Ballast water treatment during emergency response: the case of the M/T Igloo Moon

This paper describes an emergency ballast-water response incident aboard a liquid petroleum gas tanker stranded on a coral reef near Miami, Florida in November 1996. Ballast water from the stricken tanker had to be offloaded in order to move the ship off the reef. Because of the origins of the ballast water and the vessel's proximity to the sensitive environment of Biscayne Bay National Park, concerns were raised over the potential risk of introducing non-indigenous biota via the ballast water that could harm the reefs natural biota. Twelve days after the stranding, 1.1 million gals. (4.3 million L) of water in the ballast tanks were treated with a biocide, calcium hypochlorite, Ca(OCl)/sub 2/, at dosages of 50 or 100 ppm chlorine. The treated ballast water was then discharged overboard, after which assisting vessels safely towed the stricken freighter off the reef without incident or spillage (other than the discharge of the chlorinated ballast water). The primary considerations that led to the decision to treat the ballast water were confounded by many explicit and implicit uncertainties about the actual presence or absence of non-indigenous species, the holding times and sources of water in each tank, and minimum effective treatment levels. Had there been more accurate shipboard records of the vessel's ballast-water exchanges throughout its voyage, these response actions may not have been necessary. Thus, to expedite emergency ballast-water responses in the future, vessel owners need to maintain and provide accurate ballast-water records. Other lessons learned from this experience include the need for trustee-acceptable sampling and monitoring strategies before and during treatment, accurate data on biocide effectiveness (including required concentrations and contact times), and the recommendation that ships avoid taking on ballast water over foreign reefs.