Project Features:

• 4,200 Tons of Recycled Concrete & Asphalt
• 440 LF of Temporary Sheetpile
• 81,500 Tons of Excavation & Disposal
• 86,500 Tons of Backfill
• 1,236,000 Gallons of On-Site Water Treatment
• 300 CY of Sediment Dredging & Bank Soil Removal

Description of Work:

Geo-Solutions completed site cleanup for a former manufactured gas plant (MGP) site in Green Bay, Wisconsin. The site is a 4-acre parcel located within city limits and sits on a point where the East River and Fox River meet. The majority of the site consisted of a former parking lot adjacent to a four-story office building. The Green Bay Riverwalk also ran along the entire riverbank portion of the site.

As the prime contractor, Geo-Solutions was responsible for all elements of the project including site preparation and controls, demolitions, excavation, backfill, and site restoration. Site preparation and demolition included the removal of the parking lot asphalt, curbs, sidewalk, and the City Riverwalk. Several underground utilities including electric lines, storm sewers, and abandoned water and communications lines were removed. A former gas holder foundation was also demolished and removed.

The excavation of MGP impacted soil was performed in multiple overlapping phases with removal occurring as deep as 19-20’ below grade. Most of the deeper excavations’ cells were also located within 15’ of the river or the office building foundation. Two temporary sheetpile walls were installed adjacent to the river and the building to provide excavation support. As part of that process, GSI also implemented real-time vibration monitoring and structural settlement monitoring. The excavations were dewatered on a full-time basis, with the water being treated on-site with GSI’s mobile water treatment plant. Completed excavations were backfilled with granular fill and topsoil for the surface treatment.

A small but significant part of the project required near-shore dredging of MGP impacted sediment near a stormwater outfall. The work area was contained with turbidity curtain and the outfall was controlled with a diesel pump bypass. Clean rip-rap was removed first and stockpiled to be used later during restoration. Sediment dredging was completed with a long-stick excavator. After survey and sampling verification the dredge area was backfilled with pea gravel. After the dredge area was restored, the impacted bank soils were removed and restored with clean stone. The riverbank was then armored with stockpiled rip-rap and a small volume of imported rock.

Final restoration of the site included:

• Replacement of 170 LF of 30” storm sewer plus one (1) new manhole and outfall at the river.
• Replacement of 390 LF of sidewalk adjacent to the office building.
• Replacement of 990 LF of City Riverwalk which included concrete curbs, asphalt surface, trees, shrubs, lighting, and park benches.
• Topsoil and seeding of the majority of the remaining area.