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Researchers discuss SWIGG Study at Platteville Library
SWIGG results
DR. MARK BORCHARDT and his student Dr. Joel Stokdyk, Chief Investigator in the SWIGG water quality study in Grant, Iowa and Lafayette counties, report on the first round of seasonal microbial source testing to the Grant County Zoning, Sanitation and Conservation Committee. - photo by GILLIAN POMPLUN

PLATTEVILLE - Two of the lead scientists in the SWIGG Study came to Platteville on Thursday, Sept. 26 to explain the study and answer questions from the public.

Dr. Mark Borchardt is the director of the USDA-ARS Lab in Marshfield, Wisconsin. The lab’s focus in the Southwest Wisconsin Geology and Groundwater Study is pollution of groundwater from fecal sources and diseases that are associated with that kind of groundwater pollution 

The state of the art lab in Marshfield can isolate the source of fecal contamination. It can also isolate and culture specific pathogens found in the water samples.

Joel Stokdyk is employed by the U.S. Geological Survey and is also focused on groundwater contamination. Borchardt selected Stokdyk to head the SWIGG Study.

The lab has been involved in lots of studies in Wisconsin, Minnesota and Iowa over the years. Papers were published about those studies and they were reviewed internationally, according to Borchardt. The USDA and the US Geological Survey combined to conduct a groundwater survey in Kewaunee County. 

Borchardt and Stokdyk took turns explaining what had been done to date in the SWIGG Study and what it meant. The local study is focused on Grant, Iowa and Lafayette counties. It began in its first phase having randomly selected well owners take water samples on a given day that were then gathered and taken to UW-Stevens Point. 

 The first sampling was done in November. The scientists noted that the samples represented a ‘synoptic event’ or something done on the same day where weather conditions and other factors would be the same.

In November 2018, 301 samples were taken. The analysis of the water samples showed 42 percent were contaminated. It also showed 34 percent showed coliform contamination, which indicated they were contaminated from a fecal source and had bacteria in the water sample. 

The analysis also showed 16 percent had nitrate levels above 10 mg/L (milligrams per liter), meaning they were above federal safe drinking water standards. Overall, the water samples tested in the first round of testing showed 42 percent of the wells were either contaminated by coliform or had high nitrate levels.

A second water sample test was done in April of 2018 on 529 well. The results were somewhat different than analysis of the November well testing samples. Only 27 percent of water samples proved to be contaminated by bacteria or high nitrate. In fact, the wells contaminated by fecal-sourced bacteria dropped to just 16 percent of the wells sampled, while those testing high for nitrate levels were 15 percent.

Much of the information presented by Borchardt and Stokdyk was familiar to the full-house crowd assembled in the conference room of the Platteville Public Library. The scientists tried to explain some of the nuances of the study and what the results mean.

The second phase of the SWIGG Study involved taking filtered samples of 200 gallons of pressurized water from 35 randomly selected wells from wells that had previously tested contaminated. Interestingly, only 32 of 35 tested contaminated with coliform.

The more intense testing involved analyzing material collected in the filters. Through the process the lab was able to identify the source of fecal contamination by species–human, cattle, swine or some combination of the three.

The second phase of testing also identified specific pathogens in the samples including different types of salmonella, noro virus, cryptosporidium and more.

Borchardt told the group in Platteville that results of second phase testing on another randomly selected group wells from those found to be contaminated in the initial April Testing were not yet available.

In addition to the results from the study already available, Borchardt and Stokdyk discussed some observations they had already made. The scientists noted that while there wee similarities in geology from Kewaunee County to Southwest Wisconsin, there were also some differences.

“What we learned in northeast Wisconsin might not apply here,” Borchardt said.

Both areas have dolomite bedrock, which is prone to fracturing and erosion. However, an important factor in groundwater contamination appears (soil) depth to bedrock, according to Borchardt.

While both areas have wide variance of depth to bedrock, the scientists said certain areas of Kewaunee County appeared to have a much greater depth to bedrock. Some deep soils in Kewaunee range to 200 feet, while in Southwest Wisconsin 50 feet to bedrock is deep. In both places, there are areas with virtually no depth to bedrock.

However, the scientists said the Rountree Formation, found in Grant County, was interesting. The formation was created by an accumulation of clay from windborne sources. The Rountree Formation may offer some protection to groundwater contamination in the wells it covers by producing a greater depth to bedrock, according to the researchers.

Another aspect of the geology that is different in the Southwest Wisconsin, which has drawn their attention, is what is called a perched aquifer.

The meeting ended with a lively question-and-answer session.

A woman asked Borchardt whether nitrate contamination below the 10 mg/L level was harmful. The scientist explained that a lot of input and thought had gone into placing the threshold for nitrate contamination of groundwater at 10mg/L.

The woman said that her reading indicated that levels below that level could be dangerous.

Borchardt explained that anywhere there had been human input, testing would likely find 4 mg/L. The scientist said that in untouched areas in the middle of a national forest groundwater would probably test 2 mg/L.

Another member of the audience questioned whether having citizens take their own water samples, as was done in the first round of the study, was an accurate sampling method. He questioned the ability of people to take their own samples and wondered whether human error might invalidate the sampling.

In response, Borchardt said the citizen sampling method had proven to give accurate results in the Kewaunee study.

 The questioner told Borchardt that a sample he took proved positive for contamination and after consulting with a plumber and taking another sample it proved negative. He questioned if that didn’t invalidate the sampling process.

Borchardt asked how long after the first sample, the second sample was taken. The man said about one month.

The scientist said that if it had been within a day, it might have proved the first sample invalid, but it was quite possible that samples could change from positive to negative in a month. So, it might not be the sampling method.