Long-term Effects of Decentralized Wastewater Treatment in Logan, Montana

By: Steven Shope, Montana Technical Assistance Provider

In 1889, Logan, Montana, like many small communities across the west, was established to provide service to the expanding railroad industry. The community’s plat provided for the housing of railroad employees, townspeople and a commercial district. As with the railroad, the town flourished and at one point Logan even had its own school. 

The plat laid out multiple lots along several streets terraced on gently sloping topography running down into a river bottom. The lots ranged in size from 0.07 to 0.16 acres. While these lot sizes are common in towns platted during this era, they were usually meant to be served by public water and a centralized sewer. However, there is no indication that water and sewer infrastructure was ever planned for the com

munity. Over the years, residents of Logan have had to make do with the outhouse, septic tank, cesspit, and drainfield for wastewater treatment and disposal, while relying on portable water containers or individual wells for potable water. Due to these small lot sizes, drinking water wells are in very close proximity to wastewater disposal. 

The problem is that treatment relies on percolation of wastewater through soils where contaminants are broken down by biological and chemical actions as it is dispersed. This process requires the appropriate amount of distance from groundwater and potable well water before wastewater has a chance to interact with them. This distance is referred to as “separation.” Typically, 100 feet of separation is required between a well and treatment soils (drainfield). Also, four feet of vertical separation is also required between a drainfield and ground water depending on the soils. For planning, a minimum of a one-acre lot is required for an onsite well and a drainfield in order to achieve adequate separation between the two.   

Compounding the potential problems created by inadequate separation is the fact that the Ryell silt loam soil present on the lower slopes of the Logan area is prone to rapid percolation and is a poor filter media. This is complicated by...

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