Phase 2 - GQRA and DQRA
A site assessment may be completed at the conclusion of the Phase 1 PRA if it is found that neither the site or the surrounding area are thought to pose a potential risk to end users or the wider environment.
Where the outcome of the Phase 1 PRA identifies the presence of potential SPL and therefore potential risk, a Phase 2 GQRA and/or DQRA would be undertaken by TGEN in order to provide quantification of the SPL and therefore greater certainty of the significance of risk. If necessary, an appropriate programme of site investigation(s) together with suitable chemical analysis of soil, leachate and/or water samples, ground gases etc. is designed and implemented in order to gather sufficient information to provide quantification of the risks identified within the Phase 1 PRA.
The scope of the Phase 2 works would be dependent upon the outcome of the Phase 1 PRA but would potentially involve the following:-
- Site Investigation(s) (Exploratory, Main, Supplementary)
- Assessment of Risks to Human Health
- Assessment of Risks to Controlled Water
- Assessment of Risks to Other Sensitive Receptors
- Assessment of Risks from Ground Gas
The information gathered as part of the site investigation(s) is initially compared against generic assessment criteria (GAC) to assess the significance of links within the source-pathway-receptor model and as part of the Phase 2 GQRA a refined CSM can then be produced to assess the identified risks. Remedial measures and/or further works are then designed to either mitigate or further assess the identified risks.
Where necessary, the information gathered as part of the site investigation (and supplemented with additional information) can be compared against site specific assessment criteria (SSAC) in order to more fully rationalise any identified risks.
Current guidance within the UK policy framework for assessing potential risks to human health from contaminants in surface soils are contained within the Contaminated Land Reports (CLRs) and the Contaminated Land Exposure Assessment (CLEA) model produced by DEFRA & the Environment Agency (2002).
If after the completion of the GQRA contaminants of concern are identified as requiring further quantification then additional investigation, sampling and/or monitoring will be undertaken, followed by additional assessment of risks to human health, controlled waters or other sensitive receptor will be undertaken through some form of contaminant fate and transport modeling using complex risk assessment models to determine the level of risk present. These may include:-
- Environment Agency Remedial Target spreadsheet (R&D Publication 20)
- CLEA (2009 v1.06)
- GSI RBCA Toolkit
- RISC Workbench 4.0
- RISC Human 3.1
- SNIFFER
The outcome of the Phase 2 GQRA or DQRA may be that the risk is not significant and therefore further works or mitigation is not required. If the risk is identified as being significant, or is such that the site is not deemed suitable for the proposed use, then remedial measures may be required in order to break the identified SPL and in so doing reduce the risk to an acceptable level.
At TGEN our consultants have a wealth of experience in designing and implementing Phase 2 Site Investigations including undertaking appropriate risk assessments. If you would like further information on any of the techniques discussed above, or would like to discuss a particular project, please contact us at info@terragenenvironmental.co.uk