| Home | About Our Site | Introductory Risk Assessment | Advanced Risk Assessment | Search | Contact Us |

New Zealand Example



Introduction to New Zealand site - case study

In this section of the DSS, a currently operating timber treatment facility has been used to summarise and illustrate the critical features of the ERA process. Although the site is an operating industrial facility, it is located within a rural setting, with significant sensitive ecosystems and residences in the vicinity. Therefore the potential for adverse environmental effects resulting from contaminant discharges to land and water needs to be fully assessed.

The site characterisation component is based on the Site Characterisation Checklist. A series of picture files (below) illustrate the site layout, the location of the surrounding potentially sensitive surface water bodies, neighbouring properties and their landuses, site soil characteristics and residual and discharge contaminant levels.

Additional information is provided to characterise potential exposure pathways, including surface runoff and discharge characteristics, aquifer permeability, and groundwater direction and discharge rates.

Preliminary risk characterisation of the New Zealand site allows evaluation of the residual soil contamination levels and discharge quality against appropriate acceptance criteria for aquatic ecosystem protection standards and other relevant environmental criteria.

Example Documentation New Zealand Site

Refer Site Characterisation Checklist: Sections 1 and 2.

Note: Click on the thumbnails for a larger image

Site Location



Aerial photo

  • Record surrounding potentially sensitive surface water bodies Lake Waikare, Waikato River, streams, drains etc.
  • Comment on likely/potential ecological sensitivity using existing information eg. Classifications/rules in Regional Plan, Ecological assessments, other existing publications. Other resources include aerial photographs and topographical maps, landuse maps etc.
  • Neighbouring properties and landuses e.g. dairy, industrial, horticultural.
  • Note distances to relevant receiving water bodies e.g. the Waikato River is located approximately 250 m west of the site, Lake Waikare is located approximately 2 km to the northeast of the site, and a drain passes adjacent to west and north boundaries of site.
  • Is water quality information available for receiving waters? From Regional Council databases or other sources. Check Regional Plan for sensitivity of receiving waters, and water quality management standard for water body.
  • Is macro-invertebrate data available?  An example of macro-invertebrate survey data shows an assessment of the quality of species in the drain adjacent to the site, and indicates that species diversity is low; the drain is already a modified channel that collects discharge from agricultural land as well as the industrial activities in and around the site.

Possible Contaminants

Refer Checklist: Section 3

Site Activity areas 

  • Determine land use history, assess site plans, identify site activity areas, including treatment, storage and disposal areas
  • Consult present and former site occupiers, regional and district council staff etc
  • XYZ is a currently operating timber processing site (and formerly a rural "greenfields" site)
  • For XYZ site, likely contaminants may therefore include: Copper, chromium, arsenic (CCA), boron, petroleum hydrocarbons (fuel storage areas etc.) possibly pentachlorophenol (former treatment activities)

Potential exposure pathways for contaminated soil

Refer Checklist: Section 4

Refer to soil contamination information shown on surfaceplan.

  • Review surface characteristics including presence/absence of impervious surfaces, paving, roofed areas
  • Determine from plans (or preferably from walkover site assessment) nature of surface slopes, and discharge points/areas for potentially contaminated surface runoff
  • Is discharge to surface water via groundwater a potential exposure pathway? Wind-blown contaminated dust?
  • Document distances from potential contaminant sources to receptors.

Surface soil type, geology

Refer Checklist: Section 4

Refer to soil contamination information shown on Soilprofile


  • Review soil and geological maps describe soil type, depth of profile etc.
  • Describe any exposures are low-permeability layers present

Soil Contamination Characterisation

Refer to soil contamination information shown on soildata

  • Review soil contamination data (if available)
  • Describe nature, extent (lateral and depth) and magnitude of soil contamination
  • Document total and leachable (e.g. TCLP) contaminant concentrations
  • Annotate on site plans, showing proximity to surface water receptors.

Solute Transport - Attenuation mechanisms

Leaching of Contaminants in Soils

A chemical can be transported through soil or sediment by solvents (in water if the chemical is water soluble). If the chemical adsorbs to soil or sediment, it can be transported when the soil or sediment moves. Any chemical that leaches can contaminate groundwater.

Leaching Test

A leaching test may be used instead of the soil/water partition equation. The toxicity characteristic leaching procedure (TCLP) test (EPA Method 1311) is commonly used in New Zealand to provide a conservative estimate of the potential for contaminants to leach to groundwater.

For the site: The range of total concentration results compared with the TCLP results is shown in Table 1.

Table 1: Total and TCLP concentrations results





7 1,300

<0.1 0.3

Chromium (total)

5.9 1,590

<0.1 - <0.1


2.8 906

<0.1 1.0

An appropriate dilution factor (based on specific groundwater conditions) may then be applied representing the dilution available within the aquifer.

Soil/Water Partition Equations

The leaching modelling methodology presented in MfE (1999, Appendix 4E) presents a useful method to determine the potential for a contaminant in soil to leach through the soil profile provided that appropriate data is available. The soil/water partition equation (USEPA, 1996 page 29) relates concentrations of contaminants absorbed to soil organic carbon to soil contaminant concentrations in the zone of contamination.

Groundwater Contamination Characterisation

Refer to groundwater contamination information shown on map.

  • Review geological data, borehole information (if available) nature of aquifer materials? Hydraulic conductivity data available?
  • Depth to groundwater? Seasonal variability (if available)
  • Review groundwater contamination data (if available)
  • Describe nature, extent and magnitude of groundwater contamination
  • Document whether total, soluble or acid soluble contaminant concentrations
  • Annotate on site plans for ease of reference.

Groundwater Flow Characterisation

Refer to groundwater flow information shown on map.

  • Piezometric contour plans available?
  • Describe groundwater flow characteristics (if information available) including groundwater flow direction, hydraulic gradient

For the site:

  • Groundwater flow is to the northwest.
  • Hydraulic gradient = dh/hl = 1/340 = 0.003.

If adequate data are available, relatively simple calculations of contaminant mass loading in groundwater discharging to surface water can be made to asses the potential for adverse environmental effects in the surface water body (for consideration of effective mixing of contaminants).

To determine the volume of contaminated groundwater discharging to surface water:

Aquifer Throughflow

To estimate the total volume of groundwater flowing through the aquifer (and subsequently estimate mass loading of contaminants in groundwater) the following equation may be used:

Q = K.b.(dH/dL).W


Q = discharge [L3/T]

K = hydraulic conductivity [L/T]

b = aquifer thickness[L]

W = aquifer width [L]

dH/dL = hydraulic gradient [L/L]

In case of site assume:

k = 5 x 10-5

b = 3 m

w = 210 m (width of site)

Therefore Q = 5 x 10-5 x 3 x 0.003 x 210

= 9.45 x 10-5 m3/sec

Groundwater Velocity

Advective transport is the transport of solutes by the bulk movement of groundwater. Advection is the most important process driving dissolved contaminant migration in the subsurface. If information is available regarding the permeability and porosity of the aquifer, and the hydraulic gradient, an estimate of the groundwater velocity can be made. The linear groundwater velocity in the direction parallel to ground-water flow caused by advection is given by:

vx = (K/ne).(dH/dL)


vx = average linear velocity [L/T]

K = hydraulic conductivity [L/T]

ne = effective porosity [L3/L3]

dH/dL = hydraulic gradient [L/L]


In the case of site:

vx = 5 x 10-5/0.35 x 0.003

= 4.3 x 10-7 m/sec

Therefore if we take a contaminant at the treatment plant and determine how long it takes to get to the downgradient boundary (MW6) 160 m away from the plant then:

Time (x) = 160/4.3 x 10-7/86400 (seconds in a day)

= 4306 days or 12 years

Comparison with receiving water standards

Finally the contaminant concentrations being discharged to surface water via groundwater can be compared to appropriate receiving water standards.


  • Allowance for reasonable mixing;
  • Consideration should also be given to the quality of stormwater discharging from the site (including suspended solid concentrations); and
  • Establishment of the appropriate acceptance criteria for the receiving waters (see below).


Table 2 Reference MfE/MoH and ANZECC (1992) Guideline values


Soil Guideline Value (mg/kg) Industrial Unpaved

ANZECC (1992) Aquatic Ecosystem Guideline Value (mg/L)

Stock Watering Guideline Value (mg/L)

Irrigation Guideline Value (mg/L)











Chromium (III)





Chromium (IV)





Total Chromium







0.002 - 0.005




NL Indicates consideration not limited

  1. Based on sheep higher values may be tolerable for other livestock
  2. Based on acid, sandy soils higher values may be tolerable under other conditions
  3. Based on sensitive crops - higher values may be acceptable depending on the crop

As an initial conservative assessment, the maximum soil TCLP concentrations, and stormwater discharge concentrations, may be compared to the appropriate receiving water acceptance criteria, after accounting for dilution effects.


| Home | About Our Site | Introductory Risk Assessment | Advanced Risk Assessment | Search | Contact Us | Disclaimer

Page last updated: 01 May 2007

Copyright 1998 - 2003 Project Participants & their Organisations