A Review of Oil Mineral Aggregates Formation ...

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A Review of Oil Mineral Aggregates Formation Mechanisms for the Salish Sea and the Lower Fraser River Aurelien Hospital1*, James A. Stronach1 and Jordan Matthieu1 1 Tetra Tech EBA Inc. Water and Marine Engineering Practise Vancouver, B.C., Canada *[email protected] Abstract Over the past few years, several in-depth studies have been conducted to characterize the behavior of diluted bitumen in aquatic environments. The Kalamazoo River spill in Michigan, which occurred in a flooded river environment, showed that the interaction between oil and organic/inorganic particulates could be a significant factor in the fate of spilled dilbit under specific circumstances. All studies show that sufficient particulate matter, oil and turbulent energy are necessary to form such agglomerates. Some studies such as Environment Canada’s 2013 report (2013) have focused on the mechanism of oil-particulate formation using a likely upper bound for sediment concentrations and energy levels that are often higher than what can be found in most natural habitats. This paper investigates the propensity for oil-mineral aggregate (OMA) formation in the Lower Fraser River and the Salish Sea, particular the Fuca-Georgia Strait system, located on the South-West coast of Canada. The paper begins with a review of the various physical experiments that have been conducted to characterize oil and sediment interaction. Following sections provide a complementary understanding of natural conditions characterizing the study area: the Lower Fraser River and the Salish Sea whereby a campaign of suspended sediment sampling was conducted in the Lower Fraser River and its delta. The results of this campaign are combined with 40 years of observations to characterize the suspended sediment content of the Fraser River. Finally, characterization of the energy dissipation rate is provided at various locations within the study area. Natural suspended sediment concentrations and energy levels characteristic of the study area are then compared to physical experiments characterizing oil and particulate interaction. The ultimate purpose of this paper is to provide the connections between observations, theory and experiments and to highlight potential areas for future research. 1

Introduction Spilled oil is exposed to a range of weathering mechanisms in an aquatic environment. During an unmitigated spill, the majority of the oil is either evaporated, dissolved or retained by the shoreline; however, under appropriate conditions, the surface slick may become fragmented and undergo vertical dispersion, resulting in the formation of oil droplets that have the potential to interact with suspended particulate material. Suspended sediment, i.e. mineral fines primarily clay and silt, and oil droplets may aggregate together and form agglomerates. The resultant increase in density can lead to sinking of the agglomerate. Historical oil spills proved that, under certain conditions, the interaction between oil and suspended sediment could represent a pathway for the oil to reach the sea bed. As an example, during the 1993 Braer oil spill, near Shetland, Scotland, it was estimated that as much as 30% (30,000 tons) of the spilled oil deposited in

Hospital A., J.A. Stronach, and J. Matthieu, A Review of Oil Mineral Aggregates Formation Mechanisms for the Salish Sea and the Lower Fraser River, Proceedings of the Thirty-ninth AMOP Technical Seminar, Environment and Climate Change Canada, Ottawa, ON, pp. 434-454 2016.

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subtidal sediments, a significant part due to interaction between oil and suspended sediment in a very energetic environment. Several terms have been used to describe this process. The most used term was first mentioned by Lee et al. (1998), who classified the interaction of oil and mineral fines as OilMineral Aggregates (OMA). New terms have also been proposed more recently to reflect the potential for oil to interact with particulates other than minerals: Oil-Particle Aggregates (OPAs) and Oil-Suspended particulate matter Aggregates (OSAs). While the OPA term is the least restrictive (coined by the Boufadel group while addressing the Kalamazoo spill in 2010), the present paper focuses on OMA, since most of the studies have been conducted with minerals. The most extensive information that currently exists is related to OMA. Because the adhesive properties of oil are reduced through the formation of OMA, their formation was initially considered an instrumental process in the natural recovery of oil spillimpacted shorelines and in the efficacy of recovery cleanup techniques such as surf washing (Lee and Stoffyn-Egli, 2001). However, during the 2010 Enbridge Line 6B diluted bitumen oil spill into the Kalamazoo River, a low gradient lowland river, about 10% of the oil sunk to the river bed and was difficult to recover (Fitzpatrick et al., 2015). It was hypothesized that the formation of OMA increased the amount of oil that sunk. Due to the formation of OMA in the Kalamazoo River, concerns have been raised about the potential for OMA formation in the Fraser River and the Salish Sea, in light of oil tanker traffic between Vancouver, BC, and the Pacific Ocean. The conditions during the Kalamazoo spill, however, were very unique: the Kalamazoo River was in flood stage with a high suspended organics content and agglomerates between diluted bitumen oil and organic debris appear to be the cause of sunken oil. Waterman and Garcia’s experiments (2015) hindcast the Kalamazoo conditions and were able to reproduce the sinking of the oil with abundant organic debris. This set of experiments represents, so far, the only published hindcast of the Kalamazoo spill conditions; even though it is understood that NR Can (Dr. Dettman, pers. Comm. during AMOP 2015 Conference) was planning to conduct similar hindcasts over the course of 2015 or 2016. As a result of the Kalamazoo River spill and proposed pipeline and marine terminal development in Burnaby, British Columbia, recent studies have been undertaken to better understand the potential interaction between oil and sediment. This paper presents a literature review of physical experiments followed by a characterization of conditions in the Salish Sea and the Lower Fraser River. This characterization was conducted by means of two sampling campaigns undertaken by the authors, augmented by a literature review of relevant natural conditions in the Fraser River and the Salish Sea. The purpose of this study is to better quantify the extent of OMA formation in these waters. 2

Literature Review for OMA Experiments This section summarizes various OMA experiments that have been conducted in order to characterize the formation mechanism and governing parameters. In the 1980s, Payne et al. (1987) undertook laboratory experiments to quantify the rates and controlling factors important in oil droplet and suspended particulate matter interactions and subsequent sedimentation. They provided semi-empirical formulas for the modelling of OMA formation and calculation of energy dissipation rate. Five main factors contribute to the formation of a stable OMA: 

Quantity, viscosity and dispersed droplet size of the oil (Khelifa et al., 2005). The Royal Society of Canada (Lee et al., 2015) indicates that oils with a dynamic viscosity greater than 500 cP (high viscosity) tend to bind to sediments rapidly. The droplet size depends on the turbulent kinetic energy available;


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

 

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Turbulent energy in the aquatic environment (Cloutier et al., 2002), which determines the oil droplet size and the collision rate between sediment particles and oil droplets. A useful measure of the turbulent kinetic energy is the energy dissipation rate (Hinze, 1955; Delvigne and Sweeney, 1988); Suspended sediment concentration (Ajijolaiya et al., 2006); Grain size of the suspended sediment particles (Ajijolaiya et al., 2006; Khelifa et al., 2003b): OMA formation is more effective for smaller grain sizes, whereby the sediment particles coat the oil particle; Temperature and salinity: higher salinities increase the amount of formation of OMA (Khelifa et al., 2003a; Le Floch et al., 2002).

Most experiments have been conducted in a laboratory with various types of shakers agitating a flask containing oil, water and sediment. While the concentration of each solute is precisely known, the level of energy applied to the system is more difficult to quantify since the energy input is specified as the number of shaker rounds per minute. Kaku et al. (2006 a, b) have measured turbulent kinetic energy dissipation rates (ε) corresponding to various lab conditions: a shaker rate of 50 rpm corresponds to an energy dissipation rate of roughly 2.10-4 m2/s3 regardless of the type of flask (swirling or baffled). A shaker rate of 200 rpm corresponds to approximately 2.10-3 m2/s3 (swirling flask) and 1.10-1 m2/s3 (baffled flaks). He also suggested that a shaker rate of 200 rpm yields energy levels higher than most open‐channel flow environments. The National Academies of Science, engineering and medicine (NAS, 2015) argues that one pathway for sedimentation during an oil spill is the formation of oil-particle aggregates called OPAs. The term OPAs is used in the NAS report in order to encompass all kinds of particulates, i.e. minerals and organics. Two major types of OPAs can be identified: “oil droplets coated by small particles and oil trapped within or adhering to large particles”. The first type of OPAs is more common and has been studied in some detail. The formation of aggregates depends on viscosity, surface areas and the mineralogy of particles as well as the salinity of the ambient water. It has been shown that salinity enhances the formation of OPAs, becoming important at salinities as low as 1/200 that of seawater. The ultimate factor that determines the fate of the OPA is its density in combination with the level of turbulence. Khelifa et al. (2003a) illustrated the important effect of salinity in the stabilisation of OMA. Their experiment considered 200 mg/L of mineral, mixed with 310 mg/L of oil into a reciprocating shaker (160 rpm). Median size for the sediment was 0.6 µm. Increasing the salinity from a baseline of distilled water resulted in increased OMA size and concentration. Le Floch et al. (2002) used a reciprocating shaker (160 to 180 rpm) and sediment concentrations of 200 and 412 mg/L mixed with a 300 mg/L oil concentration: they found that the formation of OMA depended strongly on salinity at low salinity values and tends to stabilize above a salinity of about 2 psu. Khelifa et al. (2005) showed that the formation of OMA is strongly dependent on the kinetic energy dissipation rate. A sediment concentration of 250 mg/L with a median diameter of 3 µm was used in this study. Energy dissipation rate varied from 10-3 (sheltered estuarine) to 10+2 (breaking wave) m2/s3. Five different oils were used ranging from Hibernia (839 kg/m3) to Prudhoe Bay (905 kg/m3). Results showed that OMA did not form when the dissipation rate is below 100 m2/s3. At much higher energy dissipation rates, i.e. 10+2 m2/s3, formation of OMA increases rapidly and varied between 31% of available oil for Alaska North Slope oil to 97% for Hibernia oil.


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Environment Canada (2013) conducted a large set of physical experiments to characterize the behavior of diluted bitumen. Amongst other considerations, the potential interaction between oil and sediment was quantified. Three sizes ranges of particles were considered: Kaolin (1 to 2 µm diameter), diatomaceous earth (44 µm diameter) and sand (200 to 300 µm diameter). A rotary end-over-end mixer was used. While the specifications of the mixer used were not provided, it can be inferred that energy dissipation rate is at least the same level, if not higher, than flasks, assumed to be 1.10-1 m2/s3. A sediment concentration of 10,000 mg/L was added to 600 mL of 33 ppt NaCl brine in a 2.2 L vessel, to which 30 mL of diluted bitumen oil was added. Results concluded that OMA formed. It was acknowledged that such sediment concentration was high, as was the oil concentration. Waterman and Garcia (2015) conducted a set of laboratory tests on Cold Lake Blend (CLB) diluted bitumen to explore the oil-particle aggregates that formed during the Kalamazoo River spill following a pipeline burst of Enbridge Line 6B in July 2010. Tests were conducted with sediments from Talmadge Creek (the initial tributary contacted by the spill) and organic debris. Turbulent kinetic energy dissipation rates varied between 10-1 and 10-3 m2/s3. Initial shaking was conducted at 200 rpm in a baffled flask in order to entrain all of the oil in the water column. Tests were conducted first with abundant organic debris (800 mg/L) mixed with a concentration of 780 mg/L of CLB oil. Another set of experiments was to characterize large-size solid-type OMA and involved 420 to 830 mg/L sediment, mixed with 780 to 1,550 mg/L of CLB oil. Both results showed that OPA formed even in waters with salinity about 1/100 that of seawater. Settling velocities ranged from 1 to 11mm/s; most at 2 mm/s. The authors pointed out that little oil was entrained when shaking at 150 rpm (energy dissipation rate of about 10-2 m2/s3). Hence a higher shaking frequency was used to ensure all oil was initially entrained. Perez et al. (2014) presented interesting results characterizing the formation of OMA in turbulent streams and rivers based on the Kaolinite concentration and the level of turbulence. Intermediate Fuel Oil (IFO) was used for the experiment. IFO was subject to about 10,800 waves in 30 minute of agitation in an automatic shaker. Regardless of the level of turbulence, no OMA formed for sediment concentration less than 2,000 mg/L. When reaching 4,000 mg/L, up to 2.6% of the oil formed OMA in the case of 7 cm waves, and about 4% of the total oil formed OMA when 7 cm waves were combined with a sediment concentration of 18,000 mg/L. The approximate energy dissipation rate was calculated in the order of 2.10-4 m2/s3. Finally, King et al. (2015) conducted experiments at the Bedford Institute of Oceanography in Dartmouth, NS, to study the behaviour of Cold Lake Blend Dilbit when treated with dispersant and mineral fines in a wave tank. Each wave cycle spanned 15 s, characterized by four breaking waves of 0.4 m height, followed by a quiescence period lasting 25 s. Little oil dispersed in the tank, less than 5%, in the presence of fine kaolinite clay minerals. 3

Natural Conditions in the Lower Fraser River and the Salish Sea, British Columbia If a spill were to occur in the waters of South-West British Columbia, two factors are required for the formation of OMA: adequate suspended sediment concentration, and adequate mixing energy, as parameterized in terms of turbulent energy dissipation. In this paper, particular focus has been placed on the Salish Sea, with a main focus on the Fuca-Georgia Strait system, as well as the Fraser River and its delta (Lower Fraser River), since this is a very sensitive ecosystem and contains the highest suspended sediment concentration of the Fuca-Georgia Strait system.


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The Fraser River is the largest river reaching the west coast of Canada, from a flow and sediment discharge perspective. Sediment transport in the Fraser River has been characterized over the past 40 years through various studies and sediment collection campaigns. Most of the field observations described herein were conducted near Hope, Mission and between the Port Mann Bridge and Sand Heads, BC. (Figure 1). Milliman (1979) reported that 80% of the annual suspended sediment load is transported during freshet, about half of which is sand (typically around 300 microns in size); in contrast to non-freshet conditions when silt and clay predominate. Surface sediment concentrations are of the most interest, since they would have the highest potential to interact with a surface spill. Two sediment sampling campaigns were undertaken by the authors of this paper in 2014 and 2016 to characterize these suspended sediment matter near the surface and are presented in Section 3.1. The results of the campaigns are then put in perspective with previous campaigns conducted by others over the past 30 years, described in Section 3.2. Finally Section 3.3 focuses on the level of energy that can be encountered in the Lower Fraser River and the Fuca-Georgia Strait system.

Figure 1

South-West British Columbia and the Fraser River System

3.1

Lower Fraser River Sediment Sampling Campaigns: This Study Two campaigns to characterize suspended sediment concentration in surface waters were conducted in the Lower Fraser River. The first campaign covered the 2014 freshet (May 28 2014 during the peak of the freshet – 9,920 m3/s), while the second campaign looked at typical winter flow conditions (February 16 2016 – 1,380 m3/s). For both campaigns, flow rates were obtained from the publicly available Water Survey of Canada’s website, specifically Fraser River discharge measured at Hope, BC. Figure 2 shows the maximum and minimum Fraser flow rates recorded, as well as the 2014 Fraser flow rates. Blue circles represent Fraser flows during the


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two campaigns and the other data points correspond to the various field campaigns presented in Section 3.2.

Figure 2 Campaign)

Fraser River Flow Rates - Maximum, Minimum and 2014 (First Sampling

Figure 3

Site Sampling Locations


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Samples were taken within 0.2 m of the surface at various sites from the Port Mann Bridge to the Strait of Georgia, as shown on Figure 3. Surface water samples were then sent to ALS Environmental for a Total Suspended Solid (TSS) analysis. The analysis was carried out using procedures adapted from the American Public Health Association (APHA) 2540 D “Solids”. TSS was determined gravimetrically, by filtering a sample through a weighted glass fibre filter, then by drying the residue retained on the filter at 104 ºC. The increase in weight of the filter represents the total suspended solids. It should be noted that samples containing very high dissolved solid content may produce a positive bias by this method. The detection limit at the lab was 3 mg/L. Samples were collected on a falling tide, the tidal phase with maximum river flow and largest suspended sediment concentration. Four sites were sampled during the freshet 2014 survey, as indicated in Figure 3: PM (located at the crossing of the Fraser River and the Trans Mountain Pipeline), FRB, SH and SOG. The delineation of the freshwater from the Fraser River plume and the saline waters of the Strait of Georgia was well marked, representative of typical freshet conditions as shown on Figure 4. While the SH site was still within the Fraser River plume, the SOG site was located in saline water outside of the river plume, well into the Strait of Georgia. Sites are listed from upstream to downstream in Table 1. A maximum surface suspended sediment concentration of 224 mg/L was obtained in the Fraser River downstream of Annacis Island at Site FRB. No conductivity and temperature data were taken during this first campaign. Table 1

TSS – 2014 Freshet Campaign (Fraser Flow: 9,920 m3/s) Site TSS Near Surface Location of Sample (mg/L) PM 208.0 49º 13.009 / 122º 48.389 FRB 224.0 49º 08.674 / 123º 02.553 SH 59.6 49º 06.256 / 123º 20.764 SOG 11.4 49º 05.302 / 123º 23.715

Figure 4 Delineation of Fraser Plume in the Strait of Georgia (Photo from Ocean Networks Canada)


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Similarly, a campaign was conducted in February 2016 where samples were collected at nine different sites, as shown on Figure 3. Low river flow characterized this second campaign and were typical of winter conditions: 1,380 m3/s (Figure 2). The sampling occurred during a falling tide, to capture the maximum influence of the Fraser flow. Measurement of temperature, salinity and conductivity was conducted with a CTD YSI 6600 sonde at each site. The YSI sonde is a water quality monitoring instrument that provides simultaneous measurement of conductivity, temperature and depth. The sonde was kept at about 0.3 m to 0.4 m depth during the recording. A couple of minutes were necessary for the readings to stabilize. Sites are listed from upstream to downstream river in Table 2. Duplicates were taken at various sites and are presented when available. The suspended solids concentration were relatively uniform and ranged from 5 to 18 mg/L, which reflects the low sediment load of the river in February and the low settling rate of the fine grained particles. The maximum of 18 mg/L was obtained at the mouth of the Fraser River near Sand Heads. Low TSS values were associated with a significant variability: TSS values doubled at certain sites between the first sample and the duplicate. The difficulty of the boat to stay on stationary and drifting with currents is one explanation. The boundary between river water and Strait of Georgia water was not as distinct as in the May 2014 campaign, because the momentum and buoyancy fluxes that drive formation of the front are relatively weak during the low flows in February. Table 2 Site

PM NAF FRT FRB LR SMA SH NSH WSH

TSS – 2016 Winter Campaign (Fraser Flow: 1,380 m3/s) Temperature Salinity Conductivity TSS Near Location of Sample (ºC) (psu) Surface (µS/cm) (mg/L) 5.1 0.05 60 13.0 / 10.2 49º 13.054 / 122º 08.501 5.3 0.04 49 9.2 / 6.9 49º 11.847 / 122º 55.521 5.2 0.04 52 8.6 49º 11.584 / 122º 54.997 5.6 0.44 600 5.6 / 5.7 49º 08.907 / 123º 02.348 5.6 2.06 2,481 8.8 / 11.0 49º 06.685 / 123º 05.229 5.5 2.25 2,675 4.7 / 10.8 49º 07.208 / 123º 11.192 5.6 2.86 3,360 9.6 / 8.0 49º 06.612 / 123º 17.101 7.4 20.03 21,500 18.1 49º 06.248 / 123º 20.058 6.9 16.45 17,700 6.9 / 16.2 49º 05.620 / 123º 21.110

3.2 Suspended Sediment Concentrations Characterizing the Lower Fraser River and the Salish Sea The results of the sampling campaigns were combined with various field observations that were conducted at Hope, Mission and near Port Mann Bridge, BC, between the late 1960s and 2010 by other investigators, in particular staff from Water Survey of Canada. These observations are reported in Table 3, along with the maximum total suspended solid (TSS) concentrations near the surface and near the bottom. While the surface concentration is of most importance for interaction with a surface slick, bottom concentrations are given for comparison, when available. Fraser River flow rates corresponding to the sampling time of the various campaigns are shown in Figure 2. Data cover a wide range of Fraser River flows, ranging between low flows of 600 m3/s to high freshet flows above 8,000 m3/s. The winter and early spring low flow season in


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the Lower Fraser River is characterized by a discharge below 2,000 m3/s and a suspended sediment concentration of 7 to 80 mg/L at the surface and 50 to 95 mg/L near the bed (Milliman, 1979; Jiang and Fissel, 2005; Attard et al., 2010). Milliman concluded that outside of the freshet suspended sediment concentration is generally less than 50 mg/L, dropping below 20 mg/L during high tide. Medium flows, ranging between 2,000 m3/s and 6,000 m3/s, are representative of a small freshet and are characterized by a maximum suspended sediment concentration of 200 mg/L near the surface and 400 mg/L near the bottom (Attard et al., 2010). High flows, above 6,000 m3/s, are representative of a medium to strong freshet and are characterized by a suspended sediment concentration of 130 mg/L to 600 mg/L near the surface and 1,000 mg/L to 1,800 mg/L near the bottom (Milliman, 1979). Median suspended sediment diameter ranged between 14 to 47 µm during low to medium flows and reach over 200 µm during high river flows (Attard et al., 2010). Table 3 Year

May-68 Jun-75 Feb-76 Apr-76 May-76 May-76 19771979 Mar-02 Apr-03 Apr-10 May-10 Jun-10 May-14 May-14 Feb-16 *

Maximum TSS based on Sampling Campaigns from Other Investigators Fraser Location Maximum Maximum Source River Surface Bottom Flow Rate TSS TSS (m3/s) (mg/L) (mg/L) 8,330 Port Mann Bridge 300 Milliman (1979) 6,450 Port Mann Bridge 200 1,000 Water Survey of Canada* 1,000 Port Mann Bridge 7 95 Water Survey of Canada* 1,200 Port Mann Bridge 30 Water Survey of Canada* 8,100 Sand Heads 600 1,800 Milliman (1979) 6,860 Port Mann Bridge 130 1,400 Milliman (1979) Strait of Georgia