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Koch: Dunn County water table sensitive to contamination

By LeAnn R. Ralph

COLFAX — When you turn on the tap in your home and fill a glass with water, do you know what you’re drinking?

You really might not know what you are drinking, says Neil Koch, a retired geologist and hydrologist who presented a community forum on water quality at the Grapevine Senior Center in Colfax May 28.

Koch also serves as a supervisor on the Menomonie Town Board.

 Dunn County is in somewhat of a unique situation in that our water comes from a water table aquifer, which is recharged by rainfall and snow melt, Koch said.

In this area, water flows through the water table aquifer and then discharges to rivers, lakes and streams, he said.

Because Dunn County’s water table aquifer is recharged by rainfall and snow melt, that means the aquifer is very sensitive to contamination, Koch said.

Run-off from buildings and parking lots constructed in high recharge areas can contaminate the water because it drains directly to the aquifer, Koch said.

When snow is plowed off roads, streets and parking lots and contains road salt or other chemicals, the melting snow can contaminate the aquifer, he said.

When sludge from septic tanks or municipal wastewater treatment facilities is land-spread in recharge areas, the sludge can also contaminate the aquifer, not only with bacteria but also with pharmaceuticals and other chemicals, Koch said.

Land spreading

Acreage where sludge can be spread is approved by the state Department of Natural Resources. During the winter or when conditions are too wet, septic sludge is hauled to Menomonie and is run through the Menomonie wastewater treatment facility.

The DNR has approved 400 sites in Dunn County for spreading septic waste, Koch said.

To get an accurate picture of those waste-spreading sites in Dunn County, Koch asked for specifics on the locations and then pinpointed them on the aquifer recharge map.

As it turns out, 37 percent — which would be 148 out of 400 sites — are in violation of the DNR’s standards, Koch said.

In other words, DNR-approved waste-spreading sites in Dunn County could be contaminating the aquifer with bacteria, pharmaceuticals and chemicals, he said.

“I would like to see the state of Wisconsin ban the land spreading of septic waste,” Koch said.


A rural residential septic system also could be contaminating the homeowner’s water well if the septic system is located on higher ground than the water well or could be contaminating a neighbor’s water supply if it is too close to a property line, Koch noted.

The federal Environmental Protection Agency recommends a minimum lot size of two acres for rural subdivisions to make sure there is adequate space between the septic system and the property owner’s water supply or a neighbor’s water supply, Koch said, adding that he also has been recommending that townships in Dunn County set a minimum lot size of two acres in areas where septic systems are used.

The lot size could be as small as a half an acre if it is in an area where it could easily tie into a municipal sewer system, Koch said.

Water levels

Since surface water and the aquifer are so closely linked in this area, Koch said he would like to see townships, cities and villages take regular measurements of their water levels so historical data is available when needed.

Koch said he measures the water in his well every month, and during the drought conditions last year, the water level dropped five feet.

“We should encourage county officials to monitor water levels,” he said.

When a new industry starts up that uses large amounts of water, such as a processing plant for a sand mine or the ethanol plant near Boyceville, the county should require the industry to measure water levels in a monitoring well and then turn in the information to the land conservation office, he said.

“That way you will have historical data for the aquifer, so that if a problem occurs, you will know if the problem started quickly or came on gradually,” Koch said.


Earlier this year, the St. Croix County Zoning Board of Adjustment approved an amendment to the Milestone Materials special exception permit to mine into the groundwater at the Wilson quarry in the Town of Springfield.

The Wilson quarry is located along U.S. Highway 12 not far from the border with Dunn County, and Wilson Creek runs through the mine site.

Milestone Materials is mining frac sand out of the Wilson quarry.

Frac sand is used in hydraulic fracturing to force more oil and natural gas out of the wells.

When Koch learned that St. Croix County had approved mining into the groundwater, “I was horrified,” he said.

Mining into the groundwater has the potential to introduce contaminants, and if the water level is reduced sufficiently, chemical changes can occur, Koch said.

One example is a township east of Oshkosh where the water level was reduced to the point where naturally-occurring arsenic was released into residential wells, he said.

Frac sand mining in this part of the state has the potential to reduce water levels significantly, which makes it especially important for municipalities to monitor their water levels, Koch said.

Because of the number of sand mines and processing plants north and east of Colfax in Chippewa County, the Village of Colfax and the surrounding townships should be regularly monitoring water levels, he said.

Although the frac sand is only mined in Wisconsin and no hydraulic fracturing takes place here, the areas where hydraulic fracturing is done are facing potential disasters for their water supplies, Koch said.

“Fracking is going to mess up the aquifers big time … and when (contamination) gets into the aquifer, you’re done. Forever … once an aquifer is contaminated, it is impossible to clean it up,” he said.