The Hole That Saved a City

Posted: 9/18/2015

Laser scanner adds precision to rainwater diversion structure

By Jeff Winke

In Chicago, the Metropolitan Water Reclamation District (MWRD) is taking steps to reduce the destruction caused by future strong weather systems in our region, aka, flooding. MWRD will be undertaking an expansion project at the wastewater treatment facility located in nearby Lemont, Ill. According to MWRD, the Lemont plant will benefit from a new $30 million Wet Weather Treatment Facility to help improve storm water management at the facility. The project has begun and will be completed by summer of 2015.

The Lemont project includes a new pump station, a diversion structure for emergency high level overflow, separator and disinfection, and yard piping and tie-ins to an existing electrical and controls distribution system.

Additionally, a significant component of the project is the construction of a diversion structure for emergency high-level overflow. The new wet weather reservoir and wet well is a large in-ground concrete structure that measures 215 x 165 x 30-feet deep. The concrete walls are 2 to three-feet thick and the base measures four-feet thick. It is expected to be solid, leak-proof, and capable of handling overflow from the biggest storms.

"We won the contract for the construction of the overflow reservoir structure," stated Sam Henderson with Joseph J. Henderson & Son, Inc., based in Gurnee, Ill.

J.J. Henderson is a family-owned, design-build general contractor that was established in 1928. Water and wastewater treatment plant construction continues to be its largest division. Since 1983, when the company first entered this specialty niche, it has completed more than $750 million in work constructing water and wastewater treatment plants.

The site for the new storm water management reservoir in Lemont is predominately rock's mixture of aged dolomite, limestone, and slurry.

J.J. Henderson first used a robotic total station to set control points throughout the site as a basis for registering their 3D laser scanner point cloud data.

For the blasting operations J.J. Henderson contracted Ludwig Explosives, Inc., Lemont, Ill, and assisted them with layout of the blasting limits to match the final excavation configuration. Approximately 55,000 cubic yards of rock and soil was removed from the site in eight-foot lifts.

"Ludwig Explosives was very accurate in following the excavation plan," said Henderson. "To provide a safe work environment in the excavation, rock anchors and a chain-link fence was draped over each wall to catch and hold back any falling rock."

According to Henderson, the GLS-1500 laser scanner has been critical to the company's effectiveness and productivity on the Lemont plant wastewater treatment facility diversion structure.

The management at J.J. Henderson has said that without the laser scanner, they would have needed a different monitoring plan, requiring a crew of surveyors.

"The GLS-1500 laser scanner gives a high degree of accuracy, we're talking within hundredths of an inch accuracy," said Henderson. "I can't think of another construction tool on earth with that kind of accuracy."