Evaluating Site and Conditions at Safety Rest Area for Risk Management

Summary

The State is responsible for safety rest areas (SFA) and truck stations (TS) across Minnesota served by subsurface sewage treatment systems (SSTS). Managing these SSTS is a critical activity of the State, and a better understanding of the functionality and treatment of these systems is critical. This project uses field-based verification of groundwater mounding to estimate the influence of larger wastewater treatment systems on groundwater systems. The project is evaluating water table conditions around existing SFA SSTS to determine the amount of soil available for treatment. At a portion of these sites, temperatures will be monitored to evaluate how the site, system, and climate may be impacting treatment in the system. The field data collected will be compared to commercially available mounding software estimates. This information will assist the State in prioritizing upgrades. To evaluate soil treatment potential, oxygen levels and saturated hydraulic conductivity are being studied to understand the impacts of compaction, soil horizonation, saturated soil conditions, and wastewater application. Researchers are evaluating rest areas' current and future soil treatment areas for subsurface soil oxygen levels and potential for hydraulic performance. Data assesses current system performance and future SSTS options at the researched rest area(s). A series of studies is being conducted to evaluate septic tanks, which are the critical first step of every SSTS that the State owns and operates. Four systems are being evaluated to determine if septic tank performance can be improved with the goal of increasing longevity, reducing blockages, and the frequency of maintenance. One site has a new septic tank installed to determine if different baffle configurations could improve system performance. Additional work is being done to evaluate and limit risk with SSTS at State sites. Flammable waste trap sand from truck stations are evaluated to determine if less costly methods of disposal or reuse exist. The University will serve as a technical resource for the State on upcoming projects, will revisit five sites every year to evaluate the current conditions and update the database used to track the existing infrastructure. For the future, the project will evaluate options to regionally treat septage removed from septic tanks, reuse of storm and wastewater, and options to deal with nitrogen.