Onsite Sewage Treatment Program awarded grant to study MNDot rest areas

By Sara Heger

There is little information available on the 51 septic systems serving the rest stops and truck garages across Minnesota at MnDOT facilities. Many of these systems are more than 30 years old, and the lack of information makes managing these systems, prioritizing replacement and designing replacement systems very difficult. It is generally understood that these systems are subject to challenging site conditions and wastewater characteristics. The University of Minnesota’s Onsite Sewage Treatment Program will collect data - to assure the systems are adequately treating wastewater and will continue to do so over the long term.

The project will first develop a protocol for system assessment and then implement the assessment on five sites. The assessment will include evaluating the current system components, identify any deficiencies and provide recommendations for improvements, if needed. Initial grab sampling of wastewater characteristics including flow and effluent quality will be obtained, if accessible, and a sampling protocol developed for the system operator. The first five sites to be evaluated will help develop a risk-based assessment model focusing on site and wastewater characteristics specifically for the MnDOT sites. The remaining 46 sites will be evaluated based on the procedures developed and prioritized based on the risk-based assessment model.

Long-term research includes selecting several of these sites to conduct more in-depth studies on wastewater characterization, flow characteristics, contaminant fate and transport through these systems and soils and groundwater mounding monitoring and analysis. This research will not only better inform MnDOT on operation and maintenance activities, but provide knowledge for design of new and replacement systems. The type of data collected will not only benefit Minnesota’s surface and groundwaters, but provide insight for various other states currently struggling with rest stop design and maintenance. The Minnesota onsite industry will also benefit from the long-term data collected on these sites that will be used to modify the current MPCA Design Guidance for systems and be included in Intermediate and Advanced Design training for systems with pre-treatment and larger design flows. It is anticipated that this more in-depth research will require data collection efforts over a three to five year period. Two sites have been selected to start this more in-depth research by both evaluating impacts from their old system and installer piezometers and monitoring wells on their new systems to be installed in 2013.

This project will first and foremost evaluate the current condition of the 51 systems in relation to protection of public health and the environment. With the initial and subsequent sampling a database will be developed to aid in future system design and management.

"The data collected in this project will result in better information about how to design and manage septic systems at rest stops in Minnesota and across the US," said Dave Gustafson of the Onsite Sewage Treatment Program.

Rest Stop