Morton Arboretum in west suburban Lisle is undergoing a $43 million site-development program.

The project at the outdoor nature museum is aptly named "Branching Out."

The arboretum was founded in 1922 by Joy Morton of Morton Salt fame. It has grown to 1,700 acres, and the three-year initiative focuses on the 50 or so acres nearest the entrance. Included in the project are a new Visitor Center, Meadow Lake improvements, environmentally friendly parking lot, reconfigured entry, a Maze Garden and a Children's Garden.

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The Visitor Center will open this summer and full completion is scheduled for next year.

"Over the years we've had more traffic and we want more traffic, but we didn't have the facilities to handle it," said Ralph Grieco, Morton's capital projects director.

About 400,000 people visit the arboretum each year.

The project is backed by a mix of private and public funding, including a capital fund drive and grants from state, environmental and other agencies.

New Visitor Center

The 36,000-sq.-ft. Visitor Center replaces the one built in 1972 and more than doubles its size. With a low, horizontal design and a cedar, limestone and glass facade, the architectural style might best be described as contemporary prairie.

"Our mission was to provide a building that is a gateway to the arboretum," said architect David Woodhouse, president of David Woodhouse Architects in Chicago.
"The arboretum is an exterior museum, and the Visitor Center prepares you for and launches you into the site itself."

A curved 200-ft. exterior wall of lannon limestone, which was reused from the previous center, gently guides visitors from the parking lot to the front door. Two buildings bridged by a canopy comprise the center. The main building houses a restaurant, retail store, exhibits and visitor services, while the smaller one is for security, plant clinic and programs.

The jewel of the center is the floor-to-ceiling glass curtain wall, measuring about 125 ft. by 10 ft., on the east side, which overlooks Meadow Lake and the new gardens.
Separating the panels are vertical 1-in.-thick glass fins, positioned at 90-degree angles every few feet. The panels - a structural glazing system - are "held in place top and bottom by the building, but the fins stiffen the glass to take wind blows without the use of opaque mullions," Woodhouse said.

The ceiling is sloped upward to the curtain wall and paneled with perforated wood tiles. The tiles are carried through both buildings, although they are not perforated under the canopy.

"It's a long room with hard finishes, and we were concerned about noise," said Matt Liebing, project manager for the center's general contractor, Executive Construction in Hillside, Ill. "The perforations absorb the noise, and there is a sound blanket on top of the panels."

The combination of the ceiling and wood-clad support columns stationed every 30 ft. mimic the underside of a tree's leaf ball, Woodhouse said.

Project Accelerates

The work got off to a slow start last spring while the team waited for permits but then proceeded briskly.

"We wanted to start in April, but we lost a month and a half at the start of the job waiting for stormwater permits when the weather was decent," Grieco said. "DuPage County is one of the tightest counties in the country. Because of the flooding in this area, they have to be stringent. We hurried along so we could be closed by winter."

Working in an arboretum was a new experience for many of the contractors and their subs. Special care was required to protect plant life and soil. Protective fencing was wrapped around nearby trees.

"All of us had to go through a bit of a training," Liebing said. "When we were excavating, we had to be careful not to damage roots. And we had to coordinate with the landscapers so that we stopped our backfill within an inch so we didn't impede on their planting or contaminate their soil. On a typical building we can get within a foot or so, but they have a lot of plants that are sensitive to the soil they are in."

Improving Meadow Lake

Another big project was improving the water quality of the manmade Meadow Lake, a major arboretum attraction. Primarily fed by groundwater, the lake was high in phosphorous and created a better habitat for algae than it did for fish. Fluctuating water levels caused erosion of the shoreline.

The solution was to surround the lake with a soil-bentonite slurry cutoff wall, constructed by Williams Environmental of Frisco, Texas.

The job required a trench dug 3 ft. wide and anywhere from 30 to 45 ft. down to bedrock. A monumental backhoe with a 50-ft.-long arm, which was delivered in pieces on six transport vehicles, was used. The trench is filled with a mixture of bentonite clay, water and soil to create an impermeable barrier.

After the wall was in, the lake was drained, dredged, outfitted with better circulation capabilities and refilled with high-quality water from nearby Crabapple Lake. Runoff is steered to the East Branch of the DuPage River, which runs through the property.

"Now with the slurry wall, the groundwater has no way to get into the lake," Grieco said. "It is fed through natural rainwater."

The task took about 3.5 months, including machine assembly, said Jeff Sallas, project manager for Williams.

"I think it rained from the day we got there until the day we left," he added. "Rain really doesn't affect our work. It's a really muddy, sloppy mess to begin with, anyway. The only thing that could impact the slurry wall would be lightning."

New Entrance Method