A Strategy for Protecting Circulating Seawater Systems from Oil Spills¹

A strategy is described for establishing a simple, inexpensive monitoring program for determining approximate levels of petroleum hydrocarbons in ambient water collected near intake structures of circulating seawater systems. The ambient water is obtained from the depth of intake using a submersible pump, which delivers the sample stream to a dockside partitioning chamber that provides instantaneous grab samples for analysis. A common hand-operated fluorometer equipped for measuring the oil content of a fluid was standardized using a locally-obtained No. 2 marine diesel fuel; oil concentrations in water samples were quantified as Marine Diesel Equivalents (MDE) in parts-per-billion. Surveys conducted along the central Oregon coast following the March 1999 beaching of the drifting freighter New Carissa off Alsea Bay were conducted in that bay, and in Yaquina Bay about 20 km to the north. No evidence of oil contamination from the beached ship was found. The highest MDE levels occurred within the estuaries, especially in an anchorage for fishing vessels in Yaquina Bay. Higher levels of MDE also were measured upstream of this anchorage in February 2001, following a highway spill of No. 6 heavy fuel from a tank truck crash. Thus, this technique appears to be useful for monitoring oil levels in ambient water near seawater intake structures, and to provide a rational basis for temporarily closing down the circulating seawater system after a local oil spill.