The oil and gas industry creates an immense amount of waste, both nontoxic and toxic. This waste can be liquid or solid, and is either treated or dealt with in several ways, as described below. The Pennsylvania wells on WellWiki list the types of waste produced, and the facilities they are treated at. While the Pennsylvania Department of Environmental Protection (PA DEP) does not include definitions as to what those wastes are, other state, national, and industry sources do define them, as located below.

Definitions of Waste Types

• Produced Fluid: Water flowing from and around the wellhead, in addition to the desired oil and/or natural gas. It is naturally-occurring, but can contain various contaminants which are often toxic. It is typically treated by municipal recycling and waste centers.

• Brine: Highly saline water (>5% salt). Typically used as a component of drilling fluid to stabilize wells.

• Fracking Fluid: Fracking fluid is a combination of water, proppant (sand or ceramic solids), and over 80 possible different chemicals (some listed here) used to facilitate hydraulic fracturing and etching. The chemical additives plus proppant typically make up between 1% and 7% of the fluid as a whole. Some of the chemicals used in fracking fluid are also on the EPA’s list of hazardous waste chemicals, such as Naphthalene and Fluorene. The recipe of additives varies based on the conditions of the site, the type of proppant, the depth of the well, etc.

• Drilling Fluid Waste: This primarily consists of drilling muds, either oil-based or, more commonly, water-based, which must be cleaned up and properly disposed of after the drilling process is complete. The water-based muds are not considered to be particularly environmentally hazardous, though all are to some degree toxic. These are often reused for other hydraulic fracturing sites.

• Fracking Fluid Waste: Also referred to as “flowback,” fluid waste after fracking rises to the surface in stages after the fracking occurs over a series of months. It includes the original fracking fluid and all of its components, in addition to possible minerals or chemicals in the fractured formation as well. It is typically stored in lined pits known as centralized impoundments, and is removed to industrial treatments centers for disposal, though it is also occasionally reused.

• Drilling: {waiting on PA DEP response for a precise definition}

• Servicing Fluid: Other fluids in addition to the drilling fluid (muds) used in the drilling process. Most importantly, used to seal off the wellbore.

• Basic Sediment:’ Basic sediment and water (BS&W) is a technical specification of impurities in crude oil, not separated out in the field, sometimes occuring as a result of drilling and storage.

• Drill Cuttings: Drill cuttings are produced as the rock is broken by the drill bit advancing through the rock or soil; the cuttings are usually carried to the surface by drilling fluid circulating up from the drill bit. Burial is the most common onshore disposal technique used for disposing of drilling wastes (mud and cuttings).

• Flowback Fracturing Sand: The solids that rise with the liquid flowback and natural gas after the process of fracturing. This is the contaminated proppant that was originally pumped in with the fracking fluid.

• Spent Lubricant: Used petroleum utilized for engine lubrication. Considered toxic.

Waste Facility Types

• Industrial Treatment Facilities: These treat service fluid, flowback fluid, the majority of drilling muds, and other fluid wastes which are reclaimable or reusable. They use several different types of chemical and physical treatments to separate and clarify the water in the fluid, which is then reused or dumped into the surrounding watershed. Storage of fluids fall under the regulations for residual waste outlined in the PA DEP guidelines.

• Injection Wells: An injection well is a vertical pipe in the ground into which water, other liquids, or gases are pumped or allowed to flow. In terms of waste management, they are used to store hazardous, unreclaimable fluids in non-porous bedrock, acting similarly to a lined pit. For the Marcellus Shale region, most injection well sites are based out of Ohio, due to the differing geologies.

• Landfills: Nearly all drill cuttings are disposed of in landfills, in addition to a very small portion non-hazardous muds. They are ideal for residual solids not intended for reuse. All materials going into landfills must meet the standards for residual non-hazardous waste guidelines outlined by the PA DEP. For a complete list of locations of landfills taking residual waste from the Marcellus Shale area, see here.