Open access

Determining reasonable response actions following a fly ash spill in the headwaters of Banff National Park, Canada

Publication: FACETS
28 October 2024

Abstract

It can be challenging for practitioners to determine reasonable response actions following an environmental spill because there are risks associated with the recovery process, acute constraints on time, and few case studies available from antecedent events. Here, we evaluate environmental risk using a screening level assessment (SLA) and describe risk management actions during the response phase of a train derailment that released 600 tonnes of fly ash into a headwater creek in Banff National Park, Canada. Trace metal concentrations and physico-chemical parameters from downstream of the derailment site were compared to Canadian environmental quality guidelines and upstream reference values. There was a 1–2.2-fold exceedance of sediment quality guidelines (As, Cd, and Se) as well as a 3.6–17.5-fold exceedance of water quality guidelines (Al, Cd, Fe, and turbidity) downstream of the train derailment. Despite uncertainty about site-specific toxicity when using a SLA, we did require the removal of the settled fly ash from the creek based on the multiple exceedances of guidelines, regulatory context, wilderness setting, and potential contribution to cumulative effects downstream. Case studies that evaluate risk and describe risk management actions help practitioners make consistent and efficient decisions during the response phase of a spill.

Introduction

It is the task of resource managers and environmental regulators (herein: “practitioners”) to determine reasonable response actions following an environmental spill based on the properties of the substance, the ecological and socio-economic values at risk and regulatory context (FSCAP 2017). Early action at a spill site may help mitigate the escalation of risk to the environment, yet the role of the practitioner to determine risk management actions can be complex. The risk of the spilled substance in the environment must be weighed against the fact that operations needed to recover a substance from a waterbody may be invasive and inadvertently cause additional harm to the surrounding environment (Davies and Hope 2015; Weidhaas et al. 2016). Furthermore, this complexity is amplified by the acute constraints of an emergency response including a shortage of time to collect data and make decisions, in addition to situational uncertainty and pressures imposed by multiple stakeholders (Davis and Hope 2015).
Case studies from antecedent events can leverage experience to improve planning and make consistent and efficient decisions (Davis and Hope 2015). However, environmental spill literature tends to focus on marine oil spills (e.g., Feng et al. 2021) with few exceptions (e.g., Ruhl et al. 2009; Cooke et al. 2016). In addition, there are few published studies describing risk management decisions and actions, such as clean-up. We suspect that much of the reporting of decision making and response actions exists as grey literature that is either proprietary to the proponent that spilled the substance and/or found in regulator files as part of the regulatory or litigation processes (Vandermeulen and Ross 1995). Therefore, although the existing literature may support risk assessments of spills in freshwater, it does not necessarily meet the needs of the cross-disciplinary practitioners involved in the immediate response.
In Canada, products that are classified as dangerous goods (Transportation of Dangerous Goods Act; Minister of Justice 1992), toxic substances (Canada Environmental Protection Act; Minister of Justice 1999), or hazardous waste (Canada Environmental Protection Act; Minister of Justice 1999) are legally mandated to have safe handling, disposal and, in the case of certain higher-risk dangerous goods, emergency response plans established in the case of a spill (herein: “regulated substances”). The hazards, risks, and appropriate response actions for regulated substances are thus more readily understood by all parties engaged in an incident. The determination of what constitutes a “reasonable response” may be more complex if the substance is not regulated (herein: “unregulated substances”; Alberta Environmental Protection Commission 2005; Schnoor 2014).
Coal ash, also known as coal combustion residues, is an example of a substance that is not considered hazardous waste in most nations in the world, including Canada (Zierold and Odoh 2020). Coal ash is a solid fossil fuel combustion residue from coal-burning power plants. Coal ash is comprised of fly ash, fine powdery particles carried up the smokestack by exhaust gases, and bottom ash, a coarser material that falls to the bottom of the furnace (Rowe et al. 2002). Fly ash may contain Al, As, Cd, Cr, Cu, Hg, Ni, Pb, Se, Sr, V, and Zn (Rowe et al. 2002). Although fly ash contains organic constituents, inorganic contaminants are much more prevalent and have received greater attention from researchers (Rowe et al. 2002). Some trace metals in fly ash have been shown to degrade the environment, especially since they are soluble in water and easily transported in aquatic systems (Rowe et al. 2002; Jankowski et al. 2006). Many of these studies focused on the effects of water draining from fly-ash disposal sites (e.g., Cherry and Guthrie 1977; Cherry et al. 1979; Reash et al. 1988); the potential effects of an acute release of fly ash are harder to predict because of the lack of published studies (see Ruhl et al. 2009, 2010).
At approximately 03:00 on 26 December 2014, a train derailment occurred on the transcontinental rail line at the Forty-Mile Creek stream crossing on the west end of the Town of Banff, Banff National Park, AB, Canada. The derailment released 600 tonnes of fly ash and a carload of soybeans into a fourth-order headwater creek, Forty-Mile Creek. Section 32 (1) of the Canada National Parks Act (Minister of Justice 2000) states that where a substance that is capable of degrading the natural environment, injuring fauna, flora, or cultural resources or endangering human health is discharged or deposited in a park, any person who has charge, management, or control of the substance shall take reasonable measures to prevent any degradation of the natural environment. Furthermore, section 36(3) of the Fisheries Act (Minister of Justice 1985) prohibits the deposit of deleterious substances that would degrade or alter the water quality such that it could directly or indirectly harm fish, fish habitat, or the use of fish by humans. Despite these regulations, determining a reasonable response can be complex because the response actions are not necessarily to clean-up the spill (FSCAP 2017).
We identified a need for case studies to illustrate systematic approaches to identifying risk and subsequent risk management following a spill to support capacity-building for practitioners. As such, we present a study that evaluated human and ecological risk and explains risk management actions during the response phase of a fly ash spill. Our objectives were to (1) evaluate whether the spilled fly ash could degrade the environment due to physical deposition to the aquatic sediment, and sediment and/or water toxicity using a risk assessment framework; (2) identify response actions, including possible clean-up; and (3) identify challenges with determining risk and risk management actions. Case studies that evaluate risk and document risk management actions would help practitioners make more consistent and efficient decisions during the response phase of a spill.

Methods

Study area

Banff National Park in the Rocky Mountains of Alberta is Canada’s oldest national park and encompasses 6641 square kilometres of mountainous terrain, with numerous glaciers and icefields, dense coniferous forest, and alpine landscapes. It is the flagship of the nation’s park system and forms part of the Canadian Rocky Mountain Parks UNESCO World Heritage Site. Over three million people visited the park in 2014, drawn by its wildlife, pristine waters, and breathtaking mountain scenery. At the time of the spill, there were seven species found in Banff National Park on schedule 1 of the Canada Species at Risk Act and their ranges included Forty-Mile Creek and nearby reaches of the Bow River (e.g., westslope cutthroat trout (Oncorhynchus clarkii lewisi), little brown myotis (Myotis lucifugus), olive-sided flycatcher (Contopus cooperi), common nighthawk (Chordeiles minor) (Parks Canada Agency 2017). Bull trout (Salvelinus confluentus) were recommended for listing on schedule 1 of the Species at Risk Act at the time of the spill and we are subsequently listed in 2020 (Fisheries and Oceans Canada 2020).
Forty-Mile Creek in the Town of Banff is a fourth-order valley-bottom creek that meanders through a montane forest (Fig. 1). Wetted channel width measured in the vicinity of the fly ash spill during seasonal low flow was 15 m. Mean (±SD) discharge was 0.51 (±0.14) m3/s during the initial response. Water velocities were low (mean = 0.26 m/s, range 0.13 to 0.40 m/s) at the time of the spill which likely aided in settling out fly ash upon release from the railcars. The substrate in Forty-Mile Creek is a combination of sand and silt, which is uncommon in Banff National Park. Most other streams have steeper gradients, faster flow velocities, and coarser substrates. The riparian vegetation at the derailment site is a mix of graminoid and shrubby fen. Forty-Mile Creek enters the Bow River 300 m downstream of the derailment site. The Bow River is a fifth-order river that originates from the glacier-fed Bow Lake at the continental divide. The discharge of the Bow River is approximately 20 times greater than the discharge in Forty-Mile Creek during baseflow conditions.
Fig. 1.
Fig. 1. Map of the study area. The railroad icon indicates the location of the train derailment. The main image shows the location of the Bow River, W-RFBow (the upstream reference site), W-DN1Bow (800 m downstream of Forty-Mile Creek), and W-DN2Bow (17 km downstream of Forty-Mile Creek). Inset A with water quality sampling sites: W-RF40Mile (upstream reference site), W-DN140Mile (150 m downstream of derailment site), and W-DN240Mile (300 m downstream of derailment site). Inset B shows sediment quality sampling sites: S-RF1 to S-RF12 (upstream references sites) and S-DN1 to S-DN12 (immediately downstream of train derailment).

Risk assessment approach—the FSCAP Framework

The Framework for Addressing and Managing Aquatic Contaminated Sites Under the Federal Contaminated Sites Action Plan (FCSAP), hereafter the FSCAP Framework, is a Canadian tool designed to guide the risk management of contaminated sites (FCSAP 2017). The FSCAP Framework follows 10 steps within five sections: information gathering, screening level assessment (SLA), detailed level assessment, remediation/risk management, and monitoring of remediation/risk management (Fig. 2). Each step builds upon data, information, and decisions from the preceding level. It combines relevant aspects of human health risk assessment and ecological risk assessment approaches. The FSCAP Framework is similar to frameworks in other countries such as the U.S. and countries in Europe (e.g., U.S. Environmental Protection Agency 1998; den Besten 2007). These guidelines are more flexible to accommodate different measurement endpoints to allow for a large variety of potential stressors, whereas the FSCAP Framework was intended specifically for sediment toxicity.
Fig. 2.
Fig. 2. A schematic short-cut to understanding the ten steps of the Framework for Addressing and Managing Aquatic Contaminated Sites under the Federal Contaminated Sites Action Plan. The 10 steps are grouped within information gathering, screening level assesment (SLA), detail level assessment, and remediation/risk management.

Step 1—identify suspect aquatic contaminated site

Seven cars carrying fly ash came to rest in Forty-Mile Creek, upstream of the rail line, following their derailment (Fig. 1). The cars were mostly intact, but were stacked on their ends and partially submerged in water (Fig. 3). An additional single car carrying soybeans fell to the downstream side of the crossing and laid across the creek forming a dam with only 3–4 m of the 15 m wide creek remaining unblocked (Fig. 3). Six more cars had derailed, but were not directly impacting the stream. The largest crane available could not lift the full contents of each car and vacuuming the contents out of stacked and crumpled cars was deemed unsafe by the railway company. Therefore, by the end of the first day following the derailment, individual cars were cut open using a backhoe-mounted shearing tool and lifted out by crane. The fly ash from six of seven cars was released directly into the creek as pieces of rail cars were removed. The contents of the seventh car were vacuumed out before its extraction from the creek channel. The car containing soybeans that overturned downstream of the cluster of fly ash cars was effectively preventing the downstream movement of some of the fly ash and was therefore left in place. The Material Safety Data Sheet for the fly ash spilled into the creek stated that it was a water pollutant, should be prevented from entering waterways and may cause long-term adverse effects in the aquatic environment (Boundary Dam Fly Ash 2011). This was supported by the available literature (e.g., Rowe et al. 2002). Thus, the potential for contamination from the train derailment was clear based on the information available. All response actions were undertaken by the railway company. Regulatory oversight of spill response actions was undertaken by Parks Canada as the lead agency, under the authority of the field unit superintendent. A science advisory table supported Parks Canada with technical advice and was comprised of Environment and Climate Change Canada, and Fisheries and Oceans Canada.
Fig. 3.
Fig. 3. Photo of the train derailment site. The cars were mostly intact, but were stacked on their ends and partially submerged in water. Fly ash can be seen in suspension in the creek water. Spilled soybeans can be seen on land. This single car carrying soybeans fell to the downstream side of the crossing and laid across the creek forming a dam with only 3–4 m of the 15 m wide creek remaining unblocked.

Step 2—historical review

A contaminated site and a recent dam removal were identified at 4.6 and 6.7 km, respectively, upstream of the train derailment site on Forty-Mile Creek. Both historically impacted sites could also have potentially caused elevated concentrations of contaminants at the downstream train derailment site. The train derailment site was located immediately upstream of the Town of Banff, 100 m west of the main access road into the town from the TransCanada Highway, 200 m west of the Banff train station and rail yard, and 300 m upstream of Forty-Mile Creek’s confluence with the Bow River (Fig. 1). The Town of Banff is the main service centre in Banff National Park. Forty-Mile Creek is popular for personal watercraft as it connects paddlers from the Town of Banff canoe dock on the Bow River with the Vermillion Lakes upstream of the derailment site. The Town of Banff does not obtain its drinking water from Forty-Mile Creek or the Bow River; however, the Bow River provides drinking water to half the Town of Canmore (total population 14 000) and to nearly 60% of the City of Calgary (total population 1.3 million), located approximately 25 and 125 km downstream of the derailment site, respectively. While there is no harvest of resources from this site due to its location in a national park, the Material Safety Data Sheet for the fly ash indicated potential concerns for human health due to direct exposure. Specifically, the Material Safety Data Sheet for the fly ash identified corrosive, toxic, and irritant hazards (Boundary Dam Fly Ash 2011). Recommended mitigations to prevent risks to human health included the use of appropriate personal protective equipment, wetting down of work areas to prevent airborne dust, and closing the immediate surrounding areas to human use.
We chose sediment and water trace metals as well as water physico-chemical parameters (pH, turbidity) as contaminants of potential concern (COPCs). Although fly ash contains organic constituents, inorganic contaminants are much more prevalent (Rowe et al. 2002) and likely easier to use as a COPC given our measurement endpoints (below). The benthic invertebrate community and the aquatic life that inhabited the water column or feed on the benthic community were identified as ecological receptors of potential concern. This included two native trout, westslope cutthroat trout, and bull trout that were assumed to occur in Forty-Mile Creek at the time of the spill (Mayhood 1995). Forty-Mile Creek became critical habitat for these two species after the spill as Parks Canada gained more knowledge of the distribution of the species and their genetic purity (Fisheries and Oceans Canada 2019; Fisheries and Oceans 2020). The exposure pathways by which COPCs may reach and potentially affect receptors of concern were identified as ingestion of COPCs in sediment by benthic invertebrates; absorption of COPCs by direct contact of benthic invertebrates with sediment; absorption and ingestion of COPCs by benthic invertebrates and fishes by direct contact with water; and ingestion of COPCs through consumption of benthic invertebrate or fish prey by insectivores and piscivores. The measurement endpoints were sediment and water threshold concentrations from the Canadian Environmental Quality Guidelines (FCSAP 2017). These guidelines are scientific benchmarks that synthesize data regarding sediment and water contaminant concentrations and their relationships with adverse biological effects from toxicological studies (Canadian Council of Ministers of the Environment (CCME) 1999, 2001). More specific information addressing how we used measurement endpoints is provided in step 3.

Step 3—initial testing program

The SLA, as described in the FSCAP Framework, is expected to provide answers to the following questions: (1) Is sediment toxicity possible, based on comparison to generic sediment quality guidelines? (2) Is biomagnification likely based on the presence of elevated concentrations of organic chemicals that biomagnify?; and (3) Are these or other COPCs present at concentrations above reference concentrations? The second question was intended to account for COPCs that may not be elevated above guidelines, but that could pose a risk because of biomagnification (FSCAP 2017). Although various organic compounds have been associated with coal combustion residues (e.g., Ribeiro et al. 2014), the analysis of organic contaminants was beyond the scope of this case study because we did not collect biological tissue samples (e.g., Mathews et al. 2014). Therefore, we modified the response to these SLA questions to not include question #2. If the answers to question 1 were “yes” and the answer to question 3 was also “yes” for one or more COPCs, the specific COPC was upgraded to a contaminant of concern, meaning the site was considered a potential risk with further action required (FSCAP 2017). No further action was required if the answers to the above questions were “No.” The rationale for the comparison to a reference site included both the fact that inorganic substances occur naturally and may be naturally enriched in some areas (e.g., naturally mineralized areas), and the fact that reference conditions may not be totally pristine (FCSAP 2017).
We sampled fly ash by scooping material directly from the rail car into a 500 mL polypropylene container. Twelve spatially replicated sediment samples were collected once, 2 weeks following the incident ( 1 January 2015), from a 200 m reach immediately downstream of the derailment site (S-DN140Mile to S-DN1240Mile). Twelve samples were also collected from an upstream reference reach, randomly spaced starting at 500 m upstream and ending at 1.5 km upstream of the derailment site (S-RF140Mile to S-RF1240Mile; Fig. 1), but downstream of the landfill and dam. Samples were located by walking back and forth in the vicinity of each site over the frozen river and stopping randomly at sampling locations within the reach. The ice was cored using a 20 cm dia. hand ice auger (Nils; U.S.). Sediment was collected by reaching through 30–90 cm of water and scooping surface sediment (approx. top 10 cm layer) into a 500 mL polypropylene container. The contents were then immediately dumped into a polypropylene bag provided by the analytical laboratory (Maxxam Environmental Services, Calgary, AB). The following trace metals were analysed from the fly ash using inductively coupled plasma/mass spectrometry (ICP-MS; Agilent 7700 ICPMS): Ag, Al, As, soluble boron (B), Ba, Be, Cd, Co, Cr, Cr6+, Cu, Fe, Hg, Mo, Ni, Pb, Sb, Se, Sn, Tl, U, V, and Zn. Sediment concentrations of the same trace metals were also analysed using ICP-MS, but due to an error, Al and Fe were not included in the testing package. Samples were dried at 55 °C, sieved and digested in a nitric-hydrochloric acid and de-ionized water mixture to solubilize the solid matter and remove organic material.
We sampled and metered water daily on Forty-Mile Creek starting at 14:00 on 27 December 2014, 33 h following the train derailment, until 2 January 2015. We sampled daily again for 1 week, beginning on 23 January 2015, 5 weeks following the incident. We sampled daily for 1 week, again a third time, beginning on 14 March 2015, 14 weeks following the incident. Water was sampled from a site 150 m downstream from the derailment site (W-DN140Mile), 300 m downstream of the derailment site (W-DN240Mile), and a reference site 1.7 km upstream of the derailment, but downstream of the landfill and dam (W-RF40Mile; Fig. 1). Water was also sampled and metered from the Bow River at the same schedule as Forty-Mile Creek, from sites 800 m downstream of the derailment site (W-DN1Bow), 17 km downstream of the derailment site (W-DN2Bow), and an upstream reference site 9.2 km upstream of the derailment site (W-RFBow; Fig. 1). Selection of sampling sites included consideration of road accessibility because sampling occurred during winter. Therefore, we sampled water from all sites at least once/day for a total of 21 days. Water samples were collected by wading into the water while moving away from the shoreline and plunging 250 mL high-density polyethylene bottles, provided by the laboratory (Maxxam Environmental Services, Calgary, AB), into the water facing upstream. Bottles were rinsed with the flowing water three times before taking the samples. Water samples were analyzed for the following trace metals based on a general total metals package: Al, Ag, As, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Se, Si, Sn, Sr, Tl, Ti, U, V, and Zn using ICP-MS and -OES (Varian Vista Pro ICPOES and Agilent 7700 ICPMS) by Maxxam Analytics (Calgary, Alberta, Canada). However, not all these trace metals were evaluated (See Initial Testing Program below). We also recorded physico-chemical parameters (turbidity and pH) using a portable device (YSI ProDSS multiparameter meter; YSI Inc., Yellow Springs, OH, U.S.) at W-DN1, W-DN2 and W-RF in both Forty-Mile Creek and the Bow River at the time of water sampling.
Some studies have focused on chemical screening of the dissolved fraction of trace metals (e.g., Ruhl et al. 2009). This assessment used Canada’s national environmental guidelines, which are applicable to total concentrations, not the dissolved fraction. These guidelines were designed to inform practitioners about the biological risk thresholds of certain contaminants. Furthermore, dissolved-phase concentrations alone would not account for the potential future speciation of trace metals from total to dissolved concentrations.
Trace metal concentrations from fly ash sampled directly from the derailment site were compared to the CCME sediment quality guidelines for the protection of aquatic life (CCME 2001), using both the interim sediment quality guidelines (SQG-ISQG) and probable effect levels (SQG-PEL). The SQG-ISQG represents the concentration above which adverse biological effects may occur, while the SQG-PEL represents the concentration above which adverse biological effects occur frequently (CCME 2001). Any parameter that exceeded the reporting detection limit (RDL) was further evaluated using sediment data. We compared the concentrations of sediment trace metals identified from the previous step to the SQG-ISQG and SQG-PEL. When a CCME SQG was not available, we adopted the Government of Alberta sediment quality guidelines for the protection of aquatic life, again both ISQGs and PELs (Government of Alberta 2018). Any trace metals that exceeded SQG-ISQG and SQG-PELs and upstream reference concentrations were identified as sediment contaminants of concern. Sediment trace metal concentrations that exceeded reference concentrations, but had no guidelines were identified as uncertainties. Trace metals that were identified as contaminants of concern or uncertainties were further evaluated using water data.
We screened for potential impacts to drinking water and aquatic resources by comparing concentrations of trace metals identified in the previous step and physico-chemical parameters to the Canadian guidelines for drinking water quality (GDWQ; Health Canada 2019) and CCME Canadian water quality guidelines for the protection of aquatic life (CWQG; CCME 1999). We used long-term, rather than short-term guidelines, because long-term guidelines are more conservative and are intended to protect all forms of aquatic life for indefinite exposure periods, whereas short-term guidelines are intended to protect a fraction of individuals from severe effects such as lethality and is used for transient situations (CCME 2007). The federal environmental quality guidelines were used when a CWQG was not available (Environment and Climate Change Canada 2007). The Government of Alberta surface water quality guidelines (Government of Alberta 2018) were adopted when no CWQG or federal environmental quality guidelines were available. Water parameters that exceeded any of the water quality guidelines and exceeded concentrations from the upstream reference site were identified as water contaminants of concern.
The median daily concentrations were used as a measure of central tendency, and the Q3 was used as an upper measure of spread as most parameters were not normally distributed. On days when multiple water samples were metered or collected, the mean value for that day was used to ensure there were no days with higher weighting in the overall analyses. A significant number of trace metal concentrations were below laboratory RDLs and were often reported as being less than an analytical threshold (i.e., “censored”). Censored observations complicate the routine calculations of descriptive statistics, testing differences among groups and regression coefficients (Helsel 2012). Therefore, we used nonparametric survival analyses to estimate summary statistics for both sediment and water (Kaplan-Meier method; Helsel 2012). Nonparametric survival analysis is likely to have greater power than parametric procedures when working with skewed data (Helsel 2012). When censoring exceeded 50% of the data for any one parameter, the median for that site could not be computed and the median values were reported as less than the RDL. The 3rd quartile was reported as not applicable (N/A) when there was not enough non-censored data to compute a quartile. To statistically compare sediment and water data between sites, another non-parametric survival analysis method was used (the Generalized Wilcoxon Score Test; Helsel 2012). This method is appropriate for censored data because it uses ranks to make comparisons between two or more groups and can thus handle a higher percentage of censored values (Helsel 2012).

Step 4—pre-classification of the site

Pre-classification is used to determine if enough information on the site has been gathered to complete a site classification, to identify the site for further assessment or clean-up, or elimination from further consideration (Fig. 2). Similarly, if practitioners need to collect more data to complete a meaningful classification, they can choose to proceed to step 5, the detailed testing program (Fig. 2).

Results

Fly ash

At least 300 m2 of Forty-Mile Creek substrate was visually impacted by fly ash following the spill. Approximately 14 h after the train derailment, a rock dam was built 150 m downstream of the railway bridge as a water control structure (Fig. 1). The rock dam was made of Class 2 riprap and was ∼15 m wide and ∼3.5 m deep. Mean water depths were greater upstream (mean = 44 cm; range = 23–68 cm) compared to downstream (mean = 36 cm; range = 22–65 cm) of the rock dam, suggesting that it was effective as a control feature to reduce flow velocities and promote settlement of suspended solids. The rock dam was also successful at reducing further downstream movement of fly ash; the fly ash formed a relatively thicker layer on the upstream side (mean = 9.2 cm; range = 0–43 cm) and a relatively thinner layer on the downstream side of the dam (mean = 1.6 cm; range = 0–5.5 cm).
The following trace metals were detected at concentrations above the RDLs in fly ash: Al, As, B, Ba, Be, Cd, Co, Cr, Cr6+, Cu, Fe, Mo, Ni, Pb, Sb, Se, Sn, Tl, U, V, and Zn (Table 1). Concentrations of Ag and Hg in fly ash samples were below RDLs and were not evaluated any further (Table 1). Fly ash concentrations of As (16 mg/kg d.w.) and Cd (0.68 mg/kg d.w.) were greater than SQG-ISQGs (5.9 and 0.60 mg/kg d.w., respectively), but not the SQG-PELs (17.0, and 3.50 mg/kg d.w., respectively; Table 1). Fly ash Se concentrations (3.80 mg/kg d.w.) were also greater than Alberta SQG-ISQG (2.00 mg/kg d.w.), but there was no SQG-PEL available (Table 1). Therefore, As, Cd, and Se were evaluated further using sediment data below. Fly ash concentrations of Cr, Cu, Pb, and Zn were below the SQG-ISQGs, but were still at concentrations well above the RDLs, and therefore, were also evaluated further using sediment data (Table 1). All other trace metals tested (Al, B, Ba, Be, Co, Cr6+, Fe, Mo, Ni, Sb, Sn, Tl, U, and V) were found at concentrations above their RDLs, but did not have sediment quality guidelines (Table 1). These trace metals were also evaluated as possible sediment contaminants of concern based on uncertainty.
Table 1.
Table 1. Total trace metal concentrations (in mg/kg d.w.) from one sample of dry fly ash taken from the derailment site on 27 December 2015, 33 h after the train derailment.
 SQGFly ash
Trace metalISQGPELconcRDL
Ag  <1.01.0
Al  22,000100
As5.917.016.01.0
B  72.000.10
Ba  170010
Be  2.500.40
Cd0.603.500.680.10
Co  4.91.0
Cr37.390.030.01.0
Cr6+  4.500.15
Cu35.7197.022.05.0
Fe  8,900100
Hg0.170.49<0.050.05
Mo  8.40.4
Ni  14.01.0
Pb35.091.317.01.0
Sb  1.91.0
Se2.00* 3.800.50
Sn  1.81.0
TI  0.460.30
U  4.71.0
V  57.01.0
Zn123*3154610

Note: Light-grey highlights indicate metals that exceeded the Canadian Council of Ministers of the Environment (CCME) interim sediment quality guideline for the protection of aquatic life (SQG-ISQ). No trace metals exceeded the CCME probable effect level sediment quality guidelines for the protection of aquatic life (SQG-PEL). In the absence of an SQG for a specific parameter, a Government of Alberta environmental sediment quality guideline was adopted (ABSQG; ISQG, and PEL). RDL, reporting detection limit; ISQG, interim sediment quality guidelines; SQG, sediment quality guidelines; PEL, probable effect levels; ISQ; interim sediment quality.

*
ABSQG-ISQG.
ABSQG-PEL.

Sediment

Median sediment concentrations of As (13.0 mg/kg d.w.) and Cd (0.71 mg/kg d.w.) from downstream of the derailment site exceeded the SQG-ISQG (5.9 and 0.60 mg/kg d.w., respectively), and were significantly greater than reference values; therefore, As and Cd were identified as sediment contaminants of concern (Table 2). Median sediment concentrations of As and Cd did not exceed the SQG-PELs (17.0 and 3.50 mg/kg d.w., respectively; Table 2). The median sediment Se concentration (2.0 mg/kg d.w.) was equal to the Alberta SQG-ISQG (2.00 mg/kg d.w.), but there was no SQG-PEL available (Table 2). Sediment concentrations of Cr, Cu, Pb, and Zn from downstream sites exceeded upstream reference concentrations, but did not exceed SQG-ISQGs and were therefore dropped from further consideration (Table 2). Sediment concentrations of B, Be, Co, Cr6+, Mo, Ni, Sb, Sn, Tl, U, and V from downstream of the derailment site were significantly greater than reference concentrations (by a factor of 1.2 to 510), but there were no applicable SQGs available (Table 2). Therefore, these sediment trace metals were identified as uncertainties and considered as potential water contaminants of concern. The downstream sediment Ba concentration did not exceed reference concentrations and Ba was not evaluated any further. Unfortunately, Al and Fe were not analyzed from sediment samples even though they were detected in fly ash; however, these trace metals were evaluated as potential water contaminants of concern.
Table 2.
Table 2. Total trace metal concentrations (mg/kg d.w.) in sediment sampled from Forty-Mile Creek including: Median, 3rd quartile (Q3), % of the samples below laboratory detection limits (%cens), and the p-value from the Generalized Wilcoxon Test comparing two groups of censored data.
  SQGReferenceDownstream 
Trace metalRDLISQGPELMedianQ3%censMedian3rdquart%censp-value
As1.05.917.02.02.20%13.015.00%<0.001
B0.1  <0.1N/A58%51.073.00%<0.001
Ba10  27330%27290%<0.001
Be0.40  0.400.40100%3.103.308%<0.001
Cd0.100.603.500.340.420%0.711.420%<0.001
Co1.0  2.02.30%6.46.60%<0.001
Cr1.037.390.06.38.10%31.034.20%<0.001
Cr6+0.15  <0.15N/A100%0.391.220%<0.001
Cu5.035.7197.0<5.0N/A75%25.024.622%<0.001
Mo0.40  0.971.100%4.906.908%<0.001
Ni1.0  10.013.00%18.019.20%<0.001
Pb1.035.091.33.34.10%15.019.20%<0.001
Sb0.10  <1.00N/A100%1.702.0217%N/A
Se0.502.0* <0.50N/A67%2.02.48%<0.001
Sn1.0  <1.0N/A100%1.41.967%<0.001
Tl0.30  <0.30N/A100%0.360.4225%<0.001
U1.0  <1.0N/A100%4.75.517%<0.001
V1.0  9.011.30%60.067.30%<0.001
Zn10123*31539470%53620%0.03

Note: The Q3 was reported as “N/A” when there was not enough non-censored data to compute a quartile. Twelve sediment samples were collected once, 2 weeks following the incident (1 January 2015), from both immediately downstream of the train derailment (Downstream; sites S-DN140Mile to S-DN1240Mile) and from an upstream reference reach (Reference; sites S-RF140Mile to S-RF1240Mile). Light grey highlights indicate metals that exceeded the Canadian Council of Ministers of the Environment (CCME) interim sediment quality guidelines for the protection of aquatic life (SQG-ISQ). No trace metals exceeded the CCME probable effect level sediment quality guidelines for the protection of aquatic life (SQG-PEL). In the absence of an SQG for a specific parameter, a Government of Alberta sediment quality guideline was adopted (ABSQG; ISQG, and PEL). ISQG, interim sediment quality guidelines; SQG, sediment quality guidelines; PEL, probable effect levels; ISQ; interim sediment quality.

*
ABSQG-ISQG.
ABSQG-PEL.

Water

Regarding Forty-Mile Creek, median turbidity values from both W-DN140Mile (2.4 NTU) and W-DN240Mile (5.3 NTU) were significantly greater than at RF40Mile (1.0 NTU), and the value from W-DN240Mile exceeded the CWQG (3.0 NTU; CCME 2002; Table 3). Therefore, turbidity was identified as a contaminant of concern. The highest values were seen on days in which emergency instream work occurred with no site isolation in place. For example, on 26 January 2014, warming weather caused the creek surface ice to melt and water eroded the banks around the rock dam. Emergency instream work was undertaken to patch the rock dam with additional rip rap. No significant differences in metered pH were found between W-DN140Mile, W-DN240Mile, and W-RF40Mile sites in Forty-Mile Creek, suggesting pH was not affected over the three-month assessment period (Table 3). Regarding the Bow River, turbidity values at both W-DN1Bow and W-DN2Bow were not significantly different from W-RFBow and did not exceed the CWQG (Table S1). There was no significant differences in pH values between W-DN1Bow, W-DN2 Bow, and W-RFBow, suggesting the pH of the Bow River was not affected at the 3-month scale (Table S1).
Table 3.
Table 3. pH and turbidity (NTU) concentrations in water sampled from Forty-Mile Creek and the Bow River including: Median, 3rd quartile (Q3), and the p-value from the Generalized Wilcoxon test comparing the three groups.
   W-RF40MileW-DN140MileW-DN240Mile 
WaterbodyTrace metalCWQGMedianQ3MedianQ3MedianQ3p-value
Fort-Mile CreekpH0.2 > background8.198.328.118.238.098.20.57
Fort-Mile CreekTurbidity2 NTU > background11.72.47.25.317.15<0.001

Note A total of 21 daily water meterings starting at 14:00 on 27 December 2014, 33 h following the train derailment, until 2 January 2015. We metered daily again for 1 week, beginning on 23 January, 5 weeks following the incident, and again beginning on 14 March 2015, 14 weeks following the incident. Water was metered from a site 150 m downstream from the derailment site (W-DN140Mile), 300 m downstream of the derailment site (W-DN240Mile) and a reference site 1.7 km upstream of the derailment (W-RF40Mile). Light grey highlighted text indicates water trace metal concentrations that exceeded the Canadian Council of Ministers of the Environment water quality guideline for the protection of aquatic life (CWQG; long-term guidelines). CWQG, Canadian water quality guidelines.

All trace metals that were identified as sediment contaminants of concern or uncertainties were evaluated as possible water contaminants of concern. Median water Al concentrations sampled from both W-DN140Mile (0.18 mg/L) and W-DN240Mile (0.35 mg/L) exceeded the GDWQ (0.10 mg/L) and CWQG (0.10 mg/L) and were significantly greater than sampled at W-RF40Mile (Table 4). Sixty-three percent of water Cd concentrations were censored and medians were not calculated for W-DN140Mile or W-RF40Mile (Table 4). However, the median water Cd concentration from W-DN240Mile (0.029 mg/L) exceeded the GDWQ (0.005 mg/L), CWQG (0.00015 mg/L) and the upstream reference RDL (Table 4). Median water Fe concentrations from W-DN240Mile (0.32 mg/L) also exceeded the GDWQ (0.3 mg/L) and CWQG (0.3 mg/L) and the upstream reference concentrations (Table 4). Therefore, Al, Cd, and Fe were identified as water contaminants of concern. Median water concentrations of As, Mo, Se, and U were significantly greater at one or both downstream sites compared to the upstream reference site, but did not exceed any guidelines and these trace metals were not identified as contaminants of concern (Table 4). Most or all median water concentrations of B, Be, Co, Sb, Sn, and Tl were below the RDLs, and medians could not be calculated or compared (Table 4). Therefore, these trace metals were also not considered. Finally, downstream water concentrations of Ni and V did not exceed reference concentrations and were not considered any further.
Table 4.
Table 4. Total trace metal concentrations (mg/L) in water sampled from Forty-Mile Creek including: Median, 3rd quartile (Q3), % of the samples below laboratory detection limits (%cens), and the p-value from the Generalized Wilcoxon Test comparing three groups of censored data.
 WQGW-RF40MileW-DN140MileW-DN240Mile 
Trace metalGDWQCWQGMedianQ3%censMedianQ3%censMedianQ3%censp-value
Al0.100.10*0.020.0200.180.8400.350.800<0.001
As0.0100.005<0.0002N/A860.00040.000750.00040.000910<0.001
B5.01.5<0.02N/A100<0.02N/A81<0.02N/A76N/A
Be<0.001N/A100<0.001N/A100<0.001N/A100N/A
Cd0.0050.00015<0.020N/A81<0.020N/A620.0290.047440.03
Co0.001<0.0003N/A100<0.0003N/A81<0.0003N/A0.67N/A
Fe0.30.30.0880.11000.2100.71000.3200.8550<0.001
Mo0.07340.00110.001100.00130.001500.00140.00160<0.001
Ni0.115<0.0005N/A95<0.0005N/A570.00050.00090<0.01
Sb0.006<0.0006N/A100<0.0006N/A95<0.0006N/A100N/A
Se0.050.0010.00070.000800.00080.000800.00080.000900.06
Sn<0.001N/A100<0.001N/A100<0.001N/A100N/A
TlN/A0.0008<0.0002N/A100<0.0002N/A100<0.0002N/A100N/A
U0.020.0150.00090.000900.00090.000900.00090.00110<0.001
V0.1260.0010.0027330.0010.002848<0.001N/A100<0.001

Note: The Q3 was reported as “N/A” when there was not enough non-censored data to compute a quartile. A total of 21 daily water samples were collected starting at 14:00 on 27 December 2014, 33 h following the train derailment, until 2 January 2015. We sampled daily again for 1 week, beginning on 23 January, 5 weeks following the incident, and again beginning on 14 March 2015, 14 weeks following the incident. Water was sampled from a site 150 m downstream from the derailment site (W-DN140Mile), 300 m downstream of the derailment site (W-DN240Mile) and a reference site 1.7 km upstream of the derailment (W-RF40Mile). Dark grey highlighted text indicates water trace metal concentrations that exceeded the Canadian guidelines for drinking water quality (GDWG) and the Canadian Council of Ministers of the Environment water quality guidelines for the protection of aquatic life (CWQG; long-term guidelines). In the absence of CWQG for a specific parameter, a federal water quality guideline (FWQG) or a Government of Alberta surface water guideline for the protection of aquatic life (ASWQG) was adopted.

*
Based on pH > 6.5.
CWQG = 10{0.83(log[hardness]) – 2.46}; hardness = 120 mg/l Ca CO3.
FWQG = e{(0.414[ln(hardness)] – 1.887}; hardness = 120 mg/l Ca CO3.
Most water concentrations of As, B, Be, Cd, Co, Ni, Sb, Sn, Tl, and V sampled from the Bow River were below their RDLs; therefore, median concentrations could not be calculated and comparisons between sites could not be made (Table S2). Water concentrations of Al, Fe, Mo, Se, and U were greater at one or both downstream sites than at the upstream reference site, but did not exceed any guidelines (Table S2). Overall, no water contaminants of concern were identified for the Bow River.

Pre-classification of the site and risk management

Multiple sediment and water contaminants of concern were identified and the area downstream of the train derailment was pre-classified as a Class 2 contaminated site, which is defined as a medium priority for action. Parks Canada and the science advisory table determined that all reasonable means should be used to remove the residual fly ash deposit before it was re-mobilised downstream during the spring freshet, an annual high-water event on rivers resulting from rain and snow/ice melt. Therefore, the railway company proceeded to Step 8, remediation, without completing a detailed level assessment. The portion of Forty-Mile Creek with visible signs of fly ash deposition was isolated from the flowing creek using pumps and aqua-dams, and the fly ash was excavated following the monitoring period reported here.

Discussion

We present a case study of the response to an acute release of fly ash that illustrates a systematic approach to identifying risk. Evaluating risk in this case study was challenging given that concentrations of contaminants of concern were above thresholds where adverse biological effects may occur, but not within a range of concentrations where toxicity occurs frequently (CCME 1999). Nonetheless, the FSCAP Framework did serve as a tool that provided a systematic approach to compiling and evaluating data, information, assumptions, and uncertainties to help predict ecological and human health effects in a way that is useful for decision making. The FSCAP framework points out that it would benefit from additional guidance on different water bodies based on directed research or case studies (FCSAP 2017). We demonstrate a simple risk assessment using only chemical measures, described in ecological risk assessment frameworks from Canada, the U.S. and Europe (U.S. Environmental Protection Agency 1998; den Besten 2007; FSCAP 2017). Below we describe the evaluation of whether the fly ash could degrade the environment of Forty-Mile Creek, the response actions, and the challenges with identifying risk and risk management actions.

Objective 1—evaluate whether the fly ash could degrade the environment

Our first objective was to determine whether the spilled fly ash could degrade the environment due to physical deposition to the substrate in Forty-Mile Creek and sediment and/or water toxicity. Depth measurements of visible fly ash, as denoted by a difference in color from native substrate, were used to discern that fly ash was deposited on, and likely smothering sediment biota for approximately 300 m2 of creek substrate immediately downstream of the derailment. The basic impact of smothering has been documented in past studies, for example, Cherry et al. (1984) documented reduced densities of benthic invertebrates from sedimentation and smothering downstream of an ash basin drainage system in South Carolina, U.S. We identified a few sediment contaminants of concern that have been well characterized in several other coal combustion residue-impacted systems (i.e., As, Cd, and Se; Carlson and Adriano 1993; Rowe et al. 2002). Concentrations of these parameters in our case study were largely not as high as data summarized by Rowe et al. (2002), likely because those studies were measuring trace metals downstream of a lake or ash reservoir that received continuous discharge of coal combustion residue. We also identified several water contaminants of concern that have been characterized in coal combustion residue-impacted systems (i.e., Al, Cd, and Fe; Rowe et al. 2002). Water trace metal concentrations of these parameters in our case study were also not as high as found in the literature. For example, water Cd concentrations from streams draining ash basins associated with coal-power plants in the U.S. were multiple times higher than from Forty-Mile Creek (Cherry and Guthrie 1977; Reash et al. 1988). Finally, some unknown portion of fly ash was also mobilised downstream immediately following the incident. Turbidity, as a measure of suspended sediment, was 1.8-fold higher downstream of the derailment site compared to the CWQG for at least 14 weeks. Like sediment and water trace metals above, turbidity was one of the lines of evidence for fly ash toxicity in this case study and others in the literature (Carlson and Adriano 1993; Rowe et al. 2002).

Objective 2—risk management actions

According to the FSCAP Framework, when concentrations of one or more COPCs exceed SQG-ISQGs and are statistically higher than reference conditions, there is potential risk and further action is required (FSCAP 2017). It is at the discretion of practitioners, with support from the science advisory table, to determine whether further action is clean-up or further assessment (FCSAP 2017). In this case study, the railway company was asked to clean up the fly ash following the SLA and pre-classification without further investigation. Confirmatory sampling, using biological testing in the form of a detailed level assessment, was completed by the railway company over three years following the remediation of the site; however, the results are beyond the scope of this manuscript. The challenges for practitioners making this decision and the justification for the decision are described below.

Objective 3—challenges with identifying risk and management actions

There is uncertainty with identifying toxicity and bioavailability of contaminants based solely on chemical measurements because site-specific conditions determine whether contaminants are toxic (Hamers et al. 2010; McDonough et al. 2010). Furthermore, the risk of biomagnification was not considered in the case study even though other studies have demonstrated that plants and animals inhabiting coal combustion residue-contaminated sites can accumulate trace metals, especially in predators like fishes (Cherry and Guthrie 1977; Rowe et al. 2002). This was because biomagnification potential can typically only be evaluated during a detailed level assessment (FSCAP 2017). Indeed, the SQG documentation itself cautions against interpreting the biological significance of chemical concentrations in sediments (CCME 2001). In our case study, sediment trace metal concentrations were above thresholds where adverse biological effects may occur, but not with a range of contamination where toxicity occurs frequently (i.e., the distinction between SQG-ISQL vs. SQG-PEL). The CCME narrative suggests that CWQGs are limits below which there are no adverse toxic effects (CCME 1999), but it is not explicit that degradation of the environment occurs when SQG-ISQL or CWQGs are exceeded. Furthermore, several sediment and water trace metals were found at greater concentrations downstream compared to upstream of the derailment site, but no national environmental quality guidelines were available for comparison. The lack of national guidelines for all parameters poses a challenge for practitioners to evaluate all COPCs. Sourcing and adapting guidelines from other regions (e.g., U.S. National Aquatic Life Criteria) is not practical for practitioners who are not experts in toxicology and need to make decisions quickly. Finally, some sediment and water trace metals downstream of the derailment site exceeded their upstream reference values, but not the national guidelines. When assessed individually, these trace metals might have been considered low risk. However, consideration of the impact of multiple trace metals that may have an additive or synergistic effect on the environment is required to understand the risk of the spilled mixture of COPCs (Cedergreen 2014; Singh et al. 2017).
The challenges outlined above could have been addressed with a detailed level assessment that includes biological testing (e.g., toxicity tests or biological community assessment) because biological methods of assessment have greater relevance to the conditions at the site and integrate the effects of all contaminants at their bioavailability, including potential additive and synergistic effects (den Besten 2007). Detailed level assessments are performed when sites cannot be properly classified because of uncertainty with the SLA and classification would benefit from additional validation (FCSAP 2017). However, detailed level assessments can take months if not years to complete and our decision-making timeline did not allow for such a detailed evaluation. The spill occurred in December and the spring freshet starts in May/June in the Canadian Rockies, bringing with it the potential to re-mobilise fly ash that had settled in the vicinity of the derailment site. As a result, decisions about clean-up were required within a matter of months.
Despite the challenges described above, the FSCAP Framework points to three cases when chemical elements from the in situ physical environment could be used to trigger a clean-up: (a) adverse biological effects are likely; (b) the costs of further investigation outweigh the costs of remediation; and/or (c) there is agreement to act instead of conducting further investigations. In addition to the guidance from the FSCAP Framework, we provide the following reasons for triggering a clean-up despite the uncertainties associated with chemical, rather than biological, measurements. Firstly, the regulatory context requiring prevention and mitigation of harm from spills of a substance that is capable of degrading the environment (National Parks Act) and/or adverse effects to fish and fish habitat (Fisheries Act). As above, we interpret the cumulative risk of multiple contaminants of concern to be strong evidence that fly ash is capable of degradation to the immediate environment of Forty-Mile Creek. Secondly, the wilderness setting because exceedances of environmental quality guideline concentrations is not advocated for ecosystems of superior quality (CCME 1999). Thirdly, contaminants from the spill could contribute to cumulative watershed-scale effects downstream when considered as part of broader suite of stressors external to the fly ash spill (see aquatic stressors in Banff National Park; Schindler 2000). This included consideration of impacts to ecological receptors such as westslope cutthroat trout and bull trout as well as human health concerns about downstream drinking water (Farag et al. 1993; Novotny and Witte 1997).

Conclusions

Early action at a spill site may help mitigate the escalation of risk to the environment and it is the task of practitioners to determine reasonable response actions. This can be a complex task because of acute constraints on time to collect data and make decisions. The spilled substance may not be regulated and the appropriate response may not be found in an emergency response plan. Therefore, case studies that include risk management decisions and response actions need to be readily available to meet the needs of the cross-disciplinary practitioners involved in the incident response. The hope is that this case study contributes to an awareness of considerations, including those external to quantitative lines of evidence, to support consistent and efficient decision-making during the response phase of a spill.

Acknowledgements

Our sincere gratitude goes to the Parks Canada staff who helped with technical and logistical support. The authors also thank Angela Crowe from the Government of Alberta and Mitchell Johnsen from Environment and Climate Change Canada for their constructive early reviews.

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Supplementary material

Supplementary Material 1 (DOCX / 30 KB).

Information & Authors

Information

Published In

cover image FACETS
FACETS
Volume 9Number 1January 2024
Pages: 1 - 13
Editor: Irene Gregory-Eaves

History

Received: 29 November 2023
Accepted: 8 July 2024
Version of record online: 28 October 2024

Data Availability Statement

Data generated or analyzed during this study are available in the Dryad repository, [doi: 10.5061/dryad.7wm37pw2c].

Key Words

  1. spill response
  2. water quality
  3. sediment quality
  4. fly ash spill
  5. risk assessment
  6. environmental quality guidelines

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Plain Language Summary

Responding to Spills in Freshwater Ecosystems: A Risk Management Case Study from a Fly Ash Spill in Banff National Park

Authors

Affiliations

Parks Canada Agency, Banff National Park, Banff, AB, Canada
Author Contributions: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Visualization, Writing – original draft, and Writing – review & editing.
Helen Irwin
Parks Canada Agency, Banff National Park, Banff, AB, Canada
Author Contributions: Conceptualization, Data curation, Investigation, Methodology, Validation, Writing – original draft, and Writing – review & editing.
Department of Chemistry, University of Manitoba, Winnipeg, MB, Canada
Author Contributions: Supervision, Validation, and Writing – review & editing.
Fonya Irvine
Department of Biology, Concordia University, Montreal, QC, Canada
Author Contributions: Conceptualization, Data curation, Investigation, and Writing – review & editing.
Margaret Yole
Environmental Health Program, Health Canada, Winnipeg, MB, Canada
Author Contributions: Validation, Visualization, and Writing – review & editing.
Simon Despatie
National Environmental Emergencies Centre, Environment and Climate Change Canada, Montreal, QC, Canada
Author Contributions: Conceptualization, Investigation, Methodology, Supervision, and Writing – review & editing.
Karsten Liber
Toxicology Centre, University of Saskatchewan, Saskatoon, SK, Canada
School of Environment and Sustainability, University of Saskatchewan, Saskatoon, SK, Canada
Author Contributions: Investigation, Methodology, Supervision, Validation, Writing – original draft, and Writing – review & editing.

Author Contributions

Conceptualization: MKT, HI, FI, SD
Data curation: MKT, HI, FI
Formal analysis: MKT
Investigation: MKT, HI, FI, SD, KL
Methodology: MKT, HI, SD, KL
Project administration: MKT
Resources: MKT
Software: MKT
Supervision: MKT, GTT, SD, KL
Validation: HI, GTT, MY, KL
Visualization: MKT, MY
Writing – original draft: MKT, HI, KL
Writing – review & editing: MKT, HI, GTT, FI, MY, SD, KL

Competing Interests

The authors declare there are no competing interests.

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