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2 Principles of Site Investigation

2.1 Data quality objectives

2.1.1 The data quality objective process

Data quality objectives (DQOs) are qualitative and quantitative statements that specify the quality of the data required. Together the objectives form a DQO process, which is made up of seven distinct steps (US EPA, 2000). The DQOs focus on the nature of the problem being solved by the investigation. The approach to a site investigation will then be determined by the data required.

Figure 2: The DQO process

DQOs influence decisions on the type of investigation to be undertaken and the nature of the samples to be collected. Further information on DQOs can be found on the US EPA website (

2.1.2 Applying DQOs to the investigation of a site for hazardoussubstances

To ensure the correct data are collected during the investigation of a site, it is important to understand at the outset why the site is being investigated and how the results might be applied in subsequent decision-making. The first step in setting DQOs should therefore be to identify the purpose of the site investigation (state the problem, and identify the decision(s) that need(s) to be made). The most common purposes are to:

  • establish the condition of a site before sale, purchase or redevelopment and determine environmental liabilities
  • determine the environmental or health risks posed by contaminants in the soil
  • determine if hazardous substances in the soil pose a hazard to an ecosystem
  • assess the applicability of a particular remediation option
  • benchmark the contamination status of a site following clean-up
  • establish compliance with the Resource Management Act 1991, regional or district plan, or resource consent.

Note that investigations may be undertaken for more than one purpose.

The next step in the DQO process involves defining the study boundaries and the development of a conceptual site model. At this stage the conceptual site model is based on a review of existing information and usually includes an initial working hypothesis covering the potential nature and sources of contaminants, their likely spatial distribution in the soil (and other environmental media), and the potential effects of the contaminants on receptors at or adjacent to the site. Any data gaps should be identified. On the basis of the conceptual site model, the type and quality of additional data needed for the site investigation should be determined. Site-specific DQOs for subsequent stages of the investigation should then be defined.

DQOs should be documented to provide an audit trail for the type of investigation and the methods for sampling and analysis used. They should also be communicated to the team undertaking the site investigation. The use of written work instructions, sampling plans or similar documents to record and communicate the DQO is recommended.

Example: Communicating the DQOs to the team undertaking physical works associated with the site investigation allows flexibility. If field conditions vary from the conditions predicted by the conceptual site model, the sampler, in discussion with the project manager or other qualified staff, can revise a sampling strategy while still in the field, based on the DQOs. This can save time and money associated with returning to the field to obtain additional samples.

The DQO process for the investigation of a site is summarised in Figure 3.

Figure 3: The DQO process for a site investigation

The purpose of an investigation can alter as the investigation progresses. Therefore:

  • the conceptual site model should be updated as more information is obtained
  • the DQOs should be reviewed as the project proceeds, and revised as necessary.

2.2 Conceptual site model

A conceptual site model is a system diagram identifying contaminant sources, routes of exposure (pathways), and what receptors are affected by contaminants moving along those pathways. The conceptual site model, which should be developed before undertaking a detailed site investigation, identifies the zones of the site with different contamination characteristics (eg, whether contaminants in the soil are likely to be on the surface or at depth, distributed over an entire area or in localised 'hot spots'). Exposure pathways and receptors should be identified for both current and future uses of the site (where appropriate). The model will be based on a review of all available data gathered during the various investigation phases, and should be used to design the detailed site investigation.

2.2.1 Contaminant distribution

When determining the approach for the investigation, the contaminant distribution must be included as part of the soil-sampling strategy, as this will affect the sample locations and the number of samples collected. The contaminant distribution at a site can be affected by a number of factors, including:

  • the nature of the contaminant source and contaminant type
  • pathways for migration and dispersion
  • the type and physical nature of the soils/geology
  • any physical disturbance of the contaminants.

Both lateral and vertical contaminant distribution must be considered. Contaminant distribution within soil and fill materials is usually highly variable and depends on the make-up of the soil and fill. The type and physical properties of natural soils and the depth to groundwater may also vary within a site. These factors can contribute to the variable distribution of contaminants with depth in the soil profile.

Vertical and lateral contaminant distributions are also affected by the physical characteristics of the contaminant source and release mode.

Example: A loss from an above-ground tank could cause contamination of the soil profile from the ground surface down to the water table. A loss from the base of an underground storage tank could cause soil contamination below the base of the tank pit only, with little

2.2.2 Soil heterogeneity

The soil profile within a site where hazardous substances are present or suspected can be variable, comprising a mix of natural soils ('natural ground') and fill materials ('made ground'). Fill often comprises a complex mix of materials, including plant remains, scrap wood, scrap metal, soil and ash. Fill materials can have a marked effect on the migration of contaminants through the soil, and can also be a source of contaminants (eg, heavy metals present in ash fill). It is also sometimes difficult in the field to distinguish certain types of fill from the natural soils.

Soil samples are often sorted in the field to remove rocks and coarse fractions such as boulders and cobbles, because it is often not feasible to collect these size fractions due to the container size. Such field screening can bias the sample, however. The proportion by weight or volume of any fraction removed must be estimated, and any data interpretation should take account of the influence of strata that were not sampled within the site investigation. The laboratory can also bias the sample by sieving (see section 4.4.1), and clear instructions should be provided to the laboratory on how samples are to be handled.

2.2.3 Uncertainty in sampling

To establish the contaminant distribution at a site, small quantities of soil are collected and submitted for analysis. There is always some uncertainty about the representativeness of the samples to actual site conditions due to a number of factors, including:

  • cross-contamination
  • variations in local conditions, which can affect the vertical and lateral distribution of contaminants
  • the selective nature of the sampling process.

To minimise the uncertainty, the soil sampling must take these variables into consideration and incorporate a thorough understanding of the site conditions and history. A quality assurance programme must be considered as part of any soil-sampling investigation (see section 3.9).

2.3 Investigation phases

The investigation of a site where hazardous substances are present or suspected should be undertaken in phases. The five main investigation phases identified in this guideline and common alternative terms used to describe each phase are presented in Table 1. 2

Table 1: The five main investigation phases, and common alternative descriptors

Main investigation phases
This guideline Common alternative descriptor
Preliminary site investigation (study) Preliminary site study, stage 1; Phase 1 desk top study; Phase 1 background information study; Phase 1 contaminated site audit; Phase 1 environmental site assessment (ESA)
Preliminary site inspection Site walkover survey; Phase 1 site inspection
Detailed site investigation Stage 2; Phase 2 field investigation; Phase 2 ESA; environmental benchmarking
Supplementary site investigation

Additional phase 2 ESA; Phase 3 ESA

Site validation investigation Remediation validation investigation; soil benchmarking

The phased approach enables information on the conceptual site model to be collected. Information from each phase should be assessed to build up an overall picture of the site. The phases required for an investigation and the scope of each phase should be determined by the DQOs. Not all phases will be required at every site, and the scope within each phase should be tailored to meet the specific DQOs.

2.3.1 Preliminary site investigation (study)

The main objective of the preliminary site investigation (study) is to provide background information relevant to the DQOs.  For a full site investigation, information on the present and past uses of the site should be included in order to identify the nature of potential contaminants, their likely location and significance, and potential pathways for migration within the site or off-site.  The preliminary site investigation involves gathering and compiling information about the site to form the initial conceptual site model.  It is often combined with a preliminary site inspection.  Information gathered in the preliminary site investigation and preliminary site inspection should be documented in a preliminary site investigation report (see Contaminated Land Management Guideline No. 1: Reporting on Contaminated Sites in New Zealand (Revised 2011) Ministry for the Environment, 2001), and where possible supporting information should be appended to the report.  The preliminary site investigation should identify the sources of contamination, pathways for release and environmental receptors.  The scope of the preliminary site investigation should include the following.

Site identification

The site must be identified, including the site name, address, legal description, site boundaries, a map reference and geographic co-ordinates. Information on site identification can be obtained from the site owners/occupiers, maps, rates demands and from current certificates of title. The land area where contaminants may be present, or suspected, may not correspond with legal boundaries, and site identification should establish the boundaries of the study.

Site history

A chronological history of the site and previous site uses should be traced from the present day back to the initial use (if possible). The previous activities and processes on the site, and the chemicals and products used, stored or disposed of at the site, should be identified. Any previous investigation and remediation work should be reviewed and gaps in the information recorded.

The sources of information for the site history may include:

  • interviews with site personnel and neighbours (usually undertaken during the preliminary site inspection), covering questions relating to site history, any known incidents, management practices, waste disposal, and any chemical storage areas
  • a review of discharge permits, consents or licences (eg, land-use consents; consents to discharge to air, water or ground; trade waste consents; and dangerous goods [hazardous substances] licences)
  • a review of available environmental reports, environmental incident investigation reports, tank removal records, process descriptions, waste disposal and chemical inventories, material safety data sheets and newspaper articles
  • local authority record reviews, including land information memoranda (LIM) and regional council databases
  • certificates of title
  • a review of historical society records, and any relevant literature relating to the site
  • the layout of current and historical facilities, and site drainage plans
  • photographic records, including aerial photos.

A New Zealand list of activities and industries that are considered to have a higher potential for land contamination, referred to as the Hazardous Activities and Industries List (HAIL) (Ministry for the Environment, 2011b), is published separately.  This list should be used to assist in identifying current or historical activities or industries where hazardous substances are used that could cause land contamination.

Topography and hydrology

The site hydrology assessment should include information on the nearest surface watercourses to the site, the location of surface water drains and stormwater drainage channels, the direction of surface water flow, and information on surface water discharges and abstractions and flooding (if relevant). Typical information sources include topographical maps and regional council records, as well as observations made during site inspections.

Geology and hydrogeology

The site geology assessment should include a description of the types of strata and soil types and information on fill material (if present). Information sources include published geological survey maps and memoirs, New Zealand soil classification publications, and information from previous environmental or geotechnical investigations.

The site hydrogeology assessment should include information on:

  • the extent and use of groundwater aquifers in the area
  • local and regional direction of groundwater flow
  • anticipated depth to groundwater
  • seasonal or tidal influences
  • springs
  • local groundwater abstraction and use
  • local groundwater and/or surface water monitoring information
  • preferential pathways to groundwater (soak holes, etc.).

Information sources include regional council records on groundwater, and previous site investigation records.

2.3.2 Preliminary site inspection

The preliminary site inspection is undertaken as part of, or following, the preliminary site study. The objective in this phase is to augment or confirm the findings of the preliminary site study and identify any information that may assist with the design of the detailed site investigation.

Before undertaking a site visit, the potential hazards that may be encountered during the visit should be assessed and appropriate health and safety precautions taken (see sections 3.2 and 3.11).

Information gathered during a preliminary site inspection typically includes:

  • general site condition, current use, local topography and surrounding environmental setting
  • location and condition of surface watercourses, local surface drainage systems, ponds and springs, and information on groundwater use, wells and drains
  • visible signs of contamination or potential contamination, such as evidence of spills or leaks, surface staining, chemical storage on unsealed ground, stressed vegetation and odours
  • visible signs of areas of fill, stockpiled material, ground disturbance, burnt areas and former building foundations
  • location of chemical storage and transfer areas, bunding, waste storage areas, discharges to ground and existing tanks, pits, drains, pipelines and sumps
  • adjacent, surrounding, or up gradient land uses and the potential for contamination from these sources
  • location of former buildings, processes or activities undertaken on the site.

Information to assist with the design of site investigations

The following information may help with the design of site investigations:

  • access constraints, including the location of buildings and hardstand, canopies, the location of underground services, and other issues that could pose physical challenges to the design and implementation of future site investigations
  • location of any physical hazards such as overhead power cables
  • availability of water and electrical supply for use during site investigations
  • field readings of soil vapours in drains, sumps and trenches
  • collection of surface samples or suspect materials to assist with subsequent phases of investigation (eg, collection of a sample of suspected asbestos material, or hydrocarbon-stained soil for product identification).

2.3.3 Detailed site investigation

A detailed site investigation may be required to confirm or qualify the findings of the initial preliminary site investigation report.  This will involve intrusive techniques to collect field data and soil samples for analytical testing to determine the concentrations of contaminants of concern.  The scope of the detailed site investigation should be defined by the DQOs.

Soil samples should be analysed for contaminants identified on the basis of the preliminary site study and/or preliminary site inspection.  Samples may initially be analysed for a broad screen of contaminants which, based on experience, have typically been found on similar sites.

The results from the detailed site investigation should be assessed against the DQO, and the conceptual site model updated.  The information gathered during the detailed site inspection should be documented in a detailed site investigation report (see Contaminated Land Management Guideline No. 1: Reporting on Contaminated Sites in New Zealand (Revised 2011), Ministry for the Environment, 2001).

Before undertaking the physical works of the detailed site investigation, the potential hazards at the site should be assessed and appropriate health and safety precautions taken (see sections 3.2 and 3.11). Any authorisation required (ie, resource consents, etc.) should be obtained before commencing work.

This guideline does not cover the collection of other environmental media for testing, including (but not limited to) soil gas, groundwater, surface water and sediments, although these may also be considered as part of a detailed site investigation.

2.3.4 Supplementary site investigations

Supplementary site investigations are usually undertaken to provide:

  • data on areas of concern not investigated during the detailed site investigation
  • a clearer delineation or definition of a particular area or depth of contamination
  • information to address specific technical matters (eg, to confirm the applicability of a particular remedial option)
  • 'certainty' regarding environmental liability.

The scope of the supplementary site investigation should be defined by the DQOs.

Example: The objective of a supplementary site investigation is to establish whether vacuum extraction is an appropriate method for removing the bulk of volatile hydrocarbons from soil above the shallow water table, in the vicinity of a former underground storage tank. The DQOs require that soil properties such as grain size and porosity, together with the lateral extent of the impacted soil, are delineated by means of shallow soil sampling and analysis. This will allow the physical attributes of the vacuum extraction array to be designed. In this case, detailed information on maximum and average concentrations of the various contaminants of concern and their distribution throughout the soil profile are not important.

The other process and requirements for supplementary site investigations are similar to those set out for the detailed site investigation (section 2.3.3).

2.3.5 Site validation investigation

Site validation is undertaken after completing remediation activities on a site. The objective is to demonstrate that the concentrations of hazardous substances or other contaminants of concern that may remain in the soil within a site or part of a site meet the remediation criteria set out in a remedial action plan or similar document.

The site validation and the level of confidence required in the data should be defined by the DQOs given in the remedial action plan. However, not all site validation investigations need to meet the same level of confidence, since this will be dependent on the decisions being made based on the data.

Example: A tailings dam containing acidic soils at a mine had been recently landscaped and covered with clean topsoil, although the remediated site was never validated. Areas of no vegetation growth were noted several years after rehabilitation. If a validation investigation had been undertaken, the remaining areas of excessively acidic soil would have been discovered and further soil cover imported.

The information from the site validation investigation should be documented in a site validation report.  In the case of the removal of an underground storage tank, the site validation investigation should address all the issues included in the Report form for the removal and replacement of petroleum underground storage tanks and underground equipment (see Contaminated Land Management Guideline No. 1: Reporting on Contaminated Sites in New Zealand (Revised 2011), Ministry for the Environment, 2001).

The other process requirements for site validation investigations are similar to those set out for the detailed site investigation described in section 2.3.3 of this document.

2 The nomenclature describing these main investigation phases is not fully consistent within the industry, although general correlation of different but similar terms for the various investigation phases is possible.