Technical reports

The assessment of NSZD and use of NSZD data can be considered at different points in LNAPL site management including during:

• development of the LNAPL conceptual site model
• assessment of remedial/management options
• implementation of the remediation/management strategy.

Case studies are presented that provide a number of insights regarding NSZD in general and NSZD at Australian sites specifically. The case studies add to the growing body of evidence that NSZD rates observed at Australian sites are comparable or exceed what is considered typical overseas. Additionally, the case studies indicate that NSZD was found to be substantially outperforming conventional active LNAPL recovery performance at all sites where the comparison was possible (i.e. where active LNAPL recovery efforts were taking place).

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The methods for measurement of NSZD rates include:

• Aqueous methods using dissolved contaminant concentration trends and natural attenuation indicator parameter (NAIP) mass budgeting analysis
• Soil gas flux methods using concentration gradients, passive flux traps, and thedynamic closed chamber (DCC)
• Biogenic heat method based on soil temperatures
• LNAPL compositional change method based on chemical analysis of the oil.

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This guide complements the National Environment Protection (Assessment of Site Contamination) Measure 1999 (ASC NEPM) and the PFAS National Environmental Management Plan (NEMP). Released by the Heads of EPAs Australia and New Zealand in February 2018, the NEMP is the key reference document for PFAS in Australia and covers a range of matters relevant to the identification and management of PFAS from the perspective of regulators. This practitioner guide is compatible with those requirements of the ASC NEPM that flow through to remediation. It is designed to also be consistent with the National Remediation Framework currently being developed by CRC CARE.

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The report refers to data from animal studies to estimate effects on human health in order to derive TDI values – while this introduces interspecies uncertainties, animal models exclude human variability factors (such as diet, drugs, infections, radiation and endogenous processes). An in-depth discussion of the issues was published as a peer-reviewed paper – see Dong et al 2017, ‘Issues raised by the reference doses for perfluorooctane sulfonate and perfluorooctanoic acid’, Environment International 105: 86-94.

This report was completed in early 2016 to complement CRC CARE's work on developing PFAS guidance at a time when there was limited Australian human health advice on PFAS.  The policy, scientific and political landscape has changed substantially several times since this work was completed, and it is strongly recommended that readers refer to the most up-to-date advice published by Food Standards Australia New Zealand and the Commonwealth Department of Health, as well as any jurisdictional requirements.

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The remediation strategy known as lime assisted tidal exchange (LATE) was implemented in 2001 following a comprehensive site and operational methodology assessment. An initial trial of LATE proved successful in terms of the water quality and soil parameters. The short time period in which these parameters responded prompted the need for a research program aimed at understanding the interaction of daily tidal inundation and an acidified soil landscape. This research showed that LATE’s success can be attributed to the combination of an alkaline input alongside a huge flush of organic matter. The East Trinity site now has sufficiently high ecological function to transition from active to passive management. Under passive management, the addition of hydrated lime to the waterways ceases, and regular tidal inundation will remain in place to ensure that ASS remain protected from further oxidation.

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Analytical methodology for silica gel clean-up of soil and water extracts is proposed in this report. The methodology follows closely with NEPM Schedule B3 (NEPC, 1999 amended 2013c), that is analysis of semi-volatile hydrocarbons (TRH >C₁₀ to C₄₀) using solvent extraction followed by determination by gas chromatography–flame ionisation detector (GC-FID). The NEPM describes an optional SGC procedure but more detail is required. Appendix C details two procedures for SGC which are in common use in environmental testing laboratories – in situ and ex situ. These procedures have been adapted from CCME 2001, Reference Method for the Canada-Wide Standard for Petroleum Hydrocarbons in Soil – Tier 1 Method, and Addendum 1. The in-situ method involves adding silica to the extract to form a ‘slurry’. This silica then interacts and absorbs polar analytes. In the ex-situ method, the extract is applied to a silica gel glass column which removes polars from the extract. The extracts are then analysed by GC-FID. Advantages and disadvantages of both techniques are discussed in this report.

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In particular, the guidance has the potential to promote best practice and reduce costs, uncertainty, and the risk to human health and the environment. Consideration has been given to accounting for site-specific variables such as bioavailability and bioaccumulation, and for providing more reliable screening criteria for determining when ecological effects might occur.

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In line with international progress, there has been an increasing acceptance in recent years by contaminated sites practitioners in Australia of the usefulness of mass flux concepts for the management of groundwater contamination. However, there is no nationally consistent guidance or methodology on how mass flux or mass discharge estimates may be used to assess and manage groundwater contamination, or the endpoints that should apply. CRC CARE has therefore commissioned this user guide for the better measurement and use of mass flux and mass discharge in the management of groundwater contamination.

The purpose of this guidance is therefore to illustrate how flux concepts, tools and measurements can be used to assess and manage groundwater contamination, including engaging with regulators and other stakeholders.

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This document provides guidance in relation to the assessment, remediation and management of MTBE contaminated groundwater. MTBE will migrate rapidly from a source, through the soil profile, to groundwater and/or surface water. MTBE is
degraded rapidly in surface waters, but it is relatively stable in groundwater. Once MTBE reaches groundwater it can migrate at almost the same speed as groundwater flow, given its solubility in water, and therefore can travel rapidly in the sub-surface.

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