Daily Rules, Proposed Rules, and Notices of the Federal Government
* Hand delivery or mailing of comments via paper or disc should be addressed to Michael Payne, Chief, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910.
Comments regarding any aspect of the collection of information requirement contained in this proposed rule should be sent to NMFS via one of the means provided here and to the Office of Information and Regulatory Affairs, NEOB-10202, Office of Management and Budget, Attn: Desk Office, Washington, DC 20503,
A copy of Port Dolphin's application may be obtained by writing to the address specified above (see
Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361
Authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s), will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses (where relevant), and if the permissible methods of taking and requirements pertaining to the mitigation, monitoring and reporting of such takings are set forth. NMFS has defined “negligible impact” in 50 CFR 216.103 as “* * * an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.”
Except with respect to certain activities not pertinent here, the MMPA defines “harassment” as: “any act of pursuit, torment, or annoyance which (i) has the potential to injure a marine mammal or marine mammal stock in the wild [`Level A harassment']; or (ii) has the potential to disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering [`Level B harassment'].”
On February 1, 2011, NMFS received a complete application from Port Dolphin for the taking of marine mammals incidental to port construction and operations at its Port Dolphin Deepwater Port (DWP) facility in the Gulf of Mexico (GOM). During the period of these proposed regulations (June 2013-May 2018), Port Dolphin proposes to construct the DWP and related infrastructure—expected to occur over an approximately 11-month period, beginning in June 2013—and to subsequently begin operations. The proposed DWP, which is designed to have an operational life expectancy of 25 years, would be an offshore liquefied natural gas (LNG) facility, located in the GOM approximately 45 km (28 mi) off the western coast of Florida, and approximately 68 km (42 mi) from Port Manatee, located in Manatee County, Florida, within Tampa Bay (see Figure S-1 in Port Dolphin's application). The DWP would be in waters of the U.S. Exclusive Economic Zone (EEZ) approximately 31 m (100 ft) in depth. The proposed DWP would consist principally of a permanently moored buoy system, designed for offloading of natural gas, leading to a single proposed new natural gas transmission pipeline that would come ashore at Port Manatee and connect to existing infrastructure.
Take of marine mammals would occur as a result of the introduction of sound into the marine environment during construction of the DWP and pipeline and during DWP operations, which would involve shuttle regasification
Port Dolphin proposes to own, construct, and operate a DWP in the U.S. EEZ of the GOM Outer Continental Shelf (OCS) approximately 45 km (28 mi) off the western coast of Florida to the southwest of Tampa Bay, in a water depth of approximately 31 m (100 ft). On March 29, 2007, Port Dolphin submitted an application to the U.S. Coast Guard (USCG) and the U.S. Maritime Administration (MarAd) for all federal authorizations required for a DWP license under the Deepwater Port Act of 1974 (DWPA). Port Dolphin received that license in October 2009. The Port would consist of a permanently moored unloading buoy system with two submersible buoys separated by a distance of approximately 5 km (3 mi). The buoys would be designed to moor a specialized type of LNG carrier vessel (i.e., SRVs) and would remain submerged when vessels are not present. Regasified natural gas would be sent out through the unloading buoy to a 36-in (0.9 m) pipeline that would connect onshore at Port Manatee with the existing Gulfstream Natural Gas System and Tampa Electric Company (TECO) Bayside pipeline. The DWP would only serve SRVs. Construction of the DWP would be expected to take 11 months. Port Dolphin DWP would be designed, constructed, and operated in accordance with applicable codes and standards and would have an expected operating life of approximately 25 years. The locations of the DWP and associated pipeline are shown in Figure S-1 in Port Dolphin's application; Figure 1-1 of the same document depicts a conceptual site plan for the DWP.
The installation of the DWP facilities would include the construction and installation of offshore buoys, mooring lines, and anchors. The two unloading buoys, also known as submerged turret loading (STL) buoys, would each have eight mooring lines connected to anchor points, likely consisting of piles driven into the seabed. When not connected to a SRV, STL buoys would be submerged 60 to 70 ft (18 to 21 m) below the sea surface. The installation of the pipeline from the DWP to shore would include burial of the pipeline, selective placement of protective cover (either rock armoring or concrete mattresses) over the pipeline at several locations along the pipeline route where full burial is not possible, and the horizontal directional drilling (HDD) of three segments of the pipeline.
SRVs are specialized LNG carriers designed to regasify the LNG prior to off-loading for transport to shore. Each STL buoy would moor one SRV on location throughout the unloading cycle. An SRV would typically moor at the deepwater port for between 4 and 8 days, depending on vessel size and send-out rate. Unloading of natural gas (i.e., vaporization or regasification) would occur through a flexible riser connected to the STL buoy and into the pipeline end manifold (PLEM) for transportation to shore via the subsea pipeline. With two separate STL buoys, Port Dolphin may schedule an overlap between arriving and departing SRVs, thus allowing natural gas to be delivered in a continuous flow.
Port Dolphin is planning for an initial natural gas throughput of 400 million standard cubic feet per day (MMscfd). Although the Port would be capable of an average of 800 MMscfd with a peak capacity of 1,200 MMscfd, this level of throughput would not be achieved during the span of this proposed rule. Based on a regasification cycle of approximately 8 days and initial throughput of 400 MMscfd, maximum vessel traffic during operations over the lifetime of the proposed 5-year regulations is projected to consist of 46 SRV unloadings per year.
In the open ocean, SRVs typically travel at speeds of up to 19.5 kn (36.1 km/hr). When approaching the vicinity of the DWP (i.e., during approach to the DWP), the SRVs would typically slow to about half speed. In close proximity to the STL buoys, the SRVs would slow to dead slow and utilize thrusters to attain proper vessel orientation relative to the DWP, taking into consideration ambient ocean currents, wind conditions, and buoy position. The following subsections describe the Region of Activity and the preceding facets of construction and operation in greater detail.
The GOM is a marine water body bounded by Cuba on the southeast; Mexico on the south and southwest; and the U.S. Gulf Coast on the west, north, and east. The GOM has a total area of 564,000 km
The GOM is separated from the Caribbean Sea and Atlantic Ocean by Cuba and other islands, and has relatively narrow connections to the Caribbean and Atlantic through the Florida and Yucatan Straits. The GOM is composed of three distinct water masses, including the North and South Atlantic Surface Water (less than 100 m deep), Atlantic and Caribbean Subtropical Water (up to 500 m deep), and Subantarctic Intermediate Water.
Circulation within the GOM, and within the project area, is dominated by the Loop Current, which enters the GOM flowing north through the Yucatan Strait, flows south along the Florida coast in the vicinity of the project area, and exits the GOM through the Florida Straits. The velocity of the current in the project area ranges between 1.56 and 15.16 cm/s in summer, and 1.79 to 25.36 cm/s in winter (APL, 2006). The direction of flow in the project area is generally south to southeast.
In shallow areas along the west Florida Shelf, additional influences on water flow and circulation include wind stress, freshwater inflow, and variations in buoyancy (Gore, 1992). Wind speeds at the project site range from 2.26 to 7.61 m/s in summer, and 2.85 to 11.04 m/s in winter (APL, 2006). Tidal variation along Florida's west-central continental shelf is moderate, with an average range of approximately 2 ft (0.6 m) (Gore, 1992).
At the eastern edge of the Loop Current along the west Florida Shelf, circulation patterns result in an upwelling of deep nutrient-rich water. This upwelling supports a high level of biological activity, producing large concentrations of plankton. Nutrient levels (primarily nitrogen and phosphorus) are also affected by runoff from agricultural and urbanized areas and from submarine groundwater discharge, leading to red tide conditions. In the project area, red tide occurs on an almost annual basis (Hu
Extreme variations in water circulation patterns, tides, and wave heights can occur along the west Florida coast during periodic tropical storms and hurricanes. Warm water within the Loop Current can act as an energy source in summer and fall months, fueling the development of these storms. Features of these storms that can affect natural circulation and topography include high winds, flooding, storm surges, and beach erosion.
Tampa Bay is an estuary formed by the rise of sea level into a former river valley. Tampa Bay consists of four subregions, including lower Tampa Bay, middle Tampa Bay, Old Tampa Bay, and Hillsborough Bay. The project area would only extend to Port Manatee, within Lower Tampa Bay, near the outlet of the bay into the GOM. The bay covers an area of 1,030 km
Water circulation within the bay is driven by freshwater inflow, tides, and winds. The bay has an average depth of 3.5 to 4 m. There is well-developed horizontal stratification in the bay, with fresh water flowing along the surface out to sea, and denser saline water flowing into the bay along the bottom.
The Tampa Bay area has a population of more than two million people, and tributaries, habitat, runoff patterns, and water quality are all affected by urbanization. Specific actions that have affected the bay include removal of mangroves, dumping of sewage, artificial filling, and modification of runoff from paved surfaces (Peene
Port Dolphin has requested regulations governing the incidental take of marine mammals for the five-year period from June 2013 through May 2018. Construction and installation of the port and pipeline would last approximately 11 months, with subsequent operations (i.e., SRV docking and regasification) occurring for the remainder of the specified time period.
The DWPA establishes a licensing system for ownership, construction, and operation of deepwater ports in waters beyond the territorial limits of the United States. Originally, the DWPA promoted the construction and operation of deepwater ports as a safe and effective means of importing oil into the United States and transporting oil from the OCS, while minimizing tanker traffic and associated risks close to shore. The Maritime Transportation Security Act of 2002 amended the definition of “deepwater port” to include facilities for the importation of natural gas.
LNG is natural gas that has been cooled to about −260 °F (−162 °C) for efficient shipment and storage as a liquid. LNG is more compact than the gaseous equivalent, with a volumetric differential of about 610 to 1. LNG can thus be transported long distances across oceans using specially designed ships (e.g., SRVs), allowing efficient access to stranded reserves of natural gas that cannot be transported by conventional pipelines.
This proposed STL buoy system differs from other common LNG offload technologies insofar as it does not involve any permanent storage or regasification facility at the DWP, thus minimizing required infrastructure at the DWP itself. Rather, STL buoys receive SRVs that contain onboard LNG vaporization equipment. After mooring, LNG is vaporized onboard the vessel and discharged via the unloading buoy and a flexible riser into the subsea pipeline. Because the LNG is vaporized with the SRV's onboard equipment, no permanent fixed or floating storage or vaporization facilities are required. However, this means that the offload process can take 5 to 8 days, as compared with a standard offload of 18 hours or less. As a result of this trade-off, continuous off-loading operations are essential to minimize fluctuations in the throughput of natural gas. The SRVs proposed for use would be equipped to transport, store, vaporize, and meter natural gas. A closed-loop, glycol/water-brine heat transfer system would be used to vaporize the LNG. Closed-loop systems burn vaporized LNG in order to heat an intermediate fluid (e.g., glycol/water-brine), which warms the LNG. The closed-loop system results in reduced environmental impacts on water quality and marine resources; although these systems do require seawater for use in cooling electrical generating equipment (resulting in subsequent entrainment of fish eggs and plankton, as well as discharge of water at elevated temperatures), such usage is significantly reduced from that required in an open-loop system.
SRVs with approximate cargo capacities of either 145,000 m
The SRVs would have two thrusters forward and could have one or two thrusters aft. Thrusters allow precise control of positioning while mooring with the STL buoy. The dynamic positioning system would be used while retrieving the submerged unloading buoy handling line and moving onto the buoy. The system normally would not be used while the SRV is moored to the unloading buoy. SRVs would be equipped with an acoustic position reporting system that would monitor the buoy's draft and position before and during connection/disconnection; this would be enabled by six transponders located on the buoy itself.
Seawater would be used to ballast the SRV, cool the dual-fuel diesel engines supplying power for the regasification process, and condense the steam produced by the boilers supplying heat to the vaporization process. Ballasting the SRV is required to maintain proper buoyancy as the LNG is vaporized and offloaded through the pipeline. Water intake for ballasting the SRV would require an average intake of 360 m
Cooling water discharges would be made at points removed from the intake sea chests to avoid recirculating warmed water through the cooling system. All of the cooling water would be discharged
In-water construction of Port Dolphin is expected to begin in June 2013 and last a total of approximately 11 months. Construction would include siting the STL buoys and associated equipment and laying the marine pipeline. Construction is assumed to be continuous from mobilization to demobilization with no work stoppages due to weather or other issues. Please see Table 2-1 of Port Dolphin's application for a graphical depiction of the complete timeline of proposed construction activities. Port Dolphin anticipates that construction/installation would be accomplished in the following sequence:
• Install the Port Manatee HDD section, with installation proceeding from onshore to the offshore location.
• Install the anchor piles and the mooring lines using the main installation vessel at the DWP.
• Construction and installation of the HDD pipe sections for the segments under the existing Gulfstream pipeline.
• Install seabed pipe segments between the Port Manatee HDD segment and the Gulfstream HDD segments.
• Install the Skyway Bridge section of the pipe (requiring dredging through the causeway).
• Install the STL Buoys.
• Install the two risers from the PLEMs.
• Install the north and south PLEMs.
• Perform pipelay and diving operations towards the Y-connector.
• Install the flowlines on the seafloor.
• Complete tie-ins and bury or armor the pipeline, as necessary.
• Conduct testing of the pipeline upon completion of burial operations.
These components of in-water construction are discussed in greater detail in the following subsections.
The mooring lines would be designed so that the SRV could remain moored in non-hurricane 100-year storm conditions, and would vary in length, from 1,800 to 4,000 ft (549 to 1,219 m) for the northern unloading buoy and from 2,500 to 3,600 ft (762 to 1,097 m) for the southern buoy. The mooring lines would consist of 132-mm (5.2-in) chain and 120-mm (4.7-in) spiral-strand wire rope. The riser system for each unloading buoy would consist of one 16-in interior diameter flexible riser in a steep-wave configuration. Total length of the riser would be approximately 82 m (269 ft). The riser would be directed between two of the mooring lines, and would lie on the seafloor when not in use.
The two PLEMs near the unloading buoys would connect the flexible risers to the flowlines and a Y-connection that would connect the two flowlines to the new gas transmission pipeline. Each of the two PLEMs would be approximately 75 m (246 ft) offset from the proposed unloading buoy locations. The purpose of a PLEM is to provide an interface between the pipeline system and the flexible riser, isolate the riser between gas unloading operations, and attach a subsea pig launcher or receiver as necessary. “Pigs,” or “pipeline inspection gauges,” travel remotely through a pipeline to conduct inspections of or clean the pipeline and collect data about conditions in the pipeline. Each PLEM would include a flange connection for attaching the flexible riser or the subsea pig launcher/receiver and a full-bore subsea hydraulic control valve and electrohydraulic umbilical termination assembly. Each PLEM would have a mud mat foundation to provide a stable base for bearing PLEM and riser weight and to resist sliding and overturning forces. Please see Figure 1-1 in Port Dolphin's application for a conceptual diagram of the DWP.
Offshore installation activities at the DWP would begin with installation of the PLEMs at both STL buoy locations (north and south), followed by placement of the buoy anchors, mooring lines, buoys, and risers. Installation activities at both STL buoy locations would require a cargo barge, supported by anchor-handling support vessels, a supply boat, a crew transfer boat, and a tug. Buoy anchors would likely be installed via impact pile driving.
Pipeline trenching and burial requirements are governed by Department of the Interior regulations at 30 CFR 250 Subpart J, which requires pipelines and all related appurtenances to be protected by 3 ft (0.9 m) of cover for all portions in water depths less than 200 ft (61 m). Portions of the pipeline that travel through hard-bottom areas may not be able to be buried to the full 3 ft depth. In these areas, flexible concrete mattresses or other cover would be used to cover the pipeline. In places where the pipeline crosses shipping lanes, it would be buried 10 ft (3 m) deep if the sea floor permits plowing. Burying the pipeline and flowlines would protect them from potential damage from anchors and trawls and avoid potential fouling, loss, or damage of fishermen's trawls. The pipeline construction corridor would be 3,000 ft (914 m) wide in offshore areas. The permanent in-water right-of-way for the pipeline would be 200 ft (61 m) wide.
Under the plowing method, the pipeline is lowered below seabed level by shearing a V-shaped ditch underneath it. The plow is towed along and underneath the pipeline by the burial barge. As the ditch is cut, sediment is removed and passively pushed to the side by specially shaped moldboards that are fitted to the main plowshare. The trench is then backfilled with a subsequent pass of the plow. The estimated width of the trench (including sediments initially pushed to each side) is 67 ft (20.4 m) (see Figure 1-2 in Port
In areas that cannot be plowed (e.g., due to hard/live bottom) or complete burial cannot be achieved, the pipeline would be covered with an external cover (e.g., concrete mattresses or rock armoring). Although plowing is the preferred methodology for pipeline burial, other techniques such as dredging and HDD would be used where required. Figure 1-3 of Port Dolphin's application uses color coding of the proposed pipeline route to show where these various methodologies would be used, based on bottom structure and other barriers. The total length of the pipeline route is 74 km. Burial techniques to be used along the pipeline route and their relative lengths are characterized as follows:
• Plowing/trenching soft sediments: 39.6 km (24.6 mi; 53.2 percent of total pipeline length);
• Plowing/external cover: 23.3 km (14.5 mi; 31.4 percent);
• External cover (concrete mattress/rock armoring): 8.5 km (5.3 mi; 11.7 percent);
• Clamshell dredging/dragline burial: 0.3 km (0.2 mi; 0.5 percent); and
• HDD: 2.4 km (1.5 mi; 3.2 percent).
HDD would be employed for installation of the pipeline at three locations along the inshore portion of the route. The proposed HDD locations include drilling from land to water at the Port Manatee shore approach and from water-to-water at two crossings of the existing Gulfstream pipeline. The eastern HDD crossing would be 898 m (2,947 ft) in length, and the western HDD crossing would be 407 m (1,335 ft) in length. Both crossings would be in a water depth of 6.4 m (21 ft). The Port Dolphin pipeline would be drilled to a depth of approximately 6 m (20 ft) below the existing Gulfstream Pipeline (Port Dolphin, 2007b).
HDD is a steerable method of installing pipelines underground along a prescribed bore path, with minimal impact on the surrounding area. The process starts with location of entry and exit points. The first stage drills a pilot hole on the designed path, and the second stage enlarges the hole by passing a larger cutting tool known as a reamer. This would involve using progressively larger drill strings to eventually produce a drill bore 48 in (1.22 m) in diameter. The third stage places the product or casing pipe in the enlarged hole by way of the drill steel and is pulled behind the reamer to allow centering of the pipe in the newly reamed path. Simultaneously, bucket dredging would be employed to produce an exit hole at the end of the bore. In-water HDD may involve significant distance between the seabed and the drilling rig, and so a casing pipe may be required during the initial pilot hole drilling to provide some rigidity to the drill pipe as it is pushed ahead by the rig. Structures known as “goal posts” provide support for the casing pipe and are typically comprised of two driven piles with cross members set at predetermined elevations.
Port Dolphin has identified the need to install goal posts as part of the HDD drilling effort at the two water-to-water HDD locations. One potential option is that the goal posts are designed to self-install; however, another option is that drilling may be required. Further, at the shore-to-water transition HDD, Port Dolphin would need to install sheet piling to form a coffer dam, designed to contain the HDD exit pit so as to not impact nearby aquatic vegetation. Sheet pile segments would be installed by vibratory means.
Clam shell dredging would be required for passage under the Skyway Bridge and would be performed from a fixed working platform. Although dredging, followed by conventional lay and bury, is the most likely scenario, HDD remains a possibility for this segment. In the area near Manbirtee Key, a flotation ditch—dredging operations may require such a ditch when the minimum water depth necessary to safely float equipment is not present—would be dredged using conventional dredging equipment (i.e., the same barge that would be used to pull-in the shore approach HDD). The anticipated locations where the various methods of pipeline installation would be used are shown in Figure 1-3 of Port Dolphin's application.
There are eleven locations where tie-in operations would be required to piece the pipeline sections together. This mechanical operation is accomplished with specially designed connectors and a manned diving rig. This common operation does not require welding. Tie-ins would be required at each end of all HDD crossings, the Y-connection, and the PLEMs.
Table 1 details the vessels that would be used during the DWP and pipeline construction and installation activities. The projected duration and duty load of each vessel are also provided. Duty load is a primary consideration when characterizing project-related sound sources.
The proposed DWP operations would include SRV maneuvering/docking, regasification of LNG cargo, and debarkation. The SRVs are expected to approach the DWP from the south. In the open ocean, the SRVs typically travel at speeds of up to 19.5 kn (36.1 km/hr), reducing to less than 14 kn (25.9 km/hr) while maintaining full maneuvering speed. However, once approaching the vicinity of the DWP—within approximately 16 to 25 km (10-16 mi) of the DWP—the SRVs would begin approach by slowing to about half speed, and then to slow ahead. Inside of 5 km (3.1 km) from the DWP, the SRVs' main engines would be placed in dead slow ahead and decreased upon approach to dead slow, with final positioning and docking to occur using thrusters. Expected SRV transit, approach, and maneuvering/docking characteristics are outlined in Table 2. Only the maneuvering/docking activities and their associated sound sources (i.e., thrusters) are considered in this document; transit and approach maneuvers are considered part of routine vessel transit and are not considered further.
Based on a regasification cycle of approximately 8 days and projected DWP throughput during the first several years of 400 MMscfd, vessel traffic during operations is projected to consist of a maximum of 46 SRV trips per year. During DWP operations, sound would be generated by the maneuvering of SRVs upon approach to the Port, regasification of LNG aboard the SRVs, and subsequent debarkation from the Port.
Once an SRV is connected to a buoy, the vaporization of LNG and send-out of natural gas can begin. Each SRV would be equipped with up to five vaporization units, each with the capacity to vaporize 250 MMscfd. Under normal operation, two or more units would be in service simultaneously, with at least one unit on standby mode.
Incidental take is anticipated to result from elevated levels of sound introduced into the marine environment by the construction and operation of the DWP, as described in preceding sections. Specifically, sound from pile driving, drilling, dredging, and vessel operations during the construction and installation phase, and sound from SRV maneuvering, docking, and regasification during operations would likely result in the behavioral harassment of marine mammals present in the vicinity. Table 3 shows these proposed activities by the time of year they are anticipated to occur.
During construction, underwater sound would be produced by construction vessels (e.g., barges, tugboats, and supply/service vessels) and machinery (e.g., pile driving and pipe laying equipment, trenching equipment, and goal post installation equipment at the HDD locations) operating either intermittently or continuously throughout the area during the construction period. Vessel traffic associated with construction would be a relatively continuous sound source during the construction phase. Vessel sound would be created by propulsion machinery, thrusters, generators, and hull vibrations and would vary with vessel and engine size. Machinery sound from underwater construction would be transmitted through water and would vary in duration and intensity. Port construction (i.e., field construction and installation operations) would require approximately 11 months.
While the main sound source during SRV transit and approach to the DWP would originate from the SRV main engines (i.e., predominantly in low frequencies), the primary sound source during maneuvering and docking would be the SRV thrusters. An additional underwater sound source would be the sound produced by the flow of gas through the proposed pipeline, although very little sound would be expected to result (JASCO, 2008); therefore, this source is not considered further.
Sound travels in waves, the basic components of which are frequency, wavelength, velocity, and amplitude. Frequency is the number of pressure waves that pass by a reference point per unit of time and is measured in hertz (Hz) or cycles per second. Wavelength is the distance between two peaks of a sound wave; lower frequency sounds have longer wavelengths than higher frequency sounds, which is why the lower frequency sound associated with the proposed activities would attenuate more rapidly in shallower water. Amplitude is the height of the sound pressure wave or the “loudness” of a sound and is typically measured using the decibel (dB) scale. A dB is the ratio
Root mean square (rms) is the quadratic mean sound pressure over the duration of an impulse. Rms is calculated by squaring all of the sound amplitudes, averaging the squares, and then taking the square root of the average (Urick, 1975). Rms accounts for both positive and negative values; squaring the pressures makes all values positive so that they may be accounted for in the summation of pressure levels (Hastings and Popper, 2005). This measurement is often used in the context of discussing behavioral effects, in part because behavioral effects, which often result from auditory cues, may be better expressed through averaged units than by peak pressures.
When underwater objects vibrate or activity occurs, sound-pressure waves are created. These waves alternately compress and decompress the water as the sound wave travels. Underwater sound waves radiate in all directions away from the source (similar to ripples on the surface of a pond), except in cases where the source is directional. The compressions and decompressions associated with sound waves are detected as changes in pressure by aquatic life and man-made sound receptors such as hydrophones.
The underwater acoustic environment consists of ambient sound, defined as environmental background sound levels lacking a single source or point (Richardson
The sum of the various natural and anthropogenic sound sources at any given location and time—which comprise “ambient” or “background” sound—depends not only on the source levels (as determined by current weather conditions and levels of biological and shipping activity) but also on the ability of sound to propagate through the environment. In turn, sound propagation is dependent on the spatially and temporally varying properties of the water column and sea floor, and is frequency-dependent. As a result of the dependence on a large number of varying factors, the ambient sound levels at a given frequency and location can vary by 10-20 dB from day to day (Richardson
Very few measurements of ambient sound from Tampa Bay and the adjoining shelf are available. There are no specific data on ambient underwater sound levels for the area of the proposed Port and pipeline route. Shooter
Known sound levels and frequency ranges associated with anthropogenic sources similar to those that would be used for this project are summarized in Table 5. Details of each of the sources are described in the following text.
The sounds produced by these activities fall into one of two sound types: Pulsed and non-pulsed (defined in next paragraph). The distinction between these two general sound types is important because they have differing potential to cause physical effects, particularly with regard to hearing (e.g., Ward, 1997 in Southall
Pulsed sounds (e.g., explosions, gunshots, sonic booms, impact pile driving) are brief, broadband, atonal transients (ANSI, 1986; Harris, 1998) and occur either as isolated events or repeated in some succession. Pulsed sounds are all characterized by a relatively rapid rise from ambient pressure to a maximal pressure value followed by a decay period that may include a period of diminishing, oscillating maximal and minimal pressures. Pulsed sounds generally have an increased capacity to induce physical injury as compared with sounds that lack these features.
Non-pulse (intermittent or continuous) sounds can be tonal, broadband, or both. Some of these non-pulse sounds can be transient signals of short duration but without the essential properties of pulses (e.g., rapid rise time). Examples of non-pulse sounds include those produced by vessels, aircraft, machinery operations such as drilling or dredging, vibratory pile driving, and active sonar systems. The duration of such sounds, as received at a distance, can be greatly extended in a highly reverberant environment. Many of the sounds produced by the project would be transient in nature (i.e., the source moves), such as during vessel docking. Regasification sounds are continuous (while the SRV is docked) and stationary. The positioning (maneuvering and docking) of SRVs using thrusters is intermittent (i.e., every 8 days) and of short duration (i.e., 10 to 30 minutes).
For this project, the only pulsive sounds are associated with pile driving activities at the offshore Port location (i.e., associated with anchor installation activities). Impact hammers (proposed for use in driving buoy anchors) operate by repeatedly dropping a heavy piston onto a pile to drive the pile into the substrate. Sound generated by impact hammers is characterized by rapid rise times and high peak levels, a potentially injurious combination (Hastings and Popper, 2005). Vibratory hammers, which would be used to install sheet pile and possibly pilings for goal posts inshore, install piles by vibrating them and allowing the weight of the hammer to push them into the sediment. Vibratory hammers produce significantly less sound than impact hammers. Peak SPLs may be 180 dB or greater but are generally 10 to 20 dB lower than SPLs generated during impact pile driving of the same-sized pile (Caltrans, 2009). Rise time is slower, reducing the probability and severity of injury (USFWS, 2009), and sound energy is distributed over a greater amount of time (Nedwell and Edwards, 2002; Carlson
Sound levels can be greatly reduced during impact p