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Data Quality
The term data quality refers to all features and characteristics of data that bear on its ability to meet the stated or implied needs and expectations of the user.

Data Quality Objective (DQO)
DQOs are qualitative and quantitative statements specified to ensure that data of known and appropriate quality are obtained. The DQO process is a series of planning steps, typically conducted during site assessment and investigation, that is designed to ensure that the type, quantity, and quality of environmental data used in decision making are appropriate. The DQO process involves a logical, step-by-step procedure for determining which of the complex issues affecting a site are the most relevant to planning a site investigation before any data are collected.

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Dense Nonaqueous Phase Liquid (DNAPL)
A DNAPL is one of a group of organic substances that are relatively insoluble in water and more dense than water. DNAPLs tend to sink vertically through sand and gravel aquifers to the underlying layer.

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Detection Limit
The lowest concentration of a chemical that can be distinguished reliably from a zero concentration.

A dioxin is any of a family of compounds known chemically as dibenzo-p-dioxins. They are chemicals released during combustion. Concern about them arises from their potential toxicity and the risk posed by contamination in commercial products. Boilers and industrial furnaces are among the sources of dioxins.

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Disposal is the final placement or destruction of toxic, radioactive or other wastes; surplus or banned pesticides or other chemicals; polluted soils; and drums containing hazardous materials from removal actions or accidental release. Disposal may be accomplished through the use of approved secure landfills, surface impoundments, land farming, deep well injection, or ocean dumping.

Dual-Phase Extraction
Dual-phase extraction, also known as multi-phase extraction, is a technology that uses a vacuum system to remove various combinations of contaminated groundwater, separate-phase petroleum product, and vapors from the subsurface. The system lowers the water table around a well, exposing more of the formation. Contaminants in the newly exposed vadose zone then are accessible to soil vapor extraction. Once above ground, the extracted vapors or liquid-phase organics and groundwater are separated and treated.

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Dynamic Underground Stripping
Dynamic underground stripping is a process that employs vapor extraction during underground steaming and electrical heating. The heat, supplied by steam and electricity, vaporizes contaminants trapped in the soil. Once vaporized, the contaminants are removed by vacuum extraction. The process is monitored and guided by underground imaging.

Dynamic Work Plan
A dynamic work plan is a work plan that allows project teams to make decisions in the field about how site activities will progress. Dynamic work plans provide the strategy for the way in which dynamic field activities will take place. As such, they document a flexible, adaptive sampling and analytical strategy. Dynamic work plans are supported by the rapid turnaround of data collected, analyzed, and interpreted in the field.

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