Septic System Evaluation at MnDOT Rest Stops and Truck Garages

Project summary:

There is little information available on the 51 septic systems serving the rest stops and truck garages across Minnesota at Minnesota Department of Transportation (MnDOT) facilities. Many of these systems are more than 30 years old, and the lack of information makes managing them, prioritizing replacement, and designing replacement systems very difficult. It is generally understood that these systems are subject to challenging site conditions and wastewater characteristics. Better data are needed to ensure the systems are adequately treating wastewater and will continue to over the long term. The University of Minnesota (UM) and 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.