Accurate and consistent description of Made Ground or anthropogenic soils/materials is of importance as it may provide vital indication of the material’s likely geotechnical behaviour, the potential for contamination and/or the potential for ground gas generation. However, BS 5930:2015 and BS EN ISO 14688-1 provide only limited guidance on the description of anthropogenic “soils”, and this has led to an inconsistent approach within the contaminated land industry.

The AGS Contaminated Land Working Group have therefore produced a Guidance Note, in which a standard framework for the geo-environmental description of anthropogenic “soils” is set out. This framework is summarised in a flow chart, which has been produced to allow it to be laminated and taken to site to act as an aide memoire for those who encounter and have to describe these “soils”.

For anthropogenic material principally comprising granular or cohesive soils (Class 1 and 2) the framework follows the BS 5930:2015 process. However, it has been extended to cover:
• organic materials (Class 3), such as landfill deposits and the largely organic debris that may be encountered within a backfilled canal or dock,
• fine grained chemical deposits (Class 4), such as chemical precipitates, filter cake wastes, chemical salts, sludges, powders and materials such as foul lime and Galligu, and
• Other identifiable material, such as textiles, plastic sheeting, railway sleepers, glass and sawdust etc. that may form the principal component of the ‘soil’ in some instances.
The Guidance stresses the need for detailing the proportions of inclusions within Made Ground, be it through standardised descriptors (rare, occasional, numerous, abundant) or by listing the approximate percentage of the inclusions by volume (e.g. “grey clayey sand of ash with textile fragments (20%), polythene (10%) and paper (10%)”).

Also provided in the Guidance are standard descriptors for the commonly encountered combustion products ash, clinker, charcoal and slag, as it appears these are often mis-identified. Commentary is provided on the importance of accurate colour description as an indicator of chemical conditions and the potential presence of contaminants. It is also suggested that the following groups of odours be adopted in preference to those suggested in BS 5930 (which includes some which are unlikely to be present in Made Ground, such as “floral” or “peppermint”):

• H2S (rotten egg),
• rotten cabbage (Mercaptan),
• naphthalene (mothballs),
• solvent (acetone – nail varnish, xylene-thinners),
• chlorinated solvent (‘Tippex’ thinners in the past)
• acetic (vinegar),
• fuel (petrol, diesel, paraffin),
• mineral oil (engine oil, lubricating oil),
• creosote/coal tar,
• putrid (decaying waste)

Guidance on describing the strength of the odour (from AS 4482.1-2005) is also provided as follows;
• Weak (just detectable at source, location difficult to determine),
• Distinct (detectable immediately adjacent to source, bearable at source),
• Strong (detectable 20m from source, bearable at source),
• Very strong (detectable >20m from source, pungent at source).

The Guidance Note is designed to complement the ‘Practical Framework for the Logging of Anthropogenic Soils’ which is being produced by The Environmental Protection Group Ltd, and which provides extremely useful guidance on the description of landfilled material and other anthropogenic materials with the potential to generate ground gas.

It is hoped that the adoption of a more standardised approach to the description of anthropogenic materials will improve the quality of ground investigations in these materials and will allow the vital data contained in exploratory hole logs produced by one company to be accurately interpreted by another consultant at a later date with regard to the contaminant and gas generation potential, and the likely geotechnical properties of the soil.

References:
British Standards Institution (2015): Code of practice for ground investigations. BS 5930:2015.
British Standards Institution (2018): Geotechnical investigation and testing – Identification and classification of soil – Part 1 Identification and description. BS BS EN ISO 14688-1:2018
Australian Standards (2005): AS 4482.1-2005 Guide to the Investigation and Sampling of Sites with Potentially Contaminated Soil – Non-volatile and Semi-Volatile Compounds – Tasmania.
The Environmental Protection Group Ltd: Practical Framework for the Logging of Anthropogenic Soils.

Although every effort has been made to check the accuracy of the information and validity of the guidance given in this document, neither the members of the Contaminated Land Working Group, nor the AGS accept any responsibility for mis-statements contained herein or misunderstanding arising herefrom.

AGS Guidance on The Description of Anthropogenic Materials– A Practitioners’ Guide can be downloaded from the AGS Website.

Prepared by Mike Plimmer of Geotechnical & Environmental Associates

This article was featured in the September/October issue of the AGS Magazine.