Research Reports

Water Use at Minnesota Rest Areas

Principal Investigator:

Taylor Nelson, Sara Heger

January 2016

Report no. CTS 15-11A

Projects: Septic System Evaluation at MnDOT Rest Stops and Truck Garages

Topics: Environment

The Minnesota Department of Transportation (MnDOT) Statewide Rest Area Program consists of a coordinated system of public rest areas that are intended to help motorists travel safer. In 1979, MnDOT collected data at rest areas to refine assumptions and improve techniques for design of rest area water supply and sewage treatment. They found people used an average of 2.8 gallons with water conserving devices and 4.5 gallons with non-water-conserving devices. This study evaluated the accuracy of the 1979 MnDOT design charts and formulas based on plumbing code fixtures and traffic patterns. A total of six rest areas, Culkin Rest Area (R.A.), Frazee R.A., Fuller Lake R.A., Lake Pepin R.A., Central Minnesota Travel Information Center (TIC), and St. Croix TIC, were included in the study. Average water use estimations were calculated from hourly people counts, hourly traffic counts, and hourly water flow data. Site specific average water use per person ranged from 0.7 gallons to 3.8 gallons, with an overall average water use of 2.3 gallons and a 95% confidence level average of 3.5 gallons. When accounting for variation, error and providing a safety factor, a water use per person design value of 5 gallons per person per day is recommended. The results of this two-week study appear to indicate that the 1979 design values are still valid, but additional data is needed for further conclusions. The University of Minnesota recommended MnDOT conduct similar water use studies for longer time periods prior to designing new rest area septic systems.

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