Environmental Partitioning of Herding Agents Used During an In-Situ Burning Field Study in Alaska

The Deepwater Horizon (DWH) oil release resulted in several important learning outcomes, two of which were: that there is a greater need to be prepared and a significant need to have multiple options available to address oil spills when, where, and how they occur. It also revealed to the public, government, and industry the difficulties which are encountered when responding to an emergency in extreme environmental conditions. In addition to the deepwater marine environment, a correspondingly challenging environment to conduct an emergency response is the Arctic. The Arctic’s uniqueness is derived from its culture, ecosystem, climate, and remoteness (NRC, 2014). Each of these characteristics presents challenges when planning for and responding to an oil spill. When a spill occurs in ice-covered waters, many of the presumptively approved spill response approaches become impractical and/or highly inefficient. However, in-situ burning (ISB) may be a useful oil spill response (OSR) technique in the Arctic, especially in broken ice conditions when mechanical recovery and chemical dispersants are often impractical, or of limited effectiveness.

Since the 1970s, experiments have been conducted on the use of in-situ burning on ice and in open and ice infested waters. These studies have shown that in-situ burning can remove up to 90% or even 98% of the initial oil spill volume (API, 2004; Buist et al., 2013). Several studies have also been performed on the use of surface collecting agents (“herders”) to enhance collection and control of surficial oil spills (Buist et al., 2011; Buist et al., 2013; Buist et al, 2014). Two such products were developed and tested in the 1970’s and 1980’s: Shell Herder and Corexit OC-5 Oil Collector (Pope et al., 1985; Buist et al., 2014). Since that time, herders have continued to undergo extensive laboratory and field testing to further optimize chemical formulation, their uses and application method. The physical and chemical characteristics of the tested surfactant chemicals are documented in their Material Safety Data Sheets (MSDS), EPA submittals and certain publications (Buist et al., 2006; Pope et al., 1985; USEPA, 2016).

Although extensive laboratory testing has been conducted on herders, little is known about their fate in the marine environment. In the applications envisioned, only very small amounts of herder are needed at the outer edge of the slick to thicken it. Although the quantity of herder used is intended to be small, with the use of any novel and/or foreign chemical added to the environment, there is the corresponding need to understand its mechanism of use and persistence. Currently two chemical herders are on the EPA Products list, Siltech OP-40 and ThickSlick 6535 (US EPA. 2016). While both are surfactants, OP-40 is a polysiloxane and ThickSlick is a hydrocarbon with hetero oxygen. OP-40 was used in these tests as it had been previously shown to maintain its effectiveness and had increased ease of operations at lower temperatures (Buist et al., 2013b). In addition, while ThickSlick is readily biodegradable, less is known about environmental fate and degradation of OP-40. (Billings et al., 2016) Thus, the focus of the current work and this paper is on OP-40 and its fate in the environment post use with an in-situ burn.

Specific to this question, a series of field tests were developed and conducted in 2014–2015 to increase our knowledge as to the effectiveness of a combined response option of herder application followed by in-situ burning in cold waters containing surficial ice. The trials were conducted outdoors during the 2015 winter in Fairbanks, Alaska. This paper focuses on the three field tests which utilized OP-40 to thicken the released oil slick.

A field scale test basin was designed and constructed in the fall of 2014 at the University of Alaska Fairbanks Poker Flat Research Range (PFRR) and five field-scale tests were conducted in April 2015. The test facility is located on the road system and is approximately 50 km northeast of Fairbanks, Alaska (Figures 1A and 1B).

PFRR test basin features are:

• The test basin was built from compacted local soil with dimensions of 90m by 90m at a height of 1m.

• The square impoundment was lined with 8218 LTA fusible liner.

• Rock armoring was placed to a minimum thickness of 10 cm and maximum of 20 cm to minimize risk of liner deterioration from heat and fire.

• Metal flashing was placed at the base of the rock layer around the interior perimeter of the basin. The flashing was installed to a height of 35 cm vertical and 15 cm horizontal. The flashing served two purposes; to assist in stabilizing the rock armor and to assist in oil and residue clean-up.

• The basin as-built included 375 man-made grounded icebergs: 66 at 0.9 m diameter, 103 at 0.4 m diameter and 206 at 0.2 m diameter.

• Installation of steel bergs as weather warmed and icebergs melted. Galvanized metal flashing in 2.4 m lengths were formed into rings using one, two or three lengths to form circles of approximately 1 m, 2 m and 3 m circumference. The rings were placed in the basin interior around the oil release mechanism, providing an ‘ice coverage’ of approximately 6% in the area of oil release.

• The basin utilized water from an up-gradient, local lake. [see Figures 2A–2D] (Bullock et al., 2016)

Unweathered Alaska North Slope (ANS) crude oil was used for this study. The field test was designed to test fresh crude oil, as this material was readily available and has a relatively consistent range of chemical and physical parameters. A list of ANS spill-related properties is presented in Table 1, based upon samples tested for a laboratory study. While the ANS used for the field study was obtained from a different refinery than the samples used for the laboratory study, it is expected that the ANS used in the field tests is well represented by the properties detailed in Table 1.

The primary component of OP-40 is 3-(Polyoxyethylene) propyl-heptamethyl-trisiloxane, an organic silicone often used in agricultural applications. Siltech OP-40 properties are detailed in Table 2 (USEPA, 2016).

Three field tests were conducted from April 22 to 25, 2015 using OP-40 herder to assist in conduct of an ISB. At initiation of each test burn, ANS crude oil was released into the middle or slightly upwind location within the test basin. The oil was allowed to expand; however, it was not a test criterion for it to reach equilibrium. Instead, the intent was to apply the herder prior to the oil reaching the sidewall of the test basin. This was intended to reduce test bias resulting from oil being impounded next to a fixed structure. Herder was applied aerially via generally two passes from a helicopter and in some instances from a handheld application unit from the side of the basin. Following release of herder, the helicopter would then land and rig a heli-torch for use as the ignition source for the ISB. This process took 6 to 10 minutes, from herder application to ignition.

Following completion of each burn, residue was collected using sorbent pads, allowed to gravity drain and then weighed in order to calculate burn efficiency. Photo images were taken from aerial drones and the helicopter to document slick size and spread time. Table 3 provides the field test parameters and test results for the burns which used OP-40 herder (Potter et al., 2016).

For the investigation reported here, the source of siloxanes in the aqueous matrix was OP-40, therefore, our analysis could determine the quantity of OP-40 in the matrix without determining the exact composition of the oligomers. A gas chromatography/mass spectroscopy (GCMS) analysis method was established based on the chemical structure determined from the product MSDS. When analyzing pure herder for instrument calibration purposes, the results showed consistent retention times for the peaks and a linear response with concentration (Billings et al, 2016). (Figure 3a)

Chromatograms were also obtained when analyzing Siltech Op-40 heated to 150°C (Figure 3b). This test was completed to determine if the functional groups were altered when heated. As shown, the functional groups maintained consistent peaks. Interfacial surface tension was measured using a duNuoy ring Precision Tensiometer.

To determine if applied herder was present in the ISB field test emission plumes, air sampling was conducted utilizing sampling pumps (SKC AirChek 2000) containing granular activated carbon (GAC). Air sampling was initiated prior to ignition, and continued at least five minutes after combustion had ceased. The air program was designed to sample the ISB plume at the closest downgradient location, with the highest probability for herder detection. Therefore, air sampling was performed approximately 10 m downgradient of the bermed test basin (Figures 5A and B) (Sartz et al, 2016).

To determine concentration of herder in water, a sampling program was developed to monitor depth composite samples over time in the basin, post completion of the five test burns. Sample locations were identified through use of a random number generator which resulted in the locations as shown on Figure 6. Samples were collected within five feet of each location.

The burn residue for each test was collected from the water surface following each test burn using polypropylene sorbent booms and pads. These pads were also used to remove residual oil which had adhered to the manufactured test components: the steel ice berg forms, and the basin metal sheeting at water surface. Care had been taken during each test to limit the potential impingement of the oils on the floor of the test basin; therefore, there was no observable residual oil to remove from this location. Residue collection performed by Alaska Clean Seas served three purposes, to clean the basin between burns, to provide for residue weight and burn efficiency calculations and to allow for laboratory testing of the residue itself.

The test basin residue of unweathered ANS floated and was readily recovered. Shinganaka et al, reported that highly weathered and emulsified oil from DWH generally sank (Shinganaka et al, 2014). It is anticipated that if the residue had been left in the water overtime and in the natural marine environment, this residue would likely sink. (Figure 7).

One of the major public concerns when choosing in-situ burning as an oil spill response measure are the potential impacts to air quality (Fingas, 1995). Air samples were collected during each ISB. Following the GCMS testing described herein, no herder was detected in any sample above the method detection level. This corresponds with the understanding that the reaction mechanism for herders is one of temporary adjustment to surface water tension which allows the oil to contract and thicken; thereby minimal herder should come in contact with the oil, ignition and resultant particulate emissions. Therefore, ISB emissions would be anticipated to remain generally the same with or without the addition of herders. (See Figure 8)

Water samples were collected from the PFRR test basin for approximately 2 months following completion of the five field test burns. Samples were analyzed for surface water tension and OP-40 herder. A select number of samples were measured for hydrocarbons as part of the field test permit. Field observations were noted for depth of basin water, oil sheen, wind direction and velocity and basin surface water conditions.

During this observation and sampling period, a significant amount of evaporation occurred. As noted in Figure 9, by the end of the monitoring period the water depth within the basin was too low to sample further. No water discharge was implemented and the wastewater discharge permit closed. This influenced some of the water results as it concentrated the water in pooled locations in low areas of the basin as well as in the northwest corner which was the prevalent wind direction.

As herder is applied to the water surface and is intended to reside on the surface, it was anticipated that this location would have the greatest levels of measured herder. Surface water tension was used in the field and laboratory to test whether herder was still present at sufficient concentration to cause interference with subsequent field tests. As part of the test protocol, Alaska Clean Seas (ACS) would physically mix the water column to reduce herder at the surface as necessary. The results shown in figure 10a show surface water tension of the basin at baseline, directly post the five field tests and then over an approximate two month period. As noted, the surface tension was nearly back to baseline within three weeks.

The same test basin water samples which were tested for surface tension, were also analyzed for OP-40 herder. As anticipated, there was no herder found as part of the baseline sampling, it then spiked following the 5 test applications, and then reduced to approximately the method detection limit within one month. (Figure 10b)

In order to provide additional understanding of herder behavior in water, water samples were prepared and analyzed in a controlled setting within the laboratory. Herder was tested when added to both deionized (DI) water as well as 35ppt saltwater to test for surface vs depth concentrations. Figure 10c shows the differentiation of herder concentration at the surface vs depth. The herder concentrations were found to be 80–87% in the top cm of the water surface with DI water, and 98% in the top cm of surface water when added to salt water.

Burn residues which were observed post the ISBs are in two forms; residual oil which tends to remain on the water surface and is too thin to be effectively burned, and burn residue which result in a thicker, dense residue which can sink overtime. Both residues have low volatile compounds, as these are readily burned as part of an ISB (Fingas, 2016). The development of an analytical method to measure herder in residue continues as part of further research.

The possibility of igniting an oil slick in the Arctic by aircraft provides the opportunity to address many logistical and operational concerns with ISB use in the Arctic. This possibility however exists only when there is sufficient oil thickness to achieve ignition. The addition of herders provides the possibility to thicken the released oil, and ignite and conduct a burn. This allows for increased burn efficiency, which should correspondingly further reduce the ISB constituents of concern.

The environmental effects of ISB without the use of herders has been documented in numerous tests and publications (NRC, 2014; Buist et al., 2013b; Fingas, 1995; Allen et al., 1993). The study reported here was structured to collect and analyze each environmental media for which an introduced chemical into the environment may create an exposure pathway (air, water or residue).

OP-40 herder was not detected above the laboratory detection method in the air samples, therefore, is not anticipated to modify ISB emissions. OP-40 was measured in the water column, with the majority at the water surface. The concentrations of herder degraded overtime, with the majority in the first three weeks. Given the purposeful mixing of the water column between each trial burn to return surface tension to near baseline, the multiple applications of herder and the confinement of the water within the basin, the water results should be viewed as conservative. The residue continues to be a work in progress. The residue by volume and toxicity has been shown to be less than the released oil (Shigenaka et al., 2014; Fingas, 2016). The herder would not be anticipated to increase the volume or toxicity of this residual material. The final disposition of the burn residue should continue to be made on a spill by spill basis, depending on the environmental, management and safety considerations of the spill location and operations.

The research studies described in this paper were funded by the State of Alaska Petroleum Engineering Research for Hydrocarbon Optimization and the Institute of Northern Engineering. The design and construction of the University of Alaska Fairbanks Poker Flat Research Facility Test Basin and field tests described herein were funded by the International Association of Oil and Gas Producers (IOGP) Arctic Oil Spill Response Technology - Joint Industry Program (JIP). Particular thanks go to Shane Billings, Bill Krause, Jessica Garron, Al Allen, Dave Barnes, SL Ross, Alaska Clean Seas, and Chief Doug Schrage and Deputy Chief Ron Templeton with the University of Alaska Fire Department for their assistance with this research and maintaining safe operations at the field test facility.