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Award-winning landfill cap in Colorado

Case Studies | August 1, 2010 | By:

Project description

Phase 1: Construction of an RCRA cap/cover system over the triple-lined enhanced hazardous waste landfill at the U.S. Army CERCLA (“Superfund”) Rocky Mountain Arsenal Site in Commerce City, Colo.

Construction included a multilayered landfill cover system for a 26-acre, 1.2-million yard3 capacity hazardous waste landfill. Construction included approximately 26 acres of surface preparation work, more than 4 million ft2 of geosynthetic materials and installation—including geotextiles, geocomposites, 60-mil HDPE geomembrane, geosynthetic clay liner (GCL)—and approximately 350,000yd3 of controlled earthwork that included five separate cover components and materials.

This hazardous waste landfill has a 1,000-year design life and this cover system was the final stage in ensuring the permanent encapsulation of more than 1.2 million yds3 of hazardous waste.

Judging criteria

Teamwork and project management

Envirocon compiled a team of diverse professionals and experts to accomplish this project. The team included Envirocon, Colorado Lining, Fiore Construction, Hascall Surveys, and Reichler Engineering.


The Rocky Mountain Arsenal is an Occupational Safety and Health Administration (OSHA) Voluntary Protection Program (VPP) Star Status site. The project adopted these VPP techniques to assure the health and safety for all the workers and the community.

Every day started with an interactive detailed health and safety tailgate meeting where all the management, operators, technicians, and craft personnel were involved. Activity Hazard Analysis (AHA) was discussed and written up for every task as a proactive means to promote safety in the workplace. Prior to any new or modified task, a field safety meeting was held to discuss the work and potential hazards.

The project included approximately 50,000 man-hours with one minor recordable incident (minor back strain). In addition, there were approximately 20 minor incidents or unplanned events. These incidents were reviewed with the personnel as “lessons learned” to increase safety awareness. There were no “lost time” injuries on the project.


This project utilized typical geosynthetics capping materials, such as a geocomposite gas vent layer, geosynthetic clay liner, 60-mil HDPE geomembrane, and a nonwoven geotextile cushioning layer.

One of the most innovative portions of the project was the use of approximately 100,000 tons of recycled crushed concrete aggregate from the old Stapleton Airport runways in northeast Denver. Following the completion of the new Denver International Airport (DIA), the old Stapleton Airport runways were demolished and crushed into a rock-like matrix consisting of stone dust, up to 12-in.-diameter cobbles, all crushed concrete.

This recycled crushed concrete was applied over the landfill cover system to provide a barrier layer against burrowing animals. For the project, this particular component was named the Biota Barrier Material (BBM). Additional soil was then placed over the BBM layer and vegetated with native species for proper evapotranspiration from the landfill cover system.

Contribution to community or industry

This project was the final stage of encapsulating more than 1.2 million yds3 of hazardous waste at the Rocky Mountain Arsenal and helped transform this Superfund site into an Urban National Wildlife Refuge. The National Wildlife Refuge is open to the public and provides educational programs for schools and the general public.

Overcoming challenges

The project was scheduled to work through the winter, and adverse weather conditions and high winds created a challengingconstruction environment. The team pulled together, working long hours seven days per week, with additional personnel staffed up to keep the project on time and on budget. The installation of the geosynthetic capping system was completed one month ahead of schedule.

Construction quality and craftsmanship

All contributors said this project valued health, safety, and quality.

The team worked together to assure that all personnel understood the need to excel regarding quality of workmanship. Prior to any work, a detailed quality control manual was written to outline the QC means and methods for the project. In addition, manufacturer QC manuals were compiled from the vendors. Manufacturing plant visits were completed and materials sampled and tested to ensure they were produced in strict conformance with project requirements.

Quality control installation manuals were also written specifically for each phase of the project and for every task and type of material used. Training sessions were conducted to assure that all personnel were familiar with the project requirements and understood the importance of quality in the workmanship. The quality control manager and a multitude of QC and QA technicians worked with the craft personnel on an ongoing basis, and in a proactive manner, to ensure that everyone knew the project requirements and helped achieve 100% quality in the work on this project.

Function and aesthetic quality of the design

This landfill was designed in an unusual shape, with irregular grades to blend into the natural surrounding rolling hills in the area and to enhance the landscape.


Colorado Lining received a local Gold Hard Hat Award for its work on the Rocky Mountain Arsenal enhanced landfill cap. Gold Hard Hats is an annual competition to determine the best projects completed by Colorado firms. Judging is done by a panel of industry experts and based on design quality and innovation, craftsmanship, the project’s contribution to the community and the industry, solution of unique design and construction challenges, and overall excellence.

“It is an honor and a privilege to have been awarded the Gold Hard Hat,” said CLI president John Heap. “This award would not have been possible without CLI’s dedicated staff and personnel from Envirocon and Tetra Tech Environmental. It was a team effort and I am thrilled CLI could be part of a project of this importance.”

The Rocky Mountain Arsenal project is a 26-acre, multi-layered cap over hazardous waste. This project was the final stage of encapsulating more than 1.2 million cubic yards of hazardous materials, transforming the desolate area into a National Wildlife Refuge.

The project was scheduled throughout the winter of 2008–2009. In late December 2008, the project jobsite was hit by a 56-hour sustained windstorm that caused millions of dollars in damage to homes and businesses in the area. Approximately 6 acres of geosynthetic material was displaced by the storm.

The month of January required CLI and its partners to repair and replace the damaged lining. CLI added to its workforce on the site and worked seven days a week to get the project back on schedule. It was completed one month ahead of schedule and under budget.

About the Refuge

During World War II, the U.S. Army transformed the area into a chemical weapons manufacturing facility—called the Rocky Mountain Arsenal—to support the war effort. As production declined at war’s end, some of the idle facilities were leased to Shell Chemical Co. for the production of agricultural chemicals. The Arsenal area was later used for Cold War weapons production.

In the mid-1990s, a public-private partnership was formed with the U.S. Army, Shell Oil Co., and the U.S. Fish & Wildlife Service to plan for the future of this site. As cleanup of the area progressed and projects met federal and state regulatory requirements, the Army transferred 12,500 acres to the Wildlife Service to establish and expand the Refuge.

The Arsenal’s final cleanup details will be completed in 2010. At that point, the Refuge will reach its final size of 15,000 acres with a final land transfer from the Army, making it one of the largest urban wildlife refuges in the country.

Source: Colorado Lining International
Ron Bygness, editor of Geosynthetics magazine, also contributed to this article.

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