NHBC Standards 2006

4.1 Land quality – managing ground conditions

4.1 - Appendix 4.1A
4.1 - Appendix 4.1B
   Examples of 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'
Special Digest 1 - 'Concrete in aggressive ground'



BS 5930 - Code of practice for site investigations
BS 10175 - Investigation of potentially contaminated sites - Code of practice



Special publications 101 - 112 - Remedial treatment for contaminated land


DEFRA (Department for Environment, Food & Rural Affairs), its predecessor departments and the EA (Environment Agency):

CLR Reports and CLEA (Contaminated Land Exposure Assessment) guidance, Software, Soil Guideline Values and Toxicological Reports
Industry Profiles - information on the processes, materials and wastes associated with individual industries
Waste Management Paper No 27 - The Control of Landfill Gas
EA/NHBC 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 hazardAssociated risk
High water table or low lying landFlooding.
Effects from sulfates or toxic or noxious materials which could be concentrated or transported by ground water.
Mining, past, present and proposedGround movement which will depend on the type of workings and materials extracted.
Existence of methane and carbon dioxide.
Solution features in chalk and limestone including swallow holesUnderground cavities.
TreesShrinkage and heave of clay soils. See Technical Requirement R5.
Physical damage caused by roots.
PeatAcid attack.
Changes in volume due to variations in moisture content.
Production of methane and carbon dioxide.
Low bearing capacity groundSettlement of foundations and sub-structures.
Infill and made ground including tippingRelease of gases which may be explosive or asphyxiating.
Low bearing capacity causing settlement.
Former buildings or structuresUnderground obstructions producing variations in bearing capacity and settlement characteristics.
Adjacent buildingsEffect on stability of both the new and existing buildings.
Existing drains, including land drainsContamination, flooding, waterlogging and interruption of land drainage systems.
Sulfates in ground or ground waterExpansive reaction.
Chemical attack on concrete, mortar and bricks or blocks made with cement.
Unstable ground subject to landslipGround movement.
Seas, lakes and rivers adjacent to landErosion.
ContaminationSubstances 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 5930 Site Investigations)

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

These techniques involve actual 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

  • Shell and auger
    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.
  • 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. This is based on 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) groundwater

Samples of groundwater are taken from trial pits, trenches and boreholes for chemical testing.

c) gas

Gas sampling may be carried out in boreholes, from standpipes which have been installed in trial pits or boreholes or from spike-holes which have been driven into the ground.


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 to elaborate methods that require specialist personnel and equipment.

b) laboratory testing

It is important that testing is undertaken using quality assured procedures by laboratories which are UKAS accredited for these tests.

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, groundwater 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"

Suitable persons

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

Experiencehas 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 and environmental chemists
Project managementability to manage a project team consisting of the appropriate disciplines
Communicationable to communicate effectively within their organisation, with the client, statutory authorities and the general public
Reportingcan prepare comprehensive and well presented reports
Legislationunderstands the legislation and liabilities associated with the area of the United Kingdom in which the development is being carried out
Quality assurancehas an appropriate quality management system and uses appropriately accredited laboratories
Risk managementcan carry out risk assessments as part of the risk management process
Site investigationcan design site investigation programmes which include soil sampling, testing and laboratory analysis
Health and safetyis fully aware of all occupational hygiene issues and health and safety legislation
Engineering designunderstands effective risk reduction techniques e.g. engineered foundations and sub-structure details or suitable remediation
Professional indemnity insurancehas, and maintains, appropriate Professional Indemnity Insurance for the work being carried out.