If a preliminary site investigation report identifies a risk of site contamination (is potentially contaminated) then further investigation is required, which may mean that a detailed site investigation, or DSI, is conducted. The DSI is the site sampling, or Phase 2 investigation stage. It can include testing of the soil, groundwater and/or other segments of the environment. DSIs set out to investigate if actual site contamination exists – usually with the site’s proposed land use in mind, or to inform upon appropriate site management strategies.
Atma Environmental will assist clients in determining the most appropriate scope of DSI work needed based on a cost-effective, site-specific approach (in some cases collecting and testing vast numbers of samples adds little to the level of assurance provided).
Soil is most often always tested. Groundwater and/or surface water is tested where the past uses: may have contributed to its contamination, the soil is contaminated with compounds that can contaminate groundwater, or if a nearby site is known to be (or is potentially) contaminated and there is a risk of groundwater contamination migrating to the site. DSIs may also need to consider other potential contamination pathways such as ground gas and volatile vapour intrusion.
The site is generally investigated in accordance with the procedures and requirements found in AS4482.1-2005 and the Schedule B2 of the National Environment Protection Council’s “National Environmental Protection (Assessment of Site Contamination) Measure (NEPM)”, but these may be reduced due to the scope of a particular project (in which case the result may be referred to as a ‘limited site investigation’).
When soil is being tested with a particular land use in mind, the concentrations of soil chemicals are compared to site investigation levels found in the NEPM. The soil assessment results are used to inform if further contamination assessment, management, or remediation is required.
If the soil is being tested with removal and offsite disposal in mind, then the concentrations of soil chemicals need to be assessed against soil hazard categorization threshold levels for fill and prescribed industrial wastes provided by Environment Protection Authority (EPA) Publication IWRG621 “Soil Hazard Categorisation and Management”.
Where the DSI has been undertaken in accordance with the Australian Standard, or otherwise demonstrates to an acceptable degree of certainty that the site is not contaminated, then no further work is likely required. If the DSI demonstrates that the site is contaminated, then further investigation to delineate the extent of contamination or to enable professional advice about ecological and human health risks, may be required.