Septic System Evaluation at MnDOT Rest Stops, Truck Stations and Weigh Scales


Sara Heger, Dan Wheeler, Dave Gustafson, Mike Szmorlo

January 2016

Report no. CTS 15-11B



The University of Minnesota (UM) and the Minnesota Department of Transportation (MnDOT) performed a unique evaluation of the 52 existing subsurface sewage treatment systems at safety rest areas (SRA) travel information centers, truck stations and weigh scales at MnDOT facilities across Minnesota. This three year partnership brought together the septic expertise of the UM with the MnDOT wastewater unit?s agency and site knowledge. The goal of the assessments was to evaluate risk and provide a risk analysis ranking system. The project began with an extensive record search where many documents were digitized and a database of information created. The next step was development of a draft assessment protocol. This draft protocol was pilot tested on five systems and refined based on those experiences. The full assessment included a preliminary review of the site, a facility assessment, effluent sampling, septic tank inspections, evaluation of advanced treatment units when present and an assessment of the soil treatment system. The information from the assessment was used to develop a risk ranking of all systems. The risk assessment created can be used for planning purposes to prioritize capital upgrades, but only if a sustainable process is created and incorporated into the day to day workload.

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