Water ways: Rural sewage numbers hard to pin down

More people live in rural Flathead County than in its three cities.

By JOHN STANG

The Daily Inter Lake

The county has roughly 87,000 people, according to U.S. Census estimates.

Kalispell, unincorporated Evergreen (which hooks up to Kalispell's sewage system), Whitefish and Columbia Falls have a combined population of almost 38,000.

That means roughly 49,000 people live in rural Flathead County, where the majority of homes use septic tanks.

That translates to a tremendous number of septic systems leaching their fluids into the soil to eventually ooze to the Flathead River and Flathead Lake.

And more and more people are building new homes in the county's unincorporated parts.

The Flathead City-County Health Department has issued 750 to 800 new septic system permits each year for the past 10 years.

No one - not even the state's experts - knows what volumes of rural-based nitrogen and phosphorus enter the Flathead River, nor how those amounts are distributed throughout the Flathead's basin.

Think of the county's soil as a giant filter.

Bacteria in the soil eats phosphorus seeping through it.

Plant and grass roots reach several inches deep into the soil to suck up nutrients for their nourishment.

This leads to some basic concepts:

. Don't concentrate wastes in one spot inside a septic drainage field. Septic sludges and fluids should be spread out horizontally, which is how newer drainage fields are designed. So when septic liquids seep down, the concentrations of nutrients are less dense, and the fluids are oozing through a wider cross-section of filtering soil.

. Rainwater - through sheer force and volume - drives nutrients faster down through the soil, especially past the nutrient-sucking plant roots. Therefore, more nutrients reach the water table, then the river, then the lake.

More nutrients get filtered in the topsoil if the seeping rainwater is spread out over a wider area.

. As more roofs and driveways are built in rural Flathead County, that cuts down on the space that can absorb rainwater.

All this leads to questions of how many rural homes would create an overload of nutrients entering the Flathead River - and whether they should be clumped together or spread out.

Too many factors come into play to make blanket statements whether new rural houses should be clumped together or spread out, local observers said.

Clumping houses together could leave vast wide spaces elsewhere to absorb rainwater into the ground - or that clumping could bunch seeping septic fluids closer together.

Other factors complicate the picture.

These include the nature of the soils, the vegetation, the bacteria and oxygen in the soils, how many people live in a house, septic field designs, volumes of septic sludges and rainwater, plus other variables.

Figuring out the level of nutrients flowing from one septic drainage field is difficult - requiring lots of groundwater sampling, geological knowledge and calculating.

Then experts will have to extrapolate from a few septic drainage fields to make an educated guess about the bigger Flathead picture.

That has not been done yet.

Meanwhile, the question arises about what to do with solid wastes pumped out of septic tanks.

Some can be taken to sewage treatment plants.

Some dried sludge can be injected as fertilizer into the topsoil of farm fields under precise rules regarding amounts plus distances from houses and roads.

These regulations are needed so just enough - not too much - nutrient-laced waste is applied to the fields.

But Flathead County's population and construction booms also are swallowing up farm fields.

These fields able to receive septic wastes have become scarce enough that septic pumping firms are jealously guarding their locations.

"The land is running out. Now I just have one field. … If I don't have a place to dump, I'm closing," said Evergreen-based septic pumper Ken Pederson, who has been in the business since 1959. "This is inevitable because there's no new place to go."

Reporter John Stang may be reached at 758-4429 or by e-mail at jstang@dailyinterlake.com