TPH HRAF- Case Studies
Health Risk Assessment Fractionation (HRAF) analysis combined with a sound, scientifically defensible risk assessment can provide a practical, cost effective solution to TPH problems.

CASE STUDY #1 (WESTERN AUSTRALIA)
A refueling facility in Perth was to be decommissioned, however, the environmental site assessment identified approximately 25,000 m3 of TPH-impacted soil, with concentrations ranging from 500 to 25,000 mg/kg TPH, extending under most of the site. Estimated cost of remediation was well in excess of $250,000.

The environmental consultant approached the WA regulators and negotiated the use of the TPHCWG methodology to conduct a risk-based assessment of the TPH impact. The HRA was based on 14 HRAF analyses of samples taken over a grid pattern and at various depths within the TPH-impacted zone. Of these 14 samples, 5 indicated results in excess of criteria. These results were plotted as a HRAF histogram and used to produce a HRA based on various exposure pathways (e.g. soil ingestion, inhalation of vapours emitted by semi-volatile TPH fractions).

The HRA was approved by the WA regulators and the need for costly soil remediation/removal was avoided. A risk-based site management plan (SMP) is currently ongoing, in order to ensure that the soil TPH impact is not adversely impacting the underlying groundwater aquifer. The cost of this SMP to date is around $60,000, with small incremental costs expected in the medium term for groundwater monitoring before site closure is achieved. Significant cost savings were achieved by application of the TPHCWG method in this case.

CASE STUDY #2 (TASMANIA)
During validation of an old fuel depot located in Tasmania, extensive TPH impact ranging in concentration from 3,000 to 12,000 mg/kg TPH was identified around the former drum platform and lube oil storage. No BTEX or PAH constituents were identified, however, site closure could not be achieved due to exceedance of the regulatory TPH criteria (1000 mg/kg). The site is characterised by clay soils, low temperatures and high rainfall, all of which are not conducive to soil bioremediation efforts. Eventually the site was completely covered in impacted stockpiles up to 3 metres in height, remediating slowly. The regulators required that further site assessment be conducted around the impacted area, however, this proved impossible due to space constraints.

The environmental consultant approached the Tasmanian regulators and negotiated the use of the TPHCWG methodology to conduct a preliminary risk-based assessment on part of the TPH impacted stockpile. The primary purpose of the HRA was to negotiate backfilling of the sampled stockpile in order to allow the further site assessment activities required by the regulators.

Five samples were taken from the stockpile selected to be backfilled and analysed by HRAF. Based on the HRAF data, a HRA was conducted based on various exposure scenarios for the backfilled soils. The results indicated that with minor soil management, exposure and human health risk would be negligible. The HRA was presented to the regulators, who subsequently approved the backfilling of 700 m3 of soil still containing up to 6000 mg/kg TPH. The remainder of the stockpiles are being sampled and analysed in a similar manner. HRAF analysis, combined with a sound and technically defensible risk assessment approach, is currently saving the client considerable time and expense in achieving site closure.