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Glossary of Underground Injection Control Terms

Terms Used in the Underground Injection Control Program

If you do not find a term you're looking for here, please check the Glossary on the UIC National Program Office web page or the Office of Ground Water & Drinking Water Drinking Water Glossary.

Absolute Pressure: Absolute pressure refers to the total pressure exerted on a surface. The more usual pressure measured by most gauges is called "gauge pressure" and reflects an adjusted pressure that measures zero at the earth's surface. Since atmospheric pressure at the earth's surface is 14.7 pounds per square inch (psi), the absolute pressure is 14.7 psi higher than gauge pressure at the same location. Maximum injection pressure is fundamentally calculated as an absolute pressure and must therefore be corrected to gauge pressures by subtracting 14.7 psi, since this is the pressure measured by most gauges.

Administrative Order (AO): An administrative order is a formal enforcement action issued by the UIC Branch to those alleged to have violated conditions of permits, the regulations governing underground injection (found in Title 40 of the Code of Federal Regulations) or the Safe Drinking Water Act. An administrative order generally includes a fine.

Aquifer: An aquifer is a geological formation or group of formations or part of a formation that is capable of yielding a significant amount of water to a drinking water well or spring.

Best Management Practices (BMPs): Best Management Practices are physical, structural or managerial practices that decreases the potential for facilities to pollute drinking water. They can be used singly or in combination as appropriate in a particular situation.

Buoyancy: Buoyancy is the upward force resulting from a lighter material contacting a heavier material, such as wood floating in water.

Casing: This term refers to the steel pipe with which the well is constructed. Generally, there are at least two and sometimes three casing strings, one inside the other concentrically. They are cemented to the rock or unconsolidated material to prevent the movement of fluid into or between underground sources of drinking water (USDWs)

Class V Well: This is a term for all injection wells which are not explicitly identified as Class I, Class II, Class III or Class IV in the Code of Federal Regulations Sections 144.6 and 146.5. Classes I, II and III are different types of deep injection wells which inject fluids below underground sources of drinking water. Class IV wells inject hazardous waste into or above an underground source of drinking water and are generally banned. Class V wells include all other injection wells. They generally are shallow subsurface fluid disposal systems which are disposing of non-hazardous fluids into or above underground sources of drinking water. There are may types of Class V wells: List of Types of Class V Wells.

Class 5X16: Class 5X16 injection wells, a subclass of Class V wells, are Spent-Brine Return Flow Wells, used to re-inject spent brine into the same formation from which it was withdrawn after extraction of halogens or their salts. In Region 5, they are found in Michigan.

Closure: Closure refers to the elimination of an underground discharge into the ground. This can be the physical closure of an injection well (for example, by removing the well or plugging the well with cement or by re-routing the fluid into a holding tank or into a sewer) or the re-configuration of an injection well in such a way that certain fluids can no longer enter the well. An example would be filling the floor drains in the service area with cement so that motor vehicle service fluids can no longer enter the shallow disposal system but still allowing sanitary waste from bathrooms and sinks to enter the system.

Code of Federal Regulations (CFR): The Code of Federal Regulations is a compilation of all regulations issued by the agencies of the Federal government. It may be searched over the Internet at www.access.gpo.gov/nara/cfr/cfr-table-search.html. Title 40 of the CFR ("40 CFR") contains regulations governing the environment.

In addition, the USEPA has begun implementing a pilot project to provide access to those parts of the CFR that apply to the environment in Adobe Acrobat (pdf) format. (To view PDF files, you must have the Adobe Acrobat Reader on your computer. It is supported on various platforms and is available for free download at the Adobe Website Exit from EPA pages.) The parts most relevant to the UIC program are listed here:

Commercial Injection Wells: "Commercial" in this sense means an injection well which is permitted to accept wastes other than those generated by the owner/operator of the well. (Most injection wells are non-commercial, meaning they only inject wastes generated by the company which owns them.) When refering to Class II wells, they have been defined in US EPA Underground Injection Control Program Guidance #77 (6/22/92) as: "A single or multiple well facility that is specifically engaged in the business of underground injection of brine generated by third party producers for a fee or compensation, such as lease concessions, production sharing arrangements, or the right to salvage residual oil. In addition, the produced brine must originate off-site as a result of oil & gas production operations, only, and be transported to the facility by tank truck (page 2)."

Community Water Systems (CWS): A public water system that serves at least 15 service connections used by year-round residents of the area served by the system or regularly serves at least 25 year-round residents.

Compliance: The term "compliance" refers to conditions in which a regulated entity (usually an owner or operator of an injection well) has complied with the regulations governing underground injection (found in Title 40 of the Code of Federal Regulations), the Safe Drinking Water Act and all conditions of a permit (if one has been issued).

Compliance Monitoring: Compliance monitoring in the field includes witnessing of mechanical integrity, and other well testing, and conducting inspections including routine, compliance and complaint inspections. All Class I wells are visited at least once per year. All Class II, Class III and Class 5X16 wells are visited at least once every five years to witness the mechanical integrity testing on the well. The compliance monitoring program in the office includes review of monitoring documents submitted by regulated entities, review of mechanical integrity testing results submitted by regulated entities and the contract field inspectors, results of inspections, review of regional files and computer database files to identify potential violations.

Confining Zone: The confining zone means a geological formation, group of formations, or part of a formation that is capable of limiting fluid movement above an injection zone. It is composed of rock layers that are impermeable or distinctly less permeable than the injection zone beneath it. There may be multiple confining zones above an injection zone.

Conversion: Converting a well means changing it from one type of well to another. For example, a well which disposes of motor vehicle wastes may be converted into one which disposes of only sanitary waste.

Diffusion: Diffusion is the general process whereby particles of liquids, gases or solids intermingle as the result of their spontaneous movement from regions of higher concentrations to regions of lower concentrations. It is sometimes called self-diffusion, molecular diffusion or ionic diffusion and is only important at low velocity. Diffusion ceases only when the concentration of the constituent of interest is the same everywhere.

Direct Implementation: Direct Implementation (DI) States are those in which U.S. EPA administers the UIC program. Because a State may apply for primacy for one or more class of UIC wells, primacy may be partial or whole. In Region 5, U.S. EPA administers the UIC program as summarized in this table. In addition, the Region 5 UIC Program directly implements federal UIC regulations on Indian lands.

Dispersion: As used in the modeling of groundwater flow, dispersion is the phenomenon by which dissolved material tends to spread out from the path it would follow simply due to the motion of the groundwater in which it is dissolved. It is sometimes called mechanical dispersion or hydraulic dispersion. It causes dilution of the dissolved material. It occurs because of physical mixing during fluid movement between the solid grains in the rock (fluid in the center of the pore moves faster than fluid at the boundary of the pore) and the crossing of flow paths as the fluid flows around the solid grains in the rock and because of molecular diffusion.

Drywell: Drywell means a bored, drilled, or driven shaft or a dug hole or subsurface fluid distribution system,whose depth is greater than its largest surface dimension, which is completed above the water table so that its bottom and sides are typically dry except when receiving fluids.well. The term does not include improved sinkholes.

Environmental Justice: U.S. EPA defines environmental justice (EJ) as the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies. Fair treatment means that no group of people, including racial, ethnic, or socioeconomic groups should bear disproportionately high and adverse human health or environmental effects resulting from Federal agency programs, policies, and activities. For more information about Region 5's efforts in this area, please link to the Region 5 Environmental Justice home page.

Environmental Performance Partnership ("EnPPA", pronounced "enpah"): An EnPPA is an agreement between the US EPA Region 5 office and a state which identifies the Region's and the state's responsibilities and how best to work together for the benefit of the public and the environment. These responsibilities include meeting Federal and state environmental requirements, outlining how both agencies will collaborate to achieve joint priorities, identifying the state's work commitments and corresponding reporting requirements for the Federal grants covered by the agreement. Performance measures report on program activity and progress and environmental results. In Region 5, Illinois, Indiana, Minnesota and Wisconsin have EnPPAs with the US EPA. EnPPAs may cover one or two years. The National Environmental Performance Partnership System (NEPPS) was created in 1995 to reflect advances in environmental protection in the United States over the past two decades and proposes ways for the EPA and states to work together according to their strengths to direct reduced public resources toward improving the environment. More information about EnPPAs can be found on the National Environmental Performance Partnership System home page.

Fluid: A fluid is any material or substance which flows or moves whether in a semisolid, liquid, sludge, gas or any other form or state.

Formation: A geological formation is a body of earth material with distinctive and characteristic properties and a degree of homogeneity in its physical properties. A formation may be a made of rock or of unconsolidated material such as sand, gravel and clay and can be mapped on the earth's surface or traced in the subsurface.

Fracture Gradient: The fracture gradient is a measure of how the pressure required to fracture rock in the earth changes with depth. It is usually measured in units of "pounds per square inch per foot" (psi/ft) and varies with the type of rock and the stress history of the rock. The default value used by Region 5 in Michigan is 0.8 psi/ft. This means, for example, that at a depth of 100 ft, a pressure of 80 psi would be required to fracture the rock, while at a depth of 500 ft, the required pressure would be 400 psi; at 1000 ft, 800 psi. The fracture gradient is used in the calculation of the maximum injection pressure.

Ground Water Protection Area: Geographic areas near and/or around community and non-transient non-community water systems that use ground water as a source of drinking water. These areas receive priority for the protection of drinking water supplies.These areas are delineated and assessed under Section 1453 (Source Water Assessment and Protection Programs) of the Safe Drinking Water Act and are also referred to as source water protection areas, source water assessment areas, and ground water areas by different States. (Note: Source water protection areas for transient non-community water systems delineated under Sectioin 1453 of the Safe Drinking Water Act are not explicitly included in the Class V Rule as ground water protection areas.)

Improved Sinkhole: An improved sinkhole is defined in the Code of Federal Regulations Section 144.3 as a naturally occurring karst depression or other natural crevice found in volcanic terrain and other geologic settings which have been modified by humans for the purpose of directing and emplacing fluids into the subsurface. In Region 5, sinkholes are commonly funnel-shaped depressions in the land surface generally in a limestone (karst) regions. They allow water to flow directly from the surface into the ground water through passages in the rock created by solution. Water entering the ground water in this fashion does not go through any of the natural purification processes that happen when it flows through soil.

Indian Land: An Indian land is defined in the United States Code (18 U.S.C. 1151) Exit from EPA pages as: (a) all land within the limits of any Indian reservation under the jurisdiction of the United States government, notwithstanding the issuance of any patent, and, including rights-of-way running through the reservation; (b) all dependent Indian communities within the borders of the United States whether within the original or subsequently acquired territory thereof, and whether within or without the limits of a State; and (c) all Indian allotments, the Indian titles to which have not been extinguished, including rights-of-way running through the same. For more information about the Region 5 Underground Injection Control Program's activities related to the tribes, please see our tribal issues page, which has links to other relevant web sites.

Injectate: The word "injectate" refers to the liquid that is disposed of into an injection well.

Injection: Under the UIC Program, injection means the discharge of fluids into the ground by means of an underground injection well.

Injection Well: Injection wells are defined (in Title 40, Code of Federal Regulations, Section 144.3) as a bored, drilled, or driven shaft whose depth is greater than the largest surface dimension; or, a dug hole whose depth is greater than the largest surface dimension; or, an improved sinkhole; or, a subsurface fluid distribution system into which fluids (any material or substance which flows or moves whether in a semisolid, liquid, sludge, gas or any other form or state) are emplaced.

Injection Zone: The injection zone is the geological formation or group of formations or part of a formation receiving fluids through an injection well. In deep hazardous injection wells, it is composed of two parts: the injection interval (or emplacement interval) and the arrestment interval. The injection fluid is injected directly into the injection interval; the arrestment interval includes those rock layers into which the injection fluid may move either directly or by diffusion. Above the injection zone, there must be a confining zone.

Karst: The term "karst" refers to a type of topography that is formed over limestone, dolomite or gypsum by solution of the rock and is characterized by closed depressions or sinkholes, caves and underground drainage.

Land Disposal: Land disposal is defined in Title 40 of the Code of Federal Regulations Section 268.2(c) as "placement in or on the land" including "placement in a landfill, surface impoundment, waste pile, injection well, land treatment facility, salt dome formation, salt bed formation, underground mine or cave or placement in a concrete vault, or bunker intended for disposal purposes". It excludes corrective action management units.

Large Capacity Cesspools: Large capacity cesspools are defined in the Code of Federal Regulations Section 144.81(2) as cesspools for multiple dwellings or community or regional cesspools or other devices that receive untreated sanitary wastes, which have an open bottom and sometimes perforated sides. The UIC requirements do not apply to single family residential cesspools which receive solely sanitary waste and which have the capacity to serve fewer than 20 people a day.

Maximum Contaminant Level (MCL): The threshold concentration of a contaminant above which water is not suitable for drinking. See the National Primary Drinking Water Standards web page for more information. In the Safe Drinking Water act, an MCL is defined as "the maximum permissible level of a contaminant in water which is delivered to any user of a public water system."

Maximum Injection Pressure (MIP): The term "maximum injection pressure" generally refers to the maximum permitted injection pressure, that is, the maximum value of injection pressure at which an operator can inject into an injection well. This value is set in the injection well permit. Title 40 of the Code of Federal Regulations (40 CFR) Section 146.13(a)(1) requires that the MIP in Class I and Class III wells be set so as to assure that, except during stimuation, "the pressure i n the injection zone during injection does not initiate new fractures or propagate existing fractures in the injection zone. In no case shall injection pressure initiate fractures in the confining zone ...." For Class II wells, this restriction applies to the confining zone (40 CFR 146.23(a)(1)).

Mechanical Integrity: Title 40 of the Code of Federal Regulations (40 CFR) Section 146.8 defines mechanical integrity. An injection well has mechanical integrity if:

Mechanical Integrity Demonstration: Title 40 of the Code of Federal Regulations (40 CFR) Section 146.8 lists approved methods for mechanical integrity tests (MIT), which are summarized below.

For Part I (internal) MIT:

  1. Following an initial pressure test, monitoring of the tubing-casing annulus pressure with sufficient frequency to be representative, as determined by the Director, while maintaining an annulus pressure different from atmospheric pressure measured at the surface;
  2. Pressure test with liquid or gas; or
  3. Records of monitoring showing the absence of significant changes in the relationship between injection pressure and injection flow rate for certain Class II enhanced recovery wells.

For Part II (external) MIT:

  1. The results of a temperature or noise log; or
  2. For Class II wells only, cementing records demonstrating the presence of adequate cement to prevent migration of fluids into an underground source of drinking water; or
  3. For Class III wells where the nature of the casing precludes the use of temperature or noise logs, cementing records demonstrating the presence of adequate cement to prevent such migration; the monitoring program prescribed for Class III wells in 40 CFR Section 146.33(b) shall be designed to verify the absence of significant fluid movement.

Minor Permit Modification: Title 40 of the Code of Federal Regulations (40 CFR) Section 144.41 allows modifications of UIC permits without the formal permit modification process (which includes public notice and opportunity for public comment required by 40 CFR Part 124) in only seven specific situations. In short, minor modifications may only:

  1. Correct typographical errors;
  2. Require more frequent monitoring or reporting by the permittee;
  3. Change an interim compliance date in a schedule of compliance;
  4. Allow for a change in ownership or operational control of a facility
  5. Change quantities or types of fluids injected which are within the capacity of the facility as permitted
  6. Changed construction requirements provided that any such alteration complies with other requirements
  7. Amend a plugging and abandonment plan
Please see 40 CFR Section 144.41 for full details.

Motor Vehicle Waste Disposal Well (MVWDW): These are subsurface disposal systems which receive fluids from repair or maintenance of vehicles. They are found in places such as auto body repair shops, automotive repair shops, new and used car dealerships, specialty repair shops (for example, transmission or muffler repair shops) or any facility that does any repair work on motor vehicles, including farm machinery, boats, snowmobiles and airplanes.

Other Sensitive Ground Water Area:: States may also identify other areas in the State in addition to ground water protection areas that are critical to protecting underground sources of drinking water from contamination. These other sensitive ground water areas may includes areas overlying sole-source aquifers, highly productive aquifers supplying private wells, continuous and highly productive aquifers at points distant from public water supply wells; areas where water supply aquifers are recharged; karst aquifers that discharge to surface reservoirs serving as public water supplies, for example. In Region 5 the states of Illinois, Indiana, Michigan, Ohio and Wisconsin have chosen to apply this designation state-wide.

Non-Community Water System (NCWS). A public water system that is not a community water system. There are two types of NCWSs: transient and non-transient.

Non-Endangerment of Underground Sources of Drinking Water. Prohibition of movement of fluid containing any contaminant into underground sources of drinking water, if the presence of that contaminant may cause a violation of any primary drinking water regulation under 40 CFR 141 or adversely affect public health.

Non-Transient Non-Community Water Systems (NTNCWS). Water systems that are not community systems and regularly serve at least 25 of the same non-resident persons per day for more than 6 months per year. Non-transient non-community systems typically are schools, offices, churches, factories, etc.

Packer: A packer is a device that is placed inside the casing string and holds the base of the tubing through which the fluid is injected in place. The space between the tubing and the casing string is called the annulus and it is filled with fluid, most commonly water mixed with a corrosion-inhibitor.

Permeability: Permeability refers to the property of a solid medium, such as rock or soil, that describes how fluids flow through the medium. It is a property of both the medium and the fluid: for example, the permeability of a particular rock will be different if the fluid is water or oil. It is related to porosity in that permeability depends on the size and shape of the spaces between the rock grains or soil particles but it also depends greatly on the size and shape of the interconnections between these spaces. The term porosity only refers to the percentage of the material that is void and does not taken into consideration how this space is distributed.

Permit: EPA and certain state agencies issue permits to owners and operators of injection wells to implement the requirements of the UIC program. UIC permits are documents which detail the responsibilities and requirements related to the operation of UIC wells.

Point of Injection: Point of injection is defined in the Code of Federal Regulations Section 144.3 as the last accessible sampling point prior to waste fluids being released into the subsurface environment through a Class V injection well. For example, the point of injection of a Class V septic system might be the distribution box - the last accessible sampling point before the waste fluids drain into the underlying soils. For a dry well, it is likely to be the well bore itself.

Primacy: States and Tribes which have approved UIC programs are referred to as Primacy States. Because a State or Tribe may apply for primacy independently for the different classes of UIC wells, more than one State agency in a given State may be involved. In Region 5, the Primacy States and the well classes for which they have primacy are summarized in this table.

Pound per Square Inch: The conventional unit for measuring pressure is "pound per square inch", which is abbreviated "psi". Pressure can be measured as absolute pressure or gauge pressure. On an absolute scale, the pressure of the atmosphere at the surface of the earth is approximately 14.7 psi: this is psi-absolute (psia). However many gauges are set to read 0 at the surface of the earth, this is 0 psi-gauge (psig). Therefore, the relation between the two is: psig = psia - 14.7.

Public Hearing: A public hearing is a special type of public meeting. The sole purpose of a public hearing is to provide an opportunity for the public to make comments on a proposed agency decision. A court reporter records all remarks made during the hearing and prepares an official transcript of the proceeding. The agency prepares a Response to Comments (also called a Responsiveness Summary) that contains a response to each issue raised at the public hearing or provided as a written comment during any public comment period on the proposed agency decision. It is not a question and answer session. See Title 40 of the Code of Federal Regulations, Section 124.12, Public Hearings, for more information.

Public Notice: As used by the EPA, the term "public notice" means an official agency announcement or notice of a proposed agency action or decision or of a public hearing.

Public Water System (PWS). A water system that provides water to the public for human consumption through pipes or other conveyances, if such system has at least 15 connection or regularly serves at least 25 individuals.

Region 5: Region 5 of the U.S. Environmental Protection Agency is made up of the states of Illinois, Indiana, Michigan, Minnesota, Ohio and Wisconsin. The main office of EPA Region 5 is located in Chicago at 77 W. Jackson Boulevard. Region 5 implements the federal environmental regulations in partnership with these states and the tribes located within these states.
-More about Region 5-

Rule Authorization:: Rule authorization means the well must comply with all the requirements of the UIC program but does not require an actual UIC permit. With certain exceptions, Class V injection wells are "authorized by rule" rather than by permit. The exceptions are large-capacity cesspools and motor vehicle waste disposal wells in ground water protection areas or other sensitive ground water areas. New wells of either of these two types are prohibited.

Sanitary Waste. Liquid or solid waste originating solely from humans and human activities, such as wastes collected from toilets, showers, wash basins, sinks used for cleaning domestic areas, sinks used for food preparation, clothes washing operations, and sinks or washing machines where food and beverage serving dishes, glasses, and utensils are cleaned. Sources of these wastes may include single or multiple residences, hotels and motels, restaurants, bunkhouses, schools, ranger stations, crew quarters, guard stations, campgrounds, picnic grounds, day-use recreation areas, other commercial facilities, and industrial facilities provided the waste is not mixed with industrial waste.

Semi-volatiles: Semi-volatiles are chemicals which have a tendency to volatilize or vaporize or evaporate at temperatures higher than volatiles. Examples of semi-volatiles are hexachlorobenzene, nitrobenzene and toxaphene. EPA method #625 is used to analyze for semi-volatiles. See Title 40 of the Code of Federal Regulations (40 CFR) Section 136, Appendix A for more details. (Technically semi-volatile compounds have a Henry's Law constant, H', greater than 0.01.)

Senior Environmental Employee (SEE) Program: This program is authorized by Congress to assist the U.S. Environmental Protection Agency in protecting the environment by hiring individuals 55 or older who wish to contribute their experience in providing technical assistance to Federal, state and local governmental agencies for projects of pollution prevention, abatement and control. In EPA Region 5, the program is run under a cooperative agreement with the National Asian Pacific Center on Aging Exit from EPA pages.

Septic System: A septic system is used to dispose of human sanitary waste or effluent from dwellings, businesses, community centers or other places where people congregate. They include a septic tank and a subsurface fluid distribution system. The UIC requirements do not apply to single family residential septic systems nor to non-residential septic systems which are used solely for the disposal of sanity waste and have the capactiy to serve fewer than 20 people a day.

7520 ("Seventy-five Twenty") Forms: The 7520 forms have been generated by U.S. Environmental Protection Agency headquarters staff for permit applications, permit transfers, Plugging and Abandonment Plans, monitoring reports, etc. They are available as PDF files by clicking on the link above.

Specific gravity (SG): Specific gravity is defined as the ratio of the density of the material of interest (such as oilfield brine) to the density of fresh water. When used for gases, the term usually means the ratio of the density of the gas of interest to that of air. Specific gravity is used in the calculation of the maximum injection pressure.

Sole-source Aquifer: A Sole Source Aquifer is an aquifer which has been designated as the "sole or principal" source of drinking water for an area. The program was established under Section 1424(e) of the Safe Drinking Water Act of 1974. The regulations relating to Sole Source Aquifers are found at Title 40 of the Code of Federal Regulations Part 149.

Source Water Protection Area (SWPA). The area delineated by the state for a public water system (PWS) or including numerous PWSs, whether the source is ground water or surface water or both, as part of the state SWAP approved by EPA under section 1453 of the Safe Drinking Water Act.

Subsurface fluid distribution system: An assemblage of perforated pipes, drain tiles, or other similar mechanisms intended to distribute fluids below the surface of the ground.

Susceptibility Analysis. An analysis used to determine, with a clear understanding of where the significant potential sources fo contamination are located, the susceptibility of the PSW(s) in the source water protection area to contamination from these sources.

Total Dissolved Solids: Total dissolved solids means the total dissolved (filterable) solids present in a fluid as determined by use of the method specified in Title 40 of the Code of Federal Regulations (40 CFR) Part 136. UIC regulations protect water which has less than 10,000 milligrams per liter (mg/l) total dissolved solids. To put this value into perspective, most drinking water averages between 200 and 300 milligrams per liter total dissolved solids and water with TDS greater than 500 milligrams per liter is not recommended for human consumption. Therefore 10,000 mg/l is a very conservative value.

Toxicity Characteristic (TC): Toxicity characteristic is one of the four criteria which define hazardous waste under Federal hazardous waste regulations. Title 40 of the Code of Federal Regulations (40 CFR) Section 261.24 lists 43 specific constituents and the regulatory level for each of these constituents. Any solid waste which has a concentration of any of these contaminants at or above the level listed in Table 1 of 40 CFR Section 261.24 is considered toxic and is therefore hazardous. (The other three characteristics are ignitability, corrosivity and reactivity, all of which are defined more precisely in 40 CFR Section 261.20 Section 261.21 and Section 261.22 .) For more details, see the Code of Federal Regulations entry in this glossary.

Transient Non-Community Water Systems (TNCWS). Water systems that are not community systems and serve 25 non-resident persons per day for 6 months or less per year. Transient non-community systems typically are restaurants, hotels, large stores, etc.

Underground Source of Drinking Water (USDW): An Underground Source of Drinking Water as defined in Title 40, Code of Federal Regulations (40 CFR) Section 144.3 is an aquifer or part of an aquifer which:

  1. supplies any public water system, or contains a sufficient quantity of ground water to supply a public water system and currently supplies drinking water for human consumption or contains fewer than 10,000 milligrams/liter of Total Dissolved Solids (TDS); and
  2. is not an exempted aquifer.

An "exempted aquifer" is part or all of an aquifer which meets the definition of a USDW but which has been exempted according to the criteria found in 40 CFR Section 146.4, which specifies that the aquifer does not currently serve as a source of drinking water, and the aquifer cannot now and will not in the future serve as a source of drinking water for one of the following reasons:

  1. It is mineral, hydrocarbon or geothermal energy producing, or can be demonstrated by a permit applicant as part of a permit application for a Class II or III operation to contain minerals or hydrocarbons that considering their quantity and location are expected to be commercially producible;
  2. It is situated at a depth or location which makes recovery of water for drinking water purposes economically or technologically impractical;
  3. It is so contaminated that it would be economically or technologically impractical to render that water fit for human consumption;
  4. It is located over a Class III well mining area subject to subsidence or catastrophic collapse; or
  5. The total dissolved solids content of the ground water is more than 3,000 and less than 10,000 milligrams/liter and it is not reasonably expected to supply a public water system.

Volatiles: Volatiles are chemicals which have a tendency to volatilize or vaporize or evaporate easily at relatively low temperatures. Examples of volatiles are benzene, toluene and carbon tetrachloride. EPA method #624 is used to analyze for volatiles. See also semi-volatiles. See Title 40 of the Code of Federal Regulations (40 CFR) Section 136, Appendix A for more details.

Wellhead Protection Area (WHPA). The surface and subsurface area surrounding a well or well field, supplying a public water system (PWS), through which contaminants are reasonably likely to move toward and reach such water well or well field.

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