Soil sterilant are non-selective residual herbicides that render the treated soil unfit for plant growth for relatively long periods of time. Sterilant were commonly used in Alberta from the 1960s to late 1990s for non-selective vegetation control on oil and gas wells, gas processing plants, rights-of-way, railways, saw mills, pulp mills, and electrical utility sites ([1], [2], [7]); residues may also be found at agrochemical dealer sites ([8]). Sterilant treated areas can remain devoid of vegetation for many years depending upon the type, rate and frequency of application of soil sterilant and the climatic conditions. Soils treated with sterilant can be a source of contamination through leaching, surface runoff and wind dispersion of the sterilant to adjacent land and waterbodies. Reclamation and remediation issues arise when a treated site is no longer needed for industrial use and the site must be returned to equivalent land capability. At present, many of these sites either remain as liabilities for industry or impacted soil is excavated and disposed at a landfill.

In Alberta alone, awareness of the issues associated with soil sterilant is on the rise as more legacy oil and gas sites (constructed prior to 1970; operational prior to 1990), where sterilant were typically used, are abandoned and slated for remediation and reclamation. Cotton and Sharma ([1]) estimated the number of oil and gas sites in Alberta with soil sterilant residues to be as many as 61,750 sites. Historical work has focused on upstream oil and gas sites, however there are many others in the province. It’s estimated that there are well over 3,000 additional sites associated with distribution sites, pipelines and electric metering stations and many other industrial facilities not yet identified. While a considerable amount of literature review, experimentation and operational activities have occurred over the past 20 years on this topic in Alberta, as of 2018, many of these sites are still in the queue for reclamation and remediation due to the recalcitrant nature of the contaminants that have impacted soil and groundwater and remain as liabilities for their owners.

Treatment proceeds via reductive dechlorination of the pesticides/herbicides followed by aerobic biodegradation of the partially or fully dechlorinated breakdown products. The soil amendment is typically applied at dosages of between 0.4% and 4% (w/w) and therefore causes very little, if any, increase in soil volume following treatment. Over the last 15 years, the technology has been used successfully for in-situ and ex-situ treatment of soils contaminated with a range of organochlorine pesticides (OCPs), including Chlordane, Lindande, DDT, Toxaphene, 2,4-D, 2,4,5-T, Atrazine, Dieldrin and Metolachlor, at sites in North America and Europe.

Jean Pare, vice-président, Chemco Inc.

Jean Pare, ing., possède un diplôme en génie chimique de l’Université Laval. Il participe depuis les 25 dernières années à l’évaluation, au développement, à la conception et à la promotion de technologies environnementales conventionnelles et novatrices. À titre de vice-président de Chemco Inc., ses responsabilités comprennent la conception de l’assainissement, l’analyse technique-économique et l’approvisionnement de technologies pour l’oxydation et la réduction chimiques, le lavage des sols et la biorestauration améliorée. L’année dernière, il a travaillé sur plus de 400 sites, appliquant son expertise à divers types de contaminants organiques et inorganiques dans le sol et les eaux souterraines. Il participe également à de nombreuses organisations environnementales, comme l’Association canadienne de réhabilitation des sites dégradés, le Canadian Brownfields Network, l’Environmental Services Association of Alberta, la British Columbia Environment Industry Association et Réseau-Environnement, où il est un membre actif des comités techniques et un conférencier fréquent sur des sujets techniques.

Per- and polyfluoroalkyl substance (PFAS) may be present in biosolid amended agricultural lands. PFAS in such soil can enter the terrestrial agricultural food chain and result in human exposure. This study develops risk-based soil screening values (SSVs) for PFAS, protective of human health due to direct soil contact, food consumption and ingestion of impacted potable well water through soil leaching of PFAS. The SSVs can be used as interim values for assessing soil quality at biosolid amended agricultural lands. We have followed the United States Environmental Protection Agency (US EPA) biosolid risk assessment guidance for the derivation of SSVs for three agricultural land uses:

• Farm: A crop producing farm, where residents (i.e., farmers) consume local crops and store-bought meat;
• Ranch: A cattle ranch, where residents (i.e., ranchers) consume local meat and store-bought crops; and,
• Mixed Farm and Ranch: A crop producing farm and ranch, where residents consume local crops and meat.

The PFAS concentrations in seven groups of vegetables/crops were estimated using transfer factors from literature studies on biosolid amended agricultural lands. The PFAS concentration in beef was modeled using feed to muscle transfer factor and cattle’s daily dietary intake. The short chain PFAS (C4-C7) were not detected in the muscle tissue samples of the literature study, therefore, the human exposure to the short chain PFAS via beef ingestion was assumed to be negligible. The exposure to short chain PFAS via food was assumed to occur only through crop ingestion pathway and ingestion of drinking water. The SSVs protective of the leaching pathway (i.e., protective of potable groundwater) were estimated using three default dilution attenuation factors (i.e., 1, 13 and 20) sourced from US EPA and New Jersey Department of Environmental Protection. Generic human exposure characteristics were used. No irrigation was assumed. A hazard quotient target level of 0.1 was used to be consistent with up-to-date risk assessment and to ensure conservatism. The SSVs were derived for perfluoroalkyl carboxylic acids (PFCAs) (C4-C14) and perfluoroalkane sulfonic acids (PFSA) (C4, C6, C8 and C10).

Based on generic assumptions, the derived SSVs protective of leaching pathway are the most restrictive SSVs for PFCA with carbon chain length <=9, while for longer chain PFCA (C>=10) and PFSA, the food pathway is the dominant human exposure pathway. These observations are based on generic assumptions used in the derivation of SSVs and a dilution attenuation factor of 20 (where the SSVs are above soil detection levels) and might not be valid for a specific site with characteristics different than input parameters used in the derivation of generic SSVs.

Considering only food consumption exposure pathway, the derived risk-based SSVs are more stringent for long chain PFCA for a “Ranch” than for a “Farm” agricultural land use, while the SSVs for short chain PFAS (C4-C7) are more stringent for a “Farm” than for a “Ranch” land use. These observations are consistent with limited data on the chain length and functional group dependency of transfer factors for PFAS. Further studies are recommended to improve the understanding of short chain bioaccumulation potential in farm animals. As expected, the “Farm and Ranch” land use has the most restrictive SSVs.

Elham Arbaban, Staff Environmental Engineer, Arcadis Canada Inc.

Elham Arbaban is an experienced environmental risk assessor with excellent understanding of Canadian and international guidelines for conducting human health (HH) and ecological (Eco) risk assessment (RA). She has > 9 years of consulting and research experience in the areas of environmental RAs, environmental exposure assessment, and environmental fate and bioaccumulation modeling. She has been involved in different areas of research including studying the fate and transport mechanisms of PFAS in environment and designing the sampling programs for PFAS. 

Elham provides technical scientific support for provincial and federal HH and Eco RAs for both public and private clients. She is experienced in the full life cycle of RA projects: including site characterization, data analysis and identifying any data gaps required to be addressed for the purpose of RA/record of site condition filing, HH and Eco RAs, developing site specific target levels and developing risk management plans.

Elham has been involved with the preparation of over 20 federal and provincial site-specific risk assessments. The sites were impacted by one or more groups of contaminants including petroleum hydrocarbons, chlorinated solvents, heavy metals, polycyclic aromatic hydrocarbons, pesticides, polychlorinated biphenyl and new emerging contaminants.

Rapid small-scale column tests (RSSCTs) are being used extensively for design on granular activated carbon (GAC) water treatment systems for per- and polyfluoroalkyl substance (PFAS). RSSCTs are tests that simulate the performance of a GAC media in a water treatment system at the lab scale by passing test water through GAC media and measuring inflow and outflow concentrations to assess effectiveness. RSSCT tests can be used to test different GAC to evaluate which GAC performs the best for a specific water chemistry. RSSCTs are based on the principle that the particle size of GAC media can be reduced and analyzed proportional to column size and flow rate, which maintains similar constraints and parameters to pilot- or full-scale operation.

RSSCT results for three GAC media using groundwater from a Canadian site will be presented, together with the computer model performance analysis for anion exchange (AIX) resin which may be used to complement GAC for this project. The goal of the RSSCT testing at the study site is to improve the performance of an existing water treatment system at removing PFAS. Site-specific influent data will be used in an industry-accepted empirical model developed specifically for AIX resin.

These results will be reviewed in the context of similar studies of the same GAC and resin materials and evaluate whether any commonalities of performance can be drawn from multiple site data sets. The field-scale design of the system based on the RSSCT and resin data will also be presented.

Benjamin Kapfenberger, Project Manager, Arcadis Canada Inc.

Benjamin Kapfenberger, Environmental professional holding an undergraduate engineering degree from the Munich University of Applied Science and a master’s degree in environmental science from the University of Toronto. He has over eight years of relevant project experience in environmental site investigations, soil and groundwater remediation, remedial system design, hydro-geological assessments and calculations, groundwater monitoring and modelling. He has completed a broad variety of PFAS related projects throughout Canada and Germany.

In-situ stabilization (ISS) presents a potential per- and polyfluoroalkyl substance (PFAS) soil source zone management alternative that eliminates ex-situ management of PFAS wastes while protecting groundwater from future leaching of PFAS from soil to groundwater. The process involves adding reagents to the soil that bind and immobilize PFAS to their surfaces via chemical/physical sorption. As part of a larger project for federal government departments, bench scale studies are being conducted on PFAS-impacted soils obtained from airport sites. The bench scale study will test three different stabilizing agents, at different ratios between 0.5% and 4% by weight. The use of Portland cement as an additional additive to increase the bearing strength of the treated soils will also be evaluated.

Bench scale studies at the lab scale will be used to identify an appropriate reagent mixture. A matrix of samples of impacted soil, select stabilizing agents and de-ionized water will be mixed in test tubes. Following centrifugation, each water sample will be submitted for total oxidizable precursor (TOP) Assay analysis. A larger batch of one or more of the best performing mixtures (i.e., those showing the lowest levels of leached constituents) will be mixed and undergo Leaching Environmental Assessment Framework (LEAF) method leachate testing (Method 1314). The leachate will be analyzed for TOP Assay.

Results of both preliminary and detailed tests will be presented, in the context of bench and field scale applications at other sites.

Benjamin Kapfenberger, Project Manager, Arcadis Canada Inc.

Benjamin Kapfenberger, Environmental professional holding an undergraduate engineering degree from the Munich University of Applied Science and a master’s degree in environmental science from the University of Toronto. He has over eight years of relevant project experience in environmental site investigations, soil and groundwater remediation, remedial system design, hydro-geological assessments and calculations, groundwater monitoring and modelling. He has completed a broad variety of PFAS related projects throughout Canada and Germany.

Recent studies suggest that toxic and highly persistent per- and polyfluoroalkyl substances (PFAS) are much more prevalent in soil and tissue than in water. The increasing length of perfluoroalkyl chain in PFAS is correlated strongly to lower solubility/higher adsorption behaviour of a particular PFAS molecule in the environment. This poses a significant challenge to developing analytical methods, especially for the extraction of PFAS from solid matrices. The adsorption and mobility of PFAS (perfluoroalkyl chain length C6-C14) through soil were investigated by rinsing a soil column with 60 mL spiked rainwater at pH 3, pH 10 and pH 5.3. PFAS which adsorbed onto the soil column were extracted using a conventional vortex/sonication method. Aqueous eluate and extracts were analyzed using liquid chromatography with tandem mass spectrometry (LC-MS-MS) and quantified using an internal standard method. PFAS with chain length C6-C9 migrated completely or partially through the column and were effectively extracted from soil with 100% recovery. However, long-chain PFAS (C10-C14) did not appear to migrate through the column and had less than 50% recovery from the soil. The same extracted soil was then subjected to high-pressure accelerated solvent extraction (ASE) which yielded 100% recovery for long-chain PFAS. By extension, the application of ASE for the extraction of PFAS from mussel tissue and cooking oil was also investigated. Oil samples were spiked at 10 ng/g and tissue samples spiked at 25 ng/g. These samples were incubated and then subject to ASE. Recoveries of PFAS from these matrices were acceptable for all analytes and were highest for C11-C14. Blanks contained no significant amounts of PFAS. The use of ASE for extraction of longer chain perfluoroalkyl acids (C16, C18), sulfonates and sulfonamides from solid matrices was also investigated. The results of this study will inform our understanding of how to evaluate the transport of PFAS through soil and the assessment of PFAS bioaccumulation in tissue and food.

Matthew MacLennan, Senior Scientist and Director of LC/MS Method Development, Pacific Rim Laboratories

Matthew MacLennan is Senior Scientist and Director of LC/MS Method Development at Pacific Rim Laboratories in Surrey, British Columbia, Canada. He has obtained ISO 17025 accreditation for PFAS testing in water and soil according to EPA 537.1 and ASTM methods. Matthew has five years’ experience analyzing complex contaminant mixtures such as naphthenic acids and oil sands process-affected water using capillary electrophoresis, time-of-flight mass spectrometry (TOFMS) and Orbitrap MS, working on conjunction with Environment Canada. Matthew obtained his PhD in Analytical Chemistry from the University of British Columbia in Vancouver, BC, Canada.

As our understanding of per- and polyfluoroalkyl substances (PFAS) environmental behaviour evolves, and the available analytical methods to detect and quantify PFAS improve, we must continue to adapt PFAS sampling programs to develop and maintain robust conceptual site models (CSMs), management plans, and courses of action for PFAS-contaminated sites. This presentation will focus on the field investigation and data interpretation challenges for initial testing programs under the Federal Contaminated Sites Decision-Making Framework to obtain valid datasets that have the confidence of all stakeholders in an evolving regulatory and analytical landscape.

Over 3,000 PFAS have been commercially produced, exhibiting a wide range of molecule size, functional groups, and physico-chemical properties. This often leads to difficulty in evaluating the validity of PFAS data obtained from contaminated sites with unknown mixtures of PFAS present. This is particularly challenging on Canadian sites, since many PFAS are distributed, stored, and used in Canada that were manufactured elsewhere. While sampling protocols are established for more ubiquitous PFAS, field protocols for more recently synthesized PFAS or those specific to one or a few manufacturing processes are often lacking. The types of PFAS expected to be present at a site must be considered when developing sampling plans and assessing sample validity, for example:

1. How do the PFAS partition between aqueous and particulate phases in water samples?
2. How do the PFAS interact with the air-water interface?
3. How do the PFAS interact with typical sampling apparatus and materials?
4. What are the background levels of the PFAS in the area being sampled? How does this affect quality control?
5. What are the achievable reporting limits for the PFAS compared to expected environmental concentrations and regulatory expectations?
6. How stable are the PFAS in the sampled environmental media?

Drawing on experience from existing PFAS-contaminated sites, this presentation will discuss approaches to address these questions to better inform sampling methods and overall validity of PFAS data. Improved understanding of PFAS sample validity can support the maintenance of more robust CSMs, allowing for the development of more effective remediation strategies and more accurate PFAS signatures for individual source areas.

Carol Cheyne, Environmental Scientist, Geosyntec Consultants

Carol Cheyne is an environmental scientist with a chemistry specialization at Geosyntec Consultants. She has over five years of experience using her analytical chemistry and isotope geochemistry background to support the evaluation of contaminated sites in Canada and the United States. Carol specializes in the investigation of emerging contaminants to support the development of robust conceptual site models and effective remediation strategies, and in forensics investigations to delineate source signatures using multiple lines of evidence.

Per- and polyfluoroalkyl substances (PFAS), as an emerging contaminant, provides unique challenges within the Federal Contaminated Sites Action Plan (FCSAP) Program as the science is still evolving, there are often multiple sources contributing to plumes, understanding fate and transport is complex and variables are largely unknown, standard remediation technologies are generally not effective requiring non-standard approaches involving emerging technologies, and it is difficult to communicate to stakeholders what is and is not known from a health perspective. While it is possible to measure many PFAS substances in the environment, the understanding of the toxicology and the fate and transport of these substances are far behind the advances in analytical chemistry. As science evolves, our understanding changes. How does one manage a site and stakeholder concerns within a constantly changing scientific and regulatory environment? Topics that will be discussed will include:

• Changing guidelines and jurisdictional differences;
• Contaminant fate and transport;
• Bioconcentration and biomagnification;
• Multiple sources; and,
• Source or exposure control for mitigation.

This presentation highlights the challenges that have been faced while managing PFAS contaminated sites and will provide insights and considerations that should be taken into account when assessing PFAS sites under the FCSAP program and assessing and managing risk to human and ecological receptors.

Jennifer Kirk, National Risk Assessment Lead, Arcadis Canada Inc.

Dr. Jennifer Kirk holds a Doctor of Philosophy in Environmental Toxicology and Microbiology and a Bachelors of Science (Honours) in Environmental Toxicology, both from the University of Guelph. Jennifer is a Senior Risk Assessment Specialist and National Team Lead for Human Health and Environmental Risk Assessment. Jennifer has over 20 years of toxicology experience and over 15 years of risk assessment experience. Jennifer also has research and testing experience with a wide range of contaminants, completes technical reviews of risk assessments and risk management plans and has extensive public speaking experience. Jennifer is a reviewer for the Ontario Ministry of the Environment, Conservation and Parks (MECP) for risk assessments completed under Ontario Regulation 153/04 and for the journals of Environmental Toxicology and Human and Ecological Risk Assessment. She was a member of the MECPs Tier 2 Risk Assessment Working Group and the Toxicity Reference Value Working Group.

Beginning in September 2018, SNC-Lavalin Inc. was tasked to complete source control water treatment of surface water containing hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), metals, and per- and polyfluoroalkyl substances (PFAS) contamination at the firefighting training area (FFTA) of CFB Comox, Lazo, BC. The objective of the work was to trial water treatment using granulated activated carbon (GAC) to evaluate performance, inform long term treatment options at the base, and optimize the treatment approach while additional site remedial options could be assessed.

Fire training exercises using aqueous film forming foam (AFFF) were conducted at the FFTA at CFB Comox from the late 1960s until 2009 and fire training using water only continued until 2017. The site consists of a gravel-surfaced area draining to a retention pond. The surface water and soils within the FFTA are an area of environmental concern and a potential source for PFAS in surface water and groundwater. As PFAS compounds are highly recalcitrant, there remain challenges to the application of traditional remediation technologies. For this scope, SNC-Lavalin trialed new and existing technologies and adapted a traditional water treatment approach for treatment of PFAS contamination at the site.

SNC-Lavalin reviewed options for the treatment of PFAS impacted surface water at the FFTA retention pond and designed a water treatment process using components of an existing water treatment system and additional equipment. Treatment trials were subsequently completed with GAC to evaluate performance. Performance of the GAC removing different PFAS compounds was evaluated while treating ponded liquids, as well as liquids generated from a recent spill from an AFFF contaminated tank at another area of the base.

In addition to PFAS treatment with GAC, an evaluation of PFAS treatment with advanced oxidation was also evaluated. Surface water samples were collected for trialing the treatment of a third parties proprietary process for oxidizing PFAS compounds. While results showed a potential for achieving a decrease in dissolved phase PFAS compounds, the results weren’t conclusive enough to warrant full scale application without further evaluation.

Overall, treatment of PFAS impacted liquids with GAC was determined to be effective at removing various PFAS compounds, however, requiring a significant supply and disposal of GAC.

Results from the treatment of PFAS with GAC and with advance oxidation are presented along with considerations for improving performance and optimizing the long-term treatment of these compounds at the site. Additional options for the long-term treatment and management of PFAS compounds at the site will also be presented.

Francis Galbraith, Senior Remediation Specialist, Environment and Geoscience, SNC-Lavalin Inc.

Francis Galbraith, P.Eng., is a mechanical engineer and environmental scientist with over 18 years of environmental consulting experience. Francis has extensive experience with mitigating impacts and treating contaminants having designed, installed, and applied a wide variety of remediation approaches across Canada’s north and west. He has evaluated treatment and remediation options for a host of sites and is very knowledgeable in the considerations and limitations of applying associated technologies. Experience in pilot testing remediation and treatment options has provided him with insight into site conditions and equipment requirements for making a full-scale application successful, or for identifying issues that preclude effective remediation. Finally, his experience in the ongoing operation and maintenance of in-situ remediation and water treatment systems along with the completion of chemical injection programs has provided him with an opportunity to identify means for optimizing remediation, ensuring equipment or programs operate efficiently and remediation objectives are achieved while minimizing the input of resources.

Health Canada’s Contaminated Sites Division has updated its 2010 Supplemental Guidance for Soil Vapour Intrusion Assessment at Contaminated Sites to incorporate the most recent science, and, to the level practicable, adopt elements from A Protocol for the Derivation of Soil Vapour Quality Guidelines for Protection of Human Exposures via Inhalation of Vapours (CCME, 2014). This Health Canada supplemental guidance allows for incorporation of consistent scientific information in evaluating potential human health risks associated with the inhalation of indoor air vapours originating from subsurface contamination in groundwater or soil at federal contaminated sites.

The highlights of the updated guidance will be presented and include the following:

• A multiple lines of evidence approach to allow for flexibility in assessing the vapour intrusion pathway at federal contaminated sites.
• Additional detail on the recommended environmental data to assess the vapour intrusion pathway.
• Generic default input values for the Johnson & Ettinger (1991) model harmonized to the degree practicable with those in the CCME (2014) protocol for the derivation of soil vapour quality guidelines.
• Presentation of the J&E-derived vapour attenuation factors in a simplified and user-friendly manner.
• An update to the vertical and lateral screening distances for volatile contaminants which bioattenuate.
• An updated approach for adjusting attenuation factors for bioattenuation.
• Additional detail to guide the use of default sub-slab attenuation factors adopted from CCME (2014).

Christine Levicki, Environmental Specialist, Contaminated Sites Division, Health Canada
Christine Levicki is an Environmental Specialist with Health Canada's Contaminated Sites Division.

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 transportation 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 and ecological receptors. The previous PQRA theorized that the likely source of DDT to the aquatic environment was a combination of groundwater discharges from upland landfills, and historical loading of DDT as a result of leakage from improper disposal of drums in the adjacent lake. Golder Associates Ltd. (Golder) conducted a review of the previous PQRA and identified several data gaps and opportunities for refinement of the conceptual site model and 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 observed during the staged processing of the data. They then used the data collected during the supplemental sampling to refine the conceptual site model to provide direction for a detailed quantitative risk assessment (DQRA). The intent of a conceptual site model is to help communicate the relationship between contaminant sources, pathways and receptors. During the data gap assessment, a total of four plausible scenarios were identified for release of DDT to the lake including: groundwater discharge from upland dump sites; contaminated soil runoff from affected upland areas; release from improper disposal of drums in the lake; and, direct aerial application. It was determined through review of the available literature that aerial application of DDT to the lake may have occurred between 1949 and 1969 to control insects.

The sampling data confirmed that elevated DDT concentrations in sediment and fish tissues were found within the area of interest, however significant concentrations were also found at other in-lake locations and at a regional reference lake. The results highlight the importance of properly developing your conceptual site model to understand contaminant release mechanisms and exposure pathways. A properly developed conceptual site model is key to accurately investigating and characterizing risk and has important site management implications. The results of this investigation were important in identifying that observed contamination may be the result of a larger regional condition influenced by historical aerial application of DDT. These conclusions have significant implications for remediation planning because without the regional context identified in the updated conceptual site model, reclamation activities would have likely focused on a more localized approach (e.g., dredging), which would not have effectively managed the full extent of contamination.

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.

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 transportation 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 and ecological receptors. The previous PQRA theorized that the likely source of DDT to the aquatic environment was a combination of groundwater discharges from upland landfills, and historical loading of DDT as a result of leakage from improper disposal of drums in the adjacent lake. Golder Associates Ltd. (Golder) conducted a review of the previous PQRA and identified several data gaps and opportunities for refinement of the conceptual site model and 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. The goal was to avoid unnecessary physical remediation of areas where risk from contamination could be managed in place. The DQRA used a modified weight-of-evidence approach to integrate sediment chemistry, toxicity, and benthic community data into risk conclusions for benthic organisms that aligned with the updated understanding of the conceptual site model. This approach provided clarity on the level of sediment contamination, the likely source, and the bioavailability of DDT in sediments. Risks to fish were evaluated using a chain of evidence approach to integrate various lines of evidence related to dietary exposure, bioaccumulation and fish health. The results confirmed that northern pike, lake trout, and whitefish were accumulating DDT in their tissues, although direct effects on fish health indices were less apparent. These fish tissue results were then used to assess potential health risks to humans and semi-aquatic wildlife (mammals and birds) from potential exposure to DDT accumulating in the food-web.

The sampling data confirmed that elevated DDT concentrations in sediment and fish tissues were found within the area of interest, however significant concentrations were also found at other in-lake locations and at a regional reference lake. The DQRA determined that ecological health risks were less than previously reported in the PQRA. The results highlight the importance of selecting appropriate lines of evidence that align with a robust understanding of the conceptual site model. By continually referring back to the conceptual site model (i.e., source and exposure pathways) at each stage of the risk assessment, uncertainty in risk conclusions were reduced.

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.