Detailed Quantitative Risk Assessments (DQRA)
Ruddlesden geotechnical employ personnel who are skilled in undertaking Detailed Quantitative Risk Assessments (DQRA), which are sometimes undertaken if the Generic Qualitative Risk Assessment (GQRA) indicated a possible unacceptable risk to the health of site users, but where it is considered that further assessment might show that no or a reduced extent of contamination remediation works would be necessary.
This might include:
- additional investigation to delineate, vertically or laterally, areas of elevated contamination;
- additional sampling and testing to allow statistical analyses to be undertaken;
- more advanced laboratory testing, e.g. speciation, quantification or bioaccessibility; and/ or
- modifications to the land use or receptor within the CLEA model to produce Site-Specific Assessment Criteria (SSAC).
Bioaccessibility Testing Negates Remediation
The chemical laboratory test results obtained as part of a Phase 2 contamination investigation for a proposed residential development in South Devon indicated elevated levels of arsenic to be present in natural soils.
A generic qualitative risk assessment (GQRA) showed that all the recorded levels of arsenic exceeded the generic assessment criteria (GAC), indicating that remediation or further assessment was required.
Based on the conceptual site model (CSM), as no significantly elevated levels of contamination were expected, but given the underlying geology naturally elevated levels of metals and metalloids may be present, it was considered that further assessment should be undertaken instead of remediation.
A detailed quantitative risk assessment (DQRA) was therefore carried out, including additional bioaccessibilitytesting, as the GAC to which the recorded levels of arsenic were initially compared assumes that 100% of the arsenic is bioaccessible, whereas naturally occurring elements are typically not 100% bioaccessible. The bioaccessibility test is a laboratory test that simulates conditions in the gastrointestinal tract to assess the human bioaccessibility of potentially harmful elements by ingestion. As the ingestion pathway is the primary migration pathway for arsenic, the bioaccessibility significantly affects the assessment criteria.
The results of the bioaccessibility testing were incorporated into the CLEA, in which the end users were also modified, as the proposed development was for a residential care home rather than a standard residential land use, to produce a site-specific assessment criterion, which was greater than all of the recorded levels of arsenic.
It was therefore concluded that the recorded levels of arsenic were not likely to be harmful to end users, given the proposed end use, and that no remediation was necessary.
Carrying out this further testing and detailed quantitative risk assessment (DQRA) avoided the need to carry out unnecessary remediation.