The 2,700-acre Ada County landfill complex includes two separate municipal solid waste disposal “cells” — the older Hidden Hollow cell and the newer North Ravine cell.
Since the Hidden Hollow landfill cell opened in 1972, regulatory requirements have changed dramatically, impacting the cell’s design and structure, limiting the amount of area available for waste disposal and ultimately resulting in the need to close Hidden Hollow in favor of a newer more modern landfill cell.
Over its forty-plus years, more than 12.4 million cubic yards of waste has accumulated in the Hidden Hollow landfill cell. Last year, Hidden Hollow received its last load of trash.
This year, the county will begin the process of permanently closing the Hidden Hollow cell by capping it with a thick layer of soil harvested from the landfill property. This soil cap will cover the waste cell and help control odors, while it facilitates re-vegetation of the area with native plant species.
Landfill closure or “capping” is a lengthy and expensive process; it must happen in phases in order to give the cell an opportunity to rest and settle along the way.
This capping the cell will take several months to complete and cost about $2 million. The county on March 3 will issue a request for proposals to start the process of finding a contractor to help complete this phase of closing the Hidden Hollow cell.
The county opened the North Ravine cell in 2007 to address the need for additional landfill space as Hidden Hollow began reaching its capacity. The North Ravine is a modern landfill cell, incorporating the latest in safe and environmentally friendly technology, including a fully lined floor with a thick barrier to protect nearby soil and groundwater from contaminants. Additionally, in compliance with environmental quality standards, a sophisticated landfill gas collection well system is being incorporated into the North Ravine cell to continue to capture landfill gasses and provide an ongoing renewable energy source which the county uses to generate landfill revenue. The North Ravine cell will accommodate Ada County’s residential and commercial waste for the next 70 to 100 years.