Testing history, Part 2

In both 1993 and 1995, the Department of Geology at the University of Montana did a study called "Cumulative Effects of Domestic Sewage Disposal on Groundwater of Missoula County: An analysis of Carrying Capacity" for the Missoula County Commissioners.

The second site that was tested was within the Seeley Lake Water District, directly to the east of Highway 83. One complication they found was, although it was quite densely populated, there weren't many wells since it is in the water district. However, they did have septic systems.

The study installed three groundwater monitoring wells. These wells are two-inch diameter PVC pipe with a five foot screen interval that extend about 47 feet below the surface. The geology of the airport and water district areas are similar. The water district ground water generally flows west.

Background concentration of nitrate implied from the eastern and northern wells were at or below the detection limit at less than 0.1 mg/liter. The southern well exceeded the detection limit for nitrate at 2.6 mg/liter. While nitrate is the most common groundwater and drinking water contaminant, nitrate in the groundwater at levels below two parts per million may be considered to be naturally occurring "background concentrations."

Nitrate can come from a variety of sources related to human activity, including animal and human waste, feedlots, fertilizers and septic systems.

NEXT MONTH: More Testing