Manag.

Transcription

1 Towards a Framework for the Manag gement of Conta aminated Land Position Paper October 2009 WSP Environment & Energy

2 Contents Page 1 Introduction Background Guiding Principles Legislative Requirements The Implications Of The National Environmental Management: Waste Act, The National Environmental Management Act, And The National Water Act Towards Practical Implementation 7 2 Framework Development Proposals Methodology for Deriving Soil Screening Levels Reporting Norms and Standards for Contaminated Land 8 3 Determination of Preliminary Soil Screening Levels for Assessment of Contaminated Land and Protection of the Water Resource A Test Case Preliminary Notes on a Proposed Model for Derivation and Use of Soil Screening Values Technical Basis for Calculation of Screening VALUES 14 4 Application of Site Specific Quantitative Risk Assessment Approach and Applicability Example 19 5 Way Forward 23

3 1 Introduction 1.1 BACKGROUND The National Environmental Management: Waste Act of 2008, clearly identifies the status and risk of contaminated sites and provides a legislative mechanism for remediation activities to be instigated and controlled. A national framework is required to provide norms and standards for the authorisation and practical implementation of remediation activities in compliance with the Waste Act. Due to various factors, including the high cost involved in remediation interventions, it is essential that a holistic and generic risk based approach be adopted that is founded on international best practice, to address remediation in a uniform manner, irrespective of the sector of occurrence to safeguard both human health and the natural environment. This report and its attached technical appendices introduces proposals for a national framework for the management of contaminated land in South Africa. The report is intended to stimulate discussion with a range of stakeholders in order to formulate a set of norms and standards which can be used to effectively implement the contaminated land clauses in the Waste Act in a fair and reasonable manner which is consistent throughout the country and is based on recognised international practice. The framework proposals are based on a review of international practice in the developed countries of the world and the emergence of remediation policy from developing countries, and an assessment of alternative approaches and methodologies that may find application in the development of a South African remediation framework. 1.2 GUIDING PRINCIPLES In terms of the general background to South African environmental legislation the guiding principles for the development of a framework for the management of contaminated land can be summarised broadly as follows: Duty of care to prevent pollution A successful remediation framework should be strongly proactive to prevent pollution before actual harm has occurred and be reactive to remediate damage to acceptable levels of risk consistent with intended use of the land and associated water resources based on safeguarding the risks to human health and to the environment. Use of a risk averse approach It is accepted international practice that both source control measures and remediation activities related to control of pollution risk should be based on risk based approaches that are simple and generic and have a wide range of applications for commonly occurring situations that may give rise to a pollution risk. Apply the Precautionary Principle and assess uncertainty in all assumptions The remediation strategy should be based on a risk averse approach and follow the Precautionary Principle by taking reasonable measures to prevent significant harm even if this precedes the existence of a proven causal link between pollution and the receptor. The burden of proof shall always be on the potential polluter. WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 1

4 Best Practicable Environmental Option Remediation objectives should be the outcome of a systematic consultative and decision making procedure that emphasises the protection of the environment. The option selected must provide the most benefit or least damage to the environment as a whole at acceptable cost in the long term as well as the short term. This is a holistic approach in that reduction of pollution in one medium does not take place at the expense of another. The emphasis is on long term solutions so that there should be no bad legacy for future generations in terms of unreasonable risk or costs. Polluter Pays Principle The polluter pays principle holds that the individual or organisation causing the pollution is liable for any costs involved in its remediation. In this situation it is important to identify the responsible parties and to allocate costs in a fair and proportionate manner. Remediation costs should be limited to those costs needed to avoid unacceptable risk. Abandoned (orphan) sites requiring remediation will require financial intervention from central government. Facilitating co operative governance Environmental legislation in South Africa has developed along sectoral lines, it is incumbent on all sectors of national, regional and local government to implement regulatory activities in a coordinated manner by a process of co operative governance. The successful implementation of environmental legislation will require a committed effort from all tiers of government and co operation from industry towards proper integrated environmental management. Public Involvement Remediation activities will require involvement of key stakeholders and Interested and Affected Parties as a successful remediation outcome must have public acceptability. All management decisions should be fully documented and justified. In this way the transparency of the process will be maintained and public confidence will be enhanced. Determining future land use and associated water use objectives will establish reasonable measures for site closures and remediation. Reaching these objectives will indicate the end point for remediation. 1.3 LEGISLATIVE REQUIREMENTS THE IMPLICATIONS OF THE NATIONAL ENVIRONMENTAL MANAGEMENT: WASTE ACT, THE NATIONAL ENVIRONMENTAL MANAGEMENT ACT, AND THE NATIONAL WATER ACT The national framework for the management of contaminated land has to comply with existing functional and legislative requirements. The Waste Act contains clauses which deal specifically with contaminated land, and require supporting technical guidance. It is also important to note that there are clauses within the National Environmental Management Act and the National Water Act which concern the prevention of pollution that may apply in certain contaminated land situations, which would also benefit from the development of consistent norms and standards. The key legislative clauses that inform the practical components of the framework are outlined below: National Environmental Management: Waste Act (2008) Chapter 4 Part 8 of the Waste Act deals with Contaminated Land. Section 36 deals with the identification and notification of investigations areas. 36(1) The Minister or the MEC in respect of an area which affects the relevant province may after consultation with the Minister of Water Affairs and any other organ of state concerned, by notice in the Gazette, identify as investigation areas: (a) (b) land on which high risk activities have taken place, or are taking place that are likely, to result in land contamination: land that the Minister or MEC, as the case may be, on reasonable grounds believes to be contaminated. WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 2

5 And furthermore. (6) Despite subsection (1), the Minister or MEC may issue a written notice to a particular person identifying specific land as an investigation area if the Minister or MEC on reasonable grounds believes that the land is or is likely to be contained. Section 37 deals with the consequences of identification and notification of investigation areas. The aim is to investigate whether the land has been contaminated, and if contamination has occurred whether the contamination presents a significant risk of harm. 37 (2) (a) A site assessment report must comply with any directions that may have been published or given by the Minister or MEC in a notice contemplated in section 36 (1) or (6) and must at least include information on whether the investigation area is contaminated. Consideration of site assessment reports 38.(1) On receipt of a site assessment report contemplated in section 37, the Minister or MEC,. may decide that (a) the investigation area is contaminated, presents a risk to health or the environment, and must be remediated urgently. (b) the investigation area is contaminated, presents a risk to health or the environment and must be remediated within a specified period: (c) the investigation area is contaminated and does not present an immediate risk, but that measures are required to address the monitoring and management of that risk, or (d) the investigation area is not contaminated. (b) Where the findings of the site assessment report are that the investigation area is contaminated, the site assessment report must at least contain information on whether (i) (ii) the contamination has impacted on the environment; the substances present in or on the land are toxic, persistent or bioaccumulative or are in large quantities or high concentrations or occur in combinations; (iii) there are exposure pathways available to the substances; (iv) the uses of the land and land adjoining increases or is likely to increase the risk to health or the environment; (v) the substances have migrated or are likely to migrate from the land; (vi) the acceptable exposure for human and environmental receptors in that environment have been exceeded (vii) any applicable standards have been exceeded: and (viii) the area should be remediate or any other measures should be taken to manage or neutralise the risk. Orders to remediate contaminated land 39 (1) A remediation order issued in terms of section 38(2) or an order issued under section 38(3) must describe, to the extent that is applicable (a) the person who is responsible for undertaking the remediation; (b) the land to which the order applies; (c) the nature of the contamination; (d) the measures that must be taken to remediate the land or the standards that must be complied with when remediating the land; (e) (f) the period within which the order must be complied with; whether any limitations in respect of the use of the land are imposed (g) the measures that must be taken to monitor or manage the risk; and (f) any other prescribed matter. WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 3

6 Transfer of remediation sites 40 (1) No person may transfer contaminated land without informing the person to whom the land is to be transferred to that the land is contaminated and, in the case of a remediation site, without notifying the Minister or MEC, and complying with any conditions that are specified by the Minister or MEC as the case may be National Environmental Management Act The duty of care and remediation of environmental damage is defined in Section 28 of the Act; 1) Every person who causes, has caused or may cause significant pollution or degradation of the environment must take reasonable measures to prevent such pollution or degradation from occurring, continuing or recurring, or, in so far as such harm to the environment is authorised by law or cannot reasonably be avoided or stopped and rectify such pollution or degradation of the environment. 2) Without limiting the generality of the duty in subsection (1), the persons on whom subsection (1) imposes an obligation to take reasonable measures, include an owner of land or premises, a person in control of land or premises or a person who has a right to use the land or premises on which or in which Any activity or process is or was performed or undertaken: or Any other situation exists, which causes, has caused or is likely to cause significant pollution or degradation of the environment. 3) The measures required in terms of subsection (1) may include measures to investigate, assess and evaluate the impact on the environment; inform and educate employees about the environmental risks of their work and the manner in which their tasks must be performed in order to avoid causing significant pollution or degradation of the environment; cease, modify or control any act, activity or process causing pollution or degradation; contain or prevent the movement of pollutants or the causant of degradation; eliminate any source of the pollution or degradation; or remedy the effects of the pollution or degradation. It is important to note the above clauses are of a general environmental nature and do not refer specifically to protection of the water resource. Also it is important to define the term significant pollution, as this is the key to enforcing actions that are prescribed in subsequent clauses in Section 28 of the Act. The EIA regulations were revised in Government Notice no R 385, 21 April For the first time activities given rise to legacy pollution and the responsibilities for addressing the status of contaminated land prior to re zoning and transfer of land were formally listed as activities which may not commence without environmental authorisation from the competent authority. Section 21[23] The decommissioning of existing facilities or infrastructure, other than facilities or infrastructure that commenced under an environmental authorisation issued in terms of EIA Regulations, 2006 made under Section 24(5) of the Act and published in Government Notice No R385 of 2006.(c) industrial activities where the facility or the land on which it is located is contaminated or has the potential to be contaminated by any material which may place a restriction on the potential re use of the site for a different purpose. WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 4

7 ...in respect of which the investigation, assessment and communication of the potential impact of the activities must follow the procedure as described in Regulations 22 to 26 of the EIA Regulations of 2006 promulgated in terms of Section 24(5) of the Act. Section 19 of the NWA is being amended to read as follows: 19(1) An owner of land, a person in control of land or any person who was responsible for the land or a person who occupies or uses the land on which The National Water Act (a) any activity or process is or was performed or undertaken; or The National Water Act, Act 36 of 1998 recognises that the aim of water resource management is to achieve sustainable use of water for the benefit of all users. Protection of the quality of the water resources is necessary to ensure sustainability of the resource. It recognises the need for integrated management of the resource, and where appropriate delegate the management functions to a regional or catchment level so as to enable everyone to participate. Revisions to the Act are being proposed at present. Section 1 of the Act defines the term pollution : (xv) pollution means the direct or indirect alteration of the physical, chemical or biological properties of a water resource so as to make it less fit for any beneficial purpose for which it may reasonably be expected to be used; or harmful or potentially harmful (aa) to the welfare, health or safety of human beings; (bb) to any aquatic or non aqueous organisms; (cc) to the resource quality; (dd) to property (b) any other situation exists which causes, has caused or is likely to cause pollution of a water resource, must take all reasonable measures to prevent any such pollution from occurring, continuing or recurring. (2) The measures referred to in subsection 1 may include measures to (a) Cease, modify or control any act or process causing the pollution (b) Comply with any prescribed waste standard or management practice (c) Contain or prevent the movement of pollutants (d) Eliminate any source of the pollution (e) (f) Remedy the effects of the pollution Remedy the effects of any disturbance to the bed and banks of a watercourse The powers of enforcement are delegated to the Catchment Management Agency in the Act, although at present it is rare to see enforcement at this governance level when dealing with the remediation of significant pollution. Section 19 Pollution Prevention, deals with the situation where pollution of a water resource occurs or might occur as a result of activities on land. This Section is very similar in language and intent to the clauses of NEMA discussed above. WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 5

8 Section 20 deals with Emergency Incidents. These are accidental incidents, such as the spilling of hazardous substances that finds or may find its way into a water resource. The responsibility for remedying the situation rests with the person responsible for the incident or substance involved. If there is failure to act, the relevant catchment management agency may take the necessary steps and recover the costs from every responsible person. The same polluter pays principle is also applied in Section 19, clauses 19 (4) to 19 (8) Guiding Principles In terms of South African environmental legislation the guiding principles for the development of a framework for the management of contaminated land can be summarised broadly as follows: Duty of care to prevent pollution A successful remediation framework should be strongly proactive to prevent pollution before actual harm has occurred and be reactive to remediate damage to acceptable levels of risk consistent with intended use of the land and associated water resources based on safeguarding the risks to human health and to the environment. Use of a generic, risk averse approach It is accepted international practice that both source control measures and remediation activities related to control of pollution risk should be based on risk based approaches that are simple and generic and have a wide range of applications for commonly occurring situations that may give rise to a pollution risk. Apply the Precautionary Principle and assess uncertainty in all assumptions The remediation strategy should be based on a risk averse approach and follow the Precautionary Principle by taking reasonable measures to prevent significant harm even if this precedes the existence of a proven causal link between pollution and the receptor. The burden of proof shall always be on the potential polluter. the most benefit or least damage to the environment as a whole at acceptable cost in the long term as well as the short term. This is a holistic approach in that reduction of pollution in one medium does not take place at the expense of another. The emphasis is on long term solutions so that there should be no bad legacy for future generations in terms of unreasonable risk or costs. Polluter Pays Principle The polluter pays principle holds that the individual or organisation causing the pollution is liable for any costs involved in its remediation. In this situation it is important to identify the responsible parties and to allocate costs in a fair and proportionate manner. Remediation costs should be limited to those costs needed to avoid unacceptable risk. Abandoned (orphan) sites requiring remediation will require financial intervention from central government. Facilitating co operative governance Environmental legislation in South Africa has developed along sectoral lines, it is incumbent on all sectors of national, regional and local government to implement regulatory activities in a coordinated manner by a process of co operative governance. The successful implementation of environmental legislation will require a committed effort from all tiers of government and co operation from industry towards proper integrated environmental management. Public Involvement Remediation activities will require involvement of key stakeholders and Interested and Affected Parties as a successful remediation outcome must have public acceptability. All management decisions should be fully documented and justified. In this way the transparency of the process will be maintained and public confidence will be enhanced. Determining future land use and associated water use objectives will establish reasonable measures for site closures and remediation. Reaching these objectives will indicate the end point for remediation. Best Practicable Environmental Option Remediation objectives should be the outcome of a systematic consultative and decision making procedure that emphasises the protection of the environment. The option selected must provide WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 6

9 1.4 TOWARDS PRACTICAL IMPLEMENTATION In terms of evaluating the provisions of the Waste Act and other applicable environmental legislation in South Africa the essential elements required to allow for practical implementation are of a functional and technical nature and should include the following: a decision supporting tool to define contaminated land status that is landuse based and considers acceptable risk levels based on conservative noharm criteria for a full range of environmental exposure criteria and natural background levels. a phased approach to investigation and reporting that defines norms of technical practice with minimum requirements to ensure the quality and consistency of professional reports. a site specific level of reporting that includes elements of quantitative risk assessment, statistically based quality objectives and is properly integrated with site investigation and remediation planning. the incorporation of socio economic factors into decision making and procedures for communication of risk and benefits to relevant stakeholders. 2 Framework Development Proposals Priorities for the management of contaminated land are identified as follows: development of nationally consistent methods and numerical values that protect human health and the environment which can be implemented as standards and guidance as part of a universal national framework to enable remediation of contaminated land. development of a consistent policy on future land use for contaminated sites based on remediation objectives conforming to the above mentioned standards. development of a contaminated land register to enable transparent recording of remediation activities and current land status. 2.1 METHODOLOGY FOR DERIVING SOIL SCREENING LEVELS It has been identified that practical implementation of the contaminated land clauses of Part 8 of Waste Act cannot proceed without developing a standard with supporting guidance for the derivation of soil screening levels, which can applied at a preliminary level to characterise the environmental risks posed by contaminated sites. Numerical criteria for priority contaminants of concern need to be determined so that they can be used to define appropriate management actions. The numerical values will serve as points of compliance for authorisation of remediation activities and can be applied as: conservative clean up targets inform management actions to reduce the potential for adverse effects trigger further investigations to determine site specific risk based criteria WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 7

10 Consequences of not doing this continuing uncertainty about the most appropriate criteria and method to apply in the assessment of contaminated land, and as a result conflict on the definition of a contaminated site and requirement for statutory remediation orders. It is acknowledged that although the use of soil screening values is common in international practice the derivation of such values is a complex process and depends on the acceptability of certain scientific assumptions used in the development of standard equations used to model risk. The development of soil screening values to protect human health via direct exposures routes and indirect exposure routes is the key starting point. The incorporation of ecotoxicological criteria for water resource protection can be achieved. It may however be difficult to assess the ecological impact of contaminated soils at a simple generic level and this is perhaps an issue that is best resolved by site specific risk assessment. The Waste Act and NEMA require land to be investigated if hazardous substances are likely to have been used in or on the land. Change of land use for future development and property transfer are triggering clauses for environmental authorisations. Investigations are thus required to assess the presence and quantify the risk posed by any hazardous substances on or in the land. Risk assessment criteria are thus dependant on the activity patterns of human receptors associated with particular land use categories. Suggested possible land use categories for use in development of guidelines are: Residential and Urban Parkland Informal residential settlement Commercial Industrial Residential and Urban Parkland: sites where the primary land use is residential in formal housing with associated public open spaces for recreational use. Informal residential settlements: sites without formal housing, where open ground has been settled without the construction of roads and paved areas of hard standing and where houses may not have concrete floor slabs. Commercial: sites where the primary activity is related to commercial operations and occupancy is not for residential purposes. Offices and shopping malls are examples of Commercial land use. Industrial: sites where the primary activity involves the production, manufacture, construction, or assembly of goods. It is important consider adjoining land use in terms of defining the appropriate soil quality guideline as the migration of contaminants may contaminate surrounding areas with more susceptible land uses. For example the off site migration of dust from a remediated industrial site should not pose any unacceptable risk to nearby residential site. A preliminary model for the derivation of soil screening levels is discussed in Section REPORTING NORMS AND STANDARDS FOR CONTAMINATED LAND To provide a clear and consistent application of the Waste Act a reporting structure for contaminated land has to be developed. The commonly encountered international practice consists of three distinct reporting phases and progresses from Phase 1 desktop and site walkover assessments with limited investigation and testing to a Phase 2 detailed invasive investigation and testing to a comprehensive Phase 3 report with a risk assessment and proposed remediation plan. The reporting system requires norms and standards of practice to be strictly applied but also must retain flexibility to allow for decisions on the contaminated status of sites to be made in a cost effective manner and in a reasonable WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 8

11 timeframe. Urgent priority works may require that the phased approach to reporting has to move forward in a concurrent single report Requirements for preliminary site evaluation Phase 1 Contaminated Site Assessments A preliminary site evaluation would consider the following elements: Site description location and size Nature and extent of contamination, contaminants of concern or historical activities that may be sources of contamination. List all past and present activities at the site that involved the storage, production, use, treatment or disposal of hazardous materials that could contaminate the site. Describe the current condition of the site and the contents and results of any previous assessment reports. Local topography and geology, drainage, surface cover, vegetation Status of groundwater, approximate depth to water table Proximity to surface water demonstrates that the site activities do not pose a contamination threat then no further investigation is warranted and the site should be recommended as suitable for re use. In most cases it is likely that some level of investigation will be required to provide the level of certainty required to enable property redevelopment or transfer in compliance with the Waste Act. A limited investigation of certain sub surface activities, for example underground storage tanks, would be necessary to obtain a waiver on the contaminated status of a site at a Phase 1 level of reporting. This type of limited investigation of soil and groundwater is already common practice for certain industries in South Africa and should be reflected in the norms and standards approach Site Characterisation Phase 2 Contaminated Site Investigations Phase 2 investigations include the sampling and analysis of soil, sediment, groundwater and surface water. It is stressed that the adequacy of the investigation must be related to the site specific conditions and is a natural progression from the Phase 1 Site Assessment. It is a focussed and designed programme not a mandatory protocol, although for particular generic situations it may be possible to develop applicable protocols to standardise good practice. Proximity to drinking water supplies Annual rainfall and flood potential Land and water use for the site and nearby areas The reporting format can be developed in the form of a uniform checklist that can be used for all applications to the Department of Environmental Affairs. All data may not be available, or data may vary in terms of uncertainty, it is thus important to recognise gaps in the knowledge base and to decide whether additional data must be obtained on the site characterisation. This may trigger the commencement of Phase 2 Investigations. The Phase 1 report must make clear recommendations on the status of the contamination risk posed by the site. If a complete site history clearly WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 9

12 The Phase 2 reporting should give information on: the type, extent and level of contamination anticipated on site and the issues raised in previous reports. the nature of samples collected, the sampling procedures followed, including field sampling quality assurance and quality control requirements. the analyses undertaken, methodologies used and laboratory quality assurance quality control procedures, with laboratory certificates and appropriate accreditation listed. The report must also provide a fair and reasonable assessment of the following issues: (b) Where the findings of the site assessment report are that the investigation area is contaminated, the site assessment report must at least contain information on whether (i) (ii) the contamination has impacted on the environment; the substances present in or on the land are toxic, persistent or bioaccumulative or are in large quantities or high concentrations or occur in combinations; (iii) there are exposure pathways available to the substances; (iv) the uses of the land and land adjoining increases or is likely to increase the risk to health or the environment; the actual extent and concentrations in all appropriate environmental media on site based on verified test data. (v) the substances have migrated or are likely to migrate from the land; any likely dispersal in air, surface water, groundwater, soil and dust from the detected contaminants any potential effects of contaminants on human health, the environment, or building structures and property. The report must make a clear statement regards the adequacy and completeness of all information used in the assessment and list any further studies or investigations that may be required to verify the status of the site and the risks posed. The findings of the report must satisfy the requirements of Section 37 of the Waste Act and determine and state whether or not the following triggering clauses have been breached: A site assessment report must comply with any directions that may have been published or given by the Minister or MEC in a notice contemplated in section 36 (1) or (6) and must at least include information on whether the investigation area is contaminated. (vi) the acceptable exposure for human and environmental receptors in that environment have been exceeded (vii) any applicable standards have been exceeded: and (viii) the area should be remediate or any other measures should be taken to manage or neutralise the risk. The report must reach a conclusion as to whether the site requires clean up, management, on going monitoring or a combination thereof. Owners of site which are not in compliance with Section 37 will be required to submit comprehensive investigation reports with a remediation action plan Phase 3 Remediation Plans The Phase 3 report should include elements of qualitative or quantitative risk assessment to determine site remediation objectives and propose a remediation plan for the site. WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 10

13 Where preliminary soil screening values are to be applied as clean up criteria the assumptions on which those guidelines are based must be shown to apply to the site and the surrounding conditions under investigation. When the site conditions are not consistent with the assumptions pertaining to the generic risk profiles used to develop the soil screening values then a sitespecific quantitative risk assessment should be undertaken. Examples include: Risk to critical ecological habitats Where there is a large degree of uncertainty associated with the fate and behaviour of the contaminants unacceptable risk to human health or the environment, either on site or offsite. Document in detail all procedures to be adopted to achieve the remediation objective. Establish safeguards and contingency measures for safe implementation of all remediation activities. Establish a record of activities that ensures compliance the approved remediation action plan. Obtain the relevant approvals, permits or licenses required by regulatory authorities to undertake the proposed remediation activities in terms of Section 20(b) of the Waste Act. If the contaminant of concern poses a high potential risk to a specific receptor Where there is a significant gap in the toxicological data base related to contaminant mixtures or metabolites Where there are multiples sources of contaminants or exposure pathways not considered in the generic guidelines. In a situation where there are no generic guidelines for a specific contaminant a quantitative risk assessment may be appropriate, alternatively clean up to background levels may be an option. The establishment of a final soil remediation objective for site remediation must take consideration of technical feasibility, socio economic factors and overall risk management strategies. All management decisions should be fully documented and justified. In this way the transparency of the process will be maintained and public confidence in the resulting decision will be enhanced. The site remediation plan should be prepared as follows: Set remediation or management objectives that ensure the site will be suitable for its current or future proposed land use and will pose no WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 11

14 Figure 1: A phased approach for the assessment and remediation of contaminated land Phase I Desktop Study Initial Investigations 3 Determination of Preliminary Soil Screening Levels for Assessment of Contaminated Land and Protection of the Water Resource A Test Case Preliminary Risk Assessment Phase II Detailed Field Investigations Risk Quantification Remediation Strategy Cost Analysis Phase III Remediation Design & Implementation Control & Monitoring Long Term Stewardship 3.1 PRELIMINARY NOTES ON A PROPOSED MODEL FOR DERIVATION AND USE OF SOIL SCREENING VALUES The soil screening values outlined below represent a test case for the preliminary evaluation of a proposed methodology developed in order to provide a set of simple guidelines for a first tier assessment of risk associated with contaminated land in a South African context. In order to develop the methodology it was decided to evaluate eight commonly occurring heavy metals and metalloids associated with a variety of industrial and mining activities in South Africa. The principles applied to the development of the screening values are based on a simple risk assessment that is protective of human health in terms of exposure criteria associated with land use, and human health and aquatic ecosystem considerations associated with the protection of the water resource from land based contamination sources. The screening values are internally consistent with existing water quality guidance values published by DWA. The model proposes three series of risk exposure equations used to derive a soil screening level which is protective of human health and the aquatic ecosystem. The lowest of the three derived concentrations thus defines the acceptable risk scenario. WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 12

15 Model equations are typically based on the original US EPA models and their more recent derivatives, particularly the Canadian Environmental Quality Guidelines. Key assumptions for South Africa are related to the groundwater pathway with typical rainfall, infiltration and recharge considerations applied. In addition the human health exposure criteria have been revised to take into account the activity patterns and increased risk of residents of informal settlements. This sensitive population group is very significant in Southern Africa had has been previously overlooked in the application of risk based health assessments in the past. The use of existing published DWA water quality guidelines as the target for water quality used in the equations is to create internal harmonisation and is not an indication of our unequivocal acceptance of their scientific validity. As the derived screening values for protection of the water resource are based on a back calculation from a desired concentration in the receiving body of water, the soil screening values can be modified to be consistent with specific water quality objectives derived for individual catchments on the basis of an integrated water resource management approach that is flexible and adaptable to user needs. The screening model is not intended to be a stand alone series of regulatory standards for deriving clean up targets. We strongly advocate the use of site specific quantitative risk assessment within an overall framework of holistic risk assessment that is ethically based and takes into consideration societal values and practical implementation. A first tier of statistical uncertainty analysis has been applied to the assumptions and input data using a Monte Carlo simulation. The screening values can be considered conservative under a broad range of assumptions, however, it must be accepted that there are exposure scenarios that may not be adequately addressed by these screening values. The use of the soil screening values as an indication of a safe or clean site is thus valid in the absence of a specific risk exposure scenario not covered in the generic equations (for example, the screening lists are not fully protective of soil biota). document that evaluates the contaminants in terms of their sources, chemical properties, natural distribution and background levels, distribution coefficients, chemical modifiers in soils and water, human health toxicology and environmental risk Proposed Preliminary Soil Screening Values Definition of Preliminary Soil Screening Values Level 1 Screening Values soil quality values that are protective of both human health and ecotoxicological risk for multi exposure pathways, inclusive of contaminant migration to the water resource. Level 1 Screening Levels are applicable to all land uses, and thus represent an acceptable risk situation with no adverse effects on human health and the aquatic environment. Level 2 Screening Values soil quality values that are protective of risk to human health in the absence of a water resource. Level 2 Screening Values are land use specific and have been calculated for three key land uses namely, standard residential, informal residential and commercial/industrial land uses. Equations for the deriving the levels and input parameters are discussed in Section 3.2. It is proposed that these preliminary screening lists are extended to cover more compounds, particularly the commonly occurring hydrocarbons and other organic compounds. The recommended format for future development of the screening lists is as a laminated pocket listing for easy reference together with a companion WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 13

16 Table 1: Proposed Preliminary Soil Screening Values Parameter Units LEVEL 1 LEVEL 2 All Land Uses Protective of the Water Resource Standard Residential Commercial/ Industrial Informal Residential Lead mg/kg Copper mg/kg Chromium (III) % 5 10 * 5 Chromium (VI) mg/kg Arsenic mg/kg Cadmium mg/kg Mercury mg/kg Zinc mg/kg Nickel mg/kg * no limit Exposure Parameters Exposure parameters used for dosage calculations are summarised below. Exposure parameters for residential land use were based on a child as the most sensitive receptor whilst commercial/industrial land use was based on adult exposure. Exposures for child receptor under informal residential land use were modified to account for increased dermal contact, ingestion and dust inhalation. The modifications represent preliminary estimates in the absence of specific studies and data on activity patterns and exposures for informal land use settings in South Africa. It is noted from the draft calculated screening values that certain metals have lower values based on protection of water resource (Level 1) as compared to human health (Level 2) values. This is due to the fact that certain metals are of greater concern and toxicity to aquatic organisms whereas others are primarily a human health concern. Copper is a prime example of an important aquatic ecotoxin. 3.2 TECHNICAL BASIS FOR CALCULATION OF SCREENING VALUES Protection of Human Health Exposure Routes Soil Screening Values were calculated by determining dosages associated with the following direct exposure routes accidental soil ingestion, dust inhalation and dermal contact. Indirect exposure via ingestion of contaminated water is addressed under Section Protection of Water Resources. WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 14

17 Table 2: Input parameters for derivation of Soil Screening Values based on protection of human health Parameter Standard Informal Commercial/ (description / symbol / unit) Residential Residential Industrial Body Weight BW kg Averaging Time AT days Exposure Frequency EF days/yr Exposure Duration ED yrs Ingestion Rate (soil) IR s mg/day Inhalation Rate (air) IR a m 3 /day Particulate Emission Factor PEF m 3 /kg 4.17E E E+09 Surface Area Exposed Skin SA cm 2 /day Soil to Skin Adherence Factor AF mg/cm Dermal Absorption Factor (inorganics) ABS i Table 3: Reference Dosages and Slope Factors RfD o RfD i RfD d SF o SF i SF d Lead 3.60 x x 10 3 * * * Copper 3.70 x x 10 2 * * * Cr(III) * * * Cr(VI) 3.00 x x x 10 3 * 290 * As 3.00 x x * Cd 5.00 x x 10 4 * 6.30 * Hg 3.00 x x x 10 4 * * * Zn 3.00 x x 10 1 * * * Ni 2.00 x x 10 2 * 8.40 x 10 1 * * No accepted value available. Acceptable soil values for combined direct exposure dosages were determined based on a target risk of 1.0x10 5 for non threshold substances and a target hazard index of 1 for threshold substances. Toxicological Parameters Reference dosages (RfD) and Slope Factors (SF) for threshold and non threshold effects for each exposure route were sourced from internationally reviewed databases and were considered at the time of writing to be scientifically defensible and are summarised below. WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 15

18 Calculation Method Soil values for threshold and non threshold effects were calculated using the following formulae: Threshold contaminants C = (THIxBWxAT) / [EFxEDx((1/RfD o )x10e 06x IR s ) + ((1/RfD a )xir a x(1/pef)) + ((1/RfD d )xsaxafxabsx10e 06))] Non threshold contaminants C = (TRxBWxAT) / [EFxEDx((SF o x10e 06x IR s ) + (SF a xir a x(1/pef) + (SF d xsaxafxabsx10e 06))] A typical worked example demonstrating the application of these calculations is provided in Section The lowest soil value for threshold and non threshold effects was selected as the Preliminary Soil Screening Value for each land use Protection of Water Resources Exposure Routes Partitioning of contaminants between solid and liquid phases within soils may result in impacts to groundwater or surface water resources and thereby giving rise to potential human health risks (ingestion of contaminated water via the drinking water supply if this from natural untreated surface water or groundwater from boreholes) or the risk of adverse impacts on the aquatic ecosystem. Soil Screening Values that are protective of these potential exposure risks were calculated for protection of human health (ingestion of contaminated water) and aquatic ecosystem health based on a two phase equilibrium partitioning and dilution model. The Soil Screening Values represent the soil values required to achieve DWAF Water Quality Guideline levels for aquatic ecosystem protection and domestic water use, and are consistent both in terms of method of derivation and acceptable risk level applied in development of the existing DWAF Water Quality Guidelines. The derivation of equations to determine acceptable drinking water values is thus redundant as the point of compliance is pre set at the existing national standards. The model is thus linked to any future revisions of any applicable water quality standards applicable at either national or catchment level (for example receiving water quality objectives in a regional catchment). Partition Coefficients There is currently insufficient information available to define partition coefficients (K d values) for specific soil types in South Africa. Partition coefficients were therefore sourced from the international literature, primarily from broad based statistical studies of K d values undertaken in the US and Canada. The K d values that were used for calculation purposes were selected based on professional judgement. Neutral (ph 7) soil conditions were assumed. Dilution Factor The Dilution Factor accounts for the effects of groundwater recharge on dilution and mixing of the partitioned phase. The DF was calculated using the following formula; Where: DF = [(B x K x i) + 1] / (R x L) DF = Dilution Factor B = Effective mixing depth in aquifer K = Saturated hydraulic conductivity i = Hydraulic gradient R = Recharge L = Site length WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 16

19 An estimated factor of 50 was determined by statistical simulation using the following values and correlations; Table 4: Assumed parameters for simple dilution and mixing equation for contaminant release from soil to water resource Parameter Min Max Mode Distribution Correlations Effective Mixing Depth in Aquifer B m Triangular Saturated Hydraulic Conductivity K m/yr Triangular i,r = 0.5 Hydraulic Gradient i Triangular K,R= 0.5 Recharge R m/yr Triangular Site Length L m Triangular i,r= 0.8 The above dilution factor does not account for attenuation of contaminants within the saturated zone. For the purposes of preliminary calculations an attenuation factor of 50 was applied for attenuation with the saturated zone. Calculation Method Where: Y = Cw x Kd x DAF Y = total contaminant concentration in soil at equilibrium with pore water at defined water quality standard C w = water quality standard (aquatic ecosystem / domestic drinking water use guideline) K d = partition coefficient DAF = dilution attenuation factor Where the calculated soil values were lower than those calculated for direct human health risks (Section above) these values were then adopted as the Screening Level 1 values. The combined dilution attenuation factor applied in the soil value calculations was It should be noted that it was beyond the scope of these initial calculations to define generic attenuation relationships in the saturated zone. Both dilution and attenuation relationships require detailed research to define appropriate and meaningful values for South African conditions. WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 17

20 Are results greater than the SSV 1 Recommended Protocol for Assessment of Contamination Land Guidance on Use of Preliminary Soil Screening Values and Site Specific Risk Assessment SSV 1 Soil Screening Values protective of human health, water resources and the environment SSV 2 Soil Screening Values protective of human health by direct exposure based on land use NO No Further Action NO YES Potential Risk to Water Resource Is there current or potential future groundwater use on or within 1km of the site? Is there a permanent natural surface water course on or adjacent to the site? YES Are results greater than the SSV 2? NO No Further Action YES NO Is Site Specific Risk Assessment considered necessary? Are exposure pathways and receptors inconsistent with Soil Screening assumptions? YES Screening Values to be applied as Response Value: SSV1 to be applied if risk to water resources exists SSV 2 to be applied if no risk to water resources exists Risk Assessment Report Derivation of Site Specific Risk Value Develop Remediation and Management Strategy Are contaminant levels greater than Site Specific Risk Value? YES NO No Further Action WSP Environment & Energy Towards a Framework for the Management of Contaminated Land 18