| Adsorption |
The process by which molecules are attached to the surface of a solid particle. |
| Bioaccumulation |
The gradual accumulation of a substance (or substances) in an organism.
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| Biodegradable |
Capable of decomposition by bacteria or other living organisms. |
| Constituents of emerging concern (CEC) |
A group of compounds that have been recently detected in water and may pose negative effects on public health or the environment. This includes pharmaceuticals, personal care products, industrial chemicals and endocrine disruptors. |
| Distribution system |
Part of the water supply network where potable water (finished water treated at drinking water treatment plants) is distributed to the community through a series of residential, commercial and industrial service pipes. |
| Granular activated carbon (GAC) |
A form of particulate carbon (medium) manufactured to adsorb soluble contaminants such as organics and PFAS. This product has high surface area per unit mass and the ability to capture a large variety of contaminants. Compared with PAC, GAC uses large carbon particles and is considered a permanent and robust treatment method for long-term contaminant removal. |
| Groundwater well |
A well drilled into the ground to access underground water supplies referred to as aquifers. Some of these systems may have treatment systems in place in the well to remove fine particles like sand that can clog the well pipe. |
| Half-life |
The time required for a quantity to reduce to half of its initial value in the environment or inside plants, animals or humans. |
| Influent |
Water entering the treatment plant or process being discussed (a tank, treatment scenario, watershed, etc.). |
| Ion exchange (IX) |
A water treatment process by which one or more contaminants is removed from water by exchange with another substance embedded in a manufactured resin. |
| Intake |
A location where a drinking water treatment plant draws water from source water (usually a reservoir). This point is located at the beginning of the drinking water treatment plant process, prior to treatment. |
| Long-chain PFAS |
PFAS that have a sulfonic acid functional group (made up of sulfur, oxygen and hydrogen atoms — SO3H) and contain six or more carbons, or those that have a carboxylic acid functional group (made up of carbon, oxygen and hydrogen atoms — COOH) and contain eight or more carbons. |
| Nanofiltration (NF) |
A membrane filtration method that uses nanometer-sized pores to filter water from a multitude of contaminants, such as organic matter, out of water. |
| Organic matter |
A complex mixture of organic compounds that are found in surface water and groundwater. Types of organic matter are tracked in drinking water applications as surrogates for treatability of contaminants, operational efficiency and overall water quality. |
| Outfall |
A place where a river, drain or sewer empties into the sea, a river or a lake. |
| Powder-activated carbon (PAC) |
A form of powdered or pulverized carbon manufactured to adsorb soluble contaminants such as organics and PFAS. This product has high surface area per unit mass and the ability to capture a large variety of contaminants. Compared with GAC, PAC uses smaller carbon particles and is considered a short-term treatment option for rapid and sometimes intermittent operation. |
| Per- and polyfluoroalkyl substances (PFAS) |
A class of thousands of man-made compounds that contain within their molecular structure a chain of carbon atoms in which one or more of the carbon atoms is “perfluorinated,” meaning that other than its carbon-atom neighbors, it is bonded only to fluorine atoms (e.g., perfluorooctanesulfonic acid or C8HF17O3S). |
| Persistence |
Length of time a chemical exists in the environment before being destroyed or transformed by natural processes. |
| Precursor |
A compound that can react or degrade (via biodegradation or environmental degradation) to produce another compound. |
| Primary source |
The source that directly contributes PFAS to the environment (e.g., industrial dischargers, airfields using firefighting foam containing PFAS). |
| Raw water (also referred to as source water) |
The untreated water source (usually groundwater or a surface water source such as a reservoir) that is withdrawn for treatment at a drinking water treatment plant. |
| Reference dose |
An estimate of a daily exposure to the human population that is likely to be without appreciable risk of adverse health effects over a lifetime. |
| Reverse osmosis (RO) |
A membrane filtration method that uses osmotic pressure to direct water to pass through a membrane and separate out a multitude of contaminants, such as salts. |
| Secondary source |
A source that indirectly contributes PFAS to the environment through conveyance of PFAS from primary sources (e.g., wastewater treatment plant effluent, landfill leachate). |
| Short-chain PFAS |
PFAS that have a sulfonic acid functional group and five or fewer carbons, or those with a carboxylic acid functional group and seven or fewer carbons. |
| Total organic carbon (TOC) |
A measure of the amount of organic carbon found in a water sample, often used as a nonspecific indicator of water quality. |
| Toxicity |
The quality of being toxic and imparting an adverse health impact after exposure. |
| Utility |
An organization supplying the community with electricity, gas, water or sewerage treatment. |
