Sources of ground gas

In addition to landfill sites there are several other man-made or natural sources which contain organic materials that can be degraded by bacteria to produce gas. Gas can also be trapped in material such as coal and be released when excavations for mines take place (or in peat and released when activities such as piling occur). Each source has different generation patterns in terms of volume and duration and as a result the level of risk associated with differing sources varies. 

The various sources and typical level of risk associated with varying somces is summarised in Table 3.1 which is based on the guidance provided in C3RIA Report 152 (O Riordan and Milloy, 1995). Any such assessment of the soiu-ce can only provide an initial indication of the likely risks posed by the various sources. Because of the variability in the nature of sources, particularly any made ground or landfill, an initial assessment made using Table 3.1 should always be confirmed by a site investigation. 

Generation rates are only provided in descriptive terms as it is virtually impossible to assign typical values to the different sources, due to the number of variables involved. The generation rates in Table 3.1 are provided in order to allow a comparison of tire relative risks posed by the various sources. The main factors that affect landfill gas generation and lateral migration are discussed in more detail in Section 4.1. 

At the worst extreme a very high generation rate can be taken as 10 m per tonne of waste per year or higher, which is the typical gas generation rate of a new landfill site (Nastev, 1998 (see Chapter 4)). At the opposite end of the spectrum very low generation rates mean negligible volumes of gas are being produced that are at least 10 or 100 times lower than the peak rate from a new landfill site. Carbon dioxide can be produced by natural soils at very low rates 

There are landfill sites that have been filled predominantly with industrial waste. They are difficult to assess without a detailed knowledge of what materials have been placed in them, so they are not included in Table 3.1. They can be compared to domestic landfill sites in terms of gas generation. However, if they have been filled with predominantly chemical waste tiren the gas generation rates are often very low, because the limited degradable content and/or the chemical make up retards or prevents the degradation process occurring. 

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It should be noted that this is only applicable to landfill sites and not other sources of ground gas. 

Carbonyl sulfide is an important gas kinetic source of ground state and electronically excited sulfur atoms, and its photodissociation has been employed by several groups to study the rates and products of reactions of S(3 P2), S(3- Sq), and 3(3 02). It is, in addition, one of the Interstellar molecules, has been proposed as a minor constituent of the Venus atmosphere, and leads to laser emission in CO following photodissociation. 

A combination of measures is usually used to minimise the risks associated with ground gas. This is so that if one element of the protection fails fhe ofhers will continue to protect the development. Only where the risk posed by the presence of ground gas is very low will a single level of protection be suitable The scope of measures for any site should be related to the risk assessment, with an increasing element of redundancy (or extra protection methods) provided as the risk increases Use of precautionary gas protection without a site investigation is a valid approach for low-risk sites, provided that a desk study is imdertaken to show there are no significant gas sources that could affect the site... 

Over the next ten years (1919-1929), U.S. annual energy demand grew from nearly 18.7 to 25.4 quadrillions Btus. The percentage of energy represented by petroleum increased from a little over 12 percent to 25 percent. Natural gas also nearly doubled its share, from 4.3 perent to 8 percent. Coal continued to lose ground as a source of energy, from 78 percent to 63 percent of total energy consumption. 

Bayer P., Saner D., Bolay S., Rybach L., Blum P. (2012). Greenhouse gas emission savings of ground source heat pump systems in Europe a review. Renewable and Sustainable Energy Reviews, 16(2), 1256-1267. 

The subsoil is the principal source of radon in this house. Both the activity concentration of radium-226 in subsoil and of radon in soil gas are above levels for building ground that might result in significant indoor radon concentrations. The radon decay-product concentration in the dwelling before remedial measures were taken was substantially higher than the reference value of 120 mWL. 

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