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Contaminant Mobility Testing and Results

Ecotoxicity testing protocols 

Ecotoxicity results

Contaminant mobility

Soils report

Groundwater report

G/W assessment tool (NZ)

Soil property data


Toxicity databases

RA methodologies

Document resources


Problem Identification

Receptor Characterisation

Exposure Assessment

Toxicity Assessment

Risk Characterisation


Background to testing

Contaminants on or in soils may move into the wider environment through a number of routes. The soils themselves retain contaminants to a greater or lesser extent. The movement of contaminants from soil occurs through evaporation and dust generation, intake by plants through their roots, and flushing by or dissolution into water seeping through the soil.

Water transport of contaminants will usually result in contamination of surface water bodies through surface water drainage and by way of groundwater aquifers. The relevance of specific hydrogeological factors to groundwater contamination and the subsequent transport of contaminants to distant ecosystems have been assessed (see below). 

The factors specified in this extension are the nature of the aquifer material, the type of aquifer (confined and unconfined) and the physical nature of the soil and vadose zone connections between the surface and subsurface waters.

The role of typical New Zealand subsoils in the vadose zone on the transport of contaminants has been assessed by measuring the relative strength of the binding of arsenic, cadmium, chromium, copper, lead, mercury, nickel, zinc and the components of petrol known as BTEX (benzene, toluene, ethyl benzene and xylene). The subsoils selected were:

  • a basalt-derived soil from Auckland city;
  • a loess from near Balclutha;
  • a fine silt from Raupara, Marlborough;
  • a peat from near Hamilton;
  • volcanic ash from Wairakei;
  • coarse river sand from an overbank deposit in the Hutt Valley;
  • fine dune sand from Paekakariki;
  • weathered greywacke subsoil from the eastern Hutt Valley hills.

Several methods for measuring the distribution coefficients for metals were trialed, using columns of various sizes and batch experiments. Small batch experiments were used to determine the Kd values for the metals with the different sub-soils. The results were used to rank the strength of retention of different metals by different soils. An additional observation was that the bonding strength between the soil and the metal increases with time.

The BTEX retention measurements were measured similarly, although because the components are so volatile, care was taken in experiment design and procedure to minimise any loss by evaporation. The results showed that the soil type had little effect on the concentration of BTEX in the water solution, except the peat, which removed most of the BTEX from solution.


Two reports are available that detail the contaminant mobility study.  They are in pdf format and downloadable by clicking the appropriate links below:

An implementation of the proposed model in Part 2 is also available:


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