Adaptability of selected Montana soils for septic tank sewage disposal

Abstract

Excavation of septic tank filter fields and analysis of soil samples suggested that most nitrogen and phosphorus in sewage effluent accumulated within 5 meters of the point of input to the, soil. Amsterdam soils were found to be highly adapted to conventional septic tank sewage disposal as was a site located on a gradation between Leavitt and Bigel soils. The Bigel-Bearmouth site examined showed that a mound type system may be utilized to overcome a limitation caused by an impervious layer. Huffine soils are subject to seasonal high water and a system that raises the drain tiles above high water must be used. On the Alluvial soils along the Gallatin River high water table and spring flooding make these soils unacceptable as sites for on-site sewage disposal. From this study and the literature predictions of effluent behaviour were extrapolated to developable soils in Gallatin Canyon where installed systems were unavailable for study. Bearmouth, Bigel, and Hanson soils, being skeletal, are poor filtering media and design criteria such as a mounded system may be needed to overcome this limitation. Hobacker soils are adapted to on-site sewage disposal although sites with slopes in excess of 15 percent should be avoided. Leavitt and Michelson soils will function well as septic tank filter fields. The total nutrient load, in terms of nitrogen and phosphorus, for the Gallatin Canyon was calculated with respect to present human activity and projected human activity in 1985. Increase in residents appears to be the greatest concern with respect to increases of nitrogen and phosphorus disposal as compared to travellers or the Big Sky development.