Fitchburg Lands LLC has agreed to take the unusual step of measuring the pollution created by a planned housing development in response to public concerns that sensitive wetlands could be harmed by storm water and pollutants running off streets and hundreds of homes.

A Dane County developer has agreed to take the unusual step of measuring the pollution created by a planned housing development in addition to the standard practice of providing computer projections predicting that state water quality standards will be met.

Fitchburg Lands LLC agreed to set up four water monitoring stations in response to public concerns that sensitive wetlands around Lake Waubesa could be harmed by storm water and pollutants running off streets and hundreds of homes that are to be built just south of the Beltline.

In a lawsuit settlement signed last week by state and local officials, the developer agreed to monitor storm water and the state Department of Natural Resources increased the development zone to 511 acres.

Measuring flows and testing water samples will be costly, but an attorney for the developer said doing such actual measurements is something more developers and municipalities should consider to protect lakes, streams and wetlands.

Carl Sinderbrand, a Madison attorney who represented the developer and who also works with conservation groups, and others who work with storm water regulation said the agreement appears to break new ground.

“If it was up to me, this is something that would be done much more often,” Sinderbrand said.

Actual testing of industrial waste water is required to make sure factories and sewage plants meet standards. But regulations are different for storm water. Computer modeling is used to predict if a housing or commercial development will meet storm water standards.

Developers use the models to decide on size and placement of features such as retention ponds that slow down runoff and prevent erosion and protect water quality.

Modeling is also used by the state as it develops plans for cleaning up a growing list of lakes and streams whose uses have been impaired by phosphorus, mercury and other pollutants.

Computer programs have become increasingly precise, but there is always a margin of error, in part because they are built with data from past rainfall, said Robert Montgomery, an environmental engineer based in Cottage Grove who has worked extensively on the Fitchburg Lands proposal and many others since the 1980s.

The pattern of rain events and the total amounts that fall annually can vary widely from year to year.

“Is it ultimately accurate? No,” Montgomery said. “Is it the best we have? Yes, without spending millions of dollars.”

A single water monitoring station could cost in the range of $25,000 to $30,000 annually, said Bill Selbig, a research hydrologist for the U.S. Geological Survey’s Wisconsin Water Science Center in Middleton.

Actual storm water flow data is used to create computer models and to update them, but monitoring is seldom if ever used to ensure standards related to runoff are met, Selbig said.

“It’s expensive and it adds to the cost of the overall project and nobody wants to do it,” Selbig said.

Private companies and government agencies have created many water models for use in a variety of settings, Selbig said.

The Water Science Center has been working on updating data for average annual rainfall in a model frequently used to evaluate pollution potential of municipal storm water, he said.

When the modeling program was written several years ago, researchers selected rainfall data from 1981 as the average the program used, but recent significant changes in rainfall associated with climate change have made it necessary to make updates, Selbig said.

In 2014, the city of Fitchburg proposed to expand its urban service area — land approved by the state for sewer lines that make it possible to erect new neighborhoods and commercial developments — by more than 900 acres.

After the Capital Area Regional Planning Commission rejected the proposal, the city appealed to the DNR, which last year approved 375 acres. Fitchburg Lands, which controls most of the acreage, sued. The town of Dunn, which borders Lake Waubesa, intervened in the suit after being briefed by state officials on their plans for responding.

“The DNR started to basically cave in to the developer’s demands,” said Ed Minihan, who is a member of the regional planning commission board and Dunn town chair.

DNR water quality bureau director Susan Sylvester said the agency granted a larger development zone because the developer brought in new information.

Sinderbrand and Minihan said the monitoring requirement was included in the settlement agreement because of concern about potential harm to water quality.

Fitchburg Lands agreed to conduct 12 months of water monitoring at the outlets to four sub-watershed basins in the development area before the first phase of construction begins, according to documents provided by the DNR. After most of the first phase is completed, another 12 months of monitoring will take place.

If storm water is consistent with standards, the second phase of development is to proceed.

The neighborhood was initially projected for about 1,570 homes. Sinderbrand said it wasn’t clear how many would be built on the 511 acres, which includes areas reserved for green spaces, but he didn’t believe the number would be greatly reduced.

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Steven Verburg is a reporter for the Wisconsin State Journal covering state politics with a focus on science and the environment as well as military and veterans issues.