Science Terms Definitions - C

Cancer - An abnormal, potentially unlimited, disorderly new tissue growth.

Cap - A layer of clay, or other impermeable material installed over the top of a closed landfill to prevent entry of rainwater and minimize leachate.

Carcinogen - A substance or agent that produces or incites cancerous growth.

Carcinogenesis - Development of carcinoma; or, in more recent usage, producing any kind of malignancy.

Carcinogenic - Cancer causing.

Carcinogenic Potency - The gradient of the dose-response curve for a carcinogen.

Carcinoma - Malignant new growth made up of epithelial cells tending to infiltrate the surrounding tissues and give rise to metastasis.

CAS Registration Number - An organization from Columbus, Ohio, which indexes information published in Chemical Abstracts by the American Chemical Society and provides index guides by which information about particular substances may be located in the Abstracts when needed. CAS numbers identify specific chemicals.

Cask - A thick-walled container (usually lead) used to transport radioactive material. Also called a coffin.

Cells - In solid waste disposal, holes where waste is dumped, compacted, and covered with layers of dirt on a daily basis.

CERCLA (Comprehensive Environmental Restoration and Compensation Liability Act) - Cleanup Program focuses on human health and environmental concerns related to human health. The cleanup program is primarily carried out by EPA, working with States, on sites designated for cleanup on the NPL. Cleanup Program emphasizes local source control, prevention of further spread from sources. Cleanup Program is prohibited from "restoring" natural resources, although cleanup may prevent further injuries to natural resources.

CFR - Code of Federal Regulations. A collection of the regulations that have been promulgated under U.S. law.

CH (contact handled) waste - TRU waste that requires little or no shielding and emits a maximum external radiation dose rate of 0.2 rem/hr (200 mrem/hr).

Chronic - Having a persistent, recurring or long-term nature. As distinguished from acute.

Chronic Effect - An adverse effect on a human or animal in which symptoms recur frequently or develop slowly over a long period of time.

Chronic Exposure - Multiple exposures occurring over an extended period of time, or a significant fraction of the animal's or the individual's life-time.

Chronic Toxicity - The capacity of a substance to cause long-term poisonous human health effects.

Cladding - The thin-walled metal tube that forms the outer jacket of a nuclear fuel rod. It prevents corrosion of the fuel by the coolant and the release of fission products into the coolant. Aluminum, stainless steel, and zirconium alloys are common cladding materials.

Cleanup - Actions taken to deal with a release or threat of release of a hazardous substance that could affect humans and/or the environment. The term "cleanup" is sometimes used interchangeably with the terms remedial action, removal action, response action, or corrective action.

Closure - The procedure a landfill operator must follow when a landfill reaches its legal capacity for solid waste: ceasing acceptance of solid waste and placing a cap on the landfill site.

Cohort Study - An epidemiologic study that observes subjects in differently exposed groups and compares the incidence of symptoms. Although ordinarily prospective in nature, such a study is sometimes carried out retrospectively, using historical data.

Collective Dose - The sum of the individual doses received on a given period of time by a specified population from exposure to a specified source of radiation.

Commercial Waste - All solid waste emanating from business establishments such as stores, markets, office buildings, restaurants, shopping centers, and theaters.

Commercial Waste Management Facility - A treatment, storage, disposal, or transfer facility which accepts waste from a variety of sources, as compared to a private facility which normally manages a limited waste stream generated by its own operations.

Committed Dose Equivalent - This is the dose to some specific organ or tissue that is received from an intake of radioactive material by an individual during the 50-year period following the intake

Committed Effective Dose Equivalent - The committed dose equivalent for a given organ multiplied by a weighting factor.

Comparative Risk - An expression of the risks associated with two (or more) actions leading to the same goal; may be expressed quantitatively (a ratio of 1.5) or qualitatively (one risk greater than another risk). Any comparison among the risks of two or more hazards with respect to a common scale.

Compliance Monitoring - Collection and evaluation of data, including self monitoring reports, and verification to show whether pollutant concentrations and loads contained in permitted discharges are in compliance with the limits and conditions specified in the permit.

Composite Sample - A series of water samples taken over a given period of time and weighted by flow rate. Or a soil sample that consists of soil taken from various depths or various locations.

Concentration Ratio - The ratio of the concentration of a compound or radionuclide in an organism or its tissues to the concentration in the surrounding media under equilibrium, or steady-state conditions.

Confidence Interval - A range of values (a1 < a < a2) determined from a sample of definite rules so chosen that, in repeated random samples from the hypothesized population, an arbitrarily fixed proportion of that range will include the true value, x, of an estimated parameter. The limits, a1 and a2, are called confidence limits; the relative frequency with which these limits include a is called the confidence coefficient; and the complementary probability is called the confidence level. As with significance levels, confidence levels are commonly chosen as 0.05 or 0.01, the corresponding confidence coefficients being 0.95 or 0.99. Confidence intervals should not be interpreted as implying that the parameter itself has a range of values; it has only one value, a. On the other hand, the confidence limits (a1, a2) being derived from a sample, are random variables, the values of which on a particular sample either do or do not include the true value a of the parameter. However, in repeated samples, a certain proportion of these intervals will include a provided that the actual population satisfied the initial hypothesis.

Confined Aquifer - An aquifer in which groundwater is confined under pressure which is significantly greater than atmospheric pressure.

Confounding Factors - Variables that may introduce differences between cases and controls which do not reflect differences in the variables of primary interest.

Consent Decree - A legal document, approved by a judge, that formalizes an agreement reached between EPA and potentially responsible parties (PRPs) through which PRPs will conduct all or part of a cleanup action at a Superfund site; cease or correct actions or processes that are polluting the environment; or otherwise comply with EPA initiated regulatory enforcement actions to resolve the contamination at the Superfund site involved. The consent decree describes the actions PRPs will take and may be subject to a public comment period.

Contamination - Contact with an admixture of an unnatural agent, with the implication that the amount is measurable. The deposition of unwanted radioactive material on the surfaces of structures, areas, objects, or people. It may also be airborne, external, or internal (inside components or people).

Contingency Plan - A document setting out an organized, planned, and coordinated course of action to be followed in case of a fire, explosion, or other accident that releases toxic chemicals, hazardous waste, or radioactive materials that threaten human health or the environment.

Continuous Sample - A flow of water from a particular place in a plant to the location where samples are collected for testing; may be used to obtain grab or composite samples.

Controlled Liquid Waste - Waste that meets the definition of a liquid waste and is in a container or piping system; a waste stream that can be shut off without a release to the environment.

Cooperative Agreement - An assistance agreement whereby EPA transfers money, property, services or anything of value to a state for the accomplishment of CERCLA-authorized activities or tasks.

Corrective Action - EPA can require treatment, storage and disposal facilities (TSDF) handling hazardous waste to undertake corrective actions to clean up spills resulting from failure to follow hazardous waste management procedures or other mistakes. The process includes cleanup procedures designed to guide TSDFs toward in spills.

Cost-benefit Analysis - A formal quantitative procedure comparing costs and benefits of a proposed project or act under a set of pre-established rules. To determine a rank ordering of projects to maximize rate of return when available funds are unlimited, the quotient of benefits divided by costs is the appropriate form; to maximize absolute return given limited resources, benefits-costs is the appropriate form.

Cost-Effective Alternative - An alternative control or corrective method identified after analysis as being the best available in terms of reliability, performance, and cost. Although costs are one important consideration, regulatory and compliance analysis does not require EPA to choose the least expensive alternative. For example, when selecting or approving a method for cleaning up a Superfund site the Agency balances costs with the long-term effectiveness of the methods proposed and the potential danger posed by the site.

Cost Recovery - A legal process by which potentially responsible parties who contributed to contamination at a Superfund site can be required to reimburse the Trust Fund for money spent during any cleanup actions by the federal government.

Cost Sharing - A legal process by which potentially responsible parties who contributed to contamination at a Superfund site can be required to reimburse the Trust Fund for money spent during any cleanup actions by the federal government.

Cradle-to-Grave or Manifest System - A procedure in which hazardous materials are identified and followed as they are produced, treated, transported, and disposed of by a series of permanent, linkable, descriptive documents (e.g., manifests). Commonly referred to as the cradle-to-grave system.

Criteria - Descriptive factors taken into account by EPA in setting standards for various pollutants. These factors are used to determine limits on allowable concentration levels, and to limit the number of violations per year. When issued by EPA, the criteria provide guidance to the states on how to establish their standards.

Criteria Pollutants - The 1970 amendments to the Clean Air Act required EPA to set National Ambient Air Quality Standards for certain pollutants known to be hazardous to human health. EPA has identified and set standards to protect human health and welfare for six pollutants: ozone, carbon monoxide, total suspended particulates, sulfur dioxide, lead, and nitrogen oxide. The term, "criteria pollutants" derives from the requirement that EPA must describe the characteristics and potential health and welfare effects of these pollutants. It is on the basis of these criteria that standards are set or revised.

Critical Effect - The first adverse effect, or its known precursor, that occurs as the dose rate increases.

Critical Mass - The amount of a fissile substance that will allow a self-sustaining chain reaction. The amount depends both on the properties of the fissile element and on the shape of the mass.

Critical Organ - That part of the body that is most susceptible to radiation damage under the specific conditions under consideration.

Criticality - A term used in reactor physics to describe the state when the number of neutrons released by fission is exactly balanced by the neutrons being absorbed (by the fuel and poisons) and escaping the reactor core. A reactor is said to be "critical" when it achieves a self-sustaining nuclear chain reaction, as when the reactor is operating.

Cumulative Dose - The total dose resulting from repeated exposures of ionizing radiation to an occupationally exposed worker to the same portion of the body, or to the whole body, over a period of time.

Curie (Ci) - The basic unit used to describe the intensity of radioactivity in a sample of material. The curie is equal to 37 billion (3.7*1010) disintegrations per second, which is approximately the activity of 1 gram of radium. A curie is also a quantity of any radionuclide that decays at a rate of 37 billion disintegrations per second. It is named for Marie and Pierre Curie, who discovered radium in 1898.