Appendix E - Glossary

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

accuracy – the degree of closeness of measurements of a quantity to its actual (true) value. Together precision and bias determine accuracy.

action level – the generic term applied to any numerical concentration value which will be compared with environmental data to arrive at a decision or determination about a potential contaminant(s) of concern (from survey through remediation) or for a user-defined volume of media using environmental sample data.

arithmetic mean – the sum of x measurements divided by the number of equally weighted measurements.

average – see arithmetic mean.

bias – the tendency for a measurement to consistently over- or underestimate the actual (true) value. Together precision and bias determine accuracy.

colocated sample – a QC check sometimes performed in traditional sampling. In discrete sampling plans they provide valuable information about short-scale spatial heterogeneity and whether it is causing significant sampling error that could lead to decision errors. Because there are usually two samples involved, quantitation of the variation/precision between colocated samples usually uses the relative percent difference (RPD) as the measure.

composite sample – a sample composed of two or more increments, which generally undergoes some preparation procedures designed to reduce the variance in the errors associated obtaining a measurement from the combined sample. An ISM sample is a composite sample whose collection and preparation steps are designed using the general suggestions of Gy’s sampling theory. In general, composite samples in environmental studies do not consist of a large volume and a large number of increments and do not undergo the same preparation and subsampling steps suggested by Gy’s sampling theory.

compositional heterogeneity (CH) – the heterogeneity arising from the composition of each particle within a decision unit.

coverage – for statisticians, the probability that a confidence interval encloses or captures the true population parameter. For example, a calculated 95% UCL is intended to have a 95% chance of being equal to or exceeding the true (population) arithmetic mean. For field investigators, coverage is the extent to which the density of sampling locations represents the sampling unit (i.e., spatial coverage).

data quality objective (DQO) – a qualitative and quantitative statement derived from the DQO process that clarifies study technical and quality objectives, defines the appropriate type of data, and specifies tolerable levels of potential decision errors that will be used as the basis for establishing the quality and quantity of data needed to support decisions.

decision – a determination made about a potential contaminant(s) of concern (from survey through remediation) or a determination for a volume of media using environmental sample data.

decision error – the likelihood of making an incorrect decision based on site-specific information including measurement from samples collected within the DU.

decision mechanism – an algorithm or protocol that results in the decision about a potential contaminant of concern or for a decision for a volume of media.

decision unit (DU) – the smallest volume of soil (or other media) for which a decision will be made based upon ISM sampling. A DU may consist of one or more sampling units (SUs).

disaggregation – the act of breaking the soil clumps into individual small particles but keeping the small pebbles and hard crystalline particles intact.

distributional heterogeneity (DH) – the heterogeneity arising from the way particles are distributed within the decision unit or sample. For example, if heavy particles settling to the bottom of a sample results in less distributional heterogeneity.

Exposure Point Concentration (EPC) – The value, based on either a statistical derivation of measured data or modeled data, that represents an estimate of the chemical or radionuclide concentration available from a particular medium or route of exposure.

energetics – explosives and propellant residues as specified in USEPA SW-846 Method 8330B.

exposure unit (or exposure area) – for purposes of risk assessment, a defined area throughout which a potential receptor may be exposed to a contaminant. The receptor is assumed to move randomly across the area, being exposed equally to all parts of the area. The assumption of equal exposure to any and all parts of the exposure area is a reasonable approach (USEPA 1992) that allows a spatially averaged soil concentration to be used to estimate the true average concentration contacted over time.

field replicate samples – collected following the same the process within the DU but from a different set of locations. The manner in which the replicate is collected is determined during systematic planning. The purpose of the collection of replicates is to provide multiple estimates of the mean.

fundamental error – the error that results from the compositional heterogeneity of the sampling unit and the mass of the sample collected. Fundamental error is always present and can be estimated before sampling.

grand mean –the arithmetic mean of ISM replicates from the same DU.

grinding – a generic term for soil disaggregation or milling. The grinding type or equipment must be specified to select a particular laboratory process.

grouping and segregation error – the error that results from the distributional heterogeneity of the sampling unit.

heterogeneity – the condition of being nonuniform because of dissimilar or diverse constituents. For soils examined at the spatial scale of containerized samples, "heterogeneous" describes soils composed of different materials, such as different minerals or organic carbon. Even if all soil particles are made of the same material, soil may still labeled heterogeneous if the material is present in different forms, such as different particle sizes. These types of heterogeneity are called "compositional heterogeneity." Soils may also be heterogeneous on larger spatial scales. A prime example is differences in contaminant concentrations from one location to another within some area or volume of soil. This condition is called "distributional heterogeneity."

hot spot – generally described as an area of elevated contamination (ITRC 2008). A hot spot is not typically identified visually (i.e., stained soil, free product) but is primarily identified by soil sampling results. The specific area and magnitude of contamination constituting a hot spot should be agreed on during systematic project planning.

increment – a portion of the sampling unit that is collected with a single operation of a sampling device and combined with other increments to form an incremental sample.

increment delimitation error – the error that results from incorrect shape of the volume of material extracted from the sampling unit to form the sample.

increment extraction error – the error that results from incorrectly extracting the increment from the sampling unit.

incremental sample – a collection of increments collected from a single sampling unit, which are combined, processed, and analyzed to estimate the mean concentration in that sampling unit.

laboratory replicate sample – a sample that is split into subsamples at the lab. Each subsample is then analyzed and the results compared. They are used to test the precision of the laboratory procedures.

Long-range heterogeneity fluctuation error (CE2) - the error generated by nonrandom local trends within the population.

Lot – an explicitly defined volume of soil from which incremental samples are collected to estimate the mean concentrations of analytes of interest present. The lot changes during the ISM process: the initial Lot may be immovable, such as the soil of a residential plot, or movable, such as the incremental field sample being processed and sub-sampled in the laboratory.

milling – complete particle size reduction of all soil components including hard crystalline materials to a defined maximum particle size (e.g. <250 µm or <75 µm).

precision – a measure of reproducibility. Together precision and bias determine accuracy.

Periodic heterogeneity fluctuation error (CE3) - the error generated by cyclic nonrandom phenomena.

Preparation Error - the sum of the errors that occur during sample transfer and preparation processes.

relative standard deviation – the arithmetic standard deviation divided by the arithmetic mean. Also called the “coefficient of variation” (CV).

replicate (duplicate) sample – one of the two or more samples or subsamples obtained separately at the same time by the same sampling procedure or subsampling procedure.

representativeness – description of the degree to which an estimate agrees with the true value of the parameter of interest. The most representative estimate is the one that has the least total error (or greatest precision and accuracy).

sample – for statisticians, a set of observations collected from a population (i.e., a set of ISM samples). For field investigators, it is the mass/volume of material obtained from a sampling unit (i.e., consisting of multiple increments). For laboratory technicians, the sample is all the material delivered to the laboratory in a container collected by the field crew.

sample support – the size (mass or volume), shape, and orientation of that portion of the sampling unit that is sampled.

sampling error – anything during sample collection and handling that causes the measured properties of sample to deviate from the targeted properties of the population. The population of interest is defined in accord with the decision to be made from the data.

sampling unit – user-defined volume of soil (or other media) from which increments are collected to determine an estimate of the mean concentration for that volume of soil (or other media).

soil – the fragmented material in the surface of the earth formed as the result of the complex interaction of the rock surface with atmospheric and mechanical factors, consisting of rock and mineral particles mixed with decayed organic matter (humus), excluding only the top few inches with its organic content (known as “topsoil”). Soils can represent the parent rock types that lie below (e.g., residual soils) or can be formed by various erosional processes of water and wind far away from the parent rock materials (e.g., transported soil) or transported in bulk by anthropogenic or artificial mechanisms.

specimen – portion of the sampling unit collected prior to taking into account the suggested sampling, preparation, and subsampling activities of sampling theory intended to produce sufficiently representative estimates in specified volumes of media.

standard deviation – measure of the dispersion of imprecision of a sample or population distribution expressed as the positive square root of the variance and that has the same unit of measurement as the mean.

statistic – function of the sample measurements; for example, the sample mean or standard deviation. A statistic usually but not necessarily serves as an estimate of a population parameter. A summary value calculated from a sample of observations.

subsample – the structured composite of the increments collected from an SU sample.