British Columbia Mine Reclamation Symposia

Risk ranking methodology for abandoned mine sites in B.C. Power, B. 2009

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RISK RANKING METHODOLOGY FOR ABANDONED MINE SITES IN B.C.   B. Power1 A. Fikart1 M.J. Tinholt2 R.M. Wilson2 G.G. Stewart3 G.D. Sinnett3   1Azimuth Consulting Group Ltd #218-2902 West Broadway Vancouver, BC  V6K 2G8  2SNC Lavalin - Morrow Environmental Inc. 385D Baker St. Nelson, BC  V1L 4H6  3 Ministry of Agriculture and Lands, Crown Contaminated Sites Branch 4th Floor – 780 Blanshard Street Victoria, BC  V8W 2H1  ABSTRACT  The Crown Contaminated Sites Branch (CCSB) of the Ministry of Agriculture and Lands (MAL) manages contaminated sites on Crown land where responsibility has defaulted to the Province.  CCSB uses a multi-step prioritization process to identify and screen candidate contaminated sites, one of which is the Risk Ranking Methodology (RRM).  Initially developed for MAL’s mines portfolio, the goal of the RRM is to provide a scientifically based method for evaluation and ranking of candidate Crown contaminated sites for potential risks to human health and the environment.  MAL’s RRM has two components: (1) a risk ranking support tool (spreadsheet and documentation, known as the “Tool”) and (2) a workshop process.  The Tool considers human health and ecological aspects separately.  It calculates “weighted” chemical concentrations for various media, and then a screening quotient is determined using specified screening values.  In addition, a series of important “flags” specific to the values being protected (e.g., humans, fish, listed species) are used to characterize the site.  The RRM generates a comparative summary of the various lines of evidence for each site which is then used to support an expert process workshop to direct management decisions for undertaking additional site investigations and remediation.  INTRODUCTION  The Crown Contaminated Sites Branch (CCSB) of the Ministry of Agriculture and Lands (MAL) operates under a policy framework that provides an approach to managing contaminated sites on Crown land where responsibility has defaulted to the Province.  CCSB has focused on historic mine sites because of their high potential for metal contaminant effects and the fact that this group of sites has not been under active risk management until recently.  To aid in the management of historic mine sites, CCSB has developed a multi-step process for prioritizing candidate contaminated sites, as described in Stewart (2007).  CCSB uses a coarse screening process known as the Historic Mines Sites Atlas1 to provide relative ranking related to potential risk to human health and the environment for approximately 2,000 known historic mines in the province, using readily available geo-referenced  information.  The highest-ranked sites are then visited by field crews to undertake limited environmental investigations (Preliminary Site Investigations—PSIs).  The Atlas and PSIs provide the information and data that are available to further prioritize the mine sites for management action.  This paper reports on one component of CCSB’s overall site-prioritization process, known as the risk ranking methodology (RRM). The stated goal of the RRM is “to provide a scientifically based, defensible and systematic methodology for the evaluation and ranking of priority Crown contaminated sites based on potential risk to human health and the environment.”  Over the past year, CCSB has focused on the development and implementation of the RRM, to aid in prioritizing historic mine sites with respect to contamination and potential impacts to human health and the environment.  It is important to note that CCSB’s historic mine portfolio bridges two distinct areas of practice—contaminated sites and mines, both of which have their own regulatory regimes.  The kind of information available to support ranking was at the level of “preliminary site assessment” (i.e., historical review of site use, followed by sampling of surface soils/sources and surface water to target areas of potential environmental concern).  Also, the RRM does not address mine safety issues, which, under the Mines Act, are under the authority of the Ministry of Energy, Mines and Petroleum Resources.  The RRM is described in more detail herein, but is essentially is a two-step process (Figure 1):  1. Risk Ranking Support Tool and underlying documentation (referred to as the Tool), which automates use of information from the preliminary site investigations (PSIs) to generate an output that describes various measures of potential risk of chemical contamination to humans and ecological systems.  2. A workshop process for risk ranking, which is an expert-based process that uses the outputs of the Tool for making recommendations to CCSB on ranking and management actions at contaminated sites.  This paper focuses on the first of these two steps, describing the development process and then the RRM itself.  It concludes with a summary of the next steps for this work.  1 Historic Mines Atlas Database is a database jointly developed by the Ministry of Energy, Mines and Petroleum Resources and Environment Canada.  For more information, see  Note that in 2007, the Atlas is being revised and moved over to a different location, so the link provided here may be out of date at the time of publication of this paper.     Figure 1:  Conceptual Overview of RR Support Tool Framework DEVELOPMENT OF THE RISK RANKING METHODOLOGY  Close liaison and communication within the RRM development team and with MAL CCSB were important to tailor the Tool and process to CCSB’s needs.  It was recognized early on that contaminated sites, and mine sites in particular, are generally not one homogenous unit, but often have multiple contaminated areas within the site (e.g., tailings, waste rock, mine workings, open pits, related mine infrastructure such as mill sites and assay labs).  In addition, risks to receptors (humans and ecological systems) will vary depending on the type and magnitude of chemical concentrations and receptor exposure pattern (e.g., frequency or type of use, location of a contaminated area next to or overlapping with sensitive habitat such as riparian areas or in areas used as rangeland).  The RRM was developed through the following, step-wise, process: • Review other risk ranking systems used in other jurisdictions or applications to identify good practices and learn from their experiences • Prepare and discuss an options analysis for CCSB’s RRM • Identify the factors that could be used to rank the sites • Develop prototype risk ranking support tool (spreadsheet, referred to as the “Tool”) • Refine and test the Tool • Prepare documentation • External review of Tool (and documentation) • Development of a workshop process to translate the Tool’s outputs into recommendations on prioritized management actions (underway at the time of publication)  One of the first steps in the development process was to review other risk ranking systems, resulting in a review of good practice (Power and Fikart., in preparation).  We reviewed the literature, talked to practitioners and surveyed other risk ranking methods to develop principles of good practice that would form the basis for MAL’s RRM.  These are summarized here from Power and Fikart (in preparation), and underpin some of the early decisions which were taken in designing MAL’s RRM.  • Categorization and hierarchical design – Due to the thousands of specific risks and the sensitivity of their ordering on risk ranking, one must group risks into a manageable number of categories (categorization) and order them in terms of priority (hierarchical design).  Some RRMs have highly inter-related criteria, with the result that some risk issues are “double-counted”, skewing risk rankings.  • Link to decision-making – The choice of risk categories should reflect the risk management objectives of the organization, preferably tied to specific actions.  • Use of subjective criteria – The design of MAL’s RRM needs to weigh the balance of information which can be measured with that which is “fuzzy” (and sometimes considered of less importance), as both have an important role to play.  • Scale of response – Where possible, the scale of response should be based on data (as opposed to a subjective scale, say from 1 to 7).  • Complexity – There will be a trade-off in complexity between detail and accuracy vs. practicality, time and resources.  • Combining information can cause dilution of risks – Combining or averaging information can cause dilution of risks, which is to be avoided.  • Spatial information – It is important to consider spatial information when ranking risks on a regional basis.  • Explicit consideration of uncertainty – Scientific or other uncertainties can potentially play a significant role in risk rankings, so it is important that, where possible, they are explicitly stated. This approach allows risk managers to evaluate the influence of uncertainty on risk rankings. In the face of uncertainty, some methodologies tended to over-estimate risk, resulting in having “high risk” sites identified that are, in fact, are not as “risky” as their rank indicates.  • Stakeholder and “non-technical” inputs – MAL’s approach to risk ranking focuses on technically driven risks (human health and environment).  However, it is recommended that MAL also find a way to consider these other inputs.  • Complex risk rankings tend to be mistrusted – particularly when they build in values and/or social factors.  With these principles in mind, the development team created a conceptual design, and then built the prototype Tool.  The conceptual design is based on a classical risk assessment paradigm:  • Development of a conceptual model for the site early on (i.e., problem formulation):  site investigators are encouraged to use a pathway analysis approach in selecting sample locations.  • Exposure assessment:  site investigators characterize exposure (at a PSI level) as an approximate measure of the “hazard” of the site, and this is used to rank the site’s potential for risk (assuming the pathway is complete).  • Effects assessment: is de-emphasized because PSIs are a screening-level tool. Variations on standards are used as protective screening values for comparison to exposure data. The field work does require site investigators to look at the presence of key receptors and also to make observation about gross-scale effects (e.g., lack of vegetation on contaminated areas).  • Risk characterization: the Tool calculates screening quotients for the various environmental media, alongside information that suggests a complete pathway or other cause for concern.  SUMMARY OF THE RISK RANKING SUPPORT TOOL  The Tool is a data entry and calculation spreadsheet programmed in Microsoft Excel® and is considered a test (beta) version.  At this point, the Tool has been trialled using historic mine sites for which PSIs already exist.  Key features of the RRM are described below:  • Separation of risk criteria into ecological and human health risks, as well as aquatic and terrestrial risks, much as is done in a formal risk assessment.  This avoids the problem of “diluting” issues during ranking, as well as allowing independent evaluation of these risks, which may have different management actions.  • A site is immediately flagged as a high priority for investigation if any of the following are present: (1) high risk of major event (e.g., geotechnical collapse, flooding etc.) as determined during site visits by qualified personnel, (2) presence of mobile Light Non-Aqueous Phase Liquids (LNAPL on-site, greater than 150 mm, as per MOE, 2007), and (3) presence of persistent, bioaccumulative, and toxic compounds (PBTs) [e.g., mercury, polychlorinated biphenyls (PCBs), and dioxins] on-site > 10 times Contaminated Sites Regulation (CSR) standards, in the top meter of soils (or surface) or sediments.  • An exposure framework that allows the Tool to capture multiple exposure pathways for human health and ecological receptors.  • To screen the contaminant data for various media, the Tool uses a combination of variations on existing standards and guidelines (primarily from B.C.’s contaminated sites regime) and derived values for the purposes of the Tool.  In the case of human health, High Priority Screening Values (HPSVs) were derived for various contaminants.  The HPSVs were modified from a previous approach developed for federal site ranking by URS (2005) with consideration of unique aspects of MAL sites and the potential for acute health risks.  • The framework for both the human and ecological use follows a similar structure—calculation of screening quotients (SQ; essentially the environmental concentration divided by a given screening value for that contaminant).  The SQs calculated for ecological use are weighted by the area of the contamination to provide an indication of the spatial extent of the contamination.  SQs are calculated for each contaminant; however, only the maximum is presented as the final Tool output.  The SQs calculated for each contaminant are not summed in accordance with Ministry of Environment policy (Tier 1 Ecological Risk Assessment Policy Decision Summary).  Experience has shown that risk management is often driven by the chemical with the maximum screening quotient; as such, we have not added complexity by also considering the additive or number of exceedences.  • In addition to the screening quotients, the Tool captures information about human and ecological use of the site, described in a series of “flags”. “Flag” is a term used within the RRM tool to describe measures of potential exposure or effect/sensitivity (e.g., number of fish species, observations of ecological stress), usually more qualitative than those which are quantitative (e.g., chemical concentrations in various media). Flags are risk factors/criteria that are important, but more difficult to capture in a quantitative manner, such as a formulae.  • Consistent in principle with the CSR, sites with concentrations of potential contaminants that are lower than background concentrations (i.e., local reference conditions indicate contaminants are naturally elevated) are not prioritized.  The tool allows the entry of background soil, sediment or surface water data, if available.  Parallel to CSR guidance (but simplified), background concentrations are calculated as the 95th percentile of the background data set.  The tool then uses either the calculated screening benchmark, or the background concentration (whichever is greater) to calculate the screening quotient.  • The Tool makes use of data inputs that have inherent uncertainty—for example, estimates of soil concentrations are inherently variable, are dependant on location and number of samples, and water concentrations can fluctuate dramatically with the season.  By attaching explicit uncertainty to measures used in the Tool (where possible), the information can be used to (1) make decisions about which sites require more data and (2) compare sites with respect to certainty of the Tool’s outputs.  • Instead of automating an overall rank, risk criteria are presented as independent lines of evidence for each site.  Keeping ranking information for different kinds of risks separate has several advantages, including: (1) increased transparency of risk drivers and (2) the ability to manage sites differently depending on the nature of the risk.  Managers have the opportunity, for example, to assess whether presence of a listed fish species in receiving waters near a site is more important than the presence of a zone of dead vegetation in an upland area.  The various lines of evidence from the Tool will be packaged for the expert-based workshop process to identify management actions and their priorities across all the sites being considered.  Figure 1 provides a conceptual illustration for the human health (aquatic and terrestrial) ranking processes and ecological (terrestrial and ecological aquatic) ranking processes within the Tool.  The Tool and accompanying user manual are highly tailored for MAL’s use in their program and will remain largely an internal resource.  The overall framework and conceptual approach behind the tool will be more widely available (Azimuth and SNC Lavalin-Morrow Environmental, 2007).  NEXT STEPS  Ongoing work focuses on two aspects:  1. Testing the Tool with information from this year’s field programs at mine sites selected from the Historic Mine Site Atlas.  2. Design of an expert-based workshop to integrate the Tool’s outputs into recommendations to CCSB for prioritized management action at historic mine sites (e.g., sites requiring detailed site investigation, sites requiring immediate action, and sites requiring ongoing monitoring for acid mine drainage, etc.).  Once the Tool and other elements of the overall MAL Prioritization Process (including the Historic Mine Atlas and the workshop) have been trialed, the Tool will possibly be moved to a different platform which will provide more flexibility and robustness to manage data.  ACKNOWLEDGEMENTS  A number of people contributed to the development of the RRM and should be acknowledged: • John Balfour (Enterprise Geosciences) made important contributions to the project, through specialized advice and testing the Tool. • Patrick Allard, Gary Mann and Ryan Hill (Azimuth) were available for brainstorming on difficult issues. • Martin Gebauer (Gebauer & Associates) contributed to the development of ecological aspects of the project.  Also, there were two more formal processes for expert input that influenced the project: • On December 11, 2007, a workshop was held with a group of scientists to provide advice early on in the process—attendees included: John Balfour (Enterprise Geosciences), Dr. Marc Cameron (Hemmera), Dr. Steve Day (SRK Consulting Ltd.), Ward Kilby (Cal Data Ltd.), Dr. Wayne Landis and Dr. Paul West (Science Advisory Board for Contaminated Sites in British Columbia— SAB). • In April/May 2007, SAB reviewed a draft of the Tool and document to provide external technical review.  REFERENCES  Azimuth and SNC Lavalin-Morrow Environmental. 2007. Risk Ranking Methodology (final title TBD). Draft being revised based on SAB review.  British Columbia Ministry of Environment. 2007. Classifying Site Risk Levels. Protocol 12 for Contaminated Sites. DRAFT. Undated but distributed in February 2007.  Power, B. and A. Fikart. In preparation. Good practice in risk ranking: review and experiences in developing a system for contaminated mine sites. In preparation for submittal to Integrated Environmental Assessment and Management.  Stewart, G.G. and H.J. Johnstone. 2007. British Columbia Crown Contaminated Sites Program Overview. 31st British Columbia Mine Reclamation Symposium. Squamish B.C.  URS Canada Ltd. 2005. High Priority Classification System for Soil at Contaminated Sites. Prepared for Contaminated Sites Program, Environmental Health Assessment Services, Safe Environments Programme, Health Canada.


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