CLARC glossary

The CLARC glossary defines many of the terms and acronyms found in the Cleanup Levels and Risk Calculation (CLARC) resource pages. CLARC is a compendium of technical information that includes data tables and guidance that help you establish cleanup levels at a contaminated site. 
Term Definition
CLARC Glossary

1 x 10 -6 cancer risk

The target excess cancer risk allowed for individual carcinogens when establishing Method B cleanup levels under the Model Toxics Control Act. A cancer risk of 1 x 10-6 equates to approximately one excess cancer case in a population of 1,000,000 individuals due to exposure to the cancer-causing substance over a lifetime. This concept assumes that the risk of cancer from a given carcinogen is in “excess” of a person’s background risk of developing cancer.
1 x 10 -5 cancer risk The target excess cancer risk allowed for individual carcinogens when establishing Method C cleanup levels under the Model Toxics Control Act.  Also, the maximum excess total cancer risk for a site with multiple carcinogens. A cancer risk of 1 x 10-5 equates to approximately one excess cancer case in a population of 100,000 individuals due to exposure to the cancer-causing substance over a lifetime.
Applicable or Relevant and Appropriate Requirement (ARAR) A federal or state legal standard outside the immediate purview of the Model Toxics Control Act that must be met (applicable) or should be met (relevant and appropriate) when cleaning up a site. An example of an ARAR under MTCA are drinking water standards, such as Maximum Contaminant Levels (MCLs) specified by the Safe Drinking Water Act as amended in 1996 (WAC 173-340-710).
Brownfield 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. 
BTEX An acronym for Benzene, Toluene, Ethylbenzene, and Xylenes, a group of hazardous substances that are commonly associated with gasoline and other petroleum products.
Carcinogen Any substance or agent that produces or tends to produce cancer in humans (WAC 173-340-200).
Carcinogenesis / Cancer A multistage cellular processes characterized by initiation, promotion, and progression. Initiation is the event that transforms a normal cell into a pre-cancerous intermediate (initiated) cell. Promotion is the proliferation of a single initiated cell into a clone many initiated cells. Progression is the transformation of one of these initiated cells into a malignant cell, which then proliferates into a detectable malignant tumor characterized by an unrestrained growth of cells.

Source: Perspectives on Biologically Based Cancer Risk Assessment, edited by Vincent James Cogliano, E. Georg Luebeck and Giovanni A.Zapponi; Kluwer Academic / Plenum Publishers, copyright 1999.
Carcinogenic potency factor (CPF) The upper 95th percentile confidence limit of the slope of the dose-response curve and is expressed in unit of measure of (mg/kg-day)-1 (WAC 173-340-200). The cancer potency factor is referred to by the U.S. Environmental Protection Agency (EPA) as a "slope factor."
CERCLA The Comprehensive Environmental Response Compensation and Liability Act (CERCLA) of 1980 as amended by the Superfund Amendments and Reauthorization Act of 1986. CERCLA is the federal law that created the Superfund program administered by the EPA.
Cleanup The implementation of a cleanup action or interim action (WAC 173-340-200).
Cleanup action Any remedial action, except interim actions, taken at a site to eliminate, render less toxic, stabilize, contain, immobilize, isolate, treat, destroy, or remove a hazardous substance that complies with WAC 173-340-350 through 173-340-390 (WAC 173-340-200).
Cleanup action alternative One or more treatment technology, containment actions, removal action, engineered control, institutional control or other type of remedial actions (“cleanup action components”) that individually, or in combination, achieves a cleanup action at a site (WAC 173-340-200).
Cleanup Action Plan (CAP) The document prepared by Ecology under WAC 173-340-380 that selects the cleanup action and specifies cleanup standards and other requirements for the cleanup action (WAC 173-340-200).
Cleanup level The concentration of hazardous substance in soil, water, air, or sediment that is determined to be protective of human health and the environment under specified exposure conditions (WAC 173-340-200). Units of measure (that is, "metrics") for cleanup levels are:            
  • For soils and sediments, typically expressed as mg/kg (milligrams per kilogram, parts per million, PPM)
  • For ground waters and surface waters, typically expressed as µg/L (micrograms per liter, parts per billion, PPB)
  • For air, typically expressed as µg/m3 (micrograms per cubic meter)
Cleanup Rule Chapter 173-340 WAC, also known as the MTCA Cleanup Regulations. The Cleanup Rule sets standards and procedures for cleaning up contaminated sites under the state's environmental cleanup law, the Model Toxics Control Act (MTCA), Chapter 70.105.D RCW. Learn more on our MTCA page.
Cleanup standards Standards adopted under RCW 70.105D.030(2)(d) which requires the following:               
  • Hazardous substance concentrations that protect human health and the environmental (“cleanup levels”);
  • The location on the site where those cleanup levels must be attained (“points of compliance”); and
  • Additional regulatory requirements that apply to a cleanup action because of the type of action and/or the location of the site. These requirements are specified in applicable state and federal laws and are generally established in conjunction with the selection of specific cleanup action (WAC 173-340-200).
Exposure route to route conversion: for obtaining MTCA Cleanup Level in the appropriate metric As of January 1991, IRIS and NCEA databases no longer present RfDs or slope factors (Cancer Potency Factors, CPFs) for the inhalation route. These criteria have been replaced with reference concentrations (RfCs) for noncarcinogenic effects and unit risk factors (URF) for carcinogenic effects. However, for purposes of estimating risk and calculating risk-based concentrations, inhalation reference doses and inhalation slope factors have the appropriate metrics. To calculate an inhalation reference dose (RfDi) from an RfC, use MTCA equations (adapted from EPA’s Health Effects Assessment Summary Tables-1997) as follows:
  •   RfDi mg/(kg-day) = RfC (mg/m3) X 20m3/day X 1/70kg
To calculate an inhalation cancer slope factor (SFi) from an inhalation Unit Risk Factor, the following equation and assumptions are used:
  • SFi (CPFi) (kg-day)/mg = URF (m3/µg) X (day/20m3) X 70kg X 103µg/mg
An additional exposure route to route conversion is the use of measures of toxicity for cancer (Cancer Potency Factors, CPFs) and non-cancer (Reference Doses, RfDs) based on the oral route of exposure (ingestion) for dermal toxicity. Since there is insufficient information to define the measures of toxicity for the dermal route of exposure, then extrapolations are used to adjust an administered dose to an absorbed dose based on a chemical’s oral absorption efficiency. Consistent with MTCA terminology the following adjustments are made to a reference dose (RfDo) and cancer potency factor (CPFo) based on the oral route of exposure to evaluate the dermal route of exposure:
  • RfDo X Gastrointestinal absorption conversion factor (GI) = RfDd
  • CPFo / Gastrointestinal absorption conversion factor (GI) = CPFd
The RfDd and CPFd are measures of toxicity for non-cancer and cancer, respectively, adjusted for the dermal route of exposure. In the absence of chemical specific information, the gastrointestinal absorption conversion factor is obtained from the default exposure parameters for MTCA equations 740-4, 740-5, 745-4, and 745-5.
Groundwater / ground water Water in a saturated zone or stratum beneath the surface of land or below a surface water; water that fills spaces between soil and rock particles underground (WAC 173-340-200).
Hazard Index (HI) The sum of two or more hazard quotients for multiple hazardous substances and/or multiple exposure pathways.
Hazard Quotient (HQ) The ratio of the dose of a single hazardous substance over a specified time period to a reference dose for that hazardous substance derived for a similar exposure period (WAC 173-340-200).
Health Advisory (HA) An estimate of acceptable drinking water levels for a chemical substance based on health effects information.  A Health Advisory is not a legally enforceable Federal standard, but serves as a technical guidance to assist federal, state, and local officials.

Source: Edition of the Drinking Water Standards and Health Advisories (EPA 2018).               
  • One-Day HA: The concentration of a chemical in drinking water that is not expected to cause any adverse non-carcinogenic effects for up to one day of exposure. The one-day health advisory is normally designed to protect a 10-kg child consuming 1 liter of water per day.
  • Ten-Day HA: The concentration of a chemical in drinking water that is not expected to cause any adverse non-carcinogenic effects for up to ten days of exposure. The ten-day health advisory is also designed to protect a 10-kg child consuming 1 liter of water per day.
  • Lifetime HA: The concentration of a chemical in drinking water that is not expected to cause any adverse non-carcinogenic effects for up to a lifetime of exposure. The lifetime health advisory is based on exposure of a 70-kg adult consuming 2 liters of water per day.
Henry's Law constant The ratio of a hazardous substance’s concentration in the air to its concentration in water. Henry’s Law constant can vary significantly with temperature for some hazardous substances. The dimensionless form of Henry’s Law constant is used in the MTCA equations and the units of measure of atm-m3/mole for Henry’s Law constant are used to help identify the volatility of a chemical for the inhalation correction factor (WAC 173-340-200).
Inhalation Correction Factor (INH) Criteria: Tiered criteria to determine chemical volatility and selection of INH factor used for CLARC
  1. Chemical volatility based on EPA’s analytical methods specified in WAC 173-340-200 Definitions: “Volatile organic compound” means those carbon-based compounds listed in EPA methods 502.3, 524.2, 551, 601, 602, 603, 624, 1624C, 1661, 1671, 8011, 8015B, 8031, 8032A, 8033, 8260B, and those with similar vapor pressures or boiling points. [This definition in WAC 173-340-200 continues for petroleum-related chemicals and is not presented here].
  2. Vapor pressure > 6.75 E-03 mmHg -OR- Boiling point < 218.5 degrees C.
  3. In the absence of a chemical’s volatility being defined by the vapor pressure or boiling point then the chemical’s Henrys Law Constant is considered by the following criteria: HLC > 10-5 atm-m3/mol (EPA 1991)
Source: EPA 1991, Risk Assessment Guidance for Superfund, Part B, Development of Risk-based Preliminary Remediation Goals, OSWER Directive 9285.7-01B

Non-volatile chemicals are assigned an INH factor of 1; volatile chemicals are assigned an INH factor of 2 based on the above criteria.
Lowest Observed Adverse Effect Level (LOAEL) The lowest exposure level of chemical in a study, or group of studies, that produces statistically or biologically significant increases in frequency or severity of adverse effects between the exposed population and its appropriate control.
Maximum Contaminant Level (MCL) Maximum concentration of a contaminant that is allowed in drinking water as established by either the United States Environmental Protection Agency under the Federal Safe Drinking Water Act (42 U.S.C. 300f et seq.) or the Washington State Board of Health and published in Chapter 248-54 WAC or 40 CFR 141 (WAC 173-340-200).
Maximum Contaminant Level Goal (MCLG) Maximum concentration of a contaminant that is allowed in drinking waster as established by either the United States Environmental Protection Agency under the Federal Safe Drinking Water Act (42 U.S.C. 300f et seq.), or the Washington State Board of Health and published in Chapter 248-54 WAC or 40 CFR 141 (WAC 173-340-200).
Method Detection Limit (MDL) The minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte (contaminant) concentration is greater than zero.

Source: Guidance on Sampling and Data Analysis Methods (Ecology Publication No. 94-49, January 1995).
Model Toxics Control Act (MTCA) Washington's environmental cleanup law, Chapter 70.105D RCW. Passed by Washington voters in the November 1988 general election as Initiative 97, and adopted into law by the legislature in 1989. Learn more on our MTCA page.
Natural background The concentration of a hazardous substance consistently present in the environment that has not been influenced by localized human activities.
No Observed Adverse Effect Language (NOAEL) The dose of a chemical at which there were no statistically or biologically significant increases in frequency or severity of adverse effects seen between the exposed population and its appropriate control. Effects may be produced at this dose, but they are not considered to be adverse.
Non-cancer effects, noncancer effects Adverse biological effects not related to cancer.
Practical Quantitation Limit (PQL) The concentration that can be reliably measured within specified limits during routine laboratory operating conditions using Ecology approved methods; in the absence of a specified PQL, then, by convention, the PQL is determined by 10 times the MDL.
Reasonable Maximum Exposure (RME) The highest exposure that can be reasonably expected to occur for a human or other living organisms at a site under current and potential future site uses (WAC 173-340-200). MTCA cleanup and remediation levels are based on estimates of current and future resource uses and reasonable maximum exposure expected to occur under both current and potential future site use conditions [WAC 173-340-708 (3)]. Resource uses, residential and industrial land uses define the reasonable maximum exposure for purposes of establishing a cleanup level. For an overview of the process for establishing cleanup standards see these focus sheets:

Developing Ground Water Cleanup Standards (Ecology Publication No. 01-09-049, April 2005)
Developing Surface Water Cleanup Standards (Ecology Publication No. 01-09-050, April 2005)
Developing Soil Cleanup Standards (Ecology Publication No. 01-09-071, April 2005)
Developing Air Cleanup Standards (Ecology Publication No. 01-09-072, April 2005)
Reference dose (RfD) An estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, with uncertainty and additional modifying factors generally applied to reflect limitations of the data used. The RfD is expressed in units of milligrams per kilogram body weight per day. This includes chronic reference doses, subchronic reference doses, and developmental reference doses.

Source: EPA's Integrated Risk Information System (IRIS) online database and WAC 173-340-200
Reference concentration (RfC) An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, with uncertainty and additional modifying factors generally applied to reflect limitations of the data used. The RfC is expressed in units of milligrams per cubic meter.

Source: EPA's Integrated Risk Information System (IRIS) online database
Remediation levels Remediation levels are not the same as cleanup levels. A cleanup level defines the concentration of hazardous substances above which a contaminated medium (e.g., soil) must be remediated in some manner (e.g., treatment, containment, institutional controls). A remediation level, on the other hand, defines the concentration (or other method of identification) of a hazardous substance in a particular medium above or below which a particular cleanup action component (e.g., soil treatment or containment) will be used. Remediation levels, by definition, exceed cleanup levels.

Source: Concise Explanatory Statement for the Amendments to the Model Toxics Control Act Cleanup Regulation Chapter 173-340 WAC (February 2001)
Risk The probability (possibility or chance) that a hazardous substance, when released into the environment, will cause an adverse effect in exposed humans or other living organisms (WAC 173-340-200).
Risk assessment Evaluation of the adverse health effects (i.e., the probability to cause cancer and the potential for noncancer health effects) to human and the environment posed by contamination at a hazardous waste site. Cancer risks and noncancer effects are calculated using exposure factors, which provide numerical values for different types of exposures to contaminants, such as soil or drinking water ingestion rates and child or adult average body weights. Risk assessments may evaluate the risks to people, plants or animals, and may calculate risk as a specific value (point estimate) or a range of values (distribution). Some of the different types of risk assessments include:               
  • Baseline Risk Assessment: Risk assessment conducted before cleanup occurs.
  • Ecological Risk Assessment: Risk assessment that evaluates the threats, risks, posed to plants and animals on and/or near a hazardous waste site.
  • Human Health Risk Assessment: Risk assessment that evaluates the threats, risks, posed to people at a hazardous waste site; coming onto the hazardous waste site; living near the hazardous waste site; or potential exposure from contaminants at hazardous waste site that may migrate to other media or food sources.
  • Probabilistic Risk Assessment: Risk assessment where some or all of the exposure factor values are expressed as a distribution.
  • Residual Risk Assessment: Risk assessment that evaluates the threats, risks, posed by contamination that remains on site after cleanup.
Target Cancer Risk or Target Noncancer Hazard Quotient Target cancer risks and target noncancer hazard quotients are used to calculate risk-based cleanup levels at hazardous waste sites under MTCA. The resulting cleanup levels are expected to be adequately protective of human health and the environment.