Cherry Island Landfill Expansion


Location Wilmington, Delaware
Contract Value $90,000,000
Period of Performance September 2006 – September 2012
Role Prime Contractor

Significant Project Features

  • Construct the earth and geosynthetics components of a 472,000 SF Mechanically Stabilized Earth Perimeter Berm on soft soils
  • Over 2,000,000 cubic yards of engineered fill required to construct berm
  • Installation of over 81,000 prefabricated vertical drains. Materials totaled 6,800,000 lf
  • Installation of groundwater and landfill gas monitoring wells, and geotechnical and environmental monitoring systems to measure ground settlement during and after construction
  • Construction of temporary and permanent components of leachate and landfill gas management systems. Installation of temporary and permanent mechanical and electrical systems
  • Install 30+ acres of vapor barrier, geosynthetics clay layer, 60 mil geomembrane and geocomposite components of a liner system
  • Material volume exceeded 1,300,000 SF
  • Directional drilling at lengths over 150 lf and angles of repose greater than 35 degrees
  • Leachate divers were required during installation of the leachate transmission system
  • Strict compliance with DNREC regulations throughout the six (6) years of construction

History & Location Details

The Cherry Island Landfill (CIL), in Wilmington, Delaware underwent an expansion to provide an additional 19 years of disposal life. The landfill is located at the confluence of two rivers, creating very challenging subsurface conditions. The existing landfill was initially constructed in 1985 atop an area that was partially reclaimed from the Delaware River, and was used for many years as a dredged material disposal site for the U.S. Army Corps of Engineers. As a result, the subsurface characteristics at the CIL site consist of very soft and extremely compressible materials. Previous stability analysis indicated that the capacity of the landfill for vertical expansion was limited and, based on the incoming waste stream, the site would reach its capacity in 2006. The client’s goal was to develop a cost-effective design that could overcome the stability issues associated with the subsurface materials and allow a major facility expansion. In addition, the 513 acre landfill remained operational during the vertical expansion of the landfill footprint.


Project Description

The scope of work associated with the landfill expansion included:

Prefabricated Vertical Wick Drains

The Prefabricated Vertical Wick Drains (PVD) provided a solid subsurface to enable vertical expansion. The PVD’s were installed around the perimeter of the existing landfill to aid in the compression of the landfill perimeter soils. Sevenson installed over 81,000 PVD’s and completed wick drain installation prior to schedule milestone.

Mechanically Stabilized Earth Berm

The Mechanically Stabilized Earth Berm (MSE berm) is 60 feet high, almost two miles in length, and consists of two million cubic yards of fill. The components of the berm include welded wire forms, 20xt geogrid, high strength geotextile, Miramesh, and erosion control mat. The design allows the walls to be broad at the base and taper up steeply. Upon completion, the MSE berm will be one of the highest and most massive reinforced structures constructed over soft soils in the United States. The MSE berm had to be installed in 10.5 FT sections to accommodate settlement of the perimeter and to allow pore pressures to dissipate. Actual settlement periods varied, and Sevenson needed to adjust quickly to changing conditions.

Leachate and Landfill Gas System Expansion

Sevenson supplied and installed temporary electrical, mechanical and communication systems to operate the existing and temporary leachate transmission system and maintain the existing coast guard beacons. Sevenson was responsible for the installation of the temporary transmission system. Upon completion of the project, Sevenson is responsible for the installation of the permanent leachate transmission system. Electric and communication systems power and control the automated transmission of leachate through the new transmission system. A landfill gas collection system and landfill gas condensate system are to be installed at the completion of the landfill expansion.

Geotechnical and Environmental Monitoring Systems

This was a critical aspect of the project due to the large amounts of settlement anticipated within the MSE berm. This includes the drilling and installation of monitoring wells, landfill gas probes, piezometers, settlement sensors, inclinometers, and read out boxes. It also includes the decommissioning of monitoring wells, landfill gas probes, piezometers, settlement sensors, inclinometers

Stormwater Management System

The installation and monitoring of an extensive stormwater management system to accommodate settlement occurring during MSE berm construction. Features of the stormwater system included reinforced concrete pipe, manholes, drop inlets, pump stations, cradles, and energy dissipators.

Final Cover

Sevenson installed a multi-layer 30+ acre geosynthetic liner system along the interior 2:1 slopes of the 8,700 LF MSE berm. The liner system consisted of a 24-inch thick structural fill; a 60 mil textured geomembrane, a geosynthetic clay layer, a geocomposite drainage layer; and a 30 mil vapor barrier. The majority of the liner system was installed on a 2:1 slope along the interior perimeter of the MSE berm.

Rooted in Remedial Construction
Expanded into Environmental Dredging

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