NHBC Standards 2011

4.1 Land quality – managing ground conditions

4.1 - Appendix 4.1A
4.1 - Appendix 4.1B
    Potential hazards and associated risks
4.1 - Appendix 4.1C
    Site investigation techniques
4.1 - Appendix 4.1D
    "Suitable persons" and "Consultants or Specialists"

Appendix 4.1-A



Report BR211 - 'Radon: Guidance on protective measures for new dwellings'
Report BR212 - 'Construction of new buildings on gas-contaminated land'
Report BR376 - 'Radon: guidance on protective measures for new dwellings in Scotland'
Report BR413 - 'Radon: guidance on protective measures for new dwellings in Northern Ireland'
Report BR414 - 'Protective measures for housing on gas-contaminated land'
Digest 383 - 'Site investigation for low-rise buildings: Soil description'



BS EN 1997-2- Geotechnical design: Ground investigation and testing
BS 10175 - Investigation of potentially contaminated sites
BS EN ISO 14688 - Geotechnical investigation and testing. Identification and classification of soil: Part 1. Identification and description. Part 2. Principles for a classification.
BS EN ISO 22476 - Geotechnical investigation and testing. Sampling methods and groundwater measurements. Part 1. Technical principles for execution.
BS 8485 - Code of practice for the characterization and remediation of ground gas in affected development.



C665 - Assessing risks posed by hazardous ground gasses to buildings.
Special publications 101 - 112 - Remedial treatment for contaminated land


DCLG and its predecessor departments

Approved Documents A and C - Structures and site preparation and resistance to contaminants and moisture


DEFRA and its predecessor departments

CLAN 02/05 Soil guideline values and the determination of land as contaminated land under Part 2A
Circular 01/2006 Environmental Protection Act 1990: Part 2A Contaminated Land
Department of the Environment Industry Profiles - Information on the processes, materials and wastes associated with individual industries
Department of the Environment - Waste Management Paper No 27 - Landfill Gas: A technical memorandum on the monitoring and control of landfill gas.


Environment Agency


CLR11 Model procedures for the management of land contamination


CLEA (Contaminated Land Exposure Assessment) guidance and software Science Reports SR 1,2,3 and 7.



Guidance on evaluation of development proposals on sites where methane and carbon dioxide are present.
R&D Publication 66 - Guidance for the safe development of housing on land affected by contamination.


Appendix 4.1-B

Examples of potential hazards and associated risks

Potential hazard Associated risk
High water table or low lying land Flooding.
Effects from toxic or noxious materials which could be concentrated or transported by ground water.
Mining, past, present and proposed Ground movement which will depend on the type of workings and materials extracted.
Existence of ground gasses including methane and carbon dioxide.
Solution features in chalk and limestone including swallow holes Underground cavities.
Trees Shrinkage and heave of clay soils. See Technical Requirement R5.
Physical damage caused by roots.
Peat Acid attack.
Changes in volume due to variations in moisture content.
Production of methane and carbon dioxide.
Low bearing capacity ground Settlement of foundations and sub-structures.
Infill and made ground including tipping Release of gases which may be explosive or asphyxiating.
Low bearing capacity causing settlement.
Former buildings or structures Underground obstructions producing variations in bearing capacity and settlement characteristics.
Adjacent buildings Effect on stability of both the new and existing buildings.
Existing drains, including land drains Contamination, flooding, waterlogging and interruption of land drainage systems.
Sulfates in ground or ground water Expansive reaction.
Chemical attack on concrete, mortar and bricks or blocks made with cement.
Unstable ground subject to landslip Ground movement.
Seas, lakes and rivers adjacent to land Erosion.
Contamination Substances which may be:
  • carcinogenic
  • toxic
  • asphyxiating
  • corrosive
  • phytotoxic
  • combustive
  • explosive
  • radioactive.

Appendix 4.1-C

Site investigation techniques

(In accordance with the recommendations of BS EN 1997-2 Geotechnical design: Ground investigation and testing)

Site investigation normally comprises a combination of the following:
Direct investigation

These techniques involve intrusive activities to enable retrieval and examination of the ground using the following methods of investigation:

a) trial pits

Trial pits allow the detailed inspection, logging, sampling and in-situ testing of large volumes of natural soil or fill and the assessment of ground water conditions.

b) trenches

Trenches are extended trial pits or linked trial pits which are excavated where greater exposure of the ground conditions is required.

Trial pits and trenches should be positioned where they will not affect future foundations.

c) boreholes

  • Light cable percussion drilling
    The conventional equipment used in the UK to drill boreholes in soils and weak rocks is the light cable percussion rig, often referred to as the shell and auger rig.
  • Continuous flight auger
    Exploratory boreholes may also be drilled in soils by mechanical continuous flight augers of various sizes. Hollow stem methods are typically employed where sample retrieval is required.
  • Rotary drilling
    Rotary drilling is used to investigate rock and sometimes stiff soils such as Boulder Clay. The two basic rotary methods are open-hole drilling and rotary coring.

d) probes

Probing techniques can be used for the analysis of the relative density of soils and also for environmental sampling and monitoring (such as chemical and physical testing of gases, liquids and solids).

Indirect investigation

Geophysical techniques (for example, electromagnetic, resistivity, seismic, gravity and ground radar) provide indirect interpretations of ground conditions. These measure from the surface, variations in properties of the ground both horizontally and vertically and hence attempt to define subsurface conditions.

Geophysical methods rely for their effectiveness on marked contrasts in the physical properties being measured. The required contrasts are provided by boundaries between distinctive strata with different properties (for example, between sand and gravel and rockhead). Definable contrasts may also be provided by faulting, underground cables and pipelines or by cavities.


The number and type of samples taken and tests which are carried out for any particular investigation are designed to be appropriate to the range of ground materials encountered and to the development which is planned. The requirements should take account of the results of the desk study, the walkover survey and the site investigation.

Samples should always be taken, stored and transported carefully to avoid cross contamination.

Samples can be taken of:
a) soils and rocks

Samples from trial pits and boreholes are taken to enable soil and rock descriptions to be made and to provide material for physical and chemical testing.

Samples of soils may be either 'disturbed' (that is, not retaining the original structure and consistency) or 'undisturbed'. Having undergone minimal disturbance, it follows that 'undisturbed' samples provide a more reliable indication of physical soil properties than 'disturbed' samples.

b) ground water

Ground water should be collected from appropriately designed monitoring wells. The wells should be screened and sealed to ensure that the relevant stratum is being monitored.

c) gas

Gas sampling should be carried out from appropriately designed monitoring wells. Boreholes or window sampling holes are typically used. Identification of likely source and measurement of gas flows plays an important role in assessment of risk. 


a) in-situ testing

A wide variety of in-situ tests can be used to support the results of direct testing. These range from basic tests undertaken by geologists or engineers using simple hand-held devices or portable test kits to the more elaborate methods that require specialist personnel and equipment.

b) laboratory testing

Testing laboratories should participate in quality assrance programmes (such as Contest and Aquacheck) and be accredited for relevant tests (by the likes of UKAS and MCERTS).

Physical tests on soil and rock materials are carried out to provide the following information on ground:

  • strength
  • relative density
  • deformation
  • settlement
  • consolidation characteristics
  • permeability.

Chemical tests on soils, rocks, ground water and gases can be carried out to provide an indication of potential contamination on the site.

Appendix 4.1-D

"Suitable persons" and "consultants or specialists"


The following skills and knowledge are required by the person responsible for the Initial Assessment (Clause D3), Basic Investigation (Clause D4) and Documentation and Verification(Clause D7):

  • be able to carry out a desk study and walkover survey
  • understand the hazards that can affect the development and know from where they originate
  • know how to collect information relating to such hazards on and adjacent to the site
  • be able to recognise the signs of potential hazards
  • be able to determine when specialist advice and detailed testing is required, and
  • be able to report the findings in a clear and concise manner.


The following criteria should be used as guidance for the appointment of a consultant or specialist responsible for the Detailed Investigation (Clause D5), management of hazards (Clause D6) and Documentation and Verification (Clause D7):

Experience has experience with similar types of site and development
Appropriate discipline(s) a thorough understanding of all the relevant skills required on the project and has access to the skills of other disciplines including chemists, geologists, hydrogeologists,toxicologists and environmental chemists
Project management ability to manage a project team consisting of the appropriate disciplines
Communication able to communicate effectively within their organisation, with the client, statutory authorities and the general public
Reporting can prepare comprehensive and well presented reports
Legislation understands the legislation and liabilities associated with the area of the United Kingdom in which the development is being carried out
Quality assurance has an appropriate quality management system and uses appropriately accredited laboratories
Risk management can carry out risk assessments as part of the risk management process
Site investigation can design site investigation programmes which include soil sampling, testing and laboratory analysis
Health and safety is fully aware of all occupational hygiene issues and health and safety legislation
Engineering design understands effective risk reduction techniques e.g. engineered foundations and sub-structure details or suitable remediation
Professional indemnity insurance has, and maintains, appropriate Professional Indemnity Insurance for the work being carried out.