Introduction

Naturally enriched background concentrations of metals and elements have been reported in soils of Victoria, Australia. Where natural enrichment is not accurately distinguished from anthropogenic impacts, soils can be inappropriately categorised as “contaminated waste”; resulting in unnecessary disposal to landfill.

Publicly available and new background soil data was collated by RMIT University for the purpose of developing improved methods for estimation of background concentrations in soils.

Objectives

The objectives of this research were to:

• provide a statistical summary of expected background metal/element concentrations in Victorian soils
• improve our understanding of the distribution and variability of background metals/element concentrations
• identify elements that are naturally enriched, at concentrations in exceedance of current guidance criteria
• identify geochemical and environmental indicators of natural enrichment
• provide improved methods (using geochemical indices and composition ratios) for distinguishing natural enrichment from added contamination
• provide a framework for assessing background metal/element concentrations during environmental site assessment works

Scope

The scope of this research included:

• Development of step-wise framework for soil data collation and evaluation of background soil data from open sources (including Audit Reports)

• Collection and analysis of soil samples from 320 locations within areas representative of background.

• Chemical analysis of survey samples (n=640)

• Mapping of background soil patterns and correlations

• Identification of geochemical correlations between metals and soil binding elements, particularly iron.

• Assessment of the influence of environmental factors including precipitation, topography and parent material on background metal variability.

• Assessment of how geogenic metals are bound to Fe oxides and potential mobility of geogenic metals in the environment.

This work was undertaken as part of a doctorate of philosophy by Hannah Mikkonen and Supervised by Dr Suzie Reichman, School of Engineering, RMIT University.

Definition of Background

Ambient background concentrations are defined as the sum of the geogenic concentration of the element plus diffuse anthropogenic contamination that has been introduced from non-point sources (Panno et al., 2006, NEPC 2013). There is lack of consistency on what constitutes diffuse contamination or a point source. For the purpose of this research, ambient background concentrations include human contributions of contaminants through diffuse inputs such as atmospheric deposition of lead from the broad use of leaded fuels. However, lead impacts directly associated with an adjacent road (i.e. within 25 m of the road) were not considered representative of ambient background concentrations. Consistent with background studies undertaken across Europe, broad application of fertilisers during typical agricultural practices (excluding horticulture and application of biosolids), were considered representative of ambient background concentrations (Ottesen et al., 2013; Reimann et al., 2010; Saaltink et al., 2014).

Deliverables from this work include:

• A publicly available database and interactive map presenting background soil concentrations for soil across Victoria
• Methods for determining background concentrations of elements in Victorian soils (e.g. geochemical indices)
• Greater understanding of relationships between elements concentrations in soil and soil forming factors
• Identification of environmental and geochemical indicators of natural enrichment of metals and Fluoride in soils

The authors would like to thank the following: Andrew Barker and Paul Bentley of CDM Smith who developed the Soil Explorer and Victorian Background Soil Database interface and assisted with the presentation of the summary statistics; Ian Thomas and Nicholas May of the eResearch team at RMIT University who assisted in launching, storing and sharing Victorian Background Soil Database; and project partners Australian Contaminated Land Consultants Association (ACLCA) and the Hazwaste Fund.