Land quality – managing ground conditions

4.1.7Managing 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:

  1. design precautions
  2. remediation techniques
  3. 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.

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 (e.g. 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.