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Water Chemistry:
Red Butte Creek Oil Spill

What Data Were Collected?

Oil products contain a mixture of several hundred chemicals ranging from light and volatile, short-chained organic compounds to heavy, long-chained, branched compounds. These products differ with regard to their toxicity and chemical properties. As a result, numerous laboratory analyses were conducted to obtain data germane to the oil spill. The primary laboratory tests that were conducted include:


Biochemical Oxygen Demand is a measure of the amount of oxygen consumed by microbes as they break down, or consume, organic material. Oil spills sometimes result in low levels of dissolved oxygen, and these samples help determine whether observed low oxygen levels are caused by biological processes.


Chemical Oxygen Demand measures the amount of oxygen consumed by both microbial decomposition and the oxidation of inorganic chemicals. As with BOD, these samples were collected to identify potential problems with anoxia (low levels of dissolved oxygen) that could be attributed to the spill.


Diesel Range petroleum Organics (method SW846 8015D) are hydrocarbons found within the carbon range of n-C10 to n-C28, which allows detection of “moderately heavy” petroleum products such as diesel, lubrication oil, and mineral oil. Characterization of the relative amounts of different classes of organic compounds can be used to help distinguish among different sources of oil.


Gasoline Range petroleum Organic hydrocarbons measure the “lightest” organic components of petroleum (carbon range of C5—C12). Petroleum products with a relatively high concentration of GROs include gasoline and kerosene. Characterization of the relative amounts of different classes of organic compounds can be used to help distinguish among different sources of oil.


Oil Range petroleum Organic hydrocarbons are “heavy” (carbon range of C28—C36) petroleum hydrocarbons. Characterization of the relative amounts of different classes of organic compounds can be used to help distinguish among different sources of oil.


Semi-Volatile Organic Compounds are a class of organic chemicals that volatize above room temperature. There are many potentially toxic SVOCs associated with petroleum products. In particular, Polycyclic Aromatic Hydrocarbons (PAHs), are of a potential concern because many of these compounds are known to be carcinogenic, mutagenic or teratogenic. It is necessary to evaluate the additive effects of both VOCs and SVOCs to estimate the potential ecological threat of the oil on the Red Butte Creek ecosystem.


Total Recoverable Petroleum Hydrocarbons is a broad measure of the presence of petroleum organics in a sample. These samples are relatively inexpensive to process and provide reasonable information about whether petroleum is present. However, TRPH samples lack the specificity necessary to make statements about the risk that the petroleum poses to the environment.


Volatile Organic Compounds are organic chemicals with significant vapor pressure that cause them to quickly volatize or degrade fairly quickly at room temperature and are often associated with strong smells. There are many VOCs associated with petroleum products and many of these are known to be toxic to humans and other organisms. Measuring VOCs is important to detect the presence of these compounds, which can be used to evaluate overall environmental threats.

Where Were the Data Collected?

The sample collection locations can be viewed by exploring the Monitoring Maps and Locations page.

Water Chemistry Results

What do we know so far?

  • A spreadsheet (37 KB) was created that summarizes much of the water quality data collected at each location (please note that the second worksheet provides an explanation of the data).
  • High Chemical Oxygen Demand (COD) was observed at 1100 East sample location, continually measured (10-minute) Dissolved Oxygen (DO) at this location revealed violations of DO water quality standards (41 KB).
  • Samples collected from the Jordan River downstream of the spill revealed the presence of some petroleum hydrocarbons, but chronic or acute toxicity threats to aquatic life was not observed at any of these locations.
  • Toxicity Effects Ratios were calculated to estimate the additive threat to aquatic life from many of the potentially toxic compounds found in oil. These analyses suggest that toxic threats to aquatic life are confined to a relatively small portion of Red Butte Creek (1100 East).
  • The Toxic Effects Ratio data also show a continued decline in potentially toxic compounds, probably due to clean-up efforts and natural degradation (weathering) of oil.

How can I obtain the water quality data?

Water quality data can be obtained by exploring the Monitoring Maps and Locations page. It will direct you to tables that contain the analytical results of the toxicity effects ratio calculations. Other parameters, such as concentrations of petroleum hydrocarbons, have been summarized in a spreadsheet (37 KB). The laboratory reports are available upon request.

What are toxicity effects ratios?

Oil contains many potentially toxic compounds, many of which do not have formal water quality standards. Some of these compounds are more toxic than others. Toxicity effects ratios simply summarize the combined effects of all of these contaminants to stream biota.

How were the toxicity effects ratios calculated?

Toxicity effects ratios summarize the additive effects of groups of pollutants. These calculations also consider the relative toxicity of each of the constituent chemicals with “potency divisors.” While these potency divisors are not water quality criteria in a regulatory context, they are generated following similar analytical methods.

A tool for developing toxicity effects ratios for oil-related toxins was recently created by EPA—in collaboration with other industry experts—to help interpret data collected in response to the BP oil spill. This tool captures the results of hundreds of toxicology investigations to generate potency ratios that quantify the relative toxicity of ~40 common petroleum toxics to aquatic biota. DEQ was able to use this tool to generate data that all quantitative comparisons of the threat of the Chevron Oil to aquatic organisms.

How should the toxicity effects ratios be interpreted?

Typically, we compare water chemistry data against water quality criteria. However, many of the potentially harmful chemical in oil do not have standards. Nonetheless, numerous toxicology studies have been conducted on many of the contaminants found in oil, which can be used to develop benchmarks (e.g., acute or chronic potency divisors) to measure the potential threats to stream organisms. These benchmarks for individual contaminants can be summed to create an index (e.g., toxic effects ratio) that represents the combined threat of all contaminants to the ecosystem. If the effects ratio exceed one, then additive effects of all contaminants exceed the acute or chronic benchmarks for aquatic organisms. The greater the toxicity threat ratio, the larger the threat.

Use caution when comparing individual contaminants against the biological benchmarks (potency divisors) in the spreadsheet (37 KB) used for these analyses. Examining individual parameters, one at a time, does not consider the combined effect of these substances, which is a more accurate indication of the potential threat of the oil spill to Red Butte and Jordan River ecosystems.

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