Testing for Petroleum Hydrocarbon Compounds; Series 2
Hydrocarbon is a chemical compound consisting only of the elements: carbon & hydrogen. Hydrocarbons are combustible. They are the main components of fossil fuels, which include petroleum, coal and natural gas. Crude oil is basically a complex mixture of hydrocarbons.
The molecular structure of hydrocarbon compounds varies from the simplest, methane (CH4), a constituent of natural gas, to the very heavy and very complex. Octane, for example, a constituent of crude oil, is one of the heavier, more complex molecules.
 
Petroleum hydrocarbons consist of a very large number of compounds that are found in or derived from crude oil. There are more than 500 such compounds. Because there are so many different chemicals in crude oil and in other petroleum products, it is not practical to measure each one separately. However, it is useful to measure the total amount of petroleum hydrocarbons at a site.
TPH means Total Petroleum Hydrocarbons; all of the hydrocarbons that compose petroleum.
The use of TPH concentrations to establish target cleanup levels for soil or water is a common approach implemented by regulatory agencies in the United States.
In dealing with petroleum contaminated oil, TPH concentrations are usually given in milligrams of petroleum per kilogram of soil (mg/kg; also known as parts per million, or ppm). With groundwater, it is customary to give the levels in smaller units: microgram of petroleum per liter of water; also known as parts per billion, or ppb).
The diagram below depicts levels of total gasoline compounds (as TPH gasoline) in parts per billion (ppb) in the groundwater under one of our sites:
Approximately 75% of the states use TPH-based cleanup criteria.
Because these values have become such key remediation criteria, it is essential that everyone using TPH data — environmental coordinators, field personnel, and regulators — be knowledgeable about the various analytical methods that are used to determine these levels.
There are many analytical techniques available that measure TPH concentrations in the environment. No single method measures the entire range of petroleum-derived hydrocarbons.
Because the techniques vary in the way hydrocarbons are extracted (from the soil or groundwater sample), cleaned up, and detected, they each measure slightly different subsets of the petroleum-derived hydrocarbons present in a sample.
The definition of TPH depends on the analytical method used because the TPH measurement is the total concentration of the hydrocarbons extracted and measured by a particular method.
The same sample analyzed by different TPH methods may produce different TPH values.
For this reason, it is important to know exactly how each determination is made.
Interpretation of the results depends on understanding the capabilities and limitations of the selected method. If used indiscriminately, TPH data can be misleading and could lead to an inaccurate assessment of risk.
Acknowledgment:
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