Cleanup Definitions

Here are common terms, acronyms, and initialisms used when discussing cleanup and remediation.

[A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N]
[O] [P] [Q] [R] [S] [T] [U] [V] [W] [X] [Y] [Z]
Absorption factors
Absorption factors mean the chemical-specific values that represent the fraction of the chemical from an environmental medium such as soil that can pass across the exchange boundaries of the organism (e.g., skin, lungs, gut) for absorption. The relevant absorption factors for chemicals into humans will be those published by EPA (e.g., the EPA's Dermal Exposure Assessment: Principles and Applications [EPA/600/8-91/011B), EPA Region 4's Supplemental Guidance to Risk Assessment Guidance to Superfund [RAGS]), those published in peer-reviewed literature, or other appropriate values as approved by MCEQ.

Aqueous Solubility
Aqueous Solubility means the solubility of a pure substance in water. It is the maximum amount of a chemical that will dissolve in pure water at a temperature of 30 degrees Celsius.

Assessment endpoint
Assessment endpoint means the explicit expressions of the actual environmental value that is to be protected. See also the definition for measurement endpoint.

Background chemical
Background chemical means a substance which is: (a) consistently present in the environment at and in the vicinity of a site; and (b) attributable to geologic or natural conditions.

Bioconcentration means the uptake and accumulation or concentration of a chemical in an individual organism.

Biomagnification means the accumulation of a chemical (that has the property to bioconcentrate) in humans or an animal through the food chain, i.e., from the ingestion of organisms or other animals tainted with the chemical.

With certain legal exclusions and additions, the term 'brownfield site' means real property, the expansion, redevelopment, or reuse of which may be complicated by the presence or potential presence of a hazardous substance, pollutant, or contaminant.

Brownfield Agreement
Brownfield Agreement means an agreement between the Applicant and MCEQ for the remediation of a Brownfield Agreement Site.

Brownfield Agreement Order
Brownfield Agreement Order means an Order issued by the Commission which embodies a Brownfield Agreement.

Brownfield Agreement Site
Brownfield Agreement Site means Brownfield Property that is remediated under a Brownfield Agreement. The Site shall consist of the Brownfield Property that is the subject of the application and any other Brownfield Property: (1) for which the source of contamination is environmental contamination or activities on or under the Brownfield Property that is the subject of the application, and (2) concerning which the MCEQ determines that remediation is necessary.

Brownfield Party
Brownfield Party means any person who desires to execute and implement a Brownfield Agreement.

Brownfield PropertyBrownfield Property
Brownfield Property means any property where use is limited by actual or potential environmental contamination, or the perception of environmental contamination, and that is or may be subject to remediation under any state environmental law, regulation or program or under the Comprehensive Environmental Response, Compensation and Liability Act of 1980, as amended, 42 USCS 9601 et seq. (1997)(CERCLA), but does not include any of the following: (1) sites proposed by the United States Environmental Protection Agency for the National Priorities List (NPL) but not listed on the NPL or sites listed on the NPL, except those NPL sites for which the United States Environmental Protection Agency has issued certificates of completion of the remediation set forth in the records of decision for those sites or concerning which EPA has subsequently determined that listing is inappropriate; (2) sites for which an administrative or judicial order is issued which is still in effect or enforcement action commenced under CERCLA or Sections 3001(b)(3)(B)(iv.), 3008(h), 3013(a) or 7003(c) of the Resource Conservation and Recovery Act of 1976, as amended, 42 USCS 6901 et seq. (1994 and Supp. 1997) (RCRA); or (3) sites undergoing corrective action under RCRA Section 3004(u), 3004(v) or 3008(h), except those sites that the United States Environmental Protection Agency determines have completed corrective action.

Carcinogen means any substance which may cause cancer as identified by the U.S. Environmental Protection Agency (EPA).

Carcinogenic risk
Carcinogenic risk or upperbound excess lifetime carcinogenic risk means the likelihood of developing cancer or tumor incidence for an individual from lifetime exposure to a carcinogen, not including exposure to cancer causing background chemicals.

CERCLA means the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (Superfund) (Public Law 96-510), as amended by the Superfund Amendments and Reauthorization Act of 1986, 42 U.S.C. 9601 et seq.

Chemical of Concern (CoC)
Chemical of Concern (CoC) means a contaminant or a chemical that poses public health and environmental risks specific to the Brownfield Agreement Site.

Corrective Action Plan (CAP)
Corrective Action Plan (CAP) means a document or a set of documents that outlines remedial objectives, scope of the design investigation, conceptual designs, pre-construction design specifications, construction management and schedules, quality control, and operation and maintenance in connection with remedial actions conducted pursuant to the Act and these regulations. The content and format of the CAP is provided in MDEQ's "Brownfields Corrective Action Plan Format," which may be required as part of the application.

Corrective Action Report
Corrective Action Report means a document or a set of documents that provide information supporting the remediation of human health and environmental risks specific to the Brownfield Agreement Site to levels appropriate for the land-use of the Site.

Cumulative excess cancer risk
Cumulative excess cancer risk means the upper bound on the estimated cancer risk above the background risk associated with exposure to multiple hazardous substances or multiple exposure pathways.

Cumulative site risk
Cumulative site risk means the summation of risks to a human receptor or ecological receptor from one or more hazardous substances. The cumulative site risk for noncarcinogens is the site's hazard index. The cumulative site risk for carcinogens is the cumulative excess cancer risk.

Deterministic risk assessment
Deterministic risk assessment means the traditional approach to estimating a site's potential risk by solving the risk algorithm (intake multiplied by the dose-response) analytically by the assignment of average or high-end values in the algorithm to calculate the risk (dependent variable) posed by independent variables (such as exposure factors and exposure point concentrations that produce the intake).

DNAPL means dense non-aqueous phase liquid.

Ecological receptor of concern
Ecological receptor of concern means specific ecological communities, populations, or individual organisms protected by federal or state laws and/or regulations, or those local populations which provide important natural or economic resources, functions and values.

Ecosystem means an integrated, self-functioning system consisting of interactions among both the biotic community and abiotic environment within a specified location in space and time.

Effective Solubility
Effective Solubility means the solubility of a compound that will dissolve from a chemical mixture (e.g., gasoline). The effective solubility of a compound from a chemical mixture is less than its aqueous solubility.

Engineering control
Engineering control means an existing condition or modification to a Brownfield Agreement Site that reduces or eliminates the potential for exposure to contaminants. These conditions or modifications may include, but are not limited to, physical or hydraulic control measures (such as groundwater recovery trenches and leachate collection systems), groundwater treatment systems, engineered caps, liner systems, slurry walls, or permanent structures, but shall not include the exclusive use of security fencing.

Environmental contamination
Environmental contamination means the presence of hazardous substances or constituents that pose unacceptable risks to the environment, humans, or ecological receptors.

Exposure means contact of an organism with a chemical or physical agent. Exposure is quantified by exposure point concentration in an exposure medium (such as soil, sediment, air, groundwater, and surface water) and the intake of the medium (expressed as the amount of the medium taken into the body by the organism per unit body weight per day).

Exposure factors
Exposure factors means values used to estimate exposure in risk assessment, such as the number of days per year, number of years that exposure is expected to occur, the amount of contaminated media that a person or an organism might contact per day, the extent of uptake or absorption of the medium contacted, and the body weight.

Exposure pathway
Exposure pathway means the manner by which a person or an organism may be exposed to a chemical of concern or contaminant. A complete exposure pathway consists of a source, a release from a source, a migration and transport mechanism, an exposure medium (e.g., air) or media (in cases of intermediate transfer), an exposure point, and an exposure route.

Exposure point concentration (EPC)
Exposure point concentration (EPC) is the amount of CoC available at the exchange boundaries of the organism (e.g., skin, lungs, gut) for absorption by humans.

Exposure route
Exposure route means the portal of entry which results in the intake of a contaminated medium into the human body or an organism (e.g., ingestion, dermal contact, and inhalation).

Fate and Transport
Fate and Transport means the behavior and movement of a chemical through an environmental media. The movement is affected by many factors such as sunlight (UV radiation), wind-blown or wave actions, microbial activity, groundwater and surface water flow, chemical properties (e.g., solubility, density), physical-chemical properties of the medium (e.g., grain size, porosity, permeability, and organic carbon content), and presence of solubility-enhancing solvents or buried piping and utilities.

Free product
Free product means a discharged hazardous substance or environmental pollutant that is present in the environment as a floating or sinking non-aqueous phase liquid. Free Product is considered present if (1) measurable using best available technologies, or (2) for groundwater, the concentration of the chemical of concern is at or above the aqueous solubility limit for that pure compound or the effective solubility limit for that compound in a chemical mixture, or (3) for soils, the concentration of the chemical of concern is at or above the soil saturation limit for that compound for all chemicals with a melting point less than 30 degrees Celsius.

Groundwater quality standard
Groundwater quality standard means the chemical-specific numerical value published by EPA as Maximum Contaminant Level (MCL). Where the groundwater intersects surface water, ambient water quality criteria values identified in the "Mississippi Water Quality Criteria for Intrastate, Interstate, and Coastal Waters" or other values determined by the MDEQ to be protective will be applicable.

Habitat means the area or type of environment to which an organism or biological population is indigenous.

Hazard index
Hazard index means the sum of the hazard quotients for multiple substances and/or multiple exposure pathways.

Hazard quotient
Hazard quotient means the value which quantifies noncarcinogenic hazard for a single chemical for an individual receptor over a specified exposure period. The hazard quotient is equal to the ratio of an intake of a chemical to the chemical's reference dose. Hazard quotient shall be based on similar-acting non-carcinogens, i.e., systemic toxicants that act on the same organ or organ system.

Hazardous substance
Hazardous substance mean any substance which is a hazardous substance as defined in Section 101(14) of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, and any substance which is designated as a hazardous substance under Section 102 of such Act.

Hazardous Waste
Hazardous wastes are regulated by the Environmental Protection Agency (EPA) through the Resource Conservation and Recovery Act (RCRA), 40 CFR 260-70. Hazardous waste is defined as any waste or combination of waste which because of its quantity, quality, concentration, physical, chemical, or infectious characteristics could cause or significantly contribute to adverse effects in the health and safety of humans or the environment if improperly managed. Specific definitions of the general characteristics of hazardous waste are found in 40 CFR 261.2. They include any wastes exhibiting a general characteristic of ignitability 40 CFR 261.21, corrosivity 40 CFR 261.22, reactivity 40 CFR 261.23, or toxicity 40 CFR 261.24 (according to Toxicity Characteristic Leaching Procedure (TCLP) testing). Also included are all wastes specifically listed by the Environmental Protection Agency (EPA) in 40 CFR Part 261, Subpart D as a toxic or acutely toxic hazardous waste, or wastes derived from specific or non-specific sources.




Land-use restriction or institutional control
Land-use restriction or institutional control means the limitation on use of or access to a Brownfield Agreement Site to reduce or eliminate the potential for exposure to contaminants. These restrictions may include, but are not limited to, deed restrictions, use restrictions, restrictive covenants, or restrictive zoning.

LNAPL means light non-aqueous phase liquid.

MCL means maximum contaminant level published by EPA under the Safe Drinking Water Act (42 United States Code 300f et seq.).

mg/Kg means milligram per kilogram.

mg/L means milligram per Liter.

Monitored Natural Attenuation
Monitored Natural Attenuation means remediation by natural attenuation that is monitored to determine achievement of remediation goals over a specified time period.

Natural Attenuation
Natural Attenuation means the reduction in the concentration or mass of a substance and its breakdown products in an environmental medium (such as groundwater), due to naturally occurring physical, chemical, and biological processes without human intervention or enhancement. These processes include, but are not limited to, dispersion, diffusion, sorption and retardation, and degradation processes such as biodegradation, abiotic degradation and radioactive decay.

NAPL means non-aqueous phase liquid, which can be heavier or lighter than water. NAPL that is lighter than water is called light non-aqueous phase liquid (LNAPL) or a floater. NAPL that is heavier than water is called dense non-aqueous phase liquid (DNAPL) or a sinker.

NPL means the National Priorities List published by EPA pursuant to CERCLA Section 105.


Person means any person as defined in Section 17-17-3 of the Mississippi Code Annotated.

Potentially responsible party (PRP)
Potentially responsible party (PRP) means a person who is or may be liable for remediation under any state or federal law, regulation, or program.

Preliminary Assessments (PAs)/ Site Investigations (SIs)
The CERCLA Branch manages National Priority List (NPL) sites, conducts Preliminary Assessments/Site Investigations (PA/SI) for potential NPL listing, and oversees planning and cleanup activities at federal facilities that do not require RCRA permits. Call our CERCLA Contact at (601) 961-5302 for more information.

Previously unknown contaminant
Previously unknown contaminant means any chemical or contaminant that has not been delineated in the Brownfields Site Characterization Report and/or remediated to a risk-level appropriate for the land-use of the Site as described in the Brownfields Corrective Action Report.

Probabilistic risk assessment
Probabilistic risk assessment means a site-specific risk assessment performed using a statistical sampling technique that produces a probabilistic approximation of the potential risk from the site-specific risk assessment algorithm or model.

Quality Assurance Project Plan (QAPP)
Quality Assurance Project Plan (QAPP) means a document or set of documents that integrates all technical and quality aspects of a project, including planning, implementation, and assessment. The purpose of the QAPP is to document planning results for environmental data operations and to provide a project-specific "blueprint" for obtaining the type and quality of environmental data needed for a specific decision or use.

Quality Management Plan (QMP)
Quality Management Plan (QMP) means a document or set of documents that describes how an organization structures its quality system and describes its quality policies and procedures, criteria for and areas of application, and roles, responsibilities, and authorities. It also describes an organization's policies and procedures for implementing and assessing the effectiveness of the quality system.

Quantitation limit
Quantitation limit means the lowest concentration for an analytical test method and sample matrix at which the quantity of a particular substance can be routinely measured with a stated degree of confidence. The quantitation limit for a particular sample analysis and analytical method is called the sample quantitation limit (SQL) or reporting limit.

Radioactive material
Radioactive material means a radionuclide or substance that spontaneously emits ionizing radiation or particles.

RCRA means the Resource Conservation and Recovery Act of 1976, 42 USC 6901 et seq.

Receptor means environmental resources, including but not limited to, plant and animal species, humans, sensitive environments and habitats, water supply wells, and locations that have the potential to be, or have actually been, exposed to contamination.

Reference concentration (RfC)
Reference concentration (RfC) means a value representing a daily exposure level for the human population, including sensitive subpopulations, that is not likely to cause deleterious and non-reversible adverse noncancer health effects during a chronic or subchronic exposure period. Reference concentration is generally expressed in the unit of milligram per cubic meter (mg/m3).

Reference dose (RfD)
Reference dose (RfD) means a value representing a daily exposure level for the human population, including sensitive subpopulations, that is not likely to cause deleterious and non-reversible adverse noncancer health effects during a chronic or subchronic exposure period. Reference dose is generally expressed in the unit of milligram per kilogram body weight (mg/Kg/day).

Regionally Prevalent Chemical
Regionally Prevalent Chemical means a substance found throughout a substantial geographic region, as approved by MDEQ (e.g., Delta region), that can be attributed to conditions, as approved by MDEQ, such as atmospheric deposition and aerial application.

Remediation means action to cleanup, mitigate, correct, abate, minimize, eliminate, control, treat, remove, or to implement institutional and/or engineering controls in order to prevent the spreading, migration, leaking, leaching, volatilization, spilling, transport, exposure, or further release of a contaminant to the environment in order to protect public health or the environment.

Remediation goal (RG)
Remediation goal (RG) means the target cleanup level or objective that is cost-effective, implementable, and protective of human health and the environment. The RG can be quantitative, i.e., numerical cleanup level (generally expressed in mg/kg [soil or sediment] or mg/L [water]) or can be qualitative (e.g., basis for an engineered barrier, to prevent/minimize exposure). Fencing alone cannot be the RG.

Restricted site
Restricted site means a Site where access to the general public is limited and/or controlled. The restrictions may include, but are not limited to, deed restrictions, use restrictions, restrictive covenants, or restrictive zoning.

Risk means the likelihood or probability that a hazardous substance, when released to the environment, will cause adverse effects in exposed humans or other biological receptors. Risk is further classified as carcinogenic (from exposure to carcinogens) or noncarcinogenic (from exposure to noncarcinogens, i.e., systemic toxicants).

Risk assessment
Risk assessment or "site-specific risk assessment" means a site-specific characterization of the current or potential threats that may be posed to human health and the environment by contamination migrating to or in groundwater or surface water, discharging to the air, leaching through or remaining in soil, bioaccumulating in the food chain, or other complete and significant exposure pathways identified in the Site Conceptual Exposure Model (SCEM). Key components of a risk assessment are the identification of hazard (i.e., identifying site-related chemicals and their concentrations in the exposure media), exposure assessment (identifying complete and significant exposure pathways and quantifying intake), toxicity assessment (identifying the toxic effects and dose-response [toxicity value]), risk characterization, and discussion of uncertainties. For the purposes of these regulations, a Tier 3 Risk Assessment is considered a "site-specific risk assessment."

Risk-based remediation requirement
Risk-based remediation requirement means remediation a requirement based on public health and environmental risks specific to a Site.

Risk Management
Risk Management means the evaluation of options or measures to reduce risk, including, but not limited to, such options as no further action, monitoring only, or gathering additional data before making a decision.

Sediment means particles in surface waters or wetlands or on the bottom of surface waters or wetlands that are derived from the erosion of rock, minerals, soils and biological materials, as well as chemical precipitation from the water column. Sediment particles are transported by, suspended in or deposited by water.

Sensitive environment
Sensitive environment means an area of exceptional environmental value, where a discharge or release could pose a greater threat than a discharge to other areas, including but not limited to: wetlands; habitat used by state or federally designated endangered or threatened species; national or state fish and wildlife refuges and fish and wildlife management areas; and state and federal designated wild and scenic rivers.

Site Conceptual Exposure Model (SCEM)
Site Conceptual Exposure Model (SCEM) means a graphical presentation of actual or hypothetical conditions, based on current data and understanding of the Site, under which the chemicals of concern or contaminants from a Brownfield Agreement Site may be released from a source, moved (migration/transport) in the environment, present in the exposure media, and absorbed by the receptor through the exposure routes. The SCEM will be used to identify data needs to assess risk and may be modified to consider new data in determining whether an exposure pathway is incomplete or complete. The SCEM is used in the development of remediation goals and identification of remedial options.

Site Characterization Report
Site Characterization Report means a document or a set of documents that provides information supporting the delineation of the vertical and horizontal extent of contamination on or under a Site in order to develop remediation requirements for the Site or to determine that remediation is necessary. The contents and format of the Brownfield Site Characterization Report is provided in MDEQ's "Brownfields Site Characterization Report Format," which shall be required as part of the application.

Slope factor
Slope factor means the upperbound estimate of probability in the occurrence of excess cancer risk (increase in cancer risk over the background risk) associated with a specific carcinogen for an individual who is exposed to a unit of intake over lifetime. The unit for a slope factor is the probability per unit intake, i.e., the inverse of milligram per kilogram body weight (mg/Kg/day)-1.

SPLP means Synthetic Precipitation Leaching Procedure, an EPA analytical method (Method 1312) published in SW-846.

SSL means a soil screening level developed by EPA in the Soil Screening Guidance: Technical Background Document (EPA/540/R-95/128).

SW-846 means Test Methods for Evaluating Solid Waste - Physical/Chemical Methods published by the U.S. Environmental Protection Agency, Office of Solid Waste on November 1986, and its updates.

Systemic Toxicant
Systemic Toxicant means a substance or agent that may enter the body, injure an organ or organ system, or have an effect other than causing cancer. The toxicity value used for risk characterization of the chronic effect for a systemic toxicant is the reference dose (RfD).

Target remediation goals (TRGs)
Target remediation goals (TRGs) mean risk-based media concentrations utilized in the Tier 1 evaluation of human health and environmental impacts in these regulations. Soil TRGs are soil concentrations developed by MDEQ for individual chemicals to address the soil ingestion and inhalation exposure pathways and environmental risks. Groundwater TRGs are either the groundwater quality standards (current MCLs published by EPA) or risk-based remediation goals derived by MDEQ. Soil and groundwater TRGs are provided in MDEQ's Risk Evaluation Procedures developed for these regulations. Surface water TRGs are the water quality criteria published by the MDEQ. TRGs are to be compared with the exposure point concentrations. TRGs alone do not always trigger the need for response actions or define unacceptable levels of contaminants in soil or groundwater. The Tier 1 TRGs may either be used as "default" remediation goals or as screening values that will initiate a Tier 2 Evaluation or Tier 3 Evaluation.

Technical Impracticability
Technical Impracticability or "Technically impracticable" means the inability to achieve certain remediation requirements and is based on engineering feasibility and reliability, cost-effectiveness, and risk-based considerations. For the purposes of these regulations, EPA's OSWER Directive 9234.2-25: "Guidance for Evaluating the Technical Impracticability of Groundwater Restoration," dated September 1993 may be utilized in developing a demonstration of technical impracticability with regard to groundwater and soil remediation, free product removal, and other site-specific conditions approved by MDEQ.

Tier 1 Evaluation
Tier 1 Evaluation means a comparison of CoC exposure point concentrations in soil or sediment with chemical-specific TRGs for the evaluation of human health and environmental impacts and an evaluation of ecological impacts through completion of an Ecological Checklist. Ecological evaluations are used to determine whether ecological receptors of concern are present and may include, but are not limited to, the collection of field observation data for any readily apparent harm on the ecological receptors of concern.

Tier 2 Evaluation
Tier 2 Evaluation means a more in-depth evaluation of site-specific conditions beyond the Tier 1 Evaluation methodology. The Tier 2 Evaluation may include, but is not limited to, an evaluation of site-specific conditions by (1) comparing the UCL of the Mean for a CoC applying statistical methods to the Tier 1 TRGs, (2) comparing EPCs to calculated background chemical concentrations, (3) comparing EPCs to calculated regionally prevalent chemical concentrations, (4) utilizing site-specific variables (i.e., exposure frequency, exposure duration, etc.) to calculate site-specific RGs, (5) eliminating/minimizing exposure routes, (6) conducting an analysis of Petroleum Hydrocarbons using TPH Fractioning, or (7) other methods approved by MDEQ.

Tier 3 Evaluation
Tier 3 Evaluation means a site-specific risk assessment (Risk Assessment). The Tier 3 human health risk evaluation is the characterization of the risks of cancer and adverse non-cancer health effects in humans in accordance with EPA's Risk Assessment Guidance for Superfund (RAGS) and other risk assessment guidance published by EPA including, but not limited to, the Adult Lead Model and the Integrated Exposure Uptake Biokinetic Model (IEUBK) for lead. The Tier 3 ecological risk evaluation is the characterization of environmental effects qualitatively or quantitatively in accordance with the EPA's Framework for Ecological Risk Assessment guidance, as amended.

Treatability study
Treatability study means the testing and documentation activities to evaluate the effectiveness of a proposed remediation method (remedial action) prior to full scale design and implementation. Treatability study includes, but is not limited to, bench scale studies and pilot scale studies, and may be required by the Corrective Action Plan if the remediation method has not been evaluated by EPA or an independent consultant or trade association to be capable of treating the medium (or medium of similar physical and chemical characteristics) at the Site.

Unacceptable risks
Unacceptable risks mean that the carcinogenic risks, noncarcinogenic hazards, or ecological risks posed by the CoCs at the point of exposure, according to a Tier 1, Tier 2, or Tier 3 Evaluation, have exceeded established target risk levels for humans or ecological receptors. The term can also be applied qualitatively if there is a sufficient basis to conclude that the likelihood of impact to the ecological receptors of concern or the sensitive environment is high based on findings of an ecological risk assessment.

Uncontrolled Sites
The Assessment & Remediation Branches (I & II) manage uncontrolled sites defined as a site, facility, plant, or location where hazardous substances, pollutants, or contaminants have been released into the environment and, due to existing regulations, there is no Federal program which can handle the problem. The Branches oversee planning and cleanup activities such as environmental assessments, remedial investigations, and feasibility studies performed by responsible parties at contaminated sites. In an effort to ensure consistency of cleanup, the Branches utilize the Brownfield Risk Evaluation Procedures. For more information, call 601-961-5318 or 601-961-5217.

Unrestricted site
Unrestricted site, relevant to a Brownfield Agreement Site, means that the use of the property is not restricted by an applicable Brownfield Agreement.

Volatile Compounds
Volatile Compounds means those compounds with a Henry's Law Constant greater than 1 x 10-5 and a molecular weight less than 200 g/mole, for all media.

Wetlands means those areas where water is at, near or above the land surface long enough to be capable of supporting aquatic or hydrophytic vegetation, and which have soils indicative of wet (hydrid) conditions.