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Red Butte Creek Oil Spill
Frequently Asked Questions
Was the Clean-up of Red Butte Creek Sufficient?
Red Butte Creek was physically cleaned over the course of several weeks after the spill. The Division of Water Quality (DWQ) reviewed all analytical results as they became available. In a few locations, known oil contamination was left where bank stability, structures, or trees could be damaged by additional clean-up. Unknown pockets of oil contamination likely remain in Red Butte Creek, but these are anticipated to be limited in extent. These pockets are evaluated for cleanup as they are discovered. Because of the time since the spill and the chemical properties of these contaminants, they are likely limited to the sediments, but can be in the water when the sediment is stirred-up.
Chemical concentrations were compared to concentrations that do not affect humans or aquatic organisms. Concentrations acceptable for drinking water were used for human health benchmarks. These are conservative benchmarks because they are based on a lifetime of exposure through drinking water and exposures to Red Butte Creek water are much less in both quantity and duration. Concentrations of benzene and naphthalene were occasionally detected above drinking water concentrations on June 12 through 15, 2010 when the creek was being actively remediated. Samples collected after this period were either "nondetect" or below drinking water benchmarks.
To evaluated potential effects to aquatic organisms, chemical concentrations were compared to no-effects concentrations. The detected concentrations are divided by the no-effects concentration resulting in a toxic effects ratio (TER). Figures XX compare the chemical concentrations measured in Red Butte Creek to known toxic concentrations. When the TER is less than one, no toxic effects are predicted. When the TER is greater than one, toxic effects are possible. Contaminant concentrations exceeded the benchmarks through the 3rd week of June when the creek was being remediated.
Sediment samples representative of general conditions in the creek detected trace amounts of oil-related compounds such as polycyclic aromatic hydrocarbons that were below human health benchmarks. Targeted samples from areas visually contaminated detected higher concentrations and were usually subsequently remediated.
Chevron was tasked to prepare comprehensive ecological and human health risk assessments for any residual oil-related contamination in Red Butte Creek. Water and sediment data will be collected in June 2011 to support these assessments. The data collected to date were reviewed and used to determine when access restrictions could be removed.