When ground was broken last month on a long-sought nature sanctuary along Interstate 35E in St. Paul's North End neighborhood, it marked the beginning of the transformation of a strip of land that from 1891 until the late 1970s was a railroad right-of-way.

One of the first tasks facing the city of St. Paul as it begins work on the new Trout Brook Nature Sanctuary will be to deal with the environmental legacy of that railroad heritage. Elevated levels of arsenic, lead and petroleum byproducts have been detected on the site, requiring a $600,000 cleanup which has been funded by a U.S. Environmental Protection Agency grant.

As such brownfield remediations go, it's not a huge job, but the presence of the polluted soil played a key role in how the project could be pulled off with a $5 million development budget. The vision for the 42-acre green gem is to liberate the historic Trout Brook from an underground storm sewer system and return it to the surface as a meandering stream.

The biggest concern was making sure the site was thoroughly analyzed beforehand, said project manager Kathleen Anglo of the St. Paul Parks and Recreation Department.

"There is going to be a massive amount of excavation involved with the project — we're going to be digging a new 3,000-foot stream channel through the site as well as excavating for a series of ponds," she said. "We needed to do extensive testing in those areas to make sure we weren't going into this blind as to the level of contamination that was there."

The latest in a series of environmental studies dating back to 2003 was completed in March by the Roseville-based environmental engineering firm Braun Intertec, which concluded the contamination could safely be dealt with by overtopping public areas with clean fill found elsewhere on the site.

Hidden pollution, nasty surprises

Anglo said the city is well aware that with such brownfield projects, hidden pollution can provide nasty surprises and bump up construction costs, and so it has set aside some contingency funding if that's the case.

"We're keeping our fingers crossed," she said. "The contamination isn't at high levels, but it was used for many years as a railroad yard, so you have to be aware of it."

The bids for the entire project were revealed this week, with excavation expected to begin in August.

The idea for turning the land into a nature preserve originated with a neighborhood group, the Tri-Area Block Club, which began pushing for the concept after the former owner of the land had floated proposals to develop it into commercial and industrial uses opposed by residents.

Block club organizer Linda Jungwirth said many longtime North Enders remember when Trout Brook was still a surface stream running through an active railroad yard.

"We viewed this land as our buffer between the neighborhood and the interstate and the railroad," she said. "It was our little piece of nature. We had an environmental learning preserve in mind, like the one along the Gateway [bike] Trail in North St. Paul."

The idea gained the backing of the Capitol Region Watershed District, which saw it as an opportunity to reintroduce surface water to a city that doesn't have very much of it.

Bob Fossum, water resource project manager for the district, said the layout and features of the preserve were partly designed work around the presence of the contamination.

"It was very much part of the design, making sure that we're not disturbing the worst" of it, he said. "If not, that would be a budget-killer. Once you go there, you'd quickly get to point where you'd only be able to build half of your park."

The grading plan was also key in keeping costs down, and has been set up so large-scale hauling of materials off the site won't be necessary, Fossum added.

Don Jacobson is a St. Paul-based freelance writer and former editor of the Minnesota Real Estate Journal. He has covered Twin Cities commercial real estate for about a decade.