LONG-TERM MONITORING OF SUBMERGED OIL IN THE GULF OF MEXICO FOLLOWING THE T/B DBL 152 INCIDENT

ABSTRACT In November 2005, approximately 1.9 million gallons of Group V slurry oil was released in the western Gulf of Mexico following the allision of the double-hulled tank barge DBL 152 with the submerged remains of a pipeline service platform that collapsed during Hurricane Rita. The released oil was denser than seawater and sank to the bottom. After approximately six weeks of intermittent cleanup using diver-direct pumping, submerged oil recovery operations were suspended by the Unified Command based on the high percentage (50%) of weather-related downtime, as well as indications that recoverable accumulations of oil were dispersing naturally, which further reduced the feasibility of cleanup. However, the responsible party was required to develop and implement a long-term monitoring program (LTMP) to track the fate and transport of the sunken oil and determine the potential need for resuming oil recovery operations once more favorable weather patterns returned in the spring. This paper will present an overview of the approach, methods and results of the long-term monitoring efforts performed over a 14-month period following the incident. Major objectives of the LTMP included tracking the movement and fate of non-recovered submerged oil to assess its extent and continued dispersion; providing advance warning of potential impacts to Gulf Coast shorelines and other sensitive areas; and documenting changes in the oil'S chemical composition and physical properties through time due to weathering processes. Major findings of the LTMP include the dissipation of the main submerged oil field over the course of several months and the discovery, differential behavior and eventual dissipation of a discrete high-concentration oil patch found several miles from the incident location. The importance of long-term monitoring data in the decision-making process to determine both the need for and feasibility of resuming submerged oil recovery operations will be emphasized. Information on the fate and transport characteristics of submerged oil and the adaptation of monitoring techniques to address evolving needs will also be addressed. Both the incident-specific information and the practical lessons-learned are intended to benefit those who may be faced with monitoring submerged oil spills in the future.