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Stream 8a: Human Health and Ecological Risk Assessment
What’s in a Guideline? A Look Back at the History of Risk-Based Guidelines in Canada
Janice Paslawski, Lindsay Du Gas, Lindsay Woof, Mikhaila Paslawski
The objective of this presentation is to simply remind our interested participants of the complexity that gets buried in a single number that we base our remediation and risk management decisions on. We will discuss the sensitivity of selected inputs that are included in a freshwater aquatic life guideline recalculation as a reminder of the influence of each input on the overall risk-based target.  

This presentation will take a walk back in time to look at the history of the development of risk-based guidelines in Canada, with a focus on petroleum hydrocarbon (PHC) impacted sites. A review of the premise of a tiered system for evaluating and managing impacted sites will be discussed, including a perspective on the perceived level of protection achieved through remediation to "Tier 1", compared with a Tier 3 risk-based approach to site closure. The focus of the review will be to re-acquaint those interested in understanding the level of risk associated with residual PHC impacted sites relative to overall risk associated with options for remediation, re-development or abandonment.

The author will present a discrete sensitivity analysis of the input variables that are specifically selected as conservative default values in the derivation of risk-based guidelines, as well as those that can be modified to be site specific.

The details of the analysis will include perspective on the origin of assumptions or pathway default parameters identified in provincial and federal guidance, and uncertainties associated with some of the highly relied upon exposure pathway endpoints. Selected critical pathways, such as the vapour intrusion pathway, will be used as examples of a risk-based model that was utilized to calculate the potential for incremental risk in indoor air to human exposure. Discussion will include the outcome of analysis of soil vapour screening value derivations with respect to current vapour intrusion science for petroleum vapour intrusion (PVI). Focus will be given to the implications of our day to day decisions as risk assessors in support of our evaluation of impacted sites in the Prairies.

The discussion will include an overview of perspective of the efficacy of risk-based guidelines in the evaluation of contaminated sites in the Prairies, and the input parameters used in the derivation of these guidelines that are based on certain assumptions. Consideration of the evolution of science with respect to these pathways, and specifically to vapour intrusion, will be interpreted, in terms of how these changes influence the current pathway-specific risk-based guidelines. Potential solutions will be discussed with respect to risk-based closure and minimizing environmental liabilities to stake holders, buyers, property owners and industry.

Janice Paslawski, Director Risk Assessment Centre of Excellence, Environment and Geoscience, Engineering, Design and Project Management, SNC-Lavalin
Janice Paslawski, Ph.D., P.Eng., joined SNC-Lavalin in Saskatchewan in 2010. She spent a significant portion of her environmental engineering career in Alberta between 1990 and 2004 where she worked for clients like Health Canada, Alberta Environment and Canadian Council of Ministers of the Environment assisting with the development and implementation of risk-based guidelines across Canada. Her understanding of our regulatory framework support and assist SNC-Lavalin’s team find innovative solutions to their Environmental concerns and liabilities.

She studied Civil and Environmental Engineering at the University of Saskatchewan throughout her career and her latest move back to Saskatchewan led to her joining SNC-Lavalin in 2010 to lead the risk assessment National team and follow her interest in risk assessment for contaminated site management. She works in the Saskatoon office in site assessment and remediation and leads the Canada Risk Assessment team of 14 specialists who are dedicated as a technical resource for the management of contaminated sites and site redevelopment across Canada and abroad. Her team is committed to our regulatory framework for risk-based closures and to the protection of human health and the environment from the effects of industry and development on our environment.

Moving Beyond Upper Confidence Limits in Risk Assessment
Gillian Dunlop1, Tania Noble1, Siobhan Sutherland2
1Stantec Consulting Limited
2Crown-Indigenous Relations and Northern Affairs Canada
The objective of this presentation is to share a case study to show how area-weighted concentrations can be applied in human health risk assessment.  

In deterministic risk assessments, chemical concentrations that receptors are exposed to over time are represented by point estimates, referred to as exposure point concentrations (EPCs). Health Canada recommends the use of the mean or 95% upper confidence limit of the mean (UCLM) concentration as the EPC when sufficient data are available, when there are no known hot-spots and when there are no preferred areas of use on the site by the receptors of interest. Mean concentrations are appropriate when it is expected that a receptor may spend time on any part of the site equally and samples have been fairly evenly collected across the site. When samples have been collected more extensively in one area compared to others, a different approach for calculating EPCs is required. Area-weighted average concentrations are useful when contaminant concentrations are so unevenly distributed that upper-confidence limits on the mean do not provide reasonable estimates of the exposure concentration.

At the Crown-Indigenous Relations and Northern Affairs Canada Tundra Mine Site, an area-weighted average arsenic concentration was used in the human health risk assessment. At this site, one area of potential environmental concern (APEC) has been sampled extensively (i.e., more than half of the samples were obtained from a single APEC, although it represents less than 20% of the total area), and UCLM concentrations would therefore be biased high towards the APEC area. It is expected that human health receptors may spend time in any area of the Site, and there is no specific location that is known to be used preferentially. As such, a concentration that is weighted based on the area of the Site is more representative of exposure than a non-weighted mean concentration. Area-weighted concentrations were calculated by using Thiessen polygons to determine the portion of the larger area which is represented by a single sampling location.

This presentation will identify when area-weighted concentrations are appropriate in risk assessment, and how they were used at the Tundra Mine Site.

Gillian Dunlop, Risk Assessor, Environmental Services, Stantec Consulting Limited
Gillian Dunlop is a risk assessor in Stantec Consulting Limited's Environmental Services team. Since the start of her consulting career in 2007, Gillian has worked on numerous human health and ecological risk assessments. With extensive experience at federal contaminated sites, she has carried out risk assessment projects for numerous custodial departments in various provinces. Gillian has completed many risk assessments under Ontario Regulation 153/04 and is familiar with the Ontario regulatory process. Gillian is a recognized toxicologist by the Ontario Ministry of the Environment, Conservation and Parks, and has completed maximum concentration level assessments that have achieved regulatory approval. Gillian has conducted risk assessments for a variety of sites (e.g., residential, commercial, industrial and sensitive) and chemical groups (e.g., inorganics, organics, radionuclides) for all types of environmental media (e.g., soil, soil vapour, groundwater, surface water and sediment). Gillian has prepared the multi-media health assessment component of environmental assessments for mining, oil and gas and power projects. Gillian has a B.Sc. from the University of Guelph in Environmental Science and a Ph.D. from the University of Toronto in Chemistry.

Tiered Approach for Human Health Risk Assessment: Case Study for Two Remote Sites
Tania Noble, Gillian Dunlop, Katherine Ketis, Stephanie Demers,
Stantec Consulting Limited
The objective of this presentation is to share a case study to show how area-weighted concentrations can be applied in human health risk assessment.  

At remote sites, where excavation and removal of contaminated soil may be difficult and costly, accurately evaluating risks is especially important. Health Canada has issued a draft memorandum (October 2016) that recommends a tiered approach to evaluating chronic and less-than-chronic exposure. The guidance was provided due to concerns associated with potentially underestimating chronic health risks by time averaging exposures, as well as missing acute/sub-chronic effects. To evaluate exposure to non-carcinogenic effects, the first step is to estimate unadjusted daily exposure (i.e., using an exposure term of 1) and calculate risks with a chronic toxicity reference value (TRV) (i.e., Tier 0). For contaminants of potential concern (COPC) where risks exceed target levels, a more detailed evaluation is required. For each receptor, consideration is made as to whether exposures are intermittent (i.e., period of exposure followed by longer periods of non-exposure), and the exposure period is categorized as chronic (greater than 90 days), sub-chronic (greater than 14 days and less than 90 days) or acute (less than 14 days). For receptors with chronic exposures (e.g., leaseholder residents), the appropriateness of dose averaging is evaluated based on chemical-specific toxicity information. For receptors with repeated intermittent or short-term exposures (e.g., site visitors, maintenance workers), the next tier of risk assessment (Tier 1) is conducted by selecting TRVs which align more closely with the duration of the sub-chronic or acute exposure period. For intermittent exposures, the assessment must also consider whether comparison to a longer-duration TRV relevant to the entire exposure duration is required.

The Health Canada guidance was applied to assess risks associated with non-carcinogenic COPCs at two remote lightstation sites. This presentation will outline the tiered approach for human health risk assessment that has been applied at two Fisheries and Oceans Canada sites in Ontario (the Slate Islands Lightstation Site and the Great Duck Island Lightstation Site).

Tania Noble, Geographic Technical Lead for Site Assessment, Remediation, and Emergency Response, Stantec Consulting Limited
Tania Noble is Stantec Consulting Limited’s Geographic Technical Lead for Site Assessment, Remediation, and Emergency Response in Canada. Tania is responsible for the technical quality of over 250 environmental site assessors, risk assessors, remediation specialists and support staff, including development of internal standards and tools, and overseeing training programs. Since joining the company in 1997, her professional experience has been primarily in the fields of human health and ecological risk assessment and water resources, with particular expertise in assessment and management of contaminated sites and multi-media fate and transport modelling. Her experience spans a wide range of contaminants at sites from Newfoundland and Labrador to British Columbia and Northern Canada, as well as the United States. In recent years, Tania has developed particular expertise in the assessment of potential health effects associated with air emissions and releases from planned projects as part of various provincial and federal environmental assessment regulations. She has led, and continues to lead, these complex multidisciplinary environmental health assessments and facilitate community consultation and risk communication through open houses, workshops, and formal public meetings.

Quantitative Risk Assessment and its Applicability to Mine Closure and Long-Term Care
Lynn Pilgrim1 and Emma Mckennirey2
2Crown-Indigenous Relations and Northern Affairs Canada
The objective of this presentation is to provide an overview of the quantitative risk assessment for the Giant Mine Remediation Project, including describing the QRA process, how the specific requirements of the environmental assessment were incorporated into the scope, and the next steps in the process to support project approvals, and will discuss how the QRA will be used as a tool to help guide the closure and reclamation plan in terms of decision making and mitigation measures.  

A condition (Measure 5) of the environmental assessment (EA) requires the Giant Mine Remediation Project (GMRP) to complete a quantitative risk assessment (QRA) prior to issuance of the projects water license, which is a prerequisite to the commencement of any remediation activities of the former Giant Mine site. The former mine site is located within the city of Yellowknife boundary about 5 km north of the city centre, approximately 1.5 km from the Yellowknife Dene First Nation (YKDFN) community of Ndilo and 9 km from the YKDFN community of Dettah. Arsenic trioxide, a known carcinogen, was created during mining operations. There are underground chambers and stopes between 80 and 250 feet below the surface that have been built for storing approximately 237,000 tonnes of the arsenic trioxide waste, which will be further contained by freezing the rock around the chambers.

A QRA is a systematic approach to estimating the likelihood and consequences of hazardous events, and expresses the results quantitatively as risk to people, the environment or a business. In order to meet the requirements of Measure 5 of the EA, the QRA included the assessment of impacts to human health, the environment, socio-economic and financial components of the local region that may be affected. Assessing impacts to Way of Life (gonàowo), including traditional knowledge and traditional land use, was added to the scope in recognition of the Indigenous peoples who live in the Yellowknife region, including Ndilo and Dettah. The result is a new approach to applying QRA with a more holistic scope than traditional QRA.

A closure and reclamation plan (CRP) for the project was submitted in 2019 for review. The CRP provides a description of the activities proposed to remediate the site and presents actions for the ongoing management and mitigation of environmental effects. The QRA assesses the long-term resiliency of the CRP as the basis for the risk assessment as the QRA scope consists of assessing risks post-remediation (2032 and beyond), including specific consideration and analysis of:

• Failure scenarios – risks associated with the failure of components of the CRP (e.g., dam failure); and,
• Residual risks – risks associated with the former mining operation that remain after remediation is complete (e.g., contaminated soil).

The findings of the QRA will also be used as a tool to help guide the CRP in terms of decision making and mitigation measures.

It is anticipated that the QRA will be revisited at a minimum of every 20 years in conjunction with independent review of the GMRP to ensure that the project strives to meet the closure objectives, ensuring the continuation of ongoing management and mitigation, as well as continued research into any other innovative techniques to the storage of arsenic trioxide underground.

This presentation will describe the QRA process, how the specific requirements of the EA were incorporated into the scope, and the next steps in the process to support project approval.

Lynn Pilgrim, Environmental Engineering Direct Lead – Maritimes, Wood
Lynn Pilgrim, P.Geo., is a Senior Environmental Professional with 18 years of experience in environmental consulting, managing people and projects, as well as providing technical guidance and senior review for a wide range of projects utilizing principles of environmental assessment throughout Canada. Lynn’s primary expertise is in the area of Phase I/II and III environmental site assessments, human health and ecological risk assessments, remedial options analysis and risk management plans. Her background in geochemistry is essential in understanding contaminated sites, commercial/industrial operations and processes and contaminant transport. Her communication and leadership skills are highly regarded as she excels at bringing together diverse teams of experienced professionals with the necessary qualifications to meet the needs of specific projects and clients. A prime example of this is the quantitative risk assessment. This project is a collaborative project including team members from Wood from both Canada and the US, several project team members from Crown-Indigenous Relations and Northern Affairs Canada from both Ottawa and Yellowknife, and the skills of an engagement team, Stratos, based out of Ottawa.

Solutions for Protecting Aquatics and Drinking Water Near Giant Mine
Tasha Hall1, Emma Mckennirey2, Jennifer Singbeil3, Alison Snow1
1Golder Associates Ltd.
2Crown-Indigenous Relations and Northern Affairs
3Public Services and Procurement Canada
The objective of this presentation is to outline various levers used to protect downstream aquatics and drinking water, using Giant Mine as a case study that offers potential solutions for other mines facing similar water quality challenges.  

Finding sustainable closure solutions that protect downstream aquatic environments at major contaminated mines is already a challenge but doing so at a mine situated within city limits requires additional care. Great Slave Lake, which receives contaminated water from Giant Mine, provides drinking water for the city of Yellowknife, sport and subsistence fishing and recreational activities like swimming and boating. The stockpile of mobile soluble arsenic is a risk to the residents of Yellowknife and two nearby First Nation communities. Treatment infrastructure is aging and is unable to treat arsenic to concentrations low enough to meet national aquatic life or human health guidelines before discharge. Multiple interest groups (residents, the City, First Nations) asked for improvement in water quality and protection of Great Slave Lake. In 2014, the Canadian government responded to an environmental assessment measure and agreed to remediate the site and treat mine water to drinking water standards for arsenic. Giant Mine presents a unique legacy mine case where effluent needs to be treated to drinking water standards.

The proposed major reduction in arsenic is a positive, socially responsible decision, but makes for a very complex closure plan. Metal concentrations need to be reduced by orders of magnitude between the mine site and Great Slave Lake. Water treatment alone proved not to be the solution. Several integrated engineering and environmental practices were required. A large-scale, multi-year water monitoring and modelling program was conducted in Great Slave Lake to support the overall closure plan. A new, three-dimensional linked water quality model framework was developed. A highly debated "combined mixing zone" was designed to manage site runoff and treated effluent, which has not previously been employed in the Northwest Territories. Finally, effluent quality criteria were developed by balancing practical achievability and downstream environmental protection. Expectations are high, and the closure plan commands a high public profile. The project team is confident these approaches will protect Great Slave Lake and the City's drinking water source.

Tasha Hall, Water Quality Specialist, Golder Associates Ltd.
Tasha Hall is Water Quality Specialist with over 18 years’ experience with Golder Associates Ltd. in Calgary, Alberta, Canada. She has broad range of skills related to water protection but specializes in developing effluent quality criteria (including runoff and seepage) for mining and closure projects, designing and implementing environmental baseline and aquatic monitoring programs, regulatory risk management, and spill response.

DNAPL in Fractured Bedrock: An Approach to Build a Complex Conceptual Site Model Supporting the Development of a Remedial Options Analysis and Remedial Action Plan/Risk Management Measures Tailored to HHRA Findings
Jean-Philippe Gobeil, Stantec Consulting Limited
The objective of this presentation is to share a case study demonstrating an application of this approach to a site located at CFB Trenton featuring chlorinated solvent impacts in overburden and fractured bedrock and potential unacceptable risk via the vapour intrusion pathway for nearby building occupants.  

Building a robust conceptual site model (CSM) for sites featuring releases of dense non-aqueous phase liquid (DNAPL) in fractured bedrock can be a daunting task due to the complexity of fracture networks and the propensity of DNAPL to migrate downward following fractures and/or high permeability zones until they reach aquitards and/or structures that impede its movement. The level of effort and expenditure required to reduce the uncertainty and refine a CSM to support the development of a remedial options analysis (ROA) for such sites is typically very substantial. Focusing field investigation efforts on relevant human and ecological exposure pathways and using diagnostic tools to help target intrusive investigations on key source areas and migration pathways, can significantly improve the outcome of a remediation or risk management project. Prioritizing and sequencing the field program in this manner allows for the allocation of limited resources strategically to inform the development of a CSM, which in turn is better suited to provide answers to questions that are critical to the evaluation and design of remedial or risk management options that can address potential risks identified in a risk assessment. This presentation provides a case study demonstrating an application of this approach to a site located at CFB Trenton featuring chlorinated solvent impacts (DNAPL) in overburden and fractured bedrock and potential unacceptable risk via the vapour intrusion pathway for nearby building occupants. Diagnostic tools used to refine the selection of drilling and monitoring well locations at CFB Trenton included passive soil gas surveys, surface geophysical surveys and downhole geophysics surveys. Passive soil gas surveys were used to identify potential source areas of chlorinated volatile organic compounds (CVOC) and related shallow groundwater plumes. Surface geophysical surveys included seismic refraction and resonance surveys that allowed for the identification of potential investigation targets by mapping structures in the subsurface where DNAPL may have accumulated. Seismic refraction surveys were used to map the bedrock surface topography and identified low-lying areas where DNAPL may have pooled. Seismic resonance surveys were used to identify lithologies in the overburden and fractures or heavily weathered areas in bedrock that may have acted as DNAPL migration pathways or reservoirs. Downhole geophysics was used to identify water bearing fractures in bedrock in order to design multilevel monitoring wells, allowing for the assessment of the vertical distribution of DNAPL in bedrock at the site. Additional assessment methods to evaluate the biodegradation potential of CVOCs in order to support current and future ROAs for the site were also completed. The program included bio-trap sampling as well groundwater sampling and analysis of monitored natural attenuation (MNA) indicator parameters in order to assess the feasibility of biodegradation and MNA or enhanced MNA, as potential remedial options for the site.

Jean-Philippe Gobeil, Senior Hydrogeologist, Stantec Consulting Limited
Jean-Philippe Gobeil is a fully bilingual senior hydrogeologist with Stantec Consulting Limited’s Chicoutimi office. With over sixteen years of experience in the fields of hydrogeology and environmental site assessment, Jean-Philippe has worked on numerous hydrogeological investigations and on projects featuring large scale soil vapour monitoring, environmental site assessments, remediation/remedial options analysis, human health and ecological risk assessment, and water supply and construction dewatering for the purposes of permitting for large infrastructure and municipal programs. Jean-Philippe’s expertise includes the development of conceptual site models (CSM), completion of remedial options analyses, and the assessment of bioremediation potential for sites contaminated with chlorinated volatile organic compounds (CVOC) and petroleum hydrocarbons. He has provided technical expertise and support for projects and client sectors across Canada including First Nations Groups and numerous federal, provincial and municipal departments. Jean-Philippe is the prime hydrogeologist for a multi-year and multi-stage program currently being undertaken for chlorinated solvent impacts within overburden and fractured bedrock environments at CFB Trenton. Jean-Philippe’s diversified experience has provided him with unique insight into the completion of multidisciplinary projects requiring the construction of complex CSMs in support of remedial options analyses and remedial action/risk management plans.

How to Navigate Jurisdictional Differences in Risk Assessment Guidance and How These Differences Can Have Significant Implications on Risk Conclusions – A Case Study Using a Detailed Human Health Risk Assessment at a Former Military Airport
Brett Lucas, Ahmadreza Mehjoo, Blair McDonald
Golder Associates Ltd.
The objective of this presentation is to highlight how differences in regulatory guidance can have significant impacts on risk conclusions and provide an example on how these situations can be handled using a science-based approach.  

A preliminary quantitative risk assessment (PQRA) of the shoreline area of a local airport (confidential location) was previously conducted. The airport was constructed during World War II and had previously been used as a staging area for US Military operations during transport to Alaska. The site is currently the location of a local airport used primarily for chartered flights. The results of the original PQRA concluded that elevated concentrations of dichlorodiphenyltrichloroethane (DDT) in sediment and fish tissue could represent an unacceptable risk to human health. Golder Associates Ltd. (Golder) conducted a review of the previous PQRA and identified several data gaps and opportunities for refinement of the risk assessment. Golder conducted supplemental sampling (fish, surficial sediment, sediment cores, benthic invertebrates, and upland soil, groundwater, and porewater) using a tiered approach to manage costs while focusing analyses on key outcomes that would reduce uncertainty with respect to previously identified risk conclusions. A key objective of the current DQRA was to incorporate site-specific data to replace conservative assumptions made in the previous PQRA.

Due to the complex regulatory environment at the site caused by involvement and interests by multiple territorial and federal stakeholders, the human health risk assessment (HHRA) was complicated by jurisdictional differences in guidance related to whether DDT should be classified as a threshold (non-carcinogenic) or non-threshold (carcinogenic) acting substance. The results of the DQRA highlight how jurisdictional differences in risk assessment guidance can have significant implications on risk conclusions. Risk conclusions for human health differed in the DQRA depending on whether DDT was assessed as a carcinogen or as a non-carcinogen. This presentation will highlight how best to navigate these jurisdictional differences using a science-based approach and current best practices.

Brett Lucas, Environmental Scientist, Environmental Remediation and Water Group, Golder Associates Ltd.
Brett Lucas is an environmental scientist in Golder's Environmental Remediation and Water Group. He holds a Master's of Science degree in environmental toxicology and is a Registered Professional Biologist with the BC College of Applied Biology. His areas of expertise include human health and ecological risk assessments, aquatic and marine toxicology, environmental effects monitoring, toxicity identification evaluations, site-specific water quality guideline development, contaminated sites, and paleolimnology.

Recent Developments in Soil, Dust and Sediment Ingestion Rates for Consideration in HHRA
Ross Wilson, Wilson Scientific
Golder Associates Ltd.
The objective of this presentation is to provide an overview of the current science and important considerations in selecting ingestion rates for use in human health risk assessments.  

Although all relevant pathways need to be considered in a human health risk assessment (HHRA), the soil/dust/sediment ingestion pathway will often drive the results of at contaminated sites. Consequently, the value selected as the ingestion rate is very important. This presentation provides an overview of the current science and important considerations in selecting ingestion rates for use in HHRA.

In the case of soil ingestion, there have been a series of studies over the last 10 years that have provided new perspective on this pathway. The key types of studies that offer soil ingestion rate estimates include: tracer element studies; mechanistic hand-to-mouth models; and, correlational studies of blood measurements to soil concentrations. For toddlers, these studies seem to be converging on average soil ingestion estimates that are in the range of 20 to 40 mg/day while upper percentile estimates seem to be closer to the Health Canada assumption of 80 mg/day. Perhaps surprisingly, older children may consume soil at rates similar to toddlers; however, their greater body weight means that the older children do not often drive the results of the HHRA. Although there has been less focus on soil ingestion by teenagers and adults, it would seem that typical soil ingestion rates would be considerably less than the Health Canada assumption of 20 mg/day.

In addition to soil ingestion rates, there have been recent developments in the estimation of dust and sediment ingestion rates and these pathways can also be very important in the evaluation of human health risks at some contaminated sites. The literature seems to be suggesting that dust ingestion could be up to twice as great as soil ingestion. Expression of dust ingestion rates in units of both “mg/day” and “m2/day” offer risk assessors an opportunity to evaluate intakes using both bulk dust concentrations and surface loadings. In the case of sediments, the uniqueness of land uses at various sediment sites has resulted in expression of ingestion rates in units of “mg/hour”. It has been estimated that 11 hours per week of contact with sediment would result in exposures that are similar to those estimated using the Health Canada assumption of 80 mg/day for soil.

For soil/dust/sediment ingestion pathway, certain cautions need to be emphasized and understood in selection of the appropriate value for use in HHRA. It has generally been found that young children and older children will have the greatest ingestion rates due primarily to increased hand-to-mouth activities; however, it is possible that certain activities and occupations may result in adults having higher than typical rates of ingestion. In addition, presence of bare soils and activities that increase time spent in direct contact with soil can be very important.

Ross Wilson, Wilson Scientific
Ross Wilson is a board-certified toxicologist with 30 years of experience in human health risk assessment. In 2005, Ross was appointed by BC Ministry of Environment as an Approved Professional in risk assessment and from 2012 to 2016 served on the Board of Directors of the Society of Contaminated Sites Approved Professionals (CSAP) of British Columbia. In 2014, Ross was appointed to the editorial board of the international journal Human and Ecological Risk Assessment (HERA).

In the case of expertise in soil, dust and sediment ingestion rates, he has assisted Health Canada on several projects over the last ten years. With Health Canada as co-authors, he published Wilson et al. (2013: Revisiting Dust and Soil Ingestion Rates based on Hand-to-Mouth Transfer) which is cited as a key paper in the US Environmental Protection Agency Exposure Factors Handbook chapter 5 update. He also published a paper on sediment ingestion rates in 2015 (with Health Canada as co-authors) and dust ingestion rates in units of m2/day in 2016. In the case of evaluation of methylmercury in seafood, Ross has been involved in several projects over his career. Since 2011, he has attended all meetings of the International Conference on Mercury as a Global Pollutant (ICMGP).

An Innovative Risk Assessment Approach to Derivation of Site-Specific Toxicity Reference Concentrations for Petroleum Hydrocarbon Vapour Mixtures in Indoor Air
Ivy Liu, David Tarnocai, Chris Bestfather, Janice Paslawski
The objective of this presentation is to provide an alternative approach, which is more site-specific and less likely to be overly conservative, for indoor air inhalation risk evaluation on petroleum hydrocarbon vapour mixture.  

Conventional estimates of exposure to petroleum hydrocarbon (PHC) vapour (i.e., from gasoline) is completed through evaluation of volatile aliphatic and aromatic PHC subfractions within a carbon (C) range of C6-C16. However, it is known that PHC vapour is a complex mixture comprised predominantly of volatile subfractions within C3-C12 (i.e., >90% weight in the vapour phase), of which C5-C12 occupies >80% of the vapour composition. The Canadian Council of Ministers of the Environment (CCME) adopted reference concentrations (RfCs) for aliphatic C6-C8, C>8-C10, C>10-C12, and C>12-C16; aromatic C>7-C8, C>8-C10, C>10-C12, and C>12-C16 hydrocarbon ranges from the Total Petroleum Hydrocarbon Criteria Working Group (TPHCWG) RfC development document Volume 4. Therefore, vapour inhalation exposure risk characterization for human health is completed on a subfraction basis and then summed up to superfractions F1 and F2. This approach is considered conservative and likely to overestimate the actual risk to a PHC vapour mixture as each subfraction is treated as an individual group of compounds, complex interactions among all volatile subfractions are ignored, C5 range compounds are absent from the risk characterization. In this study, SNC-Lavalin presents an innovative alternative approach to derive a site-specific weighted RfC for a PHC vapour mixture (i.e., C5-C12) using the available fraction specific RfCs from the TPHCWG. The methodology is briefly described below:

1. Aromatic and aliphatic subfraction concentrations within the C5-C12 range from an indoor air or soil vapour sample are identified, the subfractions molecular weights are adopted from CCME and the site-specific relative weight % of each aliphatic and aromatic subfraction are then calculated;
2. TPHCWG fraction specific RfCs and the estimated weight % of each subfraction can then be used to calculate the weighted RfC of the mixture C5-C12 range using this formula: Weighted RfC=1/([(weight% of aliphatic C5-C8)/(C5-C8 aliphatic RfC) + (weight% aliphatic C9-C10)/(C9-C10 aliphatic RfC) +(weight% of aromatic C>7-C8)/( C>7-C8 aromatic RfC)+⋯]); and,
3. Targeted individual compounds known to pose carcinogenic risk, such as benzene, or compounds that may pose other potential hazards are identified and excluded from the derivation of the weighted RfC.

The holistic approach of using a derived weighted RfC for risk characterization would reflect the exposure to most volatile PHC mixture as a whole, based on their site-specific compositions due to weathering process changes of the original mixture, mixture origin, and their refinery processing. For PHC vapour exposure in indoor air, instead of evaluating each aliphatic and aromatic subfraction separately, the derived site-specific weighted RfC can be used to determine the exposure risk to total C5-C12. Similar method was applied to Shell Canada Products terminal gasoline in Ontario.

Ivy YuXia Liu, SNC-Lavalin
Ivy YuXia Liu (M.Sc., P.Geo.) is an environmental scientist, holds a master’s degree in Earth Science specialized in environmental toxicology, with ten years of environmental consulting experience focusing on human health and ecological risk assessment. She has also worked on a wide range of environmental projects such as biological studies, phased environmental site assessments, and toxicological studies. She has conducted human health and ecological risk assessments of various complexities under the Federal Contaminated Sites Action Plan for sites all across Canada such as abandoned mine sites, landfills, airports, Fisheries and Oceans Canada (DFO) navigation channels, highway maintenance yards, RCMP detachments, weather research stations, federal office building complexes, marinas, for several federal departments/agencies such as the National Capital Commission, Environment and Climate Change Canada, National Research Council, Transport Canada, DFO, Health Canada, RCMP, Department of National Defence, Public Services and Procurement Canada, Agriculture and Agri-Food Canada and Indigenous Services Canada. The contaminants she has conducted risk assessments on include but are not limited to petroleum hydrocarbons, metals, polycyclic aromatic hydrocarbons, pesticides, dioxins/furans, various other persistent organic pollutants, and volatile organic carbons.

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