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Humboldt Field Research Institute

February, 1996

UMaine Study Evaluates Impact of Wastewater Irrigation Systems on Groundwater

Spraying treated municipal wastewater over carefully prepared forests areas can have minimal impacts on groundwater and help reduce nutrient enrichment of surface waters, according to a recent report from the University of Maine Water Research Institute. The study was conducted in three Maine communities with operating forest spray irrigation systems.

There are 22 "forest spray irrigation systems" in Maine, according to the report, with several more under consideration. Most of these systems treat water from food processing facilities.

Cathy Anderson, a native of Milford, Michigan, completed the project for her masters degree and worked with Willem Brutsaert, UMaine professor of civil and environmental engineering, and research assistant John Birkhalter. Her report evaluates the design and performance of forest spray irrigation systems and suggests steps for improvement.

"Compared to other areas of the country, Maine is relatively pristine and I'd like to see it stay that way," says Anderson. "These forest spray systems are an emerging technology that is more popular in the South and the West where the climate is arid and land is available. But they are getting more widespread use in rural areas of the North to avoid discharging to surface waters."

A forest spray system uses a network of sprinklers to distribute wastewater after primary or secondary treatment. Maine regulations prohibit spray applications on frozen soil, during rain storms or when the air temperature falls below freezing.

"I had planned to study a system under construction in Indian Township, but the operation of that system was delayed," says Anderson. "When I found out that no one had ever reviewed the operation of existing systems in Maine, it made sense for me to take a closer look at them."

Anderson's report concludes that:

• groundwater at the Greenville and Sugarloaf sites has small increases in nitrate with mean concentrations well below national drinking water standards;

• groundwater at the Dexter site has significant increases in nitrate, chloride, total nitrogen, manganese and hardness. Mean concentrations of total nitrogen exceed national drinking water standards, and nitrate levels are just below those standards;

• in some cases, monitoring wells were poorly constructed and placed in depressions where wastewater collected. As a result, those wells may have provided a direct conduit for wastewater into the groundwater;

• communities considering forest spray systems should monitor groundwater regularly and purchase enough land to accommodate wastewater volumes generated by future population growth.

Anderson worked for the Maine consulting firm of Woodard and Curran during her graduate studies and currently lives in Rhinelander, Wisconsin. Her work has not yet been published in a peer-reviewed journal.

The report is available for the cost of photocopying and postage from the Water Research Institute, 5761 Sawyer Building, University of Maine, Orono, ME 04469-5761.

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