Made ground

The droplets crystallize and condense into hard, spherical prills that are dried, cooled, and sized for shipment. If calcium ammonium nitrate (CAN or nitro chalk) is made, ground calcium carbonate (limestone or dolomite) is added to the melt prior to the formation of the droplets when CAN is being made103 10S. 

The potential presence of these materials can usually be identified by a desktop study, which typically would search through the documented history of the site and determine the previous usages and changes that it may have undergone. Additionally, a site investigation may determine the presence of building rubble or made ground that is obviously not natural and may contain unknown contaminants such as ACMs. 

A more complete knowledge of the physical layout of the site and its below ground features can be obtained by non-intrusive survey methods. Ground-penetrating radar is able to locate buried features such as pipes and tanks. Soil conductivity may reveal buried objects and areas of made-ground or waste disposal. From the results of these types of survey, areas for possible intrusive investigation are identified and the zoning of the site can be refined. 

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. 

Made ground with high degradable organic content up to 15% (e.g. dock silt. No food or other easily degradable waste) Low Low/moderate Negligible... 

The effect of gas volumes and pressures is illustrated in Figure 4.4, which shows an example of two balloons filled with methane. The balloon on the left-hans side can be compared to a large domestic landfill producing large volumes of gas. If a leak is present the gas will rush out of the balloon. The one on the right-hand side is comparable to many brownfield sites underlain by predominantly inert made ground generating limited volumes of gas. There is gas in the balloon but if there is a leak it will come out very slowly, and the supply is much more limited. 

Low Made ground with limited degrad- High Close... 

For this to apply to organic degradation in soil, waste or made ground a COD value for the complete anaerobically decomposed material will need to be determined, i.e. the residual COD. The potential for gas generation for a sample is then ... 

Gas migration from made ground and hydrocarbon contamination into housing Very unlikely Severe Low risk Provide gas protection to new houses outside landfill sites... 

A site was underlain by 2 m of made ground that was inert soil with very occasional pieces of wood in it. The site was to be developed with a steel framed warehouse building with piled foundations and a reinforced concrete cast in situ suspended floor slab. Historical gas monitoring data was available but did not include flow rates. 

Thickness of migration pathway 4 m N/a Worse case maximum thickness of made ground below site (this also includes the original made ground below the made ground placed as part of the development, so is the very worse case)... 

MADE GROUND, medium to coarse gravel and coUsle size clasts of medium strong basalt in matrbc of brown, sandy, slightly clayey silt... 

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