Also see:
CIRIA Reports C716 and SP164
4.1.7 Managing the risks (sites where hazards are found)
Hazardous ground conditions shall be satisfactorily managed under the supervision of a consultant or specialist acceptable to NHBC. Items to be taken into account include:
- design precautions
- remediation techniques
- a method statement and report.
The consultant or specialist should:
- identify any results which show that design precautions and/or remediation may be necessary
- conduct a risk assessment to determine appropriate design precautions and/or remedial treatment
- specify the options for remediating any contamination that may be present and provide a remediation method statement
- make recommendations for appropriate design precautions as necessary, including all underground services on the site and any ground improvement techniques
- ensure the works are appropriately supervised
- produce a remediation report.
The proposed solutions for dealing with geotechnical and/or contamination hazards should make due allowance for any constraints that apply, for example:
- factors associated with the site and surrounding area which could restrict the design precautions or remediation techniques should be identified
- local and statutory requirements should be met to avoid abortive works
- time constraints may influence the choice of solution, but do not alter the requirement for effective remediation.
Design precautions#
Solutions for dealing with geotechnical hazards include:
- specialist foundations such as rafts, piling and ground beams
- ground improvement techniques such as vibro, dynamic compaction and surcharging.
When dealing with hazardous gases note:
- some radon barriers and gas membranes are manufactured from recycled products. However, these should not be used. Also see Annex C of BS 8485
- where protective measures are required for both radon and other hazardous gases, for example methane or carbon dioxide, it should not be assumed a radon barrier will be effective in such circumstances and further specialist advice should be sought. Also see Annex G of BS 8485.
Remediation techniques#
Solutions for dealing with contamination hazards include:
- risk avoidance by changing the pathway or isolating the target, by adjusting the layout and/or by building protective measures into the construction
- engineering-based treatments that remove or isolate contaminants or modify the pathway by excavation, providing ground barriers or covering and capping
- process-based treatment to remove, modify, stabilise or destroy contaminants by physical, biological, chemical or thermal means.
Remediation method statement and report#
The remediation method statement should detail the strategy for the site and include the:
- original risk assessment, identification of the remediation objectives and outline information for the method chosen
- remediation objectives for ground, ground water and soil gas
- working method for implementing remediation
- waste classification and methods for control and disposal
- proposed supervision and monitoring of remediation
- validation sampling and testing to be implemented.
The report should include the following information:
- photographic records, especially for work which will be buried (eg membranes)
- site diaries or drawings, environmental supervisor’s site diary and independent witness statements where appropriate
- accurate surveys of the levels and position of all remediated areas
- a description of any remedial materials used
- details of soil movements and waste transfer notes
- results of post-remediation sampling (laboratory certificates should be provided in appendices)
- validation test results
- results of monitoring
- details of all consultations and meetings with statutory authorities.
Last updated: 2nd January 2024