Cherry Island Landfill

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Wilmington, Delaware
Date of Execution: September, 2006

Significant Project Features:

  • Construct the earth and geosynthetics components of a 472,000 SF Mechanically Stabilized Earth Perimeter Berm on soft soils.
  • Installation of over 81,000 prefabricated vertical drains.  Materials total 6,800,000 LF.
  • Install groundwater and landfill gas monitoring wells, and geotechnical and environmental monitoring systems to measure ground settlement during and after construction.
  • Construct temporary and permanent components of leachate and landfill gas management systems; install 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 exceeds 1,300,000 SF.
  • 2,000,000 cubic yards of engineered fill required to construct MSE berm.

History and Location of Project

The Cherry Island Landfill (CIL), in Wilmington, DE is undergoing an expansion that will 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 would continue to operate during the vertical expansion of the landfill footprint. 

Description of Work

The activities associated with the landfill expansion included:

  • Prefabricated Vertical Wick Drains.  The Prefabricated Vertical Wick Drains (PVD) provide 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.

Health and Safety Overview:

  • All construction occurred along the perimeter of an active landfill.
  • Sevenson constructed an MSE berm averaging 60 FT tall utilizing fall protection for the entire construction period.  The interior of the MSE berm consisted of 2:1 slopes.  Confined Space was necessary when access to the manholes and pump stations were required.
  • Health and Safety Measures:  Level D was used during the majority of the work.
  • Health and Safety Staff:  One onsite health and safety officer.  During times when there were multiple tasks occurring, Sevenson brought in an additional health and safety officer.
  • How 40-Hour Training Was Implemented:  Sevenson performs all training required under OSHA 1910.120 in-house by our Certified Industrial Hygienist, Dr. Paul Hitcho.