Munitions integrity and corrosion features observed during the HUMMA deep-sea munitions disposal site investigations
Introduction
Sea disposal of military munitions, including excess, obsolete, damaged, or captured conventional and chemical munitions, was an accepted international practice until the mid-1970׳s. The United States Department of Defense (US DoD) ceased sea-disposal operations in 1970, prior to the passage of the Marine Protection, Research, and Sanctuaries Act by the US Congress that was enacted in 1972 that prohibited the practice. Between the years 1919 through 1970, the US DoD had disposed of approximately 32,000 t (29,000 metric tons) of chemical warfare material, and a significant but largely undetermined quantity of conventional munitions and munition components, at 30 designated disposal sites within US coastal waters (US DoD, 2010). In addition to aerial bombs and projectiles, confined and/or containerized gaseous, liquid, and solid propellants, bulk explosives or chemical warfare agents, pyrotechnics, chemical or riot control agents, smokes, and incendiary chemicals were also sea-disposed. These discarded military munitions (DMM) were typically removed from storage and were not armed, or otherwise prepared for action, prior to sea disposal. Therefore, these disposed munitions are not considered unexploded ordinance by definition (10U.S.C 101(e)(5)(A) through (C); Carton and Jagusiewicz, 2009). However, the risk of explosive detonation cannot be eliminated from consideration, given that available records on specific munitions disposed and quantities are generally incomplete at these sites.
There is also increasing concern over the potential human health and ecological risks associated with the release of munitions chemical fills, as these DMM have and continue to age and corrode on the seafloor. Corrosion in the marine environment is dependent on a number of factors, including the time DMM is exposed to the marine environment, the type, quality and thickness of materials used in construction, the availability of dissolved oxygen, seafloor current velocity, and the degree of burial within seafloor sediments. Additionally, the presence, absence, and condition of protective coatings (e.g., paint) and microbiological processes can either accelerate or reduce the rate of corrosion. Given the large number of variables to be considered it would difficult, if not impossible, to provide estimates of corrosion rates and time to corrosive penetration of these munitions based purely on theoretical considerations of DMM construction with great confidence (HELCOM, 1994). In recent years, the US DoD has been engaged in identifying sea-disposal areas within US coastal waters and providing an inventory of DMM within these disposal areas, based on available archival records, to better understand the scale of the issue from a risk management perspective (US DoD, 2010). However, an assessment of risk related to the release of DMM chemical fills first requires investigation of not only the potential inventory of DMM at a given site, but also the physical distribution of DMM within a particular sea-disposal area and physical assessment of the current condition of these DMM on the sea floor, to appropriately bound chemical release scenario calculations.
A key objective of the Hawaii Undersea Military Munitions Assessment (HUMMA) project was to characterize the seafloor distribution and current condition (i.e. the overall integrity and state of corrosion) of sea-disposed DMM located within a historic deep-sea disposal site (designated Hawaii-05 or HI-05) located south of Pearl Harbor, Oahu, Hawaii, and to assess the potential human and ecological risks associated with these DMM by physical measurement of potential munitions chemicals in seafloor sediments and in the seawater surrounding these DMM (HUMMA, 2010). To date, three separate investigations have been performed within HI-05, occurring in 2009, 2012, and most recently in early 2014. This article describes the spatial distribution and current condition of DMM encountered during the 2009 HUMMA investigation. An accounting of DMM observed and their current state of corrosion is provided, in addition to a discussion of general corrosion features observed. A discussion of some unusual corrosion features is also presented along with a possible microbial-mediated model for the origin of these unusual corrosion features. Additionally, an overview of marine corrosion processes relevant to the current study is provided to provide context to the discussions of observed DMM corrosion at HI-05.
Section snippets
Electrochemical corrosion processes
In the marine environment, the corrosion of metals is a complex process, mediated by a variety of electrochemical, environmental, and microbiological processes. Generally, the corrosion of metals submerged in seawater initiates as an electrochemical process in which electrons and water-soluble metal cations are produced via oxidation reactions at anodic locations on the metal surface. Soluble metal cations are released to the seawater (electrolyte), while the electrons conduct through the metal
Site background
The 69 km2 (square kilometer) HUMMA study area is located between 5.6 km (northern extent) and 14.5 km (southern extent) south of Pearl Harbor, Oahu, Hawaii. As shown in Fig. 1, the study area is positioned at the northern portion of a larger former deep-water military munitions disposal area, designated as HI-05 by the US DoD. Although individual munitions disposal operations at HI-05 were not well documented, available archival records indicate that conventional munitions disposal operations
Investigation and characterization methods
Information and data used in the present evaluation was collected from human occupied vehicle (HOV) (Pisces IV and Pisces V deep-submergence vehicles) and remotely operated vehicle (ROV) (DOER Marine H6000) video reconnaissance logs collected during 16 individual dives launched from the Research Vessel (R/V) Ka’imikai-o-Kanaloa (KoK) between 03 March and 18 March 2009. Both HOVs were outfitted with onboard SONAR, lights, digital video cameras, and global positioning capability. Both HOVs and
Observations of DMM integrity and state of corrosion
Of the 2572 sea-disposed objects observed during the 2009 HUMMA investigation, 1842 were classified as DMM and the remaining 730 objects were identified as non-munitions-related debris (e.g., various metal framework, spooled and loose steel cables, vehicle engine blocks, trash cans, aircraft parts). The DMM observed appeared to be conventional munitions and munitions-components of WWII vintage, based on visual comparison of historic images and technical specifications diagrams of munitions used
Conclusions and recommendations
DMM and non-munitions related objects sea-disposed within the HUMMA investigation area have corroded but have not completely disintegrated. Of the 1842 objects characterized as DMM during the 2009 HUMMA investigation, 5% were observed to be mild-moderately corroded while the majority (66%) were observed to exhibit significant corrosion but remain largely intact on the seafloor. The remaining 29% of the DMM observed were found to be in a state of severe corrosion, in that the exterior of the
Acknowledgments
We thank the Captain, crew and scientists of the Research Vessel Ka׳imikai-o-Kanaloa for their expert assistance in the performance of the HOV surveys. This work would not have been successful without Colin Wollerman, Terry Kerby, Max Cremer and the rest of the Hawaii Undersea Research Laboratory group. The unwavering encouragement of J.C. King and H. Wolfe has been a key component of this research program. The U.S. Army׳s Night Vision Laboratory supported this research via contract
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