This 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.
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).
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.
An acronym for Benzene, Toluene, Ethylbenzene, and Xylenes, a group of hazardous substances that are commonly associated with gasoline and other petroleum products.
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.
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.
Any substance or agent that produces or tends to produce cancer in humans (WAC 173-340-200).
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.
A registry number assigned by the Chemical Abstracts Service.
The implementation of a cleanup action or interim action (WAC 173-340-200).
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).
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).
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).
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)
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.
Standards adopted under RCW 70A.305.030(2)(e) 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).
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.
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).
The sum of two or more hazard quotients for multiple hazardous substances and/or multiple exposure pathways.
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).
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.
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).
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.
- 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].
- Vapor pressure > 6.75 E-03 mmHg -OR- Boiling point < 218.5 degrees C.
- 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.
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 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).
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).
Washington's environmental cleanup law, Chapter 70A.305 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.