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Hydraulic Fracturing
Hydraulic fracturing is a process used to extract oil and gas from geologic formations such as shale. The process consists of injecting large volumes of water, chemicals, and sand at high pressures to fracture rock formations deep in the earth to release fossil fuels. Hydraulic fracturing is also called fracking and hydrofracking.


Unconventional Oil and Gas Development (UOGD)
UOGD refers to the process of drilling horizontally into the earth to extract oil and gas via hydrofracking.


Unconventional Natural Gas Development (UNGD)
UNGD refers to the process of drilling horizontally into the earth to extract gas via hydrofracking.


Conventional Oil and Gas Development
Conventional oil and gas development can refer to the extraction of gas from dome formations or to the process of drilling vertically (not horizontally) into the earth to extract oil and gas from shale and other impermeable rock formations.


Shale Gas Development (SGD)
Shale gas development refers to the extraction of gas from shale formations via either vertical or horizontal drilling.


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Acidizing is a drilling technique used in UOGD to access hydrocarbons from specific types of geologic formations, such as sandstone or carbonate. It involves pumping an acidic solution into a well in order to increase production by increasing the permeability of the formation.


An annulus is a space between a well casing and another casing, between casing and tubing, or between casing and the open hole of the wellbore. A well may have several annuli.


Bentonite is a type of clay used in horizontal directional drilling.


Benzene is one of the BTEX compounds (benzene, toluene, ethylene, xylene). Like other volatile organic compounds, benzene is a colorless, flammable liquid that evaporates (or “volatilizes”) quickly when exposed to air. Benzene is a component of plastics, detergents, and pesticides. It is also a natural component of crude oil and gasoline. Because benzene is a known carcinogen with links to leukemia and cancers of other blood cells, the Environmental Protection Agency (EPA) limits non-industrial applications of benzene, including its concentration in gasoline.


A drill bit is a device attached to the end of the drill string that breaks, cuts, or crushes rock formations when drilling a wellbore, such as those drilled to extract water, gas, or oil.


BTEX Compounds
BTEX is the acronym for a group of four volatile organic compounds associated with oil and gas development: benzene, toluene, ethylbenzene, and xylene. Depending on level and length of exposure, BTEX compounds can irritate skin, eyes, and the respiratory system; cause nausea, headaches, and blood disorders; and lead to cancer. Because of these potential health risks, BTEX compounds are a major focus of local, state, and federal environmental regulations.


A blowout is the uncontrolled release of oil, gas, or other hydrocarbons from an oil and gas well, which occurs after pressure control systems fail.


Brine is another term for produced water. It is a byproduct of oil and gas activity, consisting of water released from underground, injection water, oil, and salt. Brine has an extremely high concentration of salt, which impairs crop and forage production. In shale gas drilling, brine also contains naturally occurring radioactive substances and chemicals added during the drilling and fracking process. For a time, it was spread on Pennsylvania roadways before being banned because it presented a health risk, although the industry continues to urge policymakers to reconsider this.


Casing refers to the steel pipe that is placed in an oil or gas well to prevent the wall of the well from caving in.


Class II Wells
There are three types of Class II wells:

  • Wastewater disposal wells

Wastewater disposal wells are wells in which operators dispose of brine and wastewater. These fluids are reinjected into the same or similar underground formations.

  • Enhanced oil recovery wells

These are wells in which operators inject fluids such as brine, water, steam, or carbon dioxide into underground formations to recover residual oil.

A compressor is a machine that raises the pressure of a gas by drawing in low pressure gas and discharging it at significantly higher pressure. Compressor stations are used for pumping gas through pipelines. Compressors are significant leakers of methane gas into the environment.


Cracker Plant
A cracker plant is a large industrial complex that heats ethane (a component of shale gas) and “cracks” it into ethylene.


Cryogenic Facility
Cryogenic facilities are large processing plants that subject a gas stream to cold temperatures so that components of the stream condense. The substances that condense are considered natural gas liquids (NGLs).


A dehydrator is a device in which a liquid absorbent (e.g., desiccant, ethylene glycol, diethylene glycol, or triethylene glycol) directly contacts a gas stream to absorb water vapor.


Deep Groundwater
Deep groundwater exists thousands of feet beneath the ground surface in geologic formations that are largely disconnected from groundwater recharge and the water cycle. When deep groundwater is removed from the subsurface during oil and gas activity, it is called produced water. It has an extremely high saline content, which is why it is often referred to as brine, and may carry minerals and compounds of a toxic nature that have dissolved from neighboring rocks over millennia.


Deep Well Injection
Deep well injection is the process of disposing of (or storing) wastewater from other oil and gas activity deep underground. The process has raised concerns because of its possible link to earthquakes. Injection well wastewater has also been known to migrate to the surface through other unplugged wells, creating hazards for people and wildlife.


Drill Cuttings
Drill cuttings consist of waste made of soil, rock fragments, and pulverized material that must be removed from a borehole. Cuttings may also include a small amount of fluid that results from the drilling process. The way operators and state regulators distinguish drill cuttings from drilling muds differs.


Drilling Muds 
Drilling muds are a type of oil and gas waste, generally measured as a liquid. The way operators and state regulators distinguish drill cuttings from drilling muds differs.


Dry Gas
Dry gas is gas composed primarily of methane without additional hydrocarbons mixed in.


The Environmental Health Project (EHP) is a nonprofit public health organization that assists and supports residents of Southwestern Pennsylvania and beyond who believe their health has been, or could be, impacted by shale gas development.


Emissions are substances released into the air and are measured by their concentrations, or parts per million, in the atmosphere.


Endocrine Disrupting Chemicals
Endocrine disrupting chemicals are chemicals, both natural and synthetic, that interfere with the hormones of humans and animals.


Epidemiology is the branch of medical science that investigates all the factors that determine the presence or absence of diseases and disorders. Epidemiological research helps us to understand how many people have a disease or disorder, if those numbers are changing, and how the disorder affects our society and our economy.


Ethane is a colorless, odorless, and flammable gas.


Ethane Cracker
See Cracker Plant. Petrochemical cracker plants are typically very large industrial facilities that take ethane, a component of gas, and reduce (or crack) it into ethylene. Ethylene is used as the basis for making various products, including plastics, resins, adhesives, and synthetic materials.


Flaring is the controlled burning of gas at a gas facility.


Flowback Fluid
Flowback fluid is fluid that returns to the surface of the ground after hydraulic fracturing. It usually consists of fracking fluid, brine, clay, and other formation materials that are released during the fracking process.


Fracking Fluid
To frack a Marcellus Shale gas well, millions of gallons of fresh water are hauled in or withdrawn from a local source. Chemicals are added to the water to allow the gas to flow more efficiently up the top of the well (called the wellhead), and sand is added to prop open fractures so the gas can escape from the rock. This mixture of water, chemicals, and sand is often called fracking fluid.


Frack Sand
Frack sand (or Frac Sand) is a high-purity quartz (silica) sand that is very durable and uniform in shape. It is used in well stimulation as a proppant. Each gas or oil well uses millions of pounds of this sand in its lifetime. Frack sand is typically mined from sandstone deposits. If not contained, the sand can blow over long distances, creating impacts 20 miles away. Breathing silica sand is a health hazard. 


Fracking is another term for hydraulic fracturing.


Fractionation Facility
After cryogenic facilities separate natural gas liquids (NGLs) from the gas stream, the different types of NGLs must also be separated from each other. Fractionation facilities do just that, creating pure sources of ethane, propane, butane, and isobutane.


HEPA is a type of pleated mechanical air filter. It is an acronym for "high efficiency particulate air [filter]" (as officially defined by the U.S. Dept. of Energy).  This type of air filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm).


Horizontal Directional Drilling (HDD)
HDD is the process of drilling and completing, for production, a directional well that begins as a vertical or inclined linear bore and extends from the surface to a subsurface location just above the target oil or gas reservoir. The well then turns horizontally to intersect and remain within the reservoir.


Hydrocarbons are organic compounds of hydrogen and carbon that produce energy when burned. Methane is a simple hydrocarbon. Petroleum is a mix of several hydrocarbons. All fossil fuels consist of hydrocarbons.


Marcellus Shale
The Marcellus Shale is one of more than 20 shale deposits in the United States and is the largest on-shore gas reserve in the world. This shale rock formation lies a mile or more beneath several states in the northeastern United States, including parts of Pennsylvania, Ohio, New York, and West Virginia.


Methane is the primary component of natural gas. Methane ranks second to carbon dioxide as the most prevalent greenhouse gas in Earth’s atmosphere. Both methane and carbon dioxide occur naturally but are presently accumulating in the atmosphere at accelerated rates due to human activities.


Mineral Rights
Mineral rights refer to the legal rights to certain minerals below the surface of the earth.


Monitoring is the process of observing the progress or quality of something over a period of time.


EHP conducts community-wide air monitoring projects. Our projects use Purple Air and AirViz monitors to measure the concentration of fine particulates (PM2.5) and continuous volatile organic compound (VOC) monitors over a period of time to establish a baseline of what air quality looks like prior to the construction of a well pad, compressor station, injection well, petrochemical complex, etc. We also conduct monitoring during operational stages of these different types of infrastructure, for pre and post comparisons.

Natural Gas Liquids (NGLs)
NGLs are components of gas that have been separated from their gas state in the form of liquids. NGLs include ethane, propane, butane, isobutane, and pentane. The separation of these hydrocarbons occurs in a field facility or in a gas processing plant. Once separated, NGLs can be converted into everyday products, such as plastic. NGLs are classified based on their vapor pressure:

  • Low = condensate

  • Intermediate = methane gas

  • High = liquefied petroleum gas

NGL Storage 
NGLs can be stored in above-ground tanks or underground, where salt caverns provide the proper temperature and pressure to keep NGLs in liquid form.


Particulate Matter
“PM” is short for particulate matter. It consists of tiny liquid and solid particles found in the air we breathe. PM in the air we breathe comes from a wide range of sources – dirt, pollen, animals, fires, cooking, and many industrial sources. Most PM is produced by the use of fossil fuels (EPA, 2018), which includes shale gas development.


Pennsylvania Department of Environmental Protection (DEP)
The Pennsylvania Department of Environmental Protection’s mission is to protect Pennsylvania’s air, land, and water from pollution and to provide for the health and safety of its citizens through a cleaner environment.

Pennsylvania Department of Health (DOH)
The mission of the Pennsylvania Department of Health is to promote healthy behaviors, prevent injury and disease, and to assure the safe delivery of quality health care for all people in Pennsylvania.


The term permeability reflects the ease with which fluids or gases travel or flow between the pore spaces in a rock. Pore spaces are the small voids of airspace inside a rock. Rocks with higher permeability better allow fluids and gasses to flow through their pore spaces, while rocks with lower permeability trap fluids or gasses. Unconventional sources of oil and gas, such as shale, have low permeabilities and require hydraulic fracturing to encourage the flow of fluids and gasses.


Petrochemicals are chemicals derived from oil and gas production. They are used to make plastic, synthetic fertilizers, personal care products, building materials, resins, car parts, and more.


Pigging Stations
The oil and gas industry inspects and cleans pipelines by “pigging.” The name originates from either Pipeline Inspection Gadget, or the squealing sound pigging tools make as they pass through the pipeline.


The pipeline network in the United States is a transportation system used to move goods and materials. The most common products transported by pipelines are for energy purposes, including natural gas, biofuels, and liquid petroleum. The United States has the most miles of pipelines than any other country, with 1,984,321 km (1,232,999 miles) in natural gas transport and 240,711 km (149,570 miles) in petroleum products. 


Produced Water
Produced water is naturally occurring water found in the earth that rises to the surface of the earth during oil and gas activity. Like flowback fluid, produced water can be dangerous because it may contain high levels of total dissolved solids (TDS) and may also contain dissolved hydrocarbons along with naturally occurring radioactive materials (NORM).


Production Casing
This is the deepest section of casing in a well. Well casing consists of a series of metal tubes installed in a freshly -drilled hole. Casing strengthens the sides of the well hole, ensuring that no oil or gas seeps out of the well hole as it is brought to the surface. Production casing is installed last. This is the casing that provides a conduit from the surface of the well to the petroleum-producing formation.


A proppant is a solid material, like sand, that is incorporated into fracking fluid and designed to keep open the fractures created during hydraulic fracturing.


Setback Distances
A setback distance is the distance a shale gas facility is required by law to be from a structure or building.


As of 2018 in PA, setback distance is 500 feet for horizontally drilled well pads from the well bore to the edge of an existing building, and 750 feet for compressor stations and processing plants. Allowances for the distance to be as little as 300 feet for well pads apply in residential districts if the 500 feet restriction cannot be met.

Shale Gas
Shale gas is the gas that is trapped within underground shale formations.

Southwest Pennsylvania Environmental Health Project (EHP)
The Environmental Health Project (EHP), formerly the Southwest Pennsylvania Environmental Health Project, is a nonprofit public health organization that assists and supports residents of Southwestern Pennsylvania and beyond who believe their health has been, or could be, impacted by shale gas development.


Unconventional Drilling
Unconventional drilling is a newer method of extracting hydrocarbons using directional drilling combined with some form of well stimulation. Unconventional drilling is typically done in tough-to-access geologic formations and requires more resources than conventional drilling.


Utica Shale
The Utica Shale is a black, calcareous, organic-rich shale that underlies significant portions of Ohio, Pennsylvania, West Virginia, New York, Quebec and other parts of eastern North America. In the subsurface, the Utica Shale is located a few thousand feet below the Marcellus Shale.


Volatile Organic Compounds (VOCs)
VOCs are compounds that have a high vapor pressure and low water solubility. They are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects.


Vulnerable Populations
Vulnerable populations include those who may be more susceptible than others to the impacts of air pollution. Vulnerable populations typically include children, pregnant women, the elderly, and those with health conditions like asthma, chronic obstructive pulmonary disease (COPD), and more.


The wellbore of an oil and gas well is the hole that is drilled for the purpose of hydrocarbon extraction. It may also be referred to as the drill hole or the borehole. Wellbores are lined with steel casing and cement in order to protect the surrounding geologic strata, including groundwater systems, from leaks of drilling and fracking fluids, produced water, or methane and other gasses. A wellbore may be vertical or horizontal.


The head of the well is the portion of the well’s anatomy that is visible above ground. It consists of pipes and valves that cap the wellbore.


Well Pads
A well pad is an area that has been cleared for a gas facility. Well pads can include more than one well and additional drilling or processing machinery. 


Well Stimulation
Well stimulation increases oil and gas production by improving flow through underground formations. Fractured wells may be stimulated through a mixture of water and chemicals, acidizing, or a combination of both depending on the nature of the target formation.


Wet Gas
As opposed to dry gas, wet gas is gas that, in addition to methane, contains other NGLs, such as ethane and butane.

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