Glossary

Annual average of the bi-weekly Δc values of the 26 most recent 14-day sampling period benzene concentration results.

Benzene is an important organic chemical compound with the chemical formula C6H6. The benzene molecule is composed of 6 carbon atoms joined in a ring with 1 hydrogen atom attached to each. As it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon.

Benzene concentration difference between the highest and lowest 14-day sampling period results from the sample pool.

Refers to taking a capped sample (no exposure to ambient air) at single monitoring location for quality assurance/control evaluation.

In chemistry, concentration refers to the amount of a substance per defined space. Concentration usually is expressed in terms of mass per unit volume (i.e., PPB, ug/m3).

Refers to taking an additional sample at a single monitoring location for quality assurance/control evaluation.

Environmental Protection Agency of United States.

Companion EPA Methods 325A (Sampler Deployment and VOC Sample Collection) and 325B (Sampler Preparation and Laboratory Analysis) select benzene as the representative compound to evaluate the overall emissions near the monitoring station. Passive sampling onto sorbent tubes followed by Thermal Desorption-Gas-Chromatography/Mass Spectrometry (TD-GC/MS) analysis has been established as the standard air monitoring technology for the new benzene technical standard.

Fenceline means the property boundary of a facility or internal monitoring perimeter established in accordance with the requirements in Section 8.2 of EPA Test Method 325.

Gas chromatography–mass spectrometry (GC-MS) is an analytical method that combines the features of Gas-Chromatography and Mass Spectrometry to identify different substances within a test sample.

Any of a class of organic chemical compounds composed only of the elements carbon (C) and hydrogen (H). The carbon atoms join together to form the framework of the compound, and the hydrogen atoms attach to them in many different configurations. Hydrocarbons are the principal constituents of petroleum and natural gas.

Data qualifiers are used in lab reports to indicate a problem or irregularity with the analytical result. The most common qualifiers are shown here; most labs also will use footnotes to explain the qualifiers they have used.

J: The number is an estimated concentration because something in the sample interfered with the analysis.

U: The contaminant was not detected at a concentration greater than the detection limit.

UJ: The contaminant was not detected, but the detection limit is estimated because of interference from something in the sample.

R: The data are unusable. Resampling and reanalysis are necessary for verification.

The lowest concentration (greater than zero) of the substance tested that can be measured and reported with 99 percent confidence.

The lowest concentration of the substance tested that can be reported reliably under normal laboratory conditions.

No concentration is available for the monitoring station.  This may occur when a field collection or a laboratory issue prevented the analysis of the sample tube.

The target compound was not detected above the MDL.

Parts per billion (ppb) is the number of units of mass of a contaminant per 1000 million units of total mass.

Quality assurance is the systematic process of checking to see whether a product or service being developed is meeting specified requirements. Quality control are the tools used to monitor or regulate the process. Quality control is an aspect of quality assurance.

Root cause analysis (RCA) is a systematic process for identifying “root causes” of problems or events and an approach for responding to them to prevent reoccurrence.

A material used to absorb or adsorb liquids or gases.

A glass or stainless-steel tube with fixed dimensions that contains a solid adsorbent material such as carbon or activated charcoal. The tubes trap and retain compounds, such as benzene, and are easily extracted for lab analysis.

Micrograms per Cubic Meter of Air. Used as a measure of ambient air concentration of a particular compound or species.

Volatile organic compounds (VOC) means any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical reactions. VOC does not include hydrocarbons that have negligible photochemical reactivity, such as methane and ethane.