Although today's landfills must be designed with sophisticated liner systems, do we really understand the importance of quality construction?
After much observation, we know how liner systems perform; models have been developed and material specifications have become more detailed. Yet, both time and money can be lost if the liner systems' construction fails to meet the highest standards.
Investigations of liner system problems reveal that poor construction often is the culprit. Landfill construction can require moving millions of cubic yards of materials and placing thousands of square yards of liner. Typically, this must be done to exact specifications, which involve moving heavy equipment around the site. Weather also is a major factor. Considering all of these potential challenges, it's not surprising that problems arise.
The engineers at Camp Dresser & Mckee (CDM), Cambridge, Mass., suggest the following tips to help minimize and eliminate construction problems:
* Constructibility review. The design should be reviewed with experienced construction personnel to ensure the facility can be built at reasonable cost without field adjustments or order changes.
* Experienced contractor. Make sure the chosen contractor is experienced in landfill construction and liner placement. Set minimum qualifications. While experience is obviously critical for proper placement of synthetic materials, it also is critical for clay liners. Many earth moving contractors do not have experience in working with and placing clay.
* Work with the contractor. Resolve issues early and fairly to the satisfaction of both parties.
* Specifications. Use material specifications that meet project requirements. In particular, be sure the various testing methods are the correct ones. If testing procedures are used that are not "standard to the industry," make sure all parties involved understand the reasons. Also, never accept alternative materials offered by a contractor unless it is fully demonstrated that they meet the design intent and requirements.
* Quality assurance (QA) program. Most construction permits require a QA program which is critical to success. Use a program that has been successful in the past and update procedures as experience is gained. Fully implement and document the program. If site conditions or special materials are mandated, use the wide range of testing procedures available.
* Full-time inspector. During liner installation, a full-time, trained inspector should be present always as work proceeds on liner installation and/or if work is being performed on or near lines. "If an inspector is not present during construction, it's easy for problems to occur," CDM's Dan Duffy said. "For example, after a liner construction project is complete, a contractor's employee may decide to perform a final task such as using a bulldozer to fine grade the sand drainage layer over the liner. Using a bulldozer, the employee risks puncturing holes in the liner."
The inspector also should be in direct contact with the design engineer/project manager to review any deviations in the materials used in the construction process. Regular contact and progress meetings are necessary to ensure that the design's intent is being met.
The solid waste industry routinely constructs landfills by using experienced contractors, proven QA programs and trained inspectors. However, the industry must apply project lessons learned to new projects, perfecting the art of landfill construction.