Landfill Capping Landfill Construction Quality Assurance

Landfills nowadays each contain huge amounts of organic materials and hold a huge potential to pollute the local groundwater for generations in the containment systems upon which their design is based fail to function as intended.

The engineering of a landfill is no different to other engineered structures, in fact in many ways, especially due to its pollution potential it may be more important that it does not fail when compared to some other structures.

Landfill base liners are by nature buried once constructed and the opportunity to do repairs is extremely limited.

The lining of a landfill is the foundation of a major civil engineering structure.

Just as for the foundation of a multi-storey building great care is taken throughout the construction, the Engineer in charge of a landfill construction would be negligent if he did not require adequate checks to be made on all aspects throughout the design and installation of a landfill liner (or capping).

Carrying out all the necessary checking that the design is implemented and results in a properly built liner (or cap) in a methodical manner and without omissions and then to be able to show others subsequently that the quality of the materials used and the way they were placed will make a proper lining which is as the designer intended everywhere it is laid, is called Landfill Construction Quality Assurance (CQA).

CQA can only be applied once a competent design engineer has completed a design process which has resulted in a detailed specification for the materials to be used, and the thicknesses, depths and positions etc, of these materials when they are used.

This is what is called landfill geomembrane CQA, and it is normally carried out under the overall supervision of a client or purchaser's professional representative (eg "Engineer") who appoints an experienced CQA Engineer to carry out Construction Quality Control (CQC).

The CQA Supervisor is best appointed to someone outside the construction Contractor's organization to ensure his/her independence.

Whilst geomembrane materials are relatively impermeable even when compared with low permeability clays, they will transmit a small amount of water even when perfectly installed.

The vapor transmission rates of the geomembrane materials used vary for different fluids, but for water they normally have a permeability in the region of 1?10^-15 m/sec.

It is only if leakage rates increase substantially above this rate that problems will occur.

Unfortunately, if a landfill design is poorly carried out without a great deal of care being paid to construction quality (especially if only one thickness or one type of single barrier will be used), leakage can be hugely increased.

Just think how quickly a bath empties if you inadvertently knock the plug out while bathing!

In the realm of CQA, knocking the plug out without noticing when you did it would be called a lining defect.

It stands to reason therefore that leakage rates through a geomembrane are very significantly increased by the presence of even a few defects, and defects when present must be found and repaired before the job is finished.

In CQA plans in these defects are methodically identified and then as much as possible completely eliminated.

Steve Evans has provided more leading information on Landfill CQA (landfill Construction Quality Assurance) at his blog. A full version of this article is available at the importance of Landfill Construction Quality Assurance.

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