The operator of a modern landfill site in responding to the requirements for minimising leachate generation is likely to fill the site rapidly within small constrained areas to reduce rainfall ingress. When the operational cell is complete to restoration levels it is likely to be capped to prevent further ingress of rain water. This means that even the oldest waste at the bottom is therefore likely to be in only the early stages of degradation.

Significant settlement can then be expected due to the following mechanisms:-

i. The load on waste in the lower levels imposed by waste above it, particularly for deep sites, will be several times greater than that imposed during the initial compaction process using mechanical compactors. This will result in continued, graded compaction through the waste. This mechanism for settlement is likely to be predominant during filling and immediately following capping.

ii. The degradation process will break down waste into a denser material.

iii. The production of gas will mean a net mass loss of possibly 18% assuming 150m3/hr of landfill gas at 1.15kg/m3 is abstracted from each tonne of waste.

iv. Removal of leachate from lower levels of waste can also cause further settlement as pore pressures are reduced.

Settlement is therefore inevitable and must be catered for in the design of the restoration capping and in the design of both gas abstraction system. It is the job of the landfill design Engineer to assess the site “condition” and determine the potential for further settlement so that he can be satisfied a suitable design is proposed.

The CQA Engineer will verify the degree of settlement on-site through the contractor’s survey etc and ensure that the landfill design Engineer’s requirements are implemented during construction of the restoration capping.

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.