Hazard Ranking System Glossary of Terms and Acronyms A - L, Superfund
AALAC: Ambient aquatic life advisory concentration.
AOC: Area of observed contamination.
AWQC: Ambient water quality criteria.
Actual Contamination in the Air Migration Pathway: A target population is subject to actual contamination if a sample location within its distance category meets the criteria for an observed release. Targets located within distance categories closer to the source than the distance category where the observed release is established are also subject to actual contamination. Targets located within distance categories beyond the most distant category containing an observed release, but within the 4 - mile target distance limit, are subject to potential contamination.
Actual Contamination for a Drinking Water Intake: Drinking water intake located in a portion of a surface water body that meets the criteria for an observed release.
Actual Contamination in the Ground Water Pathway: A drinking water well is subject to actual contamination if a sample from the well meets the criteria for an observed release. The scorer cannot infer actual contamination of a drinking water well based on other samples (e.g., from downgradient wells).
Actual Contamination for the Surface Water Pathway: A portion of a surface water body is considered subject to actual contamination if it meets criteria for an observed release. Sampling data from aqueous, sediments, or essentially sessile, benthic organisms may be used to establish actual contamination. However, the requirements for establishing actual contamination vary by threat.
Adequately Determined (for purposes of Tier A only): The total mass of all CERCLA hazardous substances in the source and releases from the source (or for the area of observed contamination) is known or is estimated with reasonable confidence. (For the site hazardous waste quantity factor value to be adequately determined for Tier A, this definition must apply for all sources.)
Adequately Determined (for purposes of Tier B only): The total mass of all hazardous wastestreams and CERCLA pollutants and contaminants for the source and releases from the source (or for the area of observed contamination) is known or is estimated with reasonable confidence. (For the site hazardous waste quantity to be adequately determined for Tier B, this must apply for all sources.)
Annual Use: Criterion for determining whether a standby intake may be used to evaluate the nearest intake factor. To meet this criterion, a standby intake generally should supply drinking water for at least one 24 - hour period in a year.
Area of Observed Contamination: Evaluated only in the soil exposure pathway and established based on sampling locations as follows:
- Generally, for contaminated soil, consider the sampling locations that indicate observed contamination and the area lying between such locations to be an area of observed contamination, unless information indicates otherwise.
- For sources other than contaminated soil, if any sample taken from the source indicates observed contamination, consider the entire source to be an area of observed contamination.
- If an area of observed contamination (or a portion of such an area) is covered by a permanent, or otherwise maintained, essentially impenetrable material (e.g., asphalt), exclude the covered area from the area of observed contamination. However, asphalt or other impenetrable materials contaminated by site - related hazardous substances may be considered areas of observed contamination.
Aquatic Human Food Chain Organism: Aquatic species directly consumed by humans, including certain finfish, shellfish, crustaceans, amphibians, and amphibious reptiles.
Aquatic Vertebrate Species: Vertebrate species that lay eggs or bear young in water. Icluded are all fishes, nearly all amphibians, and a few mammals (i.e., manatees, whales, porpoises). Note that most species of toads and salamanders and many species of frogs spend most of their adult lives on land, but most species return to water to breed.
Aquifer: One or more strata of rock or sediment that is saturated and sufficiently permeable to yield economically significant quantities of water to wells or springs. An aquifer includes any geologic material that is currently used or could be used as a source of water (for drinking or other purposes) within the target distance limit. All geologic materials combined into one aquifer are referred to as a single hydrologic unit.
Aquifer Boundary: A physical barrier to ground water flow identified as the contact between geologic materials defined as an aquifer and materials defined as non - aquifer (or as an aquifer but with a significantly lower hydraulic conductivity). (Where interconnections between aquifers are documented, aquifer boundaries are expanded to encompass the interconnected aquifers.)
Aquifer Discontinuities: Geologic and hydrologic features or structures that entirely transect an aquifer (or multiple aquifers, if interconnected) and that are expected to disrupt and/or prevent the flow of ground water and hazardous substances across the feature or structure. Aquifer discontinuities are a type of aquifer boundary.
Aquifer Interconnections: Subsurface conditions that allow two or more aquifers separated by aquifer boundaries to be combined into a single aquifer; subsurface conditions must demonstrate that the aquifer boundaries separating the aquifers do not or would not impede the flow of ground water and hazardous substances between the aquifers. Aquifer interconnections are evaluated within two miles of the site and in areas underlying contamination attributable to the site.
Associated Containment Structures: As used in HRS Table 3 - 2, constructed barriers (e.g., liners, dikes, berms) that may have been placed under, over, or around a hazardous substance source (e.g., a landfill or a waste pile) to prevent the release of hazardous substances to the environment.
Attribution: Attribution usually requires documenting that (1) at least one hazardous substance found in a release at a concentration significantly above background (or directly observed in the release) was produced, stored, deposited, handled, or treated at the site; and (2) at least a portion of the significant increase could have come from a source at the site.
BCF: Bioconcentration factor.
BPF: Bioaccumulation potential factor.
BPFV: Bioaccumulation potential factor value.
Background Level: The concentration of a hazardous substance that provides a defensible reference point with which to evaluate whether or not a release from the site has occurred. The background level should be reflective of the concentration of the hazardous substance in the medium of concern for the environmental setting on or near a site. Background level does not necessarily represent pre - release conditions, nor conditions in the absence of influence from source(s) at the site. Background level may or may not be less than the detection limit, but if it is greater than the detection limit, it should account for variability in local concentrations. Background level need not be established by chemical analysis.
Background Sample: A sample used in establishing a background level.
Below - ground Tank: A tank with its entire surface area below the surface and not visible; however, a fraction of its associated piping may be above the surface.
Benthic Organisms: Organisms that live on or at the bottom (i.e., not in the water column) of water bodies for most of their adult life cycle, such as clams, lobsters, and crayfish.
Bioaccumulation Potential: Evaluates the tendency for a substance to accumulate in the tissue of an aquatic human food chain organism and forms one component of the toxicity/persistence/bioaccumulation and toxicity/mobility/persistence/bioaccumulation factors within the human food chain threat - waste characteristics factor category.
Bioaccumulation Potential Factor Value (BPFV): BPFV is a measure based on a hierarchy of three types of data: bioconcentration factor; n - octanol - water partition coefficient (Kow); and water solubility. Bioaccumulation potential factor value reflects the tendency for a substance to accumulate in the tissue of an aquatic organism C the greater the bioaccumulation potential factor value, the greater the relative tendency of a substance to accumulate. Bioaccumulation potential factor values for commonly encountered hazardous substances are listed in SCDM.
Blended Water Distribution System: A drinking water supply system which can or does combine (e.g., via connecting valves) water from more than one well or surface water intake, or from a combination of wells and intakes.
Brackish Water: Water with an average tidal cycle chloride concentration of greater than 250 mg/l but less than 18,700 mg/l (corresponding to greater than 0.45 but less than 34 parts per thousand).
Bulk liquids: Noncontainerized liquids deposited directly into a source by pipe, tanker truck, or other means of transport.
Buried/Backfilled Surface Impoundment: A surface impoundment that has been completely covered with soil or other cover material after the final deposition of waste materials.
Burn Pit: An uncovered area on the land surface that is not presently burning but that was at one time used to burn hazardous substances or was otherwise significantly inflamed.
CERCLA: Comprehensive Environmental Response, Compensation, and Liability Act.
CERCLIS: Comprehensive Environmental Response, Compensation, and Liability Information System.
CLP: Contract Laboratory Program.
CRDL: Contract - required detection limit.
CRQL: Contract - required quantitation limit.
Capacity: The amount of water a well or intake can deliver to a water distribution system. Capacity may be expressed in units that are equivalent to a pumpage rate or as a percentage of the system's requirements.
CERCLA Hazardous Substances: Hazardous substance as defined by statute in CERCLA section 101(14); the list of CERCLA hazardous substances having reportable quantities is found in 40 CFR 302 in Table 302.4.
CERCLA Pollutant or Contaminant: Section 101(33) of CERCLA states that: "pollutant or contaminant shall include, but not be limited to, any element, substance, compound, or mixture, including disease - causing agents, which after release into the environment and upon exposure, ingestion, inhalation, or assimilation into any organism, either directly from the environment or indirectly by ingestion through food chains, will or may reasonably be anticipated to cause death, disease, behavioral abnormalities, cancer, genetic mutation, physiological malfunctions (including malfunctions in reproduction) or physical deformations, in such organisms or their offspring; except that the term "pollutant or contaminant" shall not include petroleum, including crude oil or any fraction thereof which is not otherwise specifically listed or designated as a hazardous substance under subparagraphs (A) through (F) of paragraph (14) and shall not include natural gas, liquefied natural gas, or synthetic gas of pipeline quality (or mixtures of natural gas and such synthetic gas)."
Chemical Waste Pile: A pile consisting primarily of discarded chemical products (whether marketable or not), by - products, radioactive wastes, or used or unused feedstocks.
Closed Fishery: A fishery closed or restricted by a government entity. Such closure prohibits fishing for commercial, recreational, or subsistence purposes. To be evaluated for the HRS, closure must be site - related.
Commercial Agriculture: Production of crops for sale, including crops intended for widespread distribution (e.g., supermarkets) and more limited distribution (e.g., local produce stands), and any nonfood crops such as cotton and tobacco. Commercial agriculture does not include livestock production, livestock grazing, or crops grown for household consumption (e.g., backyard garden or fruit trees).
Commercial Aquaculture: Cultivation of fish or shellfish to be sold for widespread distribution. Examples include a rearing pond used to raise catfish or a pond for nonfood crops such as goldfish and tropical fish.
Commercial Fishing: Fishing to derive income from catching and selling organisms taken from fresh or salt waters.
Commercial Food Crops: Crops that are intended to be sold widely, such as in supermarkets, and locally, such as those sold at local produce stands. Crops grown for domestic consumption or for use in a single restaurant are not considered commercial food crops.
Commercial Forage Crops: Crops grown to be sold as food for livestock (it is not necessary to document that these crops were sold only for commercial livestock); and grasslands used for grazing by commercial livestock (including some areas technically defined as "pasture/rangeland" by the USDA).
Commercial Livestock: Livestock raised for sale to commercial wholesalers or supermarkets. Livestock raised for private or domestic use is not considered commercial livestock.
Commercial Livestock Production or Commercial Livestock Grazing: Raising or feeding of livestock for sale (e.g., chicken coop used for housing commercially sold poultry, pastureland used for grazing on a commercial farm.)
Commercial Silviculture: Cultivation of trees for sale (e.g., Christmas tree farm, trees raised for lumber).
Confining Layer: A layer of low hydraulic conductivity (relative to adjacent geologic materials) that is not expected to be used as an aquifer.
Container or Tank: (1) Any stationary device constructed primarily of nonearthen materials (such as wood, concrete, steel, or plastic) used to contain an accumulation of a hazardous substance; or (2) any portable device in which a hazardous substance is stored or otherwise handled.
Contaminated Soil (excluding land treatment): Soil onto which available evidence indicates a hazardous substance was spilled, spread, disposed, or deposited.
Contiguous With Regard to Wetlands: Hydraulic connection (constructed or natural) between other surface water bodies and the wetland that allows water to move between the other surface water bodies and the wetland. Evidence to support an assertion that a wetland is contiguous to another surface water body includes (but is not limited to):
- Wetland is in the annual floodplain of the other surface water body;
- Wetland is supplied by the water body via a natural or constructed channel; or
- Water flows between the other surface water to the wetland via seepage or ground water.
Contour Line: Line that connects points of equal elevation on a topographic map; contour lines are colored brown on USGS topographic maps.
Contract Laboratory Program (CLP): The analytical program developed for CERCLA waste site samples to fill the need for legally defensible analytical results supported by a high level of quality assurance and documentation.
Contract - Required Detection Limit (CRDL): For HRS purposes, a term equivalent to the contract - required quantitation limit (CRQL), but used primarily for inorganic substances.
Contract - Required Quantitation Limit (CRQL): The substance - specific level that a CLP laboratory must be able to routinely and reliably detect in specific sample matrices. The CRQL is not the lowest detectable level achievable, but rather the level that a CLP laboratory must reliably quantify. The CRQL may or may not be equal to the quantitation limit of a given substance in a given sample. For HRS purposes, the term CRQL also refers to the contract - required detection limit (CRDL).
DNAPL: Dense non - aqueous phase liquid.
Designated for Drinking Water Use: Section 305(a) of the Clean Water Act requires states to prepare a water quality inventory that designates and classifies certain waters for drinking water use. The water can have such a classification even if it is not currently used for or is not currently suitable to be used for drinking water.
Detection Limit (DL): The lowest quantity of a hazardous substance that can be distinguished from the normal random "noise" of an analytical instrument or method. For HRS purposes, DL is the method detection limit (MDL) or, for real - time field instruments, the instrument detection limit (IDL) as used in the field.
Dilution Weight: A unitless parameter that adjusts the assigned point value for certain targets subject to potential contamination as a function of the flow or depth of the water body at the target. For the drinking water threat, use HRS Table 4 - 14 to assign a dilution - weighted population.
Direction of Overland Flow: Determined on a topographic map by drawing flow lines perpendicular to contour lines. Direction of flow will normally be along these flow lines, from areas of higher elevation towards areas of lower elevation but can be affected by man - made barriers such as walls and sewers. The determination of flow direction is important for identifying the drainage area upgradient of sources at the site and for identifying the overland segment of the hazardous substance migration path.
Drainage Area: The area upgradient of a source contributing water to the source via overland flow; this area is based on topography, except where overland flow is captured and/or diverted (e.g., storm sewers, run - on control features, walls) around the source. In cases where upland flow is captured or diverted, only the area of the source and areas upgradient of the source between the source and the device or structure diverting overland flow from the source are included in the drainage area.
Drum: A type of container used to hold hazardous substances. For HRS purposes, drums are standard 55 - gallon cylindrical containers.
EPA: Environmental Protection Agency.
Ecological - based Benchmarks: Reference data by which the level of contamination of sensitive environments is evaluated within the environmental threat - targets factor category.
Ecosystem Bioaccumulation Potential: Ecosystem bioaccumulation potential evaluates the tendency for a substance to accumulate in the tissue all aquatic organisms, not just human food chain organisms (as in bioaccumulation potential), and forms one component of the ecosystem toxicity/persistence/bioaccumulation and ecosystem toxicity/mobility/persistence/bioaccumulation factors within the environmental threat - waste characteristics factor category. HRS Table 4 - 15 and sections 188.8.131.52.1.3 and 184.108.40.206.1.3 provide the data hierarchy to follow when evaluating bioaccumulation potential.
Ecosystem Toxicity: The toxicity of a substance to aquatic organisms. It forms one component of the ecosystem toxicity/persistence/bioaccumulation and ecosystem toxicity/mobility/persistence/bioaccumulation factors within the environmental threat - waste characteristics factor category. HRS Table 4 - 19 provides the data hierarchy to follow when evaluating ecosystem toxicity.
Essentially Impervious Base: A base underlying containers that is free from cracks and gaps and prevents penetration of leaks, spills, or precipitation.
Essentially Sessile Benthic Organisms: Organisms that essentially stay at or near a localized spot in a water body during the adult stage of their life cycle (e.g., barnacles, oysters, muscles, sponges, and stalked diatoms). These organisms may not live on the bottom, but must not live suspended in the water column. They may be attached to rocks, pilings, or submerged banks at or near the surface. Samples from these organisms should be limited to the adult forms and can be used in the HRS for two purposes:
- To establish an observed release (use any essentially sessile benthic organism); and
- To establish actual contamination and the level of contamination (use only human food chain organisms).
Evidence of Hazardous Substance Migration: Chemical analyses and/or visual evidence that demonstrate hazardous substances attributable to a source have migrated away from that source into the surrounding soil, ground water, surface water, or air (e.g., leachate containing hazardous substances coming out of the source; stained or contaminated soil that can be attributed to migration from the source; evidence of the overflow from a surface impoundment containing hazardous substances).
Fishery: Any area of a surface water body from which human food chain organisms are taken or could be taken for human consumption on a commercial, recreational, or subsistence basis. Food chain organisms include fish, shellfish, crustaceans, amphibians, and amphibious reptiles. Fisheries are delineated by changes in dilution weights, level of contamination, or annual production.
Flow Rate: The long - term average annual discharge of a river or stream (i.e., the annual discharge averaged over many years of record).
Free Liquids: Liquids that readily separate from the solid portion of a substance under ambient temperature and pressure.
Freeboard: Vertical distance between the top of a tank or surface impoundment dike and the surface of the hazardous substance contained therein. Freeboard is intended to prevent overtopping resulting from normal or abnormal operations, wind and wave action, rainfall, and/or run - on.
Fresh Water: Water with an average tidal cycle chloride concentration of 250 mg/l or less (corresponding to salinity of 0.45 parts per thousand).
Functioning Ground Water Monitoring System: A system of test wells installed around a source to detect migration of hazardous substances. In evaluating the containment factor in the ground water pathway, the emphasis is on the functioning of the monitoring system. Thus, wells that are not sampled or maintained do not constitute a functioning ground - water monitoring system.
GIS: Geographic Information System.
GW: Ground water.
HFC: Human food chain.
HRS: Hazard Ranking System.
HRSGM: Hazard Ranking System Guidance Manual.
HWQ: Hazardous waste quantity.
Hazardous Constituent Quantity: The mass (in pounds) of CERCLA hazardous substances allocated to a source (with certain exceptions for RCRA wastes).
Hazardous Substances: Hazardous substances consist of CERCLA hazardous substances, pollutants, and contaminants as defined in CERCLA sections 101(14) and 101(33), except as otherwise specifically noted in the HRS.
Hazardous Substance Migration Path: The path that hazardous substances travel (or would travel) overland from a source to surface water (overland segment) and within surface water to the target distance limit (in - water segment). In certain cases (e.g., sites consisting only of contaminated sediments, sites where sources are located in surface water bodies), the hazardous substance migration path consists of only an in - water segment.
Hazardous Waste Quantity Factor Value: An assigned value for the pathway that is based on the sum of all source hazardous waste quantity values, and assigned using HRS Table 2 - 6.
Hazardous Wastestream: Material containing CERCLA hazardous substances as defined in CERCLA section 101(14), that was deposited, stored, disposed, or placed in, or that otherwise migrated to, a source.
IDL: Instrument detection limit.
In - water Segment: Portion of the hazardous substance migration path from the probable point of entry (PPE) to the target distance limit. For tidally - influenced rivers, the in - water segment may include portions of surface water bodies upstream from the PPE to the extent that the in - water migration path is reversed by tides. For contaminated sediments with no identified source, the in - water segment begins at the upstream boundary (for streams and rivers) or center of the area of contaminated sediments (for water bodies with no direction of flow).
Ingredient in Commercial Food Preparation: Surface water used for wholesale food preparation falls into this category (e.g., a manufacturer that prepares food products to be sold in supermarkets or produce stands). Food prepared in restaurants is not included in this category.
Intermittent Water Body: Water bodies that do not contain water throughout the year under normal conditions.
Karst: A kind of terrain with characteristics of relief and drainage arising from a high degree of rock solubility. The majority of karst conditions occur in limestone areas, but karst may also occur in areas of dolomite, gypsum, or salt deposits. Features associated with karst terrain may include irregular topography, abrupt ridges, sinkholes, caverns, abundant springs, disappearing streams, and the lack of a well - developed surface drainage system of tributaries and streams.
LNAPL: Light non - aqueous phase liquid.
LR: Likelihood of release.
Landfarm/Land Treatment: A method of waste management in which liquid wastes or sludges are spread over land and tilled or liquids are injected at shallow depths into soils.
Landfill: An engineered (by excavation or construction) or natural role in the ground into which wastes have been disposed of by backfilling or contemporaneous deposition of soil and wastes.
Land Treatment Zone: Soil layer in the unsaturated zone of a land treatment unit within which hazardous substances are intended to be degraded, transformed, or immobilized.
Layer of Lower Relative Hydraulic Conductivity: A geologic material with lower hydraulic conductivity than adjacent geologic materials. If used to establish aquifer boundaries, the difference in hydraulic conductivity should be at least two orders of magnitude.
Level I Concentrations for the Air Migration Pathway: Level I concentrations are established at sampling locations where the concentration of at least one hazardous substance that meets the criteria for an observed release is at or above its health - based benchmark for air. Level I concentrations also may be established if multiple hazardous substances are present below their respective benchmarks, but the I or J index is greater than or equal to one. Benchmarks for air include National Ambient Air Quality Standards (NAAQs), National Emission Standards for Hazardous Air Pollutants (NESHAPs), screening concentrations for cancer, and screening concentrations for noncancer toxicological responses.
Level II Concentrations for the Air Migration Pathway: Level II concentrations are established at sampling locations where the concentration of at least one hazardous substance meets the criteria for an observed release, but the conditions for Level I concentrations are not met. In addition, Level II is assigned to observed releases established by direct observation.
Level I Concentrations for the Drinking Water Threat: Level I concentrations are established in aqueous samples in which the concentration of at least one hazardous substance that meets the criteria for an observed release and is present at or above its drinking water benchmark. A drinking water intake also may be subject to Level I concentrations if multiple hazardous substances that meet the criteria for observed release are present below their respective benchmarks, but the I or J index is greater than or equal to one.
Level II Concentrations for the Drinking Water Threat: Level II concentrations are established for samples in which the concentration of at least one hazardous substance meets the criteria for an observed release, but the conditions for Level I concentrations are not met. In addition, Level II concentrations are assigned to observed releases established by direct observation.
Level I Concentrations for the Environmental Threat: Level I concentrations are established in samples in which the concentration of at least one hazardous substance meets the criteria for an observed release and is present at or above the appropriate ecological - based benchmark level (i.e., the appropriate EPA ambient water quality criteria (AWQC) or EPA ambient aquatic life advisory concentrations (AALAC) for the substance). Because AWQC and AALAC apply only to surface water samples, Level I concentrations can only be established based on aqueous samples. The I and J indices (see HRS section 2.5.2) do not apply because there are no screening concentration benchmarks for sensitive environments.
Level II Concentrations for the Environmental Threat: Level II concentrations are established for samples in which the concentration of at least one hazardous substance meets the criteria for an observed release, but the conditions for Level I concentrations are not met. In addition, Level II is assigned for observed releases that are based on direct observation.
Level I Concentrations for the Ground Water Pathway: Level I concentrations are established for samples from drinking water wells in which the concentration of a hazardous substance that meets the criteria for an observed release is at or above its specific health - based benchmark. A drinking water well also may be subject to Level I concentrations if multiple hazardous substances that meet the observed release criteria are present below their respective benchmarks, but the I or J index is greater than or equal to one. Benchmarks for the ground water include maximum containment levels (MCLs), nonzero maximum containment level goals pathway (MCLGs), and screening concentrations for cancer and chronic noncancer effects.
Level II Concentrations for the Ground Water Pathway: Level II concentrations are established for samples from drinking water wells in which the concentration of at least one hazardous substance meets the observed release criteria, but the conditions for Level I are not met. In addition, Level II is assigned to observed releases established by direct observation.
Level I Concentrations for the Human Food Chain Threat: Level I concentrations are established for tissue samples from aquatic human food chain organisms in which the concentration of a hazardous substance that meets the criteria for an observed release is at or above its specific health - based benchmarks. The tissue sample must also be taken from within the boundaries of the area of actual contamination. Aqueous and sediment sample results cannot be used to establish Level I concentrations for this threat.
Level II Concentrations for the Human Food Chain Threat: Level II concentrations are established in aqueous samples, sediment samples, or tissue samples from essentially sessile benthic organisms in which the concentration of hazardous substances meet the criteria for an observed release, but the conditions for Level I concentrations are not met. In addition, Level II concentrations are assigned to observed releases established by direct observation.
Level I Concentration for the Surface Water Pathway: Level I concentrations are established in samples in which the concentration of a hazardous substance that meets the criteria for an observed release is at or above its specific health - based benchmark for the surface water threats, with certain exceptions for the human food chain threat. Targets also may be subject to Level I concentrations if multiple hazardous substances that meet the criteria for an observed release are present below their respective benchmarks but the I or J index is greater than or equal to one. Benchmarks for the surface water pathway include maximum contaminant level (MCLs), non - zero maximum contaminant level goals (MCLGs), Food and Drug Administration advisory levels (FDAAL) for fish or shellfish, ambient water quality criteria (AWQC) for protection of aquatic life, ambient aquatic life advisory concentrations (AALAC), and screening concentrations for cancer and chronic non - cancer effects.
Level II Concentration for the Surface Water Pathway: Level II concentrations are established in samples in which the concentration of at least one hazardous substance meets the criteria for an observed release, but the conditions for Level I concentrations are not met, with certain exceptions for the food chain threat. In addition, Level II concentrations are assigned to observed releases established by direct observation.
Liner: A continuous barrier that covers all the earth likely to be in contact with a source so that hazardous substances or leachate containing hazardous substances would not migrate to the surrounding earth. The barrier may be synthetic material (e.g., a thick, continuous polyethylene membrane) or engineered, compacted natural material (e.g., re - worked and low permeability clay). However, an in - situ clay layer that has not been re - engineered by compaction or other methods is not considered a liner.
Listed Sensitive Environment: Areas that are evaluated as one or more of the sensitive environments listed in HRS Table 4 - 23, even if these areas (or portions of these areas) also are being evaluated as a wetland. The distinction is necessary because a wetland that is also a listed sensitive environment (e.g., a wetland area that also is habitat known to be used by an endangered species) would be evaluated as two separate sensitive environments. Point values are assigned differently for wetlands than for the other types of sensitive environments.