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Contaminated and Hazardous Waste Site Management

Glossary R

Radar: A system whereby short electromagnetic waves are transmitted and any energy which is scattered back by reflecting objects is detected. Acronym for "radio detection and ranging".

Radius of Influence: The radial distance from the center of a wellbore to the point where there is no lowering of the water table or potentiometric surface (the edge of its cone of depression). The radial distance from an extraction well that has adequate air flow for effective removal of contaminants when a vacuum is applied to the extraction well.

Reagent: A substance or solution used in a chemical reaction, especially those used in laboratory work to detect, measure, or produce other substances.

Reagent Blank: A volume of deionized/distilled water containing the same acid matrix as the calibration standards carried through the entire analytical scheme.

Reagent Water: Water in which an interferant is not observed at or above the minimum quantitation limit of the parameters of interest.

Realization: One simulation of a hydrogeological problem using one set of input parameters. Normally, many realizations are produced and the statistical distribution of results examined.

Recalcitrant: Unreactive, nondegradable; refractory.

Receiver: The part of an acquisition system which senses the information signal.

Recharge: Addition of water to the groundwater system by natural or artificial processes.

Recharge Area/Zone: Area in the aquifer where there are downward components of hydraulic head. In this area, infiltration travels downward into the deeper sections of the aquifer.

Reclaimed Surface: The shallow surface zone which was contaminated, but has been cleaned up.

Reconnaissance Sampling: A non-systematic sampling, in which sampling locations are based, in large part, on knowledge about the site. For example, former lagoon sites could be selected for sampling, while unused areas of the site are not sampled.

Record of Communication: A register of all verbal communications between the EPA and citizens regarding site concerns.

Reconstructed Ion Chromatogram (RIC): A mass spectral graphical representation of the separation achieved by a gas chromatograph; a plot of total ion current versus retention time

Recovery: The rise in static water level in a well, after discharge from that well or a nearby well has ended. Redox: short for oxidation-reduction.

Redox Level: The level of oxidation in a redox system which is a chemical system in which reduction and oxidation reactions occur.

Reducing Conditions: Geochemical conditions favouring reduction reactions (e.g., SO4- conversion to H2S). Indicated by the occurrence of reduced forms of iron (Fe2+) and other species.

Reflection Coefficient: A term used in seismic reflection and GPR to describe the ratio of the reflected to incident amplitudes of a pulse reflected from an interface.

Refractory Index: A measure of the ability of a substance to be biodegraded by bacterial activity. The lower the refractory index, the greater the biodegradability.

Relative Percent Difference (RPD): As used in the SOW and elsewhere to compare two values, the relative percent difference is based on the mean of the two values, and is reported as an absolute value (i.e., always expressed as a positive number or zero). In contrast, see Percent Difference above.

Relative Permeability: The permeability of the rock to gas, NAPL, or water, when any two or more are present, expressed as a fraction of the single phase permeability of the rock.

Relative Response Factor (RRF): A measure of the relative mass spectral response of an analyte compared to its internal standard. Relative Response Factors are determined by analysis of standards and are used in the calculation of concentrations of analytes in samples. RRF is determined by the following equation:
A = area of the characteristic ion measured
c = concentration
is = internal standard
x = analyte of interest

Remanent Magnetization (Remanence): Magnetization remaining after the application of magnetic field has ceased.

Remedial Action (RA): The actual construction or implementation phase of a Superfund site cleanup following the RD.

Remedial Design (RD): A phase of site cleanup where engineers design the technical specifications for cleanup remedies and technologies.

Remedial Investigation (RI): An in-depth study designed to gather the data necessary to determine the nature and extent of contamination at a Superfund site, establish the criteria for cleaning up the site, identify the preliminary alternatives for cleanup actions and support the technical and cost analyses of the alternatives. The RI is usually done with the FS. Together they are customarily referred to as the RI/FS.

Remediation: The clean up of contaminated soil or groundwater.

Removal Action: Short-term, immediate actions taken to address releases of hazardous


Residual: The amount of a pollutant remaining in the environment after a natural or technological process has taken place, e.g., the sludge remaining after initial wastewater treatment, or particulates remaining in the air after the air passes through a scrubbing or other process.

Residual Saturation: Saturation below which fluid drainage will not occur.

Resistivity (electrical): Electrical resistance to the passage of a current, expressed in ohm-meters; the reciprocal of conductivity.

Resolution: Also termed separation or percent resolution, the separation between peaks on a chromatogram, calculated by dividing the depth of the valley between the peaks by the peak height of the smaller peak being resolved, multiplied by 100.

Retardation, Retard: Retention of certain contaminants in the subsurface due to one or more physical, chemical, or biological factors. Also known as attenuation.

Rotary Drilling: A hydraulic drilling process which uses a hard-toothed bit attached to a rotating drill pipe. Cuttings are carried up by circulating a drilling fluid.

Roughness: A parameter describing a surface characteristic of a fracture plane. Roughness is important in determining resistance to flow.

Rounding Rules: If the figure following those to be retained is less than 5, the figure is dropped and the retained figures are kept unchanged. As an example, 11.443 is rounded off to 11.44. If the figure following those to be retained is greater than 5, the figure is dropped and the last retained figure is raised by 1. As an example, 11.446 is rounded off to 11.45. If the figure following those to be retained is 5, and if there are no figures other than zeros beyond the 5, the figure 5 is dropped and the last-place figure retained is raised by 1 if it is an odd number or it is kept unchanged if it is an even number. As an example, 11.435 is rounded off to 11.44, while 11.425 is rounded off to 11.42. If a series of multiple operations is to be performed (add, subtract, multiply, divide), all figures are carried through the calculations. Then the final answer is rounded to the proper number of significant figures.

Run: A continuous analytical sequence consisting of prepared samples and all associated quality assurance measurements as required by the Contract Statement of Work.

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