This resource is provided to help Australian businesses and organisations understand the issues surrounding contaminated land.

RELATED ISSUES:

Contaminated land can have major economic, legal and planning implications for the community. Contamination can limit land use potential or increase costs for developers and councils. Their investigation and clean-up is important to protect human health and the environment.

What is Contaminated Land?

Land which is contaminated by hazardous chemical substances that may pose a risk to human health or the environment is called contaminated land. Land contamination can occur as a result of poor environmental management and waste disposal practices, or accidental spills in industrial or commercial activities. In the past, land was sometimes contaminated by activities that were not known to be dangerous at the time, often using chemicals which have since been banned or now are subject to much stricter controls.

Activities that have been identified as likely to cause land contamination are listed as notifiable activities. Common land uses which may cause contamination include service stations, cattle dips, tanneries, wood treatment sites, landfills, fuel storage and refuse tips.

Contaminated land is managed through statutory processes leading to the prevention of health and environmental risks through environmental management of potentially contaminating activities. In each State or Territory, The relevant regulatory department reviews contaminated site investigations and approves site management plans in addition to providing advice to local government, industry and the community on legislative and technical requirements for contaminated land matters.

Contaminated Land in NSW

In very broad terms, the management framework for contaminated land in NSW consists of two tiers:

  1. Department of Environment, Climate Change and Water (DECCW), which uses its powers under the Contaminated Land Management Act 1997 (CLM Act) to deal with site contamination that is significant enough to warrant regulation under the CLM Act given the site's current or approved use; and
  2. Local councils deal with other contamination under the planning and development framework, including State Environmental Planning Policy No. 55 - Remediation of Land and the Managing Land Contamination - Planning Guidelines. This type of site, although contaminated, does not pose an unacceptable risk under its current or approved use. The planning and development process will determine what remediation is needed to make the land suitable for a different use.

The CLM Act sets out the role of the DECCW and the rights and responsibilities of parties it might direct to manage significantly contaminated land.

Significantly Contaminated Land

If DECCW has reason to believe that land is contaminated and that the contamination is significant enough to warrant regulation, DECCW may declare the land to be 'significantly contaminated land'. The former declarations of land as investigation areas and declarations of remediation sites are taken to be declarations of significantly contaminated land on 1 July 2009.

Section 12 of the CLM Act defines matters to be considered by DECCW in assessing a site to determine whether or not to declare the land to be significantly contaminated land. These matters include:

  • Whether the substances have already caused harm;
  • Whether the substances are toxic, persistent or bioaccumulative or are present in large quantities or high concentrations or occur in combinations; Whether there are exposure pathways available to the substances (that is, the routes whereby the substances may proceed from the source of the contamination to human beings or other aspects of the environment);
  • Whether the uses to which the land and land adjoining it are currently being put are such as to increase the risk of harm from the substances (for example, use for child care, dwellings or domestic food production);
  • Whether the approved uses of the land and land adjoining it are such as to increase the risk of harm from the substances;
  • Whether the substances have migrated or are likely to migrate from the land, and
  • Any relevant guidelines.

Along with the matters listed in section 12 of the CLM Act, the DECCW may also consider site-specific factors. These matters remain unchanged under the amendments to the CLM Act.

Notification policy

DECCW notifies those responsible for significant contamination, owners, occupiers and local authorities once it has declared that contamination is significant enough to warrant regulation. The declaration is a means of informing affected parties and the broader public about the contamination.

The declaration is published in the Government Gazette and online via the contaminated land management public record as well as via direct consultation with identified interested parties.

Duty to Notify

Persons whose activities have contaminated land and owners of land who become aware, or ought reasonably to be aware, that the land has been contaminated must notify DECCW as soon as practicable after becoming aware of the contamination, if the contamination meets certain criteria. The duty to notify is a requirement under section 60 of the CLM Act. A person has a duty to notify if that person ought reasonably to have been aware of the contamination. DECCW can be notified using the site¬Ýcontamination notification form.

The Guidelines on The Duty to Report Contamination under the Contaminated Land Management Act 1997 provide information on two key aspects of the duty to report contamination. The guidelines set out the duty of landowners and persons whose activities have contaminated land to report to DECCW. This includes a range of considerations for those who encounter land contamination (including particular trigger levels for various contaminants) and information on how to proceed where there is uncertainty. The guidelines also outline how DECCW assesses and determines whether or not contamination is significant enough to warrant regulation.

Preliminary Investigation Orders

DECCW may require certain persons to carry out a preliminary investigation of land if DECCW reasonably suspects the land is contaminated. DECCW may require persons to:

  • Investigate whether the land is contaminated with the substances that DECCW reasonably suspects contaminated the land, and
  • Investigate the nature and extent of any contamination, and
  • Provide DECCW with information with respect to the investigation.

Preliminary investigation orders are intended to provide a "snap shot" for the DECCW to determine whether the land is contaminated and whether that contamination is significant enough to warrant regulation.

If the findings of the preliminary investigation lead DECCW to believe that the land contamination is significant enough to warrant regulation, DECCW may declare the land to be significantly contaminated land.

Management Orders

DECCW may order certain persons to manage the significantly contaminated land in the following hierarchy (as far as practicable):

  • 1. Persons responsible for the contamination.
  • 2. The landowner.
  • 3. The notional owner.

A management order can include actions to investigate and/or remediate the land. The former investigation orders and remediation orders are taken to be management orders on 1 July 2009.

Voluntary Management Proposals

DECCW may approve a voluntary management proposal for the management of significantly contaminated land (with or without conditions). Anyone can put forward a voluntary management proposal.

The former voluntary investigation proposals and voluntary remediation proposals to which the DECCW had agreed are taken to be approved voluntary management proposals on 1 July 2009.

Contaminated Land in QLD

In Queensland the management of contaminated sites is somewhat different to NSW. "Contaminated Land" refers to land contaminated by hazardous substances (such arsenic, DDT or oil) which may pose a risk to human health and/or the environment. Activities identified as being likely to cause contamination in Queensland are listed as notifiable activities in Schedule 2 of the Environmental Protection Act (EP Act). In general, Part 8 of the EP Act deals with management of contaminated land.

Integrated Planning Act 1997

Through the Integrated Planning Act (IP Act), the land use planning process is used when there is a change of land use or when a subdivision application is made, to determine the public and environmental exposure to contaminated land and environmental harm. The IP Act is administered by the Department of Local Government, Planning, Sport and Recreation. It provides a process to appropriately investigate the land (through a contaminated site investigation) using the process stipulated in the EP Act for contaminated land management.

Environmental Protection Act 1994

Contaminated land is managed through statutory processes leading to the prevention of health and environmental risks through environmental management of potentially contaminating activities. The department reviews contaminated site investigations and approves site management plans in addition to providing advice to local government, industry and the community on legislative and technical requirements for contaminated land matters.

Under the EP Act, the department maintains two public registers that contain land use planning information - the Environmental Management Register and the Contaminated Land Register.

1. The Environmental Management Register (EMR)

Land that has been or is being used for a notifiable activity and is notified to the relevant department is recorded on the EMR. The EMR provides information on historical and current land use, including whether the land has been or is currently used for a notifiable activity, or has been contaminated by a hazardous contaminant. Sites on the EMR in most circumstances pose a 'low risk' to human health or the environment under their current land use. Entry on the EMR does not mean that the land must be cleaned up or that the current land use must stop.

2. Contaminated Land Register (CLR)

This is a register of proven contaminated land ('risk' sites) that is causing or may cause serious environmental harm. Land is recorded on the CLR when a scientific investigation shows that the land is contaminated and that action needs to be taken to remediate or manage the land (for example, technical measures to prevent migration of contaminants or full removal and off-site treatment) to prevent serious environmental harm or other adverse public health risks.

Under the Integrated Planning Act 1997, when a development application is made for a material change of use or reconfiguration of a lot recorded on the EMR or CLR, a site investigation and, where necessary, remediation are required.

How is land recorded on the registers?

Landowners and occupiers have responsibilities under the EP Act to notify the department when they become aware that their land has been or is being used for a notifiable activity or contaminated by a hazardous contaminant. When a landowner notifies the department that the land has been used for a notifiable activity, the land is recorded on the EMR.

Local governments also notify the department of land in their local government area that has been used for a notifiable activity or has been contaminated by a hazardous contaminant. Before land is entered on the EMR, the department informs the landowners of the notification. The landowners may make a submission to the department about the notification if they believe the information to be incorrect the department decides whether or not to record the land on the EMR.

The department issues written notices to landowners and local governments advising them when the land is recorded on the EMR.

How is land removed from the registers?

Land will be removed from the EMR if, at any time, the landowner or local government provides evidence to the department that no notifiable activity has occurred on the site, or that the land has not been contaminated. When land has been investigated by a suitably qualified person or consultant, a site investigation report about the land is submitted to the department for assessment. If the department is satisfied that the land is not contaminated, the land is removed from the EMR.

Land is also removed from the CLR after work has been done to remediate the land and a site investigation report satisfies the department that the land no longer poses a risk to the environment or public health. In addition, land can be transferred from the CLR to the EMR where there is a site management plan for the land to manage the contamination so it no longer causes environmental harm or poses a risk to human health.

Local government responsibilities

Local governments have obligations under the EP Act relating to the identification, notification and management of contaminated land. Under the EP Act, all local governments in Queensland are required to notify the department of land that has been or is currently used for a notifiable activity within their local government area. This information is gathered by local governments through sources such as historical information, local knowledge and town planning records.

Land owner responsibilities

Landowners are required under the EP Act to inform the department of any known 'notifiable activity' on their property. The owner is also required to inform any occupier, such as persons who are renting, managing or leasing the land, if the property:

  • is listed on the CLR;
  • is listed on the EMR and subject to the conditions of any site management plan; or
  • is the subject of a notice under Chapter 7, Part 8 of the EP Act.

Anyone selling or otherwise disposing of land that is listed on either of the registers is required to give written notice of the land's listing to any potential purchaser before agreeing to dispose of the land.

What are site management plans?

In some cases, (e.g. land used for industrial purposes or park land), it is not necessary or practical to remove the entire contaminated area. The land can be partly remediated, and the department can approve a site management plan which states the conditions under which the site can be used while preventing the contamination from causing environmental harm or posing a risk to human health.

Site management plans are recorded on the EMR and are provided with any related search of the registers. Information on whether land is recorded on the EMR or CLR can be obtained by a search of those registers.

Safeguards for land purchasers

The EP Act requires anyone selling or otherwise disposing of land that is recorded on the EMR or CLR to give written notice to the prospective purchaser of the recording and particulars of any current or outstanding notices given under the EP Act in relation to the land. This is an important provision, ensuring that potential buyers of land listed on the EMR or CLR can allow for any costs associated with assessment and possible remediation before purchase.

Both the EMR and CLR are public registers and can be searched for a fee.

What is a Contaminated Land Assessment?

A contaminated land assessment is a 4 stage assessment process conducted on potentially contaminated sites in order to determine the level and extent of contamination (if any) and the different remediation options available for each particular site. The 4 stage process is explained in detail below:

Stage 1 - Preliminary Site Investigation

A preliminary site investigation includes the following components:

  • Develop a Conceptual Site Model (CSM);
  • Development of a site history;
  • An inspection of the site;
  • A basic sampling program to determine if contamination is present; and
  • Report preparation.

The 1st part of any site assessment is the development of a CSM. Developing a CSM is a critical step in the investigation of contaminated sites. The CSM is a comprehensive representation of the site that documents current site conditions. It characterizes the potential distribution of contaminants across the site in three dimensions and identifies all potential exposure pathways, migration routes, and potential receptors. The CSM is initially developed from very preliminary site data which can be as much as a site description from the land owner. This site data should also include input from community members about their site knowledge, concerns, and interests. The CSM is a key component of the Data Quality Objectives (DQO) process, and should be continually revised as new site investigations produce updated or more accurate information. Once the CSM is complete, the preliminary site investigation can commence.

The most important part of a preliminary site investigation is the preparation of a comprehensive site history to identify all past and present potentially contaminating activities. Information obtained from the site history research should be used to assess the potential for contamination on the site and determine the most appropriate locations for sampling.

Submissions must incorporate investigation of the entire real property description area of the site and not be limited to the area of the notifiable activity. The investigation may be confined to site history only, for areas where no past contaminating activities have been conducted. However, sampling is required in areas where the site history research indicates that possible contaminating activities have been conducted. Site history information should be supported by all available copies of original site plans, local authority zoning records, flammable and combustible liquids licence details, sewerage/ trade waste and stormwater drainage plans, aerial photographs, environmental licences etc.

All available evidence, including verbal interviews and analysis reports, must be included. Interviewees' relationship to site activities should be documented. The possibility of contamination due to activities on adjacent land and the possibility of contamination extending beyond the site boundaries should also be examined. Areas which have received imported fill should also be assessed.

Stage 2 - Detailed site investigation

A detailed site investigation is required when the results of preliminary site investigation indicate potential or actual contamination (i.e. levels above investigation threshold values). The detailed site investigation should delineate the lateral and vertical extent of contamination, and provide information about:

  • Maximum and average concentrations of the various contaminants;
  • Volumes of soil requiring remediation;
  • Leachability and mobility of contaminants;
  • Potential for groundwater contamination; and
  • Possibility of off-site migration through soil, surface water or groundwater.

The decision on how to proceed in the second stage of investigation will require professional judgement of the site-specific issues and be dependent on the findings of the preliminary investigation. Depths of samples will be determined by site history, soil morphology and the need to sample to natural ground in cases where fill material is present. The extent of fill across the site should be delineated and representative samples collected from each fill type.

Close sample spacing is required when delineating a known zone of contamination. Where a point source of contamination is identified, the extent and depth of the contaminated area needs to be defined by sampling, using the site history to guide the form and density of sampling. Surface water and groundwater should always be sampled where present. Some additional samples should be taken in areas not expected to be contaminated in order to establish local background levels.

The Australian Standard - Guide to the Sampling and Investigation of Potentially Contaminated Soil (AS4482) or the equivalent NEPM module on data collection should be used to assist with the determination of the most appropriate sampling pattern and density of sampling for the particular site under investigation. However, professional judgment is fundamental for consideration of site-specific observations.

Stage 3 - Health and environmental assessment and determination of remediation plan

Assessment of risk

The results obtained from the detailed site investigation should be used to determine the potential human exposure and environmental impact of the contaminants on the current and proposed landuses. If the landuse would result in unacceptable levels of human exposure or unacceptable environmental effects, then partial or full remediation or some other strategy for managing the contamination must be implemented before a Suitability Statement can be issued. It is usual practice for Stage 2 and Stage 3 investigations to be incorporated in one report for assessment by DoE.

Where complete removal of contamination is an approved remediation strategy, detailed health and environmental assessments are not normally required. However, in cases where contaminant levels above health and environmental investigation thresholds are to remain, more definitive assessment of the respective risk is required. In some instances, qualitative risk assessments only may be required. However, in situations where it is proposed to leave contaminants which are significantly above threshold levels or where contamination is widespread or where numerous contaminants are present, quantitative risk assessments will be required or a site management plan is to be developed. This minimises or eliminates the risk.

Health and environmental risk assessments should follow the protocols described in the Contaminated Sites Monograph Series, The Health Risk Assessment and Management of Contaminated Sites, and in the NEPM for contaminated land. The health and environmental risk assessment may lead to the establishment of site-specific remediation criteria for particular contaminants which can be used as clean-up levels. The rationale for such criteria is to be fully documented for assessment and approval by DoE, before commencement of remediation work. Should a circumstance arise where remediation work reveals substantial unexpected contamination, DoE is to be consulted regarding revision of remediation plans or the setting of site-specific remediation criteria for completion of work.

Remediation

The draft remediation plan should document the strategies to be implemented for reducing the risks to acceptable levels for the current and/or proposed landuse. Consideration should also be given to public consultation and risk communication if a site has significance for the community (e.g. school) or when residential properties are affected. If the site is an industrial/commercial premises, occupational health specialists and unions should be consulted.

Where the remediation plan involves some or all contamination remaining on site, a draft site management plan must be prepared to ensure that the redevelopment is undertaken without posing a health or environmental risk. Strategies for managing the contamination in the long term, following redevelopment, must also be documented. Draft remediation plans should include requests for a disposal permit in cases where it is proposed to remove contaminants from the site. Contaminated soil must not be removed from a site without a disposal permit.

Stage 4 - Implementation of remediation plan and validation sampling

In relation to section 118X of the EP Act, applicants are advised to submit a remediation plan with the detailed site investigation report on sites where significant contamination is present. On many small sites, the investigation and remediation processes often coincide. It is essential to validate that the site has been satisfactorily remediated. This is achieved by conducting a validation sampling program. If sampling shows that the targets have not been achieved, additional work to fulfil the agreed plan should be proposed.

Statistical analyses of results should be provided in validation reports to support recommendations that a site is no longer contaminated, or no longer poses an unacceptable health or environmental risk. The Australian Standard, Guide to the Sampling and Investigation of Potentially Contaminated Soil (AS4482) and the proposed NEPM module on data collection are useful references to establish the sampling pattern and density required.

What is the data collected during the investigation used for?

Upon initiating a soil investigation, a site manager develops a Sampling and Analysis Plan (SAP). The SAP should identify sampling strategies for filling any data gaps in the CSM requiring collection of site-specific information. These strategies typically address contaminant concentrations in surface and subsurface soil, as well as soil characteristics. Existing data can be used to determine what level and type of investigation may be appropriate. Areas with known contamination will be thoroughly investigated and characterized. Areas that are unlikely to be contaminated based on good historical documentation of the location of current and past storage, handling, or disposal of hazardous materials at the site may generally be screened out at this stage; however, samples should be taken to confirm this hypothesis.

For the purpose of soil assessment, consultants distinguish between surface and subsurface soils as follows: surface soils are located within two centimetres of the ground surface, and subsurface soils are located more than two centimetres below the surface. Because exposure to contaminants in these two soil regions may occur via different mechanisms, sampling plans for these two categories of soil should be designed to collect reliable data appropriate to the exposure models involved. For example, the surface soil strategy should collect data appropriate for evaluating exposure via direct ingestion, dermal contact, and inhalation of fugitive dusts as individuals move randomly around a site. Typically, this requires a reliable estimate of the arithmetic mean of contaminant concentrations in surface soils in exposure areas of concern. In general, the subsurface soil sampling strategy should provide data to model the types of indirect exposure to subsurface contamination that occurs when chemicals migrate up to the soil surface or down to an underlying aquifer. Modelling these pathways usually requires an estimate of the average contaminant concentration through each source, estimates of the dimensions of the source, and average soil properties within the source. However, as discussed below, at some sites a sampling plan designed to evaluate direct contact exposures may be appropriate for some subsurface soils.

Different Sampling Options

Site managers have two options for developing an SAP for surface soils: composite sampling or discrete sampling. Either approach should allow you to calculate a reliable estimate of the arithmetic mean of contaminant concentrations in surface soils. Composite sampling involves the physical mixing of soils from multiple locations and then collecting one or more sub-samples from the mixture.

The maximum contaminant concentration from composite sampling is a conservative estimate of the mean concentration and can be used for soil evaluations. This approach can be an effective way to estimate the mean contaminant concentration with lower sampling costs, because fewer samples are needed. However, the mixing of soils in composite samples may disperse volatile contaminants and also may dilute concentrations of other contaminants, resulting in less sensitivity to hot spots and to other variations in contaminant concentrations. Alternatively, site managers can collect discrete un-composited samples using a simple random sampling scheme (SRS), a stratified SRS6, or systematic grid sampling with a random starting point. Because there is no spatial averaging of soil concentrations with this method, a much larger number of soil samples is required to produce a reliable estimate of the mean contaminant concentration. As a result, estimating the 95th percentile upper confidence limit (UCL95) on the mean contaminant concentration as a conservative estimate of the mean when performing a soil evaluation is recommended for data sets of un-composited samples.

The subsurface soil sampling strategy addresses exposure to subsurface contamination that occurs when chemicals migrate up to the soil surface or down to an underlying aquifer. It focuses on collecting the data required for modelling volatilization and migration to ground water. As a result, the goals of this strategy are to measure the area and depth of contamination, the average contaminant concentration in each source area, and the characteristics of the soil. Generally speaking, conservative assumptions are used to develop hypotheses on likely contaminant distributions. This can involve taking 2 or 3 soil borings located in the areas suspected of having the highest contaminant concentrations within each source. Because the subsurface sampling approach is likely to be less comprehensive than the surface soil SAP, the soil analysis focuses on the highest mean soil boring contaminant concentration within the source as a conservative estimate of the mean contaminant concentration for the entire source area. The subsurface SAP also should include the collection of site characteristics including the following soil parameters: Soil Classification System (SCS) soil type, dry bulk density (pb), soil organic carbon content (foc), and pH.

For some sites, these three sampling approaches will suffice to characterize exposures to contaminants in soil. However, other sites may feature residential activities (e.g., gardening) or commercial/industrial (e.g., outdoor maintenance or landscaping) or construction activities that may disturb soils to a depth of up to two feet, potentially exposing receptors to contaminants in subsurface soil via direct contact pathways such as ingestion and dermal absorption. In such cases, it is anticipated that site managers will need to characterize contaminant levels by taking shallow subsurface borings where appropriate. The specific locations of such borings should be determined by the likelihood of direct contact with these subsurface soils and by the likelihood that soil contamination is present at that depth. Given that contamination in these deeper soils is unlikely to be characterized to the same extent as contamination in surface soils, the maximum measured concentration of each contaminant in these borings should used as a conservative estimate of the mean contaminant concentration for purposes of the soil evaluation.

Alternatively, if available evidence strongly indicates that contaminated subsurface soils will be disturbed and brought to the surface (e.g., as the result of redevelopment activities), site managers will need to characterize subsurface contamination more thoroughly and should collect a sufficient number of samples to develop a UCL95 value for use in the soil screening evaluation. For both surface and subsurface soils, site managers should use the CSM and Data Quality Objectives (DQO) process in developing SAPs to ensure that sufficient data are collected to properly assess site contamination and support decision-making.

How are the Sample Results Used?

Once sampling strategies have been developed and implemented, the samples are analysed according to the methods specified in the SAP. The analytic results provide the concentration data for contaminants of concern that are used in the comparison to environmental investigation thresholds. Soil analysis also helps to define the areal extent and depth of contamination, as well as soil characteristics data. This information is needed to calculate site-specific environmental and occupational investigation thresholds for the inhalation of volatiles and migration to ground water pathways. The analyses of soil contaminants and characteristics may reveal new information about site conditions.

Once site-specific environmental investigation thresholds have been calculated, they are compared to the measured concentrations of contaminants of concern. At this point, the CSM is reviewed to confirm its accuracy in light of the actual site data that have been collected in previous steps of the soil assessment process. This also helps to ensure that the environmental investigation thresholds are applicable to the site.

What if there are Multiple Contaminants Identified?

If multiple contaminants are identified during the SAP, the project manager should coordinate with the risk assessor to determine the health end points caused by each chemical and combinations of several chemicals. It is believed that the 1x10-6 target cancer risk level for individual chemicals and pathways generally will lead to cumulative site risks within the 1x10-4 to 1x10-6 risk range for the combinations of chemicals typically found at contaminated sites.

For non-carcinogens, it is recommended that non-carcinogenic contaminants be grouped according to the critical effect listed as the basis for the RfD/RfC. If more than one chemical detected at a site affects the same target organ or organ system, occupational exposure standards for those chemicals should be divided by the number of chemicals present in the group.

Different Exposure Pathways for Contaminants

Generally speaking, there are National Exposure Standards (NES) for most contaminants found during site investigations. There are however, also quantitative methods that can be used to derive occupational exposure thresholds for the following exposure pathways under a residential soil exposure scenario:

  • Direct ingestion;
  • Dermal Absorption;
  • Inhalation of volatiles outdoors;
  • Inhalation of fugitive dust outdoors; and
  • Ingestion of ground water contaminated by the migration of soil leachate to an underlying aquifer.

Direct Ingestion and Dermal Absorption of Soil Contaminants

Exposures to contaminants can occur via the direct ingestion and dermal absorption pathways. The approach to assessing these types of exposure consists of a set of equations that allows a site manager to estimate the soil contaminant concentration for which the combined potential exposure via these two pathways is equivalent to an incremental lifetime cancer risk of 1x10-6 or an HQ of one - the same target risks used for other pathways. This yields concentration levels of contaminants that are protective of exposures that occur via these pathways simultaneously. This approach was developed because concurrent exposures via these two pathways are very likely during activities such as gardening, outdoor work, children's outdoor play, and excavation.

Dermal Absorption

The dermal pathway should be evaluated for both residential and non-residential soil exposure scenarios depending on the types of activities occurring at a site (e.g., landscaping) and on the contaminants of concern present. Because no toxicity data are presently available for directly evaluating dermal exposures to contaminants, a method has been developed to extrapolate oral toxicity values for use in dermal risk assessments. This extrapolation method is necessary because most oral RfDs and cancer slope factors are based on an administered dose (e.g. in food or water) while dermal exposure equations estimate an absorbed dose. Specifically, dermal exposure equations account for the relative ability of a given contaminant to pass through the skin and into the bloodstream. The extrapolation method applies a gastro-intestinal absorption factor (ABSGI) to the available oral toxicity values to account for the absorption efficiency of an administered dose across the gastro-intestinal tract and into the bloodstream. Oral toxicity values should be adjusted when the gastro-intestinal absorption of the chemical in question is significantly less than 50 percent; this cut off reflects the intrinsic variability in the analysis of absorption studies.

To be protective of exposures to carcinogens in a residential setting, investigations should focus on individuals who may live in an area for an extended period of time (e.g., 30 years) from childhood through adulthood. Although children will have a smaller total skin surface area (SA) exposed than adult receptors, they are assumed to have a much higher soil to skin adherence factor (AF). Recent data provide evidence to demonstrate that:

1) Soil properties influence adherence;
2) Soil adherence varies considerably across different parts of the body; and
3) Soil adherence varies with activity.
(Kissel et al., 1996, Kissel et al.,1998, Holmes et al., 1999).

Because children are assumed to have additional, more sensitive body parts exposed (e.g., feet) and to engage in higher soil contact activities (e.g., playing in wet soil), the use of a body part-weighted AF of 0.2 for children and 0.07 for adults in residential exposure scenarios is recommended. In order to remain adequately protective, residential exposures to non-carcinogenic contaminants via the ingestion/dermal absorption pathways should be based on a conservative "childhood only" scenario in which the receptor is assumed to be between ages one through six.

Migration of Volatiles into Indoor Air

Subsurface contamination in either soil or ground water may also adversely affect indoor a quality through the infiltration of contaminant vapours into the basement or ground floor of an on-site building. This pathway may apply to both residential and non-residential scenarios. A site manager's decision to evaluate this pathway should be based on current and expected future site conditions (i.e., the current and/or potential future existence of a building on or near a source area) and on the contaminants of concern at the site.

Compounds most likely to pose a significant risk via this pathway include volatile organic compounds (VOCs), such as benzene, trichloroethylene, and vinyl chloride. This pathway may also apply to mercury, the only metal that has an appreciable vapour pressure.

It is recommended that this pathway be evaluated at sites where volatile contaminants have been detected in subsurface soil or soil gas, or in groundwater above environmental investigation thresholds, and where buildings either currently exist or are expected to be developed above or near the contamination.