SOUTHWEST WISCONSIN - The latest results from the Southwest Wisconsin Groundwater and Geology study (SWIGG) are a concerning mid-study progress report. Dr. Mark Borchardt and Joel Stokdyk reported on the first of four rounds of microbial source testing of wells previously identified to be contaminated with either coliform bacteria or nitrate.
Many with vested interests will be quick to leap on these partial ‘microbial source testing’ results to support one or another point they are eager to make. But, the fact of the matter is that, as Dr. Mark Borchardt explained, “like Kewaunee County, there are three large animals on the landscape in Grant, Iowa and Lafayette counties. The samples showed groundwater contamination from fecal sources from humans, cattle and hogs.”
Source testing results
What were those results? The SWIGG study originally started with two rounds of well water testing in the three counties in November of 2018 and April of 2019. A total of 301 wells were tested in 2018, and 539 were tested in 2019. Of those, 42 and 27 percent respectively were found to be contaminated with either coliform bacteria or nitrate, or both, including a relatively low number, which showed E.coli, a particularly dangerous coliform bacteria.
The results reported last week were from round one of four of seasonal ‘microbial source testing’ on a randomly selected subset of wells found to be contaminated with coliform bacteria, nitrate or both in the November 2018 round of testing.
In this first round of seasonal ‘source testing,’ 32 of 35 wells tested, or 91 percent, were found to be contaminated with bacteria from a fecal source. That high percentage is not surprising, since the wells that were tested in this round had already been found to have contamination in previous testing. Dr. Borchardt was quick to explain that these results do not mean that 91 percent of wells in the three counties are contaminated.
In this spring round of microbial source tracking, 30 of 35 samples showed bacteria traceable to human sources; 17 were traceable to bovine sources or from cattle; and five were traceable to swine sources or hogs. The testing focused only on fecal sources of contamination, and does not identify sources of nitrate from other sources such as synthetic fertilizers.
“Following this microbial source testing out over a year, through all four seasons will give us a more accurate picture of what sources of fecal contamination are in the groundwater,” Stokdyk explained. “We are guessing that concentrations of bacteria can change quickly underground, and could be low today and high tomorrow.”
In the report, he explained that “the percentage of wells that test positive is expected to differ as weather and land use changes over time, and it’s too soon to assess which contamination source is more prevalent. Contamination sources are expected to vary seasonally. For example, in Kewaunee County, contamination by human wastewater was more common in early spring when groundwater levels were high, while bovine contamination was more common in the fall after manure had been applied.”
Overall, Borchardt said, the concentrations of fecal markers in the samples are low, and he said, “I personally wouldn’t be that concerned.” However, he also explained that it could be of relatively low concern for a healthy adult, and much more concerning for children ages one to three, the elderly and those with compromised immune systems.
Perhaps even more concerning were the results that showed the presence of microorganisms capable of causing illness in 13 of the samples, or 37 percent. Those microorganisms were Salmonella, cryptosporidium, rotavirus group A, adenivirus, and enterovirus.
Cryptosporidium is the contaminant that caused headlines when it was found in Milwaukee drinking water. Salmonella can come from humans or livestock.
“I told the members of the State of Wisconsin Speaker’s Task Force on Water Quality in Stevens Point that if given the choice to drink a glass of water containing coliform bacteria versus a glass containing nitrate, I’d drink the glass with coliform bacteria,” Borchardt said. “However, if I was given the choice between drinking a glass of water containing nitrate versus one containing Salmonella or one of the other pathogens identified in the recent testing results, I’d drink the glass with nitrate in it.”
Borchardt said that the two microorganisms found in the microbial source testing that were most concerning were Salmonella and Cryptosporidium. He said the levels of Salmonella were very high. He said it is possible that the rotavirus found could be traceable back to vaccines, and further analysis will be required to determine the exact source.
He emphasized that in addition to implications for human health, the presence of bacterial and nitrate contamination of water could be a herd health problem for farmers. He described one producer in Kewaunee County who had discovered high Salmonella in his well and connected it to problems with calf scours he had been experiencing. Based on the testing information, the producer was able to change some of his practices and vastly reduce his problem with scours.
Wisconsin State Representative Travis Tranel queried Dr. Borchardt about whether there is any history that could be used with which to compare the current results.
“It is true, that with our new, first-in-the-nation, sampling methodology, there is no historical data for this area that the current results can be compared to,” Borchardt responded. “What we have available for comparative purposes is the Kewaunee County study and a study done in Minnesota.”
Dr. Borchardt explained to Tranel that another thing that is lacking in their analysis is information from agricultural producers about manure application, times and rates. He said that if the agricultural community was willing to provide this information, it would allow researchers to work with them to develop manure application best management practice recommendations.
Wisconsin Farm Bureau’s Robert Nigh of Viroqua, who sits on their board and represents District 3, asked Dr. Borchardt if the nitrate contamination could be traced to sources other than agriculture.
“Given what we know and the tests available to us, I am reluctant to link nitrate contamination to fecal markers,” Dr. Borchardt explained. “There really aren’t good methods to identify the sources of nitrate.”
Dr. Borchardt explained that in Kewaunee County, his research had shown that high levels of nitrate are linked to surrounding land use. He said there is no connection between high nitrate and septic systems. There is a high relationship between nitrate contamination and proximity to agricultural fields.
Dr. Borchardt also pointed out that in the first two rounds of testing for coliform, E.coli and nitrate, levels of coliform had varied a lot, but that levels of nitrate had remained steady.
“Bacteria can die over the winter, but nitrate will persist in water over a long period of time,” Borchardt said.
Stokdyk explained that his team would conduct the next round of seasonal microbial source testing sample collection in the second week of August. He said that the study team’s overall goal is to conduct four rounds of 35 samples each.
“The process to collect the samples is quite involved, and microbial source testing is much more expensive than the basic testing that was done in the first two rounds of the SWIGG study,” Stokdyk explained. “In the end, our study will yield enough data to analyze well contamination and its relation to well construction and surrounding land use.”
Stokdyk explained the sampling process, which can take as long as three hours to complete, to the meeting participants.
“Collecting the samples for the microbial source testing requires a special sampling device because the low concentrations of the microorganisms in the water,” Stokdyk said. “We shoot for a sample of about 200 gallons, and run it through a filter. It is actually the filter that goes back to the lab for analysis.”
After the microbial source testing is completed, the final phase of the study will be undertaken by Dr. Kenneth Bradbury, Wisconsin State Geologist, and his team at the Geology and Natural History Survey. Bradbury’s team will identify specific geologic features where the tested wells are located, as well as the particulars of the well construction of the sampled wells. This information will be statistically correlated with the results of the microbial source tracking.“In Kewaunee County, we found that well characteristics were not a factor in well susceptibility to contamination,” Dr. Borchardt said. “However, Kewaunee County has just one aquifer whereas the Driftless has multiple aquifers at different depths that wells draw upon. For this reason, it is too early to draw the same conclusions for Grant, Iowa and Lafayette counties that we arrived at in Kewaunee County.”