A Landfill Cell is a Complex System

Cross Section of a Landfill

posted 7/31/2013

A landfill is a meticulously engineered depression in the ground. Unlike the old “dumps” of the past, it is a very complicated system designed to protect groundwater from contamination. Landfills take years of planning and development and require a significant investment. The landfill is divided into cells or designated areas where the land will be prepared for trash disposal. Currently, a new cell is under construction at Metro Waste Authority’s Metro Park East Landfill (MPE) in eastern Polk County.

Building a new landfill cell takes months and involves various stages of construction. Many of the steps in building the cell must be tested to make sure standards are being met before moving on to the next phase of construction. A new cell is built about every two years at MPE. The one currently under construction covers approximately 10 acres.

Step-by-Step Landfill Cell Construction (see illustration at top of page)

  • Excavation (digging) down to the bottom of the sub-grade.
  • Excess material (mostly clay) hauled to on-site stock pile.Rocak Trench
  • Rock trenches are dug 7-foot deep, wrapped with geotextile mat and filled with 6-foot of rock (this cell will have three rock trenches in the bottom and one in the north slope) to keep groundwater from the liner.
  • Two feet of clay is recompacted into 6-inch lifts (layers).
  • Each of the four clay lifts are watered; clay is ground by a reclaimer (large machine) so nothing is larger than 1-inch diameter; clay packed down with a sheepsfoot roller (heavy equipment). Each lift is then tested for optimal moisture and density.
  • Cell is smoothed and surveyed.
  • Edges of existing liner on adjacent closed cell are exposed and cleaned to join with new liner.
  • Plastic cell liner is installed extending up sides of cell (60 mil polyethylene).
  • Geotextile (permeable fabric) mat goes over the liner to protect it.
  • Existing leachate pipe system (8-inch perforated PVC) is extended through new cell. Leachate is theGrinding Clay Lift liquid that filters down through the garbage, typically as a result of rain. Leachate is collected in pipes that drain into a lagoon to keep it from contaminating groundwater.
  • Pea gravel is hauled in and placed over liner and mat to a depth of 1-foot on bottom and slopes of cell.
  • Temporary berms with rain guards are built around the perimeter. 
  • The cell is ready for a “fluff” layer. The “fluff” layer is typically residential trash and does not contain bulky items. 
  • As the cell is filled, wells are dug to capture the landfill gas (methane) that results from theCompacting clay on side of cell decomposition of waste materials. At MPE, the gas travels through pipes to a facility on the property where it is turned into electricity.
  • After a cell is filled to capacity, the same liner system is placed over the top acting like a giant garbage bag keeping the trash contained and the water out to protect the environment.

The biggest challenge of cell construction is usually the weather and it has been a factor at MPE this spring. “We’ve probably lost eight days because of wet conditions” says Harold Slagoski, superintendent for contractor, Veit USA – the company that is building the cell.

The project at MPE began in early June and is expected to be completed by mid-August.