Sarah Houlahan has built a career around her passion for safe land remediation. With 10+ years’ experience in scientific research focusing on climate change and environmental protection, she has helped hundreds of NSW clients remove and manage contamination.


As NEO Consulting’s contaminated land management expert, Sarah shares her insights on effective land remediation options, the bioremediation process, monitoring high-risk sites and more. 


NEO Consulting provides in-situ and ex-situ land remediation. When would you apply one over the other?


We can implement a range of remediation options like on-site treatment tanks, natural attenuation and bioremediation. We generally make the decision based on minimising costs to the client, the impact to their construction project and the environmental impact of each approach. Wherever possible, we will manage contamination on-site over off-site disposal. We need to consider the energy required to remove and transport contaminated material, then the waste facility receiving and managing this material.


Do you have any recent examples?


One of our projects involves pumping petroleum contaminated groundwater into an on-site treatment tank. Once treated, clean water will be pumped back into the aquifer. This is not strictly in-situ but the water will not leave the site. For this project we will use a remediation approach called natural attenuation or bioremediation.


Can you explain this bioremediation process?


This is a preferred in-situ remediation option because we’re letting nature take its course! Petroleum products contain organics referred to as hydrocarbons. We introduce aliphatic hydrocarbons, which are simple carbon chains readily consumed by microbes (also known as ‘hydrocarbon degrading microbes’, microscopic organisms that are found in soils and water everywhere – even the sub-Antarctic!). 

Petroleum products like diesel fuels and lubricating oils also contain aromatic hydrocarbons which are heavier carbon compounds that are more resistant to degradation. Basically, the structure of the heavier components are harder for the microbes to consume, so they preferentially consume the lighter chains and will eventually leave only the heavy aromatic hydrocarbons. So this is a low impact, viable remediation approach.


How does bioremediation work for contaminated groundwater and soil?


We first need to assess the extent of the plume and whether it is migrating off-site. This usually includes removing underground petroleum storage systems (UPSS) and implementing filters (activated carbon) or trenches to prevent contaminated water from migrating off site. We also use water physicochemical parameters to determine the activity of the microbial community.

Using bioremediation for contaminated soil, we would typically need to excavate, stockpile and allow oxygenation of the stockpile over months for the same process to occur. We then backfill using the cleared soil material. Sometimes the use of a heat pad or thermal treatment can be used for soils and/or heavier contamination.


What other common remediation methods are used by NEO Consulting?


Another in-situ approach we regularly use is capping and containment. This requires a Site Management Plan that oversees the maintenance of the containment cell. A physical barrier – such as concrete, asphalt, synthetic material liners (geo-fabric), and/or clean soil – may be installed to cap the contaminated material. 

We also use other in-situ options like chemical injection for groundwater contamination. This approach will neutralise and stabilise contaminants so it can be converted into a more stable, less damaging compound. This approach is used in conjunction with other complementary remediation options outlined in the Remediation Action Plan.


Can in-situ remediation be used for every project?


In-situ remediation is not appropriate for every project, especially for sites marked for high human use like residential and childcare centres. Managing contamination on these types of sites will usually require excavation and off-site disposal. Although capping may be an option, it is often easier to remove contamination because: 

  • Under the Contaminated Land Management Act 1997, a landowner will need to maintain an environmental management plan on the land title if they cap and contain contamination. 
  • If the proposed development plans require excavation for a basement, the soil will be removed anyway. 
  • Some NSW councils will only accept ex-situ removal based on their understanding and experience with other remediation approaches.


Are service stations still a major cause of contaminated land in NSW?


The example above is for a service station that has caused significant contamination. Service station regulations have improved significantly since the Protection of the Environment Operations (Underground Petroleum Storage Systems) 2019.

That said, there are still some problems. New builds are required to have double walled fibreglass tanks but the older service stations have old metal tanks with single walls that do not have an overfill alarm. Building residential buildings on this type of contamination can cause vapour intrusion and this is a real human concern. As part of NEO Consulting’s site investigation process, our team will always review the surrounding environment and proximity to high-risk sites like service stations.


How does NEO provide routine monitoring for high-risk or contaminated sites, like service stations?  


Service stations in NSW are required to have a leak detection system like SIRA (Statistical Inventory Reconciliation Analysis). They are also required to have at least three groundwater monitoring wells that must be inspected twice per year by a qualified environmental consultant. At NEO Consulting, our team will visit the site for routine inspections and tests for quality assurance and control. If our team suspects a leak, we will conduct tank and line integrity testing to identify the source and manage any contamination.


Need remediation advice for your site? Contact us today.