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OIL SPILL BOOKS |
Texaco Storage TankTexaco Storage TankBahia Las Minas, Panama 04/27/86 Incident Summary On April 27, 1986, a Texaco storage tank at a refinery near Isla Payardi, Panama, ruptured, releasing approximately 240,000 barrels of medium-weight crude oil. Some of the oil was contained within dikes at the facility. Approximately 140,000 barrels of oil flooded through a dike and overflowed separators and a retaining lagoon and flowed into Bahia Cativa. Refinery personnel reported that a total of 60,000 barrels of oil were recovered. It is not known how much of this recovered oil was from the sea. Behavior of Oil Isthmus crude oil has an API gravity of 32.8, and a pour point of 10 degrees F. Onshore winds initially confined the spill within Bahia Cativa, adjacent to the refinery. On May 3, winds and rain runoff pushed much of the oil out to sea, beyond a containment boom at the mouth of the bay. Once the spill was no longer contained, dispersant application began. The distribution of oil was surveyed from aircraft for two months following the release. Surveys covered the area between Rio Chagres, 17 miles to the west, and Punta San Blas, 61 miles to the east of the refinery. During the surveys, the degree of oiling was assessed visually and quantified as heavy, moderate, light, or absent. Also noted during the surveys were the habitat types and organisms affected by the oil. By May 15, the oil was contaminating fringing reefs, sand beaches, mangroves, and estuaries within 6 miles of the refinery. Heavy oiling was reported along much of the shoreline between Isla Margarita and Islas Naranjos. Two partially isolated lagoons with entrances facing the northwest were spared the effects of heavy oiling. A total of 51 miles of shoreline was heavily oiled. Oiled shorelines within this distance included extensive mangroves, intertidal reef flats, seagrass beds, and subtidal coral reefs. Little of the oil was spotted west of the Panama Canal entrance or east of Maria Chiquita. The most heavily oiled habitats were those closest to the refinery. Concentrations of beached oil were highly variable within each habitat type. Variable oiling was likely due to variation in distance from the spill source, water depth, and directional orientation of the shoreline. Shorelines facing north or northeast were the most severely affected since much of the oil that escaped from Bahia Cativa moved to the west. Shorelines that faced the south or west tended to be less heavily oiled. Low tides between May 10 and 19 resulted in the oiling of the seaward reef flat margins. As a result of the low tides, the heaviest accumulations of oil were observed in the intertidal areas slightly above mean low water. Habitats impacted included mangroves, seagrass beds, coral rock, and beaches. Small-scale patchiness was also observed visually and among replicate samples of the surface sediments. Reoiling of the shoreline and mangroves was a continuing problem. Oil slicks were regularly observed within Bahia Las Minas for at least four years following the spill with oil coming predominantly from the areas of the fringing mangroves. It is believed that as the red mangrove trees (Rhizophora mangle)that were killed by the oiling decay, the erosion of the underlying sediments released trapped oil. Some observed oil appeared to originate from the landfill beneath the refinery. Countermeasures and Mitigation The deployment of boom across the mouth of Bahia Cativa helped contain the spilled oil during the first six days of the incident. When wind and rain water run off pushed the oil out of the bay, dispersant application was begun. Approximately 132 barrels of the dispersant Corexit 9527 were applied from aircraft. Dispersant application took place in Bahia Cativa, Islas Naranjos, offshore of Bahia Las Minas, near Portobelo, and along the northern breakwater at the mouth of the Panama Canal. The dispersant application appeared to be ineffective due to the weathered state of the oil and the calm seas. Floating oil was recovered by skimmers. Vacuum trucks were used as part of the shore-based cleanup effort. Several channels were dug through the mangroves in an effort to drain the oil. These channels appeared instead to have the detrimental effect of aiding the movement of the oil inshore. Increased disturbance due to the construction of the channels may have also contributed to subsequent erosion. Manual removal of oiled rocks and debris was conducted along the more accessible shorelines. Seawater was sprayed on some sandy areas to aid oil removal. The recovery of floating oil by pumping appeared to be the most effective oil recovery method. The shallow waters and mangroves made many of the typical oil spill cleanup techniques impractical. Other Special Interest Issues Many of the affected shoreline habitats were sites of ongoing study by the Smithsonian Tropical Research Station at Punta Galeta. A great amount of research has been conducted in the affected areas since the spill. Historical time-series data on the biota and physical conditions greatly aided the documentation of the pre-spill conditions. The first heavy oiling of the Punta Galeta area occurred on May 9. Although the oil had weathered for 12 days, it was still fluid, and had the appearance of used crankcase oil. The heaviest oiling occurred along the seaward side of the reef flat at low tide. Organisms within a 6-meter wide zone were directly immersed in oil, and included zoanthids, corals, and calcareous and fleshy algae. A systematic visual survey determined that less than 10 percent of the original sessile community survived the oiling. None of the crabs that normally inhabit this zone were found. Some live crabs (Grapsus grapsus) that were found on nearby emergent structures appeared to be blind. By June, patches of oil remained in some areas of the reef flat. Algal growths showed no visible damage in the deep tide pools, but were much less abundant on emergent substrates than before the oiling. Some areas of coralline algae and active crab burrows were bare of algal growth. Microalgae quickly colonized the vacant substrate created by the mortality of other organisms The short-term effects of the oil on the common shallow subtidal corals were studied. The number of corals, total coral cover, and species diversity decreased significantly with increased oiling. The greatest decrease in percent cover was found in the large branching coral Acropora palmata. Growth of three species of massive corals was less on oiled reefs during 1986, than the average of the nine previous years. A study of mangrove trees revealed that one- to two-year-old seedlings appeared to survive where the surrounding adults died. It was believed that somehow, young seedling structure (perhaps lack of prop roots) enabled the young trees to tolerate periods of oil immersion. It was suggested that the disruption of the substrate before replanting may remove such survivors, hampering forest recovery. Oil persisted in the mangroves through May 1989. Initial oiling of the trees produced measurable amounts of oil on 100% of all the roots that were sampled. Through May 1989, the mangrove roots in the open coast and channel areas showed 70 percent oiling, while the oiled proportion in the stream mangroves remained 100 percent. The decrease in oil coverage resulted from weathering, microbial degradation, and loss of oiled bark or encrusting organisms. Observed root mortality was greater in oiled areas. References This content has been excerped from: Oil Spill Case Histories 1967-1991: Summaries of Significant U.S. and International Spills |
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