By Philip Kedrowski Redleaf Consulting
In the last Engineer’s Corner, I discussed the Montana Sanitation in Subdivision Act regarding health-related septic system concerns. In addition to protecting human health, environmental health is a concern for the Montana Department of Environmental Quality (MDEQ). As a result, it has established a standard for nutrient-reducing septic treatment technologies.
MDEQ refers to these as “Level II” systems, the highest standard, or the best treatment, the department recognizes.
Nutrient reduction in septic system drain fields is important because nutrients (primarily Total Nitrogen) can cause excessive algae growth in streams and lakes. This algae then consumes the Dissolved Oxygen (DO) present in the water as part of its growth process. However, fish and other aquatic organisms also need the dissolved oxygen to breath. Reduced DO levels tied to algae growth caused by nutrient loading negatively affect fish growth and populations.
In addition to reducing nutrients, Level II advanced treatment systems significantly reduce Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) in wastewater. BOD is an indicator of microbial growth – excessive microbial growth and suspended solids are two primary causes for failures of drain fields due to clogging.
If a drain field clogs, sewage can seep up to the ground surface or, in severe cases, back into the house. Treatment for lower BOD and TSS allows for a smaller drain field area because cleaner water seeps into the ground more readily.
In Montana, the drain field size can be reduced by as much as 50 percent when using a Level II treatment system. In addition to being environmentally positive, it can be a financial advantage for the property owner. In areas with high property values like Big Sky, using less land for the drain field is financially beneficial.
It’s a win-win for the environment and the pocket book.

Philip Kedrowski, PE, LEED-AP, is owner/engineer of Redleaf Consulting, PLLC. Redleaf is the only engineering company based in Big Sky.