TasWater biosolids reuse: Reducing false contamination testing risks through improved hydrocarbon assessment
At a glance
TasWater operates more than 20 sewage treatment plants across Tasmania and relies on biosolids reuse as a cost‑effective and environmentally sustainable alternative to landfill disposal. When routine testing indicated higher than expected petroleum hydrocarbon in biosolids, TasWater engaged GHD to investigate whether results reflected true contamination or analytical interference. Using the Biogenic Interference Calculation (BIC) method, developed by GHD’s own Francine Kelly-Hooper, we helped TasWater distinguish between genuine contamination and false positives, supporting more informed reuse and remediation decisions.
The challenge
Biosolids are a valuable resource for land application, but regulatory frameworks require strict compliance with total recoverable hydrocarbon (TPH/TRH) thresholds. Exceedances can trigger costly disposal or remediation, even when no contamination source is evident.
TasWater identified inconsistent hydrocarbon results across historical laboratory reports. In some cases, diesel-range organics appeared to exceed limits despite no known contamination pathways within treatment operations. Without clarity on whether results reflected true petroleum contamination or naturally occurring biogenic material, TasWater faced uncertainty around regulatory compliance, reuse approvals and long‑term biosolids management strategies.
Our response
GHD worked with TasWater to apply the BIC method to their biosolids samples. The project began with a desktop data gap analysis of TasWater’s historical chemistry results, confirming that some exceedances were likely false positives while others required further investigation. GHD determined that certain diesel signatures were associated with polymers used in dewatering processes.
To improve confidence in results, TasWater approved a multi-laboratory benchmarking study, with biosolids samples split between the Australian National Measurement Institute (NMI), Australian Laboratory Services (ALS) Sydney and ALS Waterloo in Canada.
This comparative testing approach allowed TasWater and regulators to better understand variability in results and assess the applicability of the BIC method under Australian conditions. The NMI is monitoring outcomes as part of its consideration of potential legislative updates.
The impact
By distinguishing between true petroleum contamination and biogenic interference, TasWater gained a more accurate understanding of biosolids quality across its treatment network. This helped to avoid unnecessary disposal of reusable materials.
The project also contributed to broader regulatory dialogue in Australia, with the BIC method being evaluated for formal adoption nationally.