Significant Project Features:
- Excavation of 102,000 CY of soil and debris
- Subsurface demolition and removal of MGP structures
- Pilot test
- In-situ solidification of 299,590 CY MGP impacted soil
- Site preparation and Waste Drum Consolidation
- Restoration, Backfill, Topsoil and Seeding gravel cover
- On-site management of materials and spoils
Description of Work:
The former North Plant site (site) is located within 3,000 feet of Lake Michigan in Illinois. Presently, the site has the distinction of being the largest in-situ solidification (ISS) remedy constructed on a former manufactured gas plant (MGP) site in the United States, with approximately 299,590 cubic yards of soils solidified.
Past MGP operations resulted in significant impacts to the site soil and groundwater. ISS was the selected remedy to meet time critical removal action objectives within the USEPA SAS program, and meet IEPA requirements for approval of the first ISS remediation constructed in the state of Illinois.
The scope of work includes but is not limited to the following: mobilization, site preparation, site clearing, pilot testing, concrete slab demolition, excavation of impacted soils and subsurface structures, soil solidification, on-site management of materials, off-site transportation of materials, demobilization and site restoration.
Within the remedial limits, Geo-Solutions performed an excavation 4-5 feet below ground surface (bgs) to create a work platform for the ISS work as well as provide freeboard to manage spoils for the 13-27 foot deep columns. The excavation continued deeper to locate and remove any debris beneath. The excavation included demolition and removal of subsurface MGP structures and impacted soils prior to the in-situ solidification.
Geo-Solutions performed ISS utilizing the large diameter auger soil mixing method, to depths of up to 27 feet bgs. Approximately 299,590 CY of soils were solidified in-place to an average depth of 23 feet bgs for this project. Geo-Solutions utilized two soil mixing rigs to maintain the overall schedule of 14 months. A Delmag RH 28 hydraulic drill rig was used in conjunction with a Calweld CH-200 crane mounted drill platform mounted on a Manitowoc 4000w. The ISS contained complex sequencing including approximately 200 columns in close proximity to an active rail site and a 54-inch sewer line. Following solidification, spoils were graded per the design to direct surface water away from the mass.
Restoration includes removal of site facilities, placement and compaction of over 50,000 CY of select fill, 6-inches of topsoil and seeding.