Absorption is the passage of one substance into or through another.

        Adsorption is the adhesion of molecules of gas, liquid, or dissolved solids to a surface. The term also refers to a method of treating wastes in which activated carbon removes organic matter from wastewater.

        In air sparging, air is injected into the ground below a contaminated area, forming bubbles that rise and carry trapped and dissolved contaminants to the surface where they are captured by a soil vapor extraction system. Air sparging may be a good choice of treatment technology at sites contaminated with solvents and other volatile organic compounds (VOC). See also Soil Vapor Extraction and Volatile Organic Compound.

       Air stripping is a treatment system that removes or "strips" VOCs from

contaminated groundwater or surface water as air is forced through the

water, causing the compounds to evaporate. See also Volatile Organic

Compound.

        The ASTM sets standards for many services, including methods of sampling and testing of hazardous waste and media contaminated with hazardous waste.

        As chemicals migrate, the contamination level for each chemical decreases. This attenuation, or decrease, may be due to chemical degradation, which results from decomposition by biological processes, adherence to soil particles underground, and dilution due to both infiltration of surface water runoff and the combining of the contaminated groundwater with other groundwater or surface water.

        An aquifer is an underground rock formation composed of such materials as sand, soil, or gravel that can store groundwater and supply it to wells and springs.

                        The amount or level of any constituent that occurs naturally in soil, water, or air.

        A baseline risk assessment is an assessment conducted before cleanup activities begin at a site to identify and evaluate the threat to human health and the environment. After remediation has been completed, the information obtained during a baseline risk assessment can be used to determine whether the cleanup levels were reached.

        Bedrock is the rock that underlies the soil; it can be permeable or non-permeable. See also Confining Layer and Creosote.

        A BDAT is a technology that has demonstrated the ability to reduce a particular contaminant to a lower concentration than other currently available technologies. BDATs can change with time as technologies evolve.

        Bioremediation refers to treatment processes that use microorganisms (usually naturally occurring) such as bacteria, yeast, or fungi to break down hazardous substances into less toxic or nontoxic substances. Bioremediation can be used to clean up contaminated soil and water. In situ bioremediation treats the contaminated soil or groundwater in the location in which it is found. For ex situ bioremediation processes, contaminated soil must be excavated or groundwater pumped before they can be treated.

        A biosensor is a portable device that uses living organisms, such as enzymes, tissues, microbes, and antibodies, to produce reactions to analytes.

        Bioventing is an in situ remediation technology that combines soil vapor extraction methods with bioremediation. It uses vapor extraction wells that induce air flow in the subsurface through air injection or through the use of a vacuum. Bioventing can be effective in remediating releases of petroleum products, such as gasoline, jet fuels, kerosene, and diesel fuel. See also Bioremediation and Soil Vapor Extraction.

                        A borehole is a hole cut into the ground by means of a drilling rig.