The purpose of Landfill Construction Quality Assurance is to ensure that the landfill is constructed in full compliance with the specification. The primary responsibility for ensuring this, rests with the landfill construction (civil engineering) contractor. The CQA Engineer (provided by Rowe Environmental), on site, provides independent inspection and verification of the work, and receives all the contractor’s site construction quality assurance records.

We’ve been asked just where Landfill Construction Quality Assurance fits into the various components and stages of landfill development.

A typical landfill consists of the following subsystems such:

• Landfill liner
• Leachate collection and management system
• Landfill gas management system
• Landfill gas monitoring & leachate monitoring systems
• Final landfill cap
• Drainage system
• Road network

Their function is to secure the normal landfill operations and to control the anticipated emissions generated mainly by the decomposition of organic matter, such as leachate and landfill gas.

The appointed Landfill CQA Engineer is normally required to inspect all parts of the works constructed during the landfill development contract works which will control the potential emissions from the site. So, from the list above, the CQA Engineer is normally required to inspect, witness test, and verify the recording of all the above listed subsystems except for the road network. Even within the road network he/she would also inspect the work such that the road networks installed for access close to the development works will not be such as to risk damage the integrity of the liner, walls, or capping.

The widely used definition of geophysics is that provided by Sheriff in the Encyclopedia of Exploration Geophysics.

For the purposes of this site, we refer more specifically to the following definitions – these focus on Environmental and Engineering Geophysics:

1. Geophysics is: The subsurface site characterization of the geology, geological structure, groundwater, contamination, and human artifacts beneath the Earth’s surface, based on the lateral and vertical mapping of physical property variations that are remotely sensed using non-invasive technologies. Many of these technologies are traditionally used for exploration of economic materials such as groundwater, metals, and hydrocarbons.
2. Geophysics is: The non-invasive investigation of subsurface conditions in the Earth through measuring, analyzing and interpreting physical fields at the surface. Some studies are used to determine what is directly below the surface (the upper meter or so); other investigations extend to depths of 10′s of meters or more.

Both of these definitions have a common component, namely that geophysics represents a class of subsurface investigations that are non-invasive (i.e. that do not require excavation or direct access to the sub-surface). The exceptions are borehole geophysical methods that expand the use of holes already drilled to access the subsurface on a very localized basis.

We will occasionally post capping design information on this blog. We hope that you will find these posts interesting.

To guarantee a landfill cap which will drain adequately and for effective gas collection, the landfill cap should incorporate a drainage layer above and preferably also, a gas collection layer below the cap’s low permeability lining system. 

The geosyntheic “Pozidrain” may be able to provide these functions with higher performance and lower cost than conventional crushed stone filters. The Pozidrain is also favoured by operators who want to squeeze the last once of waste into their landfill as the thickness of this material is much less than a stone layer, allowing more waste to be put in the landfill before the planning consented top of site levels are reached.

ABG Geosynthetics tell us that:

Pozidrain has been specially designed to be compatible with both HDPE and clay liners and to give the optimum performance over the whole life of the landfill capping. Pozidrain will enhance the performance of the GCL or HDPE liners by providing an additional barrier that prevents the majority of the water or gas reaching the liner. Pozidrain geocomposite drainage layer has a proven record in landfill capping.

If you are still wondering what Pozidrain material is, think of a very big area of a membrane material comprising many “egg boxes” joined together. Across the face remote from the low permeability landfill seal is “tack” welded a geotextile filter material. The egg box profile creates a continuous void which allows water penetrating the filter to drain away. A very simple but useful idea.

The Landfill CQA technician/supervisor must at all times ensure that the Pozidrain supplied meets the specified requirements, and is laid in accordance with the specification. This is likely to involve the checking, and acceptance of the contractor-provided supplier CQA records, plus some additional independent testing for verification of factory test data.

We have been asked where the necessary skills can be obtained for Landfill Construction Quality Assurance work.

The core skill needed for Landfill CQA is an good appreciation of soils mechanics, as most of the CQA work relates to civil engineering earthworks, so a good grounding comes from the Soils Mechanics tought within any practically based Civil Engineering Course, at HNC, HND, or BSc/degree level.

From time to time, for those who need additional training there are also specialist Soils Mechanics and Geotechnical Engineering courses available.

In addition, experience of construction site work is also very important. It is during site work that a CQA Supervisor will obtain familiarity with the wide variety of proprietory geosynthetic materials available, and the various methods of testing employed to ensure contract compliance with the specified installation tests and inspections.

For geomembrane liners and cappings there are very few courses available, so most training in good practice for membrane testing is “on the job” and provided for CQA staff within the consulting organisations undertaking this work.

A good starting point for anyone seeking employment in Landfill CQA in the UK, would be to visit the Charterd Institute of Waste Management (CIWM) web site and look for the next courses in such subjects as “Advanced Landfill Management”.

Southampton University (UK) for example provides a good Soil Mechanics course here.