Study looks at surface water influence on groundwater

Channah Rock, Ph.D.

University of Arizona

Throughout the years, legislation and industry rules have raised awareness about surface water’s role in potential produce contamination and its prevention. But significantly less is known about possible microbial issues tied to groundwater under the influence of surface water as well as water distribution systems.

To fill in those knowledge gaps, Channah Rock, Ph.D., at the University of Arizona, is leading a two-year project to develop innovative microbial sampling techniques and evaluate interventions, such as pipe flushing, shock chlorination and water treatment.

KEY TAKEAWAYS

Compared to surface water quality, much less is known about microbial issues tied to groundwater under the influence of surface water.

Researchers worked with cooperating growers in four U.S. produce-production states to review their water source and irrigation records.

The researchers also used innovative microbial sampling techniques that involved unusually large water volumes— 100 liters.

This year, the researchers plan to evaluate potential mitigation measures in pipe loops that mimic grower water distribution systems.

Joining her as co-investigators are Faith Critzer, Ph.D., at the University of Georgia, and Michelle Danyluk, Ph.D., at the University of Florida. Both having experience as Extension specialists bring established relationships with growers in their states, which will be “critical” to the success of the project, Rock said.

“Working with them is nice because everything we do is going to be vetted by industry and how their local production systems align,” she said. “Faith and Michelle are able to call up growers quickly and ask them questions to make sure we’re doing the right thing by them.”

During the first year, the researchers reviewed records of cooperating growers in four produce-production areas to identify wells potentially under the influence of surface water.

“These growers know water sources and the challenges they face more than we do, so it’s really important for us to learn from the experts to help guide our questions,” Rock said.

The researchers also used innovative water sampling techniques that involved 100-liter volumes, which is significantly more than the small samples typically collected for groundwater analysis. They assayed the samples for both traditional and non-traditional indicators, including generic E. coli, total coliform bacteria, protozoa, bacteriophage — virus that infects and replicates within bacteria — and microscopic particulate analysis.

Microscopic particulate analysis involves identifying, sizing and estimating populations of microorganisms and organic or inorganic debris found in surface water. Many states use the analysis to determine whether a water system is under the influence of surface water.

During the second year, the researchers plan to construct model irrigation distribution system pipe loops at three locations. Essentially these are closed systems that mimic traditional irrigation water distribution systems within each region, including flow rates and pipe material.

The pipe loops are designed to mimic the growers’ own systems and will be constructed of the same materials. In one location, for example, the grower uses PVC so the researchers will, too. The same is true for another system built around layflat hose and aluminum pipe.

The researchers also plan to use the same nitrogen sources as the cooperating growers, whether it is fish emulsion or another nitrogen product. The pipe loops will be used to assess the effectives of atmospheric and water quality conditions on water quality degradation.

Once biofilm — slime-encased microbial communities — becomes established in the pipes, the researchers will then evaluate industry best management practices for mitigating distribution system contamination. They include pipe flushing, pipe shocking using sodium hypochlorite and routine water treatment.

Image: Cross section of aluminum pipe used for irrigation of fresh produce with surface water over one season showing substantial biofilm development and/or sediment accumulation.

In the end, the comprehensive monitoring and records review should guide the industry on appropriate sampling methods to detect whether surface water may or may not be influenced by groundwater.

The researchers also hope to provide a list of recommendations and mitigation measures that growers can use immediately to clean up their systems and bring them back into compliance if they may have had an issue. And Rock said she foresees benefits beyond their recommendations.

“It will create increased awareness of how their distribution systems can be contaminated and ways to mitigate it,” she said.

View - Project Page, Channah Rock, Ph.D., "Methods for determining groundwater under the influence of surface water, and BMPs for mitigating distribution system contamination"

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The Center for Produce Safety (CPS) is a 501(c)(3), U.S. tax-exempt, charitable organization focused exclusively on providing the produce industry and government with open access to the actionable information needed to continually enhance the safety of produce.

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