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Contaminated and Hazardous Waste Site Management

Glossary S

S-Wave: A body wave in which particles move perpendicular to the direction of propagation. Also known as secondary or shear wave.

Saline Ground Water: Groundwater consisting of or containing salt.

Salt Water Intrusion: Movement of salty or brackish groundwater into wells and into aquifers previously occupied by fresh or less mineralized groundwater either through upconing or sea water encroachment.

Sample: A portion of material to be analyzed that is contained in single or multiple containers and identified by a unique sample number.

Sample Delivery Group (SDG): A unit within a sample Case that is used to identify a group of samples for delivery. An SDG is a group of 20 or fewer field samples within a Case, received over a period of up to 14 calendar days (7 calendar days for 14-day turnaround contracts). Data from all samples in an SDG are due concurrently. A Sample Delivery Group is defined by one of the following, whichever occurs first:
- Case; or
- each 20 field samples within a Case, or
- each 14-day calendar period (7-day calendar period for 14-day data turnaround contracts) during which field samples in a Case are received, beginning with receipt of the first sample in the Case or SDG. Samples may be assigned to Sample Delivery Groups by matrix (i.e., all soils in one SDG,
all waters in another) at the discretion of the laboratory.

Sample Number: A unique identification number designated by EPA for each sample. The sample number appears on the sample chain of custody report which documents information on that sample.

Sandpoint: A well pipe with a screen, equipped with a hardened, conical point at the bottom, that is driven into the ground to tap shallow groundwater.

Sanitary Surface Seals: A grouted anular space around the well casing which usually extends from the land surface to several metres deep. The sanitary well seal funtions to prevent any contaminated surface and near surface water from seeping down the side of the well to the aquifer.

Saturated Zone: Portion of the subsurface environment in which all voids are ideally filled with water under pressure greater than atmospheric. The zone in which the voids in the rock or soil are filled with water at a pressure greater than atmospheric. The water table is the top of the saturated zone in an unconfined aquifer.

Saturation: The ratio of the volume of a single fluid in the pores to pore volume expressed as a percentage or a fraction.

Scan: A qualitative analysis, usually conducted for trace organics by gas chromatography/mass spectroscopy, to identify, not accurately determine the concentration of, chemicals present in the sample.

Screening: A rapid analysis to determine if further action (detailed analysis, clean-up, etc.) is warranted.

Scrubber: An air pollution device that uses a spray of water or reactant or a dry process to trap pollutants in emissions.

Seal: A low hydraulic conductivity material (e.g. cement grout, bentonite) placed in the space between permanent well casing and the borehole wall, in order to prevent downhole movement of surface water and/or vertical mixing of water from various water-bearing areas.

Search Sampling: See Reconnaissance Sampling.

Sea Water Encroachment: The lateral landward movement of sea water into wells and freshwater aquifers.

Secondary (magnetic field): The magnetic field that is generated by currents that are induced to flow in the ground by time variations in the primary magnetic field of the transmitter.

Secondary Porosity: See Porosity, Secondary.

Sediment: The layer of soil, sand and minerals at the bottom of surface waters, such as streams, lakes and rivers that absorbs contaminants.

Seepage Pits: A hole, shaft or cavity in the ground used for storage of liquids, usually in the form of leachate, from waste disposal areas. The liquid gradually leaves the pit by moving through the surrounding soil.

Seeps: Specific points where releases of liquid (usually leachate) from waste disposal areas, particularly along the lower edges of landfills.

Seismic Reflection: A surface geophysical method recording seismic waves reflected from geologic strata, giving an estimate of their depth and thickness.

Seismic Refraction: A surface geophysical method recording seismic waves refracted by geological strata.

Self Potential (SP): A geophysical method measuring the natural, static voltage existing between sets of points on the ground surface.

Semivolatile Compounds: Compounds amenable to analysis by extraction of the sample with an organic solvent. Used synonymously with Base/Neutral/Acid (BNA) compounds.

Sensitivity: The slope of the analytical curve (i.e., functional relationship between emission intensity and concentration).

Sensitivity Analysis: After a model is calibrated, a sensitivity analysis is often completed to address the sensitivity of the simulation result to specific input parameters. A sensitivity analysis is useful in determining additional field data requirements and for identifying non-uniqueness.

Septa Fitting: A special fitting used to seal vials (a liner for a threaded cap) or gas chromatographs (GCs) to provide closure. Septas can be manufactured in single, double, or triple layers of silicone rubber, Teflon, or other materials. A syringe is typically inserted through the septa of the sample vial in order to withdraw a measured quantity of sample. The same syringe is then used to inject the sample through the septa on the GC for chromatographic analysis.

Septage: Residue remaining in a septic tank after the treatment process.

Sentinel Well: A groundwater monitoring well situated between a sensitive receptor downgradient and the source of a contaminant plume upgradient. Contamination should be first detected in the sentinel well which serves as a warning that contamination may be moving closer to the receptor. The sentinel well should be located far enough upgradient of the receptor to allow enough time before the contamination arrives at the receptor to initiate other measures to prevent contamination from reaching the receptor, or in the case of a supply well, provide for an alternative water source.

Sequester: To undergo sequestration.

Sequestration: The inhibition or stoppage of normal ion behavior by combination with added materials, especially the prevention of metallic ion precipitation from solution by formation of a coordination complex with a phosphate. May reflect the influence of interferents.

Serial Dilution: The dilution of a sample by a factor of five. When corrected by the dilution factor, the diluted sample must agree with the original undiluted sample within specified limits. Serial dilution may reflect the influence of interferents.

SESOIL: A one-dimensional model for estimating pollutant distribution in an unsaturated soil column. SESOIL results are commonly used to estimate the source term for groundwater transport modeling of the saturated zone.

Shale: A fine-grained sedimentary rock, formed by the consolidation of clay, silt, or mud. It is characterized by finely laminated structure and is sufficiently indurated so that it will not fall apart on wetting.

Shear Modulus: The stress-strain ratio for simple shear in isotropic materials which obey Hooke's law.

Shear Strength: The maximum resistance of a soil or rock to shearing stresses. It can also refer to the measure of shear or gel properties of a drilling fluid or grout.

Short Circuiting: The entry of ambient air into an extraction well without first passing through the contaminated zone. Short circuiting may occur through utility trenches, incoherent well or surface seals, or layers of high permeability geologic materials.

Sink: A process or mechanism by which water or chemicals are removed from the subsurface system. A Karst Channel is sometimes a sink for groundwater flow. Biodegradation is a sink for a biodegradable chemical.

Site Characterization: The technical process used to evaluate the nature and extent of environmental contamination, which is necessary for choosing and designing cleanup measures and monitoring their effectiveness.

Site Inspection (SI): The technical process used to evaluate the nature and extent of environmental contamination, which is necessary for choosing and designing cleanup measures and monitoring their effectiveness.

Skin Depth: The effective depth of penetration in a conducting medium of electromagnetic energy (when displacement currents can be ignored); the depth at which the amplitude of a plane wave has been attenuated to 1/e or 0.37.

Slag: The fused refuse or dross separated from a metal in the process of smelting.

Slingram: A popular configuration of transmitter and receiver for HLEM profiling whereby the two coils are coplanor (usually with axes vertical) and a fixed distance apart.

Sludge: Semi-solid residues from industrial or water treatment processes that may be contaminated with hazardous materials.

Slug Test: A test carried out to determine in situ hydraulic conductivity by instantaneously adding a known water quantity (or solid cylindrical object of known displacement) to a well, and measuring the resulting well recovery. Used for single wells in low to moderate hydraulic conductivity formations. Also called falling head test.

Slurry Wall: Barriers used to contain the flow of contaminated groundwater or subsurface liquids. Slurry walls are constructed by digging a trench around a contaminated area and filling the trench with an impermeable material that prevents water from passing through it. The groundwater or contaminated liquids trapped within the area surrounded by the slurry wall can be extracted and treated.

Soil Gas: Gaseous elements and compounds that occur in the small spaces between particles of soil. Such gases can move through or leave the soil or rock, depending upon the changes in pressure.

Soil Moisture: The water contained in the pore spaces in the unsaturated zone.

Soil Vapor Extraction (SVE): A treatment process that uses vacuum wells to remove hazardous gases from soil.

Soil Washing: A water-based process for mechanically scrubbing soils in-place to remove undesirable materials. There are two approaches; dissolving or suspending them in the wash solution for later treatment by conventional methods; and concentrating them into a smaller volume of soil through simple particle size separation techniques.

Solidification/Stabilization: A chemical or physical reduction of the mobility of hazardous constituents. Mobility is reduced through the binding of hazardous constituents into a solid mass with low permeability and resistance to leaching.

Solubility: The total quantity of chemical that will remain in a solution in contact with the solid or NAPL from which the chemical is derived.

Solute: A substance dissolved in a solution.

Solution Channel: An open cavity created when rock is dissolved by groundwaters moving along a narrow path, such as a fracture.

Solvent: Any substance that can dissolve another substance (e.g. petroleum hydrocarbons). Although water is a solvent, the term is often reserved for organic liquids.

Solvent Extraction: A means of separating hazardous contaminants from soils, sludges and sediment, thereby reducing the volume of the hazardous waste that must be treated. It generally is used as one in a series of unit operations. An organic chemical is used to dissolve contaminants as opposed to water-based compounds, which usually are used in soil washing.

Sorbent Canisters: Gas-tight canisters typically filled with activated carbon (charcoal) for collection and transport of vapor samples. In the laboratory the vapors are desorbed and analyzed to identify the organic compounds and quantify their concentration.

Sorbent Tubes: Glass tubes filled with an sorbent material that reacts chemically with specific organic compounds. Based on the nature of the sorbent and the extent of the chemical reaction, organic compounds can be identified and the concentration quantified.

Sparge or Sparging: Injection of air below the water table to strip dissolved volatile organic compounds and/or oxygenate the groundwater to facilitate aerobic biodegradation of organic compounds.

Sorption: Process by which some material leaves the fluid phase and associates with the solid phase. The chemicals associated with the solid phase are sorbed.

Sorption Coefficient: A parameter that represents the tendency of a solute to sorb onto solids. Usually expressed as Kd in units of ml/mg.

Sorptive Retardation: The slowing of a chemical's migration in groundwater or soil vapour due to interaction (sorption/desorption) with the subsurface solids.

Sounding: In geophysics, a survey method whereby the geometry and/or frequency of an array of sensors is varied so as to measure the physical properties of the earth as a function of depth beneath the configuration. The alternative is usually profiling.

Source: This is a term meaning different things to different people. To some lawyers and administrators, source refers to surface or very near surface causes or potential causes of groundwater contamination, such as drums, sludge or contaminated surface soil. To scientists and engineers operating in the context of conceptual models contamination in the subsurface, a source of most significance is generally a mass of immiscible-phase liquid (residual, lens or pool) located below ground surface, often below the water table.

Specific Conductance: The ability of a cubic centimeter of water to conduct electricity; depends on the quantity of ionized minerals in it. Measured in microohms per centimeter.

Specific Capacity: The rate of discharge of a water well per unit of drawdown. Specific capacity can be expressed as L/s/m of drawdown.

Specific Gravity: The dimensionless ratio of the density of a substance with respect to the density of water. The specific gravity of water is equal to 1.0 by definition. Most petroleum products have a specific gravity less than 1.0, generally between 0.6 and 0.9. As such, they will float on water--these are also referred to as LNAPLs, or light non-aqueous phase liquids. Substances with a specific gravity greater than 1.0 will sink through water--these are referred to as DNAPLs, or dense non-aqueous phase liquids.

Specific Storage: The quantity of water released from or taken into storage per unit volume of a porous medium, per unit change in head.

Specific Yield: The ratio of the volume of yield of water by gravity drainage from a rock or soil (after being saturated), to the volume of the rock or soil.

Spectral Induced Polarization (IP): See Complex Resistivity.

Spring: A discrete place where groundwater flows onto the land surface or into a body of water.

Stabilization: The process of changing an active substance into inert, harmless material or physical activities at a site that acts to limit the further spread of contamination without actual reduction of toxicity.

Standard Analysis: An analytical determination made with known quantities of target compounds; used to determine response factors.

Static Water Level: The level of water in a well that is not being influenced by groundwater withdrawals. The distance to water in a well is measured with respect to some datum, usually the top of the well casing or ground level.

Steady State: The state of a system whereby conditions at each point do not change with time.

Stillbottom: Residues left over from the process of recovering spent solvents.

Storage Coefficient: The water volume released from storage per unit surface area of aquifer per unit decline of the water table or other piezometric surface.

Storativity: The volume of water released from or taken into storage per unit surface area of aquifer, per unit change in head. Also known as storage coefficient.

Stratigraphy: The study of original succession (stratigraphic sequence) and age of unconsolidated materials and rock strata, dealing with their form, distribution, lithologic composition, fossil content, as well as geophysical and geochemical properties.

Stratification: Layering or bedding of geologic materials (e.g., rock or sediments).

Stratum: A horizontal layer of geologic material of similar composition, especially one of several parallel layers arranged one on top of another.

Stream Function: Stream functions are mathematical entities which define the steady state groundwater flow paths within a groundwater flow system. In combination with hydraulic potentials, stream functions are used to simulate groundwater flownets.

Streaming Potential: A voltage resulting from flow of an ionic fluid.

Stripping: A process used to remove volatile contaminants from a substance.

Sump: A pit or depression where liquids drain, collect, or are stored.

Surface Water: The portion of water which appears on the land surface; oceans, lakes, rivers, etc.

Surface Wave: A wave which travels along, or near to, the surface; its motion dropping off rapidly with distance from it. A distinct seismic mode from the body waves, P- and S.

Surfactants: Chemicals that are used to reduce the resistance to flow of certain fluids.

Surficial Deposits: -Deposits overlying bedrock and consisting of soil, silt, sand, gravel and other unconsolidated materials.

Surrogates (surrogate standard): For semivolatiles and pesticides/Arochlors, compounds added to every blank, sample, matrix spike, matrix spike duplicate, and standard; used to evaluate analytical efficiency by measuring recovery. Surrogates are brominated, fluorinated, or isotopically labelled compounds not expected to be detected in environmental media.

Suspended: Those elements which are retained by a 0.45 micron membrane filter.

Sustained Yield: Rate at which groundwater can be withdrawn from an aquifer without long term depletion of the supply.

System Monitoring Compounds: compounds added to every blank, sample, matrix spike, matrix spike duplicate, and standard for volatile analysis, and used to evaluate the performance of the entire purge and trap-gas chromatograph/mass spectrometer system. These compounds are brominated or deuterated compounds not expected to be detected in environmental media.

Systematic Sampling: Sampling that follows a pre-set, regular pattern. For example, sampling at a fixed depth at the nodes of a rectangular grid laid over a site.

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