Risk-based ranking system will help prioritize upgrades for rest area septic systems

rest area sign
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A unique research partnership between the University of Minnesota and the Minnesota Department of Transportation (MnDOT) has led to the creation of a new risk-analysis ranking system for the 52 septic systems located at safety rest areas, travel information centers, truck stations, and weigh scales at MnDOT facilities across Minnesota. This three-year partnership brought together the septic system expertise of the U of M with the wastewater expertise of the Water Services Unit of MnDOT’s Office of Maintenance Building Services Section.

“One key goal for this project was developing a risk-analysis ranking system that can be used to help decision makers allocate funding to sites on a need-basis in order to provide up-to-code systems that protect public health and the environment,” says Neile Reider, water services engineer with the MnDOT Office of Maintenance.

The project, led by Sara Heger of the U of M’s Onsite Sewage Treatment Program in the Water Resources Center, began with an extensive record search in which many documents were digitized and a database of information was created. Many of these records were previously paper-only copies and were not stored in a centralized location; records included septic permits, soil survey information, septic system drawings and specifications, well permits and logs, water usage, drinking water testing results, and past inspection reports.

The next step was the development of a draft protocol for septic system assessment. The draft protocol was then pilot-tested on five septic systems and further refined based on those experiences. The result was a full assessment protocol that includes a preliminary review of the site, a facility assessment, effluent sampling, septic tank inspections, evaluation of advanced treatment units, and an assessment of the soil treatment system. The research team then used this full assessment protocol to perform detailed, consistent evaluations of all 52 MnDOT-operated septic systems.

Throughout the investigation, data were collected on more than 100 characteristics of the septic systems—such as environmental conditions, soil treatment systems, and management methods—at each of these 52 sites. The information then was used to develop a risk ranking for all systems.

Overall, 45 of the 52 wastewater systems evaluated were in “average” to “above average” condition, with five facilities in “excellent” condition. The remaining seven are most in need of repairs or replacement, Heger says. In addition, the rating system flags all systems with public safety or health issues as “below average” until those items are rectified.

“Through the partnership, we were able to collaborate and create a useful tool that we could use for planning purposes,” says Reider. “Also, this is not a one-time analysis, but a tool we will use to continually reassess our systems.”

Heger adds that the project and process could be modified to evaluate facilities in other states or those owned by other entities.

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Michael McCarthy
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