Common Shoreline Response Options
Oil spills in the environment that threaten a shoreline are met with a variety of response options for the containment, cleanup, or protection of sensitive resources and structures. This toolbox of response strategies is an ever-evolving list of options that has no singular “right” option for all spills. Each release of oil carries unique challenges and considerations. The oil type and its particular chemistry and characteristics, such as viscosity, emulsification, and environmental considerations, such as shoreline type and sensitivity of habitat, must be considered when choosing a response method. Appendix G describes shoreline types and expected oil behavior in detail; the more advanced responses: surface-washing agents, burning of oil in marshes, and bioremediation are described in Section 4.2.4. The following is an abbreviated description of some of the most common forms of shoreline response and cleanup methodologies.
E.1 BARRIERS, BERMS, AND TRENCHING
- Barriers and berms are structures that are often built from materials at hand such as soils and sands that are purposely designed, built, and/or deployed to prevent migrating oil across it or to divert the direction of flow of the oil. Other materials and designs include but are not limited to sand bags, wood, timbers, metal, or fiberglass sheet-pile. Responders must seriously consider disruptions of water flow and destruction of vegetation in the construction or deployment process.
- Underflow dams often share similar construction materials and designs as those of barriers and berms. An underflow dam utilizes a system of channels or pipes that divert water from below the water line, on the upstream side of the dam where the oil is collecting, to the downstream side, thereby stopping the oil migration for collection and allowing clean water to pass.
- Trenching is a method of directing the movement or collection of oil by physical excavation of a pathway below the normal topographic elevation. As with any earth movement response options, care must be taken not to permanently disrupt normal water flow of an area or cause permanent vegetation or impacts to other habitats.
E.2 NATURAL ATTENUATION
Also known as response by natural recovery, this is one of the most often used response options available. Oil can be left in place to degrade naturally as a variety of processes immediately begin to remove, relocate, and degrade oil once it enters into the marine environment. A non-exhaustive list includes evaporation, dispersion, photo-oxidation, and microbial degradation (see Section 5.1). Components of crude oil are found in the environment and, assuming that they are accessible to the degrading processes and processors along with necessary nutrients, natural attenuation (NA) will occur, although residual oil may remain for years or decades. When this process of non-intervention is coupled with a monitoring and reporting system, it is called monitored natural attenuation (MNA).
One of the benefits to this method is that, unlike almost all other human responses to oil, NA and MNA are much less likely to inflict ancillary impacts on the environment. Whenever personnel actively enter a spill area, transferring the oil to a new vulnerable location is possible and having the responders themselves placed into the hazardous zone is unavoidable. By allowing for NA these possibilities are minimized. However, NA is a much slower process than many other responses, and this must be considered. During this residence time there is a higher potential of secondary contamination of nearby areas, further impacting the environment. Two methodologies used to augment the processes of NA are shoreline tilling and surfwashing, described below. It should be noted that the removal or redistribution of materials from a beach inherently carries an additional burden of potential habitat destruction and may accelerate erosion of the location.
E.2.1 Tilling and Aeration
Oil that has stranded on the shoreline is often subjected to burial by sand, shell, cobble, or other materials due to response activities, wave action, and tidal cycles. Once buried, this oil is often deprived of oxygen, which may slow the degradation processes. To bring the oil to the surface for the faster aerobic NA process to continue, substrate tilling is often done. This tilling brings oil into an area where it is no longer sequestered from oxygen and thus degrades much more quickly. The tilling process also tends to break up the oil into smaller particles, resulting in a larger surface area for natural processes to more efficiently proceed.
Also called translocation, surfwashing is another form of response that not only allows for more efficient NA of oil but improves access to the oil for further physical cleanup measures. This response involves the manual or mechanical movement of oiled substrates such as sand, shell, or cobble that have been subjected to oiling back into the sea. This response measure utilizes the continuous force of wave action to remove and break up oil that has contaminated the shoreline materials. This oil can then be accessed by natural degraders and at times even recovered with other response technologies.
E.3 MANUAL OIL RECOVERY OR CLEANING
Manual oil recovery or cleaning of a shoreline is the technique of removing or remediating oil from a surface using hands and hand tools (rakes, shovels, scrapers, etc.) including cloth or sorbent materials, and placing the materials into containers for collection, recovery, removal, and possible disposal. These methods may be employed on all shoreline types. They are often labor intensive but also allow for a more precise cleanup of small or hard-to-reach surfaces. Manual operations may pose a risk to response personnel by placing the responders in direct or close contact with the oil and necessitating the need for the responders to access hazardous areas and positions where the oil made contact with the surface. Manual oil recovery is often used in conjunction with other cleanup methodologies such as surface-washing agents or mechanical cleanup.
E.4 MECHANICAL CLEANUP
Mechanical cleanup involves the use of light, medium, and heavy machinery, often not designed as a specific tool for oil spill response. Equipment such as road graders, maintainers, front end loaders, bulldozers, compact excavators, and lawn/garden equipment are just a few examples of equipment that is often brought into the response. This type of machinery has considerable pros and cons that need to be considered before use. Mechanical recovery has the potential to expedite the removal of large quantities of oil from an affected area. Oil stranded on a beach or buried in the sediment can be removed, allowing for an area to be reopened for public use or for species at risk to utilize without the hazard of secondary contamination. Oil is either scraped off the surface as efficiently as possible, or large amounts of sediments are collected for oil separation or removal. Regardless of the care taken, mechanical excavation of stranded oil additionally removes a massive amount of irreplaceable sediment that provides equally important areas of forage, habitat, and recreational opportunities. Another method involves the mechanical removal of gross amounts of contaminated sediment such as sand, shell, or cobble, which is then cleaned by methods such as incineration or cleaning baths and then returned to the original location. This methodology still has the propensity to harm biota within and utilizing the substrate.
- Specialized mechanical equipment. Some mechanized equipment has been developed specific to oil spill response with the intent to remove the contamination while minimizing secondary detrimental impacts to the environment. These devices utilize methods such as sweeping, sifting, or vacuuming to remove the contamination, which is then recovered for proper disposal or reclamation. These pieces of equipment are heavy and, although less invasive than other mechanical equipment operations, still may disturb and impact local flora and fauna utilizing the area.
- Vacuum systems. This method involves the use of small to large air vacuum systems, from small self-contained systems to large truck- and vessel-mounted systems, with or without external storage tank systems that can operate in a wet environment. Vacuum systems are used on floating oils that can be sucked off the surface of the water or substrate. The material collected may contain large quantities of water if skimmed on or near the water. A process of decanting can be utilized on site to separate the liquids, with oil being reclaimed and the water either returned to the environment, if permitted, or disposed of. Vacuum systems can be very efficient but are dependent on an operator’s skill level.
Sorbents are a method of oil removal utilizing an oleophilic material that is either absorbent or adsorbent to capture or clean oil from the water surface or a solid substrate for disposal or reclamation. Many types of sorbent materials are available, with many meant for specific applications. Oil sorbents are made of many types of materials including natural products such as cellulose from trees, plants, seeds, hair, and clays. Synthetic products are widely available and used and offer the ability to be both oleophilic as well as hydrophobic. Used materials can have the oils collected, squeezed out,
and recovered, and the sorbent reused, but more often it is not efficient from the cost and logistics perspective; hence both the sorbents and oil are usually disposed of. A few of the methods are described below. It should be noted that the U.S. Environmental Protection Agency (U.S. EPA) requires that all sorbent materials used be removed after deployment and use.
- Flat pads and sheets. These adsorbent products are often referred to as diapers, sorbent pads, or “sweep” when configured in an elongated fashion. These are some of the most widely used sorbent products within the industry. Sheets are made of either natural or synthetic material and are used extensively for routine maintenance and cleanup operations. Sheets that are synthetic are both oleophilic and hydrophobic, which makes them amenable to deployment directly into the water where the oil is taken up into the pad. Pads can be deployed in open water and in confined spaces or used directly on oil surfaces to remove the contamination. Sweep is sometimes deployed as a barrier around sheens to retard migration of the thin oil. Saturated sheets are then manually removed for disposal or recycling.
- Sausage boom. This is made of the same variety of adsorbent materials as sorbent pads and sheets. This response option is manufactured in a cylindrical manner with varying diameters and lengths, often with attachment points for joining to create an elongated response option specific to the need. A sausage boom can be used as a response option where oil is actively corralled and collected by the boom and removed when saturated or as a defensive response at outfalls or around fueling vessels and oil transfers as a precautionary response.
- Snare. Snare is also referred to as pom-poms, due to its resemblance to the hand-held tufts used by cheerleaders. This response option consists of varying lengths of thin strips of oleophilic, hydrophobic, usually synthetic material that can be deployed defensively or offensively. Snare is particularly good at picking up tacky oils that other sorbent products do not perform as well on. It can be used manually where it is directly administered to an oil product or left to collect oil that may migrate to its location.
- Loose sorbent. Also known as bulk sorbents, this methodology involves the use of a particulate or granular absorbent or adsorbent material that is applied or otherwise positioned to encounter an oil product, after which the contaminated material is retrieved for proper disposal. These materials are made from natural products such as sorghum, cotton seed hulls, clays, and so on as well as synthetic materials and are deployed manually or by an air blower system. Loose sorbents are used extensively to clean up land spills but are generally not an acceptable form of response of on-water recovery as containment and retrieval of the material is problematic. One application of loose sorbents that historically has been used is the deployment of the material onto oiled surfaces such as plants and other areas where there is a high potential of secondary oiling of avian, invertebrate, and other biota. The loose material reduces the tackiness of the oil, thereby protecting species that may encounter it. Materials that cause an oil to sink, aka sinking agents, are not authorized for use in U.S. waters.
- Solidifiers. Though sometimes considered within the same category as loose or other similar sorbents, these differ in that the materials are most often dry polymers that are oleophilic in nature and have physical properties similar to oil. These materials not only sorb oils but also form bonds between oil particles, resulting in masses of material that can be retrieved more easily than if contained with loose sorbent material. These products are considered a chemical response alternative and thus must be approved for use by the U.S. EPA with authorization from the applicable Regional Response Team prior to use.
E.6 WATER WASHING, FLASHING, AND DELUGE
This method is one of the most common and widely accepted forms of response to oil that has impacted man-made structures, vegetation, or other natural shorelines. Oil tends to exhibit nonpolar tendencies and thus adheres firmly to other materials. Water is polar and must exert force on an oil sufficient to break the surface tension between the oil and solid surfaces to which it may attach. Using water to remove oil that has coated such structures carries the risk of unintended or unanticipated secondary impacts. The force necessary to remove oil from a solid surface may also cause harm to biota that utilize that surface as a home or an area of forage. The water may cause erosion to the substrate, disrupting or even permanently altering the normal water flow. A consequence of water washing is that, once removed, the oil is then free to migrate further unless properly captured, potentially contaminating other areas or structures. Some common methods of water washing under different temperatures, pressures, and orientation of flow are discussed below.
- Low pressure washing. This method utilizes seawater at pressures generally <10 psi to forcibly move or remove pooled and trapped oil from interstitial spaces to locations where another form of cleanup can be undertaken. Low pressures generally are less disruptive to resident and encrusting organisms and cause less erosion issues than more aggressive pressures. Low pressures do not generally remove all contamination from a surface: those areas are either allowed to be further
- cleaned using manual or chemical alternatives or by natural degradation and hydrodynamic processes.
- High pressure washing. This method utilizes seawater at much greater pressures, generally >100 psi. These high pressures are often sufficient to remove highly viscous or tacky oils, or oils that have weathered and adhered to surfaces. This is a highly efficient method of removing oil from a surface and relocating it to where it can be removed by some other response method. High pressures may have the detrimental consequence of removing encrusting flora and fauna or causing erosional issues. Organisms removed may take very long periods of time to recover, and areas eroded can also suffer long-lasting impacts. Another known issue is the possibility of creating oil droplets small enough to disperse into adjacent waters, causing additional impacts to aquatic organisms.
- Low and high temperature washing. Though not a distinct method of washing, different seawater temperatures can be employed at both low and high pressure to aid in the removal of oils that have adhered to a solid surface. High temperature washing at water temperatures of >30°C to very hot (but below that which would be steam, discussed below) can be employed to loosen stubborn oil. Higher temperatures applied either at low or high pressure may also increase detrimental secondary impacts of the relocated oil.
- Steam cleaning. This method utilizes steam that is directed onto a solid substrate to remove oil and adhered residues. Much less water is needed for this type of application, and thus less volume is generated for subsequent cleanup. This is method is highly intrusive to resident organisms; as such, it is usually reserved for areas that are being cleaned for aesthetics or when other removal responses have been attempted and found inadequate to achieve the desired level of cleaning.
- Deluge. Also called flooding, this method of spill response involves the inundation of an area with copious amounts of water deployed in a sheet flow scenario meant to lift and migrate oil away from its stranded location along a shoreline. This method can be used to remove oil that has made its way deep within vegetated areas, such as mangrove roots or marsh vegetation, or deeply embedded with cobble or boulders. Care should be taken to avoid channelization of the applied waters, which may cause erosion issues.
- Sandblasting and dry ice blasting. Though not often used, both sandblasting and dry ice blasting have been used to remove oil from solid substrates. Both methodologies employ high pressure air systems with a secondary material that abrades adhered oil from the surface. These methods are good for removing stubborn oils but may heavily impact the surface biota. Dry ice blasting involves the use of dry ice pellets (frozen carbon dioxide) as the abrasive. It has the benefit of not adding any additional secondary waste material that would need to be cleaned in addition to the removed oil.
E.7 VEGETATION CUTTING
This response involves the cutting and removal of all or parts of the affected vegetation that has been subjected to oiling from a release. This method increases the efficacy of oil removal from the substrate and that which has clung to the vegetation. The cutting and removal of oiled vegetation decreases the possibility of secondary impacts to wildlife using the area for foraging or shelter and aids survival of existing vegetation or regrowth of new vegetation. Vegetation cutting should only be done after consultation with resource managers familiar with this methodology as the location, season, type of oil, and species of plant and their susceptibility to the oiling must be considered to prevent longer term impacts to the area than would be seen by using other response options. The vegetation may also be considered critical habitat or be a habitat for species of concern and thus fall under the jurisdiction of state and federal agencies that must provide approval for this type of response action.
E.8 DEBRIS REMOVAL
As the name implies, this response involves the recovery of (un-oiled) debris located within the area of a potential spill impact and which may be subject to being oiled. Removal of this material must be determined to be beneficial to the overall response in some way. Debris that has been oiled becomes a hazardous material and will need to be cleaned or removed by personnel having proper training and credentials and must be transported to an appropriate waste management site. Pre-spill debris removal is a common preemptive response operation as this material can represent a significant mass given the amount of driftwood, timbers and seaweed, algae, and so forth that may be found on a shoreline and be subject to oiling. If materials can be relocated pre-spill, significant savings of response time and waste generation during spill mitigation may be realized. As pre-spill debris removal does not require personnel with hazardous waste response training, many areas have identified this effort as being amenable to volunteers during an oil spill.