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April’s nearly 200-million-gal BP oil spill has received significant coverage in the general media. Here WWD and Chris Piehler of the Louisiana Department of Environmental Quality (DEQ) bring you up to speed on the spill’s water quality impacts and response efforts.
Caitlin Cunningham: How has the spill affected Louisiana’s water resources?
Chris Piehler: There are a tremendous number of impacts, both ecological and economic. Our beaches are the front line of Louisiana’s coast and stand between the interior marshes and the spill site. They have received the brunt of the oiling that has come ashore. There are crews that go out daily to clean areas, knowing full well that they may be back the next day to clean the same area again.
Barrier islands are not contiguous in Louisiana. There are breaks and passes that go through barrier islands into interior marshes. Oil will and has gotten through those passes into some interior marshes and oiled some wetlands. Those wetland areas, different from other states’ in their magnitude and susceptibility to severe land loss rates, have a lot of surface area associated with them, so SCAT [shoreline cleanup assessment team] crews are also needed there.
Analytical measurements of water will increase. When you’re dealing with a contaminant that’s visible like oil, very robust analyses aren’t necessary for response, but there have been a number of water quality analyses done. The U.S. Environmental Protection Agency has done a lot of water sampling. The Louisiana DEQ’s water and sediment sampling will increase as natural resource damage assessments progress. One of the really good news stories associated with that was that they have not been able to detect any of the dispersant compounds that have been used offshore in state waters.
Cunningham: What water-related consequences has the contamination had on the Gulf Coast region? And beyond?
Piehler: I think a lot of the earlier fears—it gets into the loop current, goes into the Atlantic Ocean and even into Europe—will be pretty unlikely.
Oil is organic. In a very organic, rich environment like the Gulf of Mexico, which is also very warm and provides a lot of natural exposure to hydrocarbon seeds, there are microbes naturally present that will break down oil. Oil does not persist in the manner that some contaminants like chlorinated hydrocarbons would. The microbes break the oil down over time; some fractions break down more quickly than others. There have been reports from all Gulf states that tar balls have been showing up. Demonstrable impacts probably will be limited to the Gulf area.
Dispersants have been used as a response measure. The trade-off here is to impart that toxicity to the water column, minimizing the effects on wetland shorelines, beaches, marine mammals, birds, etc., in favor of distributing oil into a wider area of the water column at a lot of depth. At depth, the effects of dispersed oil are not particularly well understood. The pressures are much greater down deep into the water column, and it’s quite possible that because of changes in physical attributes of dispersed oil in water, the pressure could increase toxicities that we’re not really clear about. As such, the unified command has placed a limit of about 15,000 gal a day of dispersants using subsea injection that they’re allowed to use, roughly at an application rate of 10 gal per minute.
Cunningham: When, if ever, will impacted areas see pre-spill water quality?
Piehler: Water quality is not going to be affected uniformly. There are areas where currents take either dispersed oil or oil on the surface, and those areas are adversely affected. Pre-spill water quality is actually measurable now in other places.
Usually what gets mixed in and dispersed into the water column is the lighter, more toxic fractions—the ones that tend to degrade more quickly. The heavier ones—the tars, the asphaltenes—just don’t degrade very rapidly. They’re larger, more sticky and cohesive.
In the case of the Exxon-Valdez, heavier-end oils are still found. I would not expect that to occur in Louisiana, as the growing season is much longer, the water is warm and microbes are present and active. I would be speculating to say how long it will take for all materials to break down, but with the heavier ends, we’re probably talking at least a couple of years.