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Facilities that have temporary abnormally high emissions that are caused by an equipment malfunction, accident, operator error, or some other unintended failure of a process to operate in a normal or usual manner. Sometimes referred to as super-emitters. (Source: Zavala-Araiza et al. 2015)

horizontal or directional drilling

Deviation of a wellbore from vertical toward a horizontal inclination in order to intersect targeted fractures or maximize contact with a productive formation. (Source: Michigan Department of Environmental Quality 2013)

hydraulic fracturing

A stimulation treatment routinely performed on oil and gas wells in low-permeability reservoirs. Specially engineered fluids are pumped at high pressure and rate into the reservoir interval to be treated, causing a vertical fracture to open. The wings of the fracture extend away from the wellbore in opposing directions according to the natural stresses within the formation. Proppant, such as grains of sand of a particular size, is mixed with the treatment fluid to keep the fracture open when the treatment is complete. Hydraulic fracturing creates high-conductivity communication with a large area of formation and bypasses any damage that may exist in the near-wellbore area. (Source: Schlumberger 2019)


Organic compounds of hydrogen and carbon, whose densities, boiling points, and freezing points increase as their molecular weights increase. Although composed of only two elements, hydrocarbons exist in a variety of compounds because of the strong affinity of the carbon atom for other atoms and for itself. The smallest molecules of hydrocarbons are gaseous; the largest are solid. (Source: OSHA 2001)


A supposition, arrived at from observation or reflection, that leads to refutable predictions; any conjecture cast in a form that will allow it to be tested and refuted. (Adapted from: Centers for Disease Control and Prevention 2014)