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Phase 1: Desk Study And Preliminary Assessment
Site Assessments may be required for a number of reasons. Contaminated Land Assessments, Pre Purchase Assessments, Due Diligence, Planning Applications, Contamination caused during Construction, Remediation Design and Validation are but a few.
The first step is usually a Phase 1 Desk Study. This interprets recorded information about the site and surrounding area and highlights any potential concerns. There are complex and multiple information sources interrogated during Phase1. The following are examples only and most would normally be included. Ordnance Survey, Borehole Index re Geology, British Geological Index, Petroleum Index, Environment Agency, Local Planning Authority, British Geological Survey, National Monument Records, Coal Mining Reports, Health Protection Agency etc.
This stage will then be combined with the results of a physical walkover site survey. Observations of the site will reveal potential concerns, for example evidence of tipping, other potential sources of contamination, invasive plants, weak ground, waterlogging, asbestos in buildings etc.
It is important to note that Phase1 Reports are interpretive, based on the information and observations from any walkover and information from records, maps, and other information relevant to the project.
Whilst the report will focus on the objectives of the client, its function is also to identify all concerns caused by the environmental and geotechnical conditions of the site. This will include all potential forms of pollution, the sources of such pollution, the migration pathways the contaminants may take to potentially harm receptors (such as humans), groundwater and the general environment.
If concerns are present the information is used to develop a Conceptual Site Model (CSM) The CSM results, together with all other information, will be combined to produce a final report that will address any such issues by recommendations. These may include further site investigations, remediation, cost liabilities etc.
Phase 2: Exploratory Geo-Environmental Investigations
Phase 2 Generic Quantative Risk Assessment (GQRA Interpretative reports) will normally take place if the Phase 1 investigation revealed any causes for concern. This stage involves the collection of soil and groundwater samples for laboratory testing. Detailed information of the processes involved during this phase of works is contained in British Standard BS10175: 2011.
The site investigation is designed to provide sampling points across the site and at targeted locations identified as potential sources of contamination during the Phase 1 desk study. Following laboratory testing a Quantitative Risk Assessment (QRA) is carried out by comparing the test results for each contaminant to the Soil Guidance Values (SGV) and Generic Assessment Criteria (GAC) for various land use scenarios such as residential and commercial.
If the contamination levels are below the SGV and GAC for the appropriate land use the assessment process is complete. However, should the levels of contaminants be greater than the SGV and or GAC, then further assessment in the form of a Detailed Quantitative Risk Assessment (DQRA) is required.
Phase 3: Full Exploratory Geo-Environmental Investigations (DQRA Interpretative reports)
This phase generally involves additional site investigation works to either characterise a previously identified hot spot of contamination or provide additional information required to refine the CSM and carry out a Detailed Quantative Risk Assessment.
The additional sampling and laboratory testing results may be subjected to statistical analysis and or used to generate Site Specific Assessment Criteria (SSAC). Specialised DQRA assessment tools such as the Environment Agency CLEA software and BP RISC version 4 are used to generate the SSAC by using site specific information such as soil properties, contaminant properties, infiltration rates and groundwater flow as well as receptor exposure times to individual contaminants. The SSAC are then compared to the laboratory test results and where the testing results are below the SSAC the assessment is complete with no remediation required.
However, should levels of contamination be greater than the SSAC, remediation or mitigation measures would to be required. It is crucial that close liaison with the Local Authority and Environment Agency is maintained during the Phase 3 process as approval of the SSAC by one or both organisations will be required before remediation can begin.