Environmental site assessment for statutory environmental audit: 42 Wilson Street, South Yarra
Summary of works
ESG Environmental (ESG) was engaged by Skylife to conduct a Detailed Site Investigation (DSI) for a Statutory Environmental Audit of the site. The site was proposed for redevelopment to mixed commercial/high density residential land use. The approximately 238 m² site was previously used for storage and general warehousing by a variety of tenants, including a taxi truck company and textile distributor. In addition, historical evidence suggest that site may have been used as a storage facility for dry cleaning chemicals, equipment and materials. Separate Phase Hydrocarbons (SPHs) on the water table on commercial/light industrial land surrounding the site presented a potential risk to users of the site in terms of ingress of contaminated soil vapour into site buildings.
A comprehensive site history desk top study (Phase 1) was initially undertaken for the land to identify issues of potential environmental concern at the site. This information was then used to develop a Sampling Quality and Analysis Plan (SQAP) for intrusive investigations. The Phase 2 intrusive investigation was designed to identify and investigate areas of potential environmental concern identified during Phase 1, and to assess whether further investigations or remedial works were necessary.
An intrusive soil investigation was designed based on results of a passive soil gas assessment undertaken across the site. This involved soil sampling at 8 locations and installation of 3 groundwater monitoring wells including in areas identified as potentially containing elevated concentrations of soil vapour. Soil vapour probes were subsequently installed and two rounds of soil vapour sampling from beneath the existing concrete slab and from a depth representing a proposed slab for a car stacker at the site was performed using in-house developed equipment.
The intrusive soil investigation identified elevated metal and polycyclic aromatic hydrocarbon concentrations in site soils above adopted criteria for the Audit. However, the risks from the contaminants were assessed as acceptable for the proposed land use and will be managed through the proposed concrete building envelope across the entire site which will act as a separation layer between site users and the contamination.
Some chlorinated hydrocarbons (including trichloroethylene) in the soil vapour samples were found to be above the Audit screening criteria. However, a vapour health risk assessment demonstrated that the risk to site users was low and acceptable for the proposed land use.
At the conclusion of the Audit, the Auditor agreed that groundwater remediation was not necessary and determined that the groundwater at the site had been Cleaned Up to the Extent Practicable (CUTEP) and that the site is a Groundwater Quality Restricted Use Zone due to an offsite source of groundwater pollution.
Client: Skylife Group Pty Ltd
Client contact: Mr Robert Feldman, Director
Duration: October 2012 – December 2013
Specific issues / problem solving
- Site located in a commercial/light industrial area with known separate phase hydrocarbons on the water table, potentially presenting a soil vapour risk to future site users
- Development of safe work practices within a confined site with limited access.
- Evaluation of the potential for adverse concentrations of volatile compounds to ingress into indoor air via soil vapour
- Liaison with the Client and Auditor to develop an acceptable outcome to the Audit that considered the mixed commercial and high density residential land uses.
- Desk top study investigation.
- Development of a Sampling Quality and Analysis Plan (SQAP) for the environmental assessment of the site.
- Soil, soil vapour and groundwater investigations involving soil sampling at seven locations, direct vapour at two locations and groundwater at three locations, including one off-site location.
- Statistical and risk based assessment of contaminants of concern.
- Appraisal of groundwater impact in the local area, including surrounding properties where separate phase hydrocarbons were identified in the groundwater.
- Reporting for Audit requirements.
- Avoidance of a direct groundwater investigation (installation of wells and analysis of groundwater samples) at the site and associated delays to the completion of the Audit
- Provided deliverables (Statement of Environmental Audit with acceptable conditions) within timeframes and to the satisfaction of the client.