Situation: The site of the new Aldi Wyong store had previously been used for a hardware business and mechanical workshop. It contained a metre-thick layer of asbestos-contaminated fill and four underground fuel tanks, one of which was leaking.
Actions: To prepare the site for development, Geo-Logix was engaged to:
• Remove and dispose of the asbestos-contaminated fill
• Remove and dispose of the underground fuel tanks
• Neutralise the exposed acid sulphate soils
• Assess the contamination risks to groundwater in relation to the fuel tank leak
Challenges: The deadline was tight and the project was plagued by high rainfall and ongoing wet weather. Geo-Logix had to adapt remediation efforts to cater to conditions.
The high rainfall made site operations difficult, especially once excavations had exposed the acid sulphate soils and the soft sub-grade became saturated and unstable for machinery.
Attempts to use lime to stabilise the wet and spongy subgrade were hampered by the inclement weather and an alternative solution was needed. Geo-Logix proposed an engineered solution using screw piles to support the proposed car park and building slab; with less stringent compaction requirements backfilling could then be completed in just a few days.
Petroleum contaminated groundwater was identified at the site boundary and offsite under the footpath and utilities and a conceptual model indicate chemical vapours posed a potential risk. The wet weather impeded Geo-Logix’s ability to investigate subsurface chemical vapour. Consequently, Geo-Logix adopted a qualitative risk assessment approach comparing site conditions against international research data to demonstrate that the residual contamination in groundwater was well within safe levels.