By LeAnn R. Ralph
HUDSON — A nitrate analysis conducted by St. Croix County shows that agriculture is the primary source of nitrate contamination in water wells.
Baseline work was a big priority for the county, said Tim Stieber, resource management administrator, at the St. Croix County community development committee meeting July 19.
The groundwater study group wanted to know what was going on as far as groundwater is concerned — is it getting much worse, is it an immediate concern or is it a longtime problem? he said.
The well at the Emerald Town Hall, for example, has consistently been testing at around 40 milligrams per liter (mg/L) for nitrate over the past several years. The well was first drilled in September of 2007, and at the time, the nitrate reading was 6.9 mg/L. A town resident requested in 2017 that the town board start regular testing on the town hall well, and the testing revealed that the nitrate levels were above the public health standards and have remained above the public health standards since then.
In April of this year, the Emerald Town Hall well tested at 45.3 mg/L for nitrate. In May, the result was 46.8 mg/L, and in June, the test came back at 44.9 mg/L, according to information provided by Emerald Clean Water For All.
The Emerald Town Hall is located across the road from Emerald Sky Dairy on county Highway G.
According to a report from UW-Stevens Point on the water sample at the Emerald Town Hall from October of 2020, “water greater than 10mg/L of nitrate should not be consumed by infants less than 6 months of age or pregnant women. The Wisconsin Department of Health Services recommends that all persons should avoid long-term consumption of water with nitrate/nitrogen concentrations greater than 10 mg/L.”
Goal
The goal of the St. Croix County analysis was to classify the sources of nitrate, Stieber said at the July 19 meeting.
The analysis, conducted by UW- Stevens Point, looked at the indicators that are highly related to specific sources. Tests were run on specific samples that analyzed 12 septic system indicators, five agricultural indicators and one manure indicator, he said.
As an example, artificial sweetener is an indicator of a residential septic system source while sources for agricultural indicators are a breakdown of herbicides, Stieber said.
The analysis began in 2019 with 14 samples, and another 39 were analyzed in 2020. All together, 53 samples were analyzed, and under the budget at that time, the samples were the maximum that St. Croix County could afford, he said.
Correlation
The analysis from Stevens Point came back last spring and showed that 79 percent of the samples had pesticides detected, Stieber said, noting that the tests were very sensitive and measured to parts per billion.
The summary of the results is that there is a statistical correlation between nitrate concentrations and three of the five agricultural tracers, he said.
“It supported what we kind of thought. That (the contamination) was from agriculture,” Stieber said.
There was a correlation between nitrates in the wells sampled and the land around it between a half mile circle and a mile, he said.
“It was a very positive correlation to the amount of agricultural land that was within a half mile to a mile of the wells we were sampling,” Stieber said.
The analysis did not find a positive correlation between septic wastewater and nitrate concentrations, he said.
“What we did find was a negative correlation, meaning if you had detection for POWTS (private onsite wastewater treatment system) in the water, we had lower levels of nitrate,” Stieber said.
If there was a lower detection of agricultural chemicals in the well, then there was a lower detection of nitrates, he said, adding that the highest nitrate samples had the least amount of POWTS detection.
“It was very related to agriculture and not very related to POWTS. POWTS are having an impact on our wells but are probably not the cause of our nitrates,” Stieber said.
The information gained from the analysis agreed with the information from the citizens’ groundwater monitoring, and there were similar results from statewide studies that showed 90 percent of nitrates are from agricultural sources, he said, noting the septic indicators are common but do not relate to nitrate.
“It is important to remember those septics are having an impact but they are not what is causing the nitrates,” Stieber said.
Two sources
Another important piece of information learned from the analysis is that the studies could not differentiate between the two main sources of nitrates: fertilizer or manure, Stieber said.
Out of all of the tests, there was only one with a manure indicator, he said.
“I did not even think that was possible,” Stieber said.
The other four agricultural indicators were not related to fertilizer but were related to pesticides put on crops, and there could have been manure put on the field, Stieber said.
“The study only went so far and did not do a very good job of telling us if manure was the problem for a lot of our wells. I know that’s a question we think of a lot and that we get questions on from our citizens,” he said.
More testing?
“One of the things we could do is testing that could differentiate between fertilizer and manure,” Stieber said.
“We dug into it quite a bit, and it was very expensive, but then we realized we had an opportunity in front of us because we have 17 samples we have identified in our network that do not have any septic in there at all,” he said.
“We could go to those wells as a source, and if we ran tests on those samples, it would be about $3,200. We might need a little bit of sampling equipment, but for less than $4,000 we could sample 17 (wells) and that would tell us what is the most likely source of nitrate in those wells — manure or fertilizer,” Stieber said.
“The reason I believe that’s important is because we often talk about should we do some more in regard to regulations or an ordinance on manure, and I have yet to prove we have a problem with manure in groundwater, which is frustrating because I think that there is (a problem) but I have to go with the data,” he said.
“I believe this overall groundwater project has come to a spot where we should support the additional sampling next year,” Stieber said.
The analysis shows that agriculture is the source of the nitrate contamination, but it does not show if it is fertilizer or manure, and additional testing might guide St. Croix County as to whether additional time and resources should be put into regulation or education, he said.
One community development committee member said he agreed that the analysis was at the point where additional testing should be supported.
The well study was a compromise on moratoriums on concentrated animal feeding operations (CAFOs) in St. Croix County, said Daniel Hansen, a member of the community development committee.
The community development committee should put resources into groundwater and surface water studies, because at some point, the St. Croix County Board may decide to halt the permitting process for concentrated animal feeding operations (CAFOs), which makes it difficult for the agricultural community and causes problems with the confidence the agricultural community has in the government, he said.
“I would like to continue to fund the work,” Hansen said.
Stieber noted that the testing done on 53 wells was a small sample of the 40,000 wells in St. Croix County, of which 25,000 are rural wells.
