on, it could be difficult or impossible to tease apart the different sources."

Given the complexity of the Lost Creek plume, Alvey said her office plans to do another round of water-quality testing this spring and summer.

At least one new monitoring well will be installed, and she expects to collect soil samples from potential nitrate source areas to help narrow the possible origins of the plume.

Alvey encouraged anyone who's living on the Lost Creek fan and who has a shallow well to contact her if they would like their well sampled. She can be reached at (406) 841-5062.

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