Interpretive Glossary of Water-related Terms and Expressions - S

Safe Drinking Water Act: SDWA. Federal legislation that regulates the treatment of water for human consumption. Requires testing for and elimination of contaminants for the protection of human health. CSU.

safe yield: (1) Rate of surface-water diversion or groundwater extraction from a basin for consumptive use over an indefinite period of time that can be maintained without producing negative effects; (2) The annual extraction from a groundwater unit which will not, or does not, produce a negative effect, (3) the attainment and maintenance of a long-term balance between the amount of ground water withdrawn annually and the annual amount of recharge; (4) the maximum quantity of water that can be guaranteed from a reservoir during a critical dry period. GWAC.

saline water: Usually considered to contain more than 10,000 ppm of total dissolved solids. See total dissolved solids.

salinity: Pertains to the concentration of ions in a solution containing dissolved salts.

sand: A sedimentary rock, of igneous origin, unconsolidated or consolidated, composed of individual grains of silicon dioxide. See quartz and rock (1).

sand control: Any means to prevent sand from entering the casing and tubing. See gravel pack and sand production.

sand count: The net footage of sand strata of specific quality within a formation.

sand production: Production of water from unconsolidated aquifer sands sometimes causes sand to flow into the casing, filling up the casing to the perforations and getting into the downhole equipment, causing obstruction and rapid wear.

sandstone: A sand that has been consolidated to some degree by minerals, that cement the grains together, precipitated from formation water.

sanitary well seal: At the wellhead, the cap at the top of the protective casing to prevent contamination of the well.

saturated, saturation: Generic. (1) Usually thought of as the portion of a rock body that is filled with water. The saturated zone or thickness.

(2) Specific. The degree that a specific geofluid occupies the pore volume of a rock. Expressed as a fraction or percent of the available pore space.

saturated thickness: Generic. The thickness of the zone considered to be completely saturated with water. The thickness containing 100 percent water.

scale: Chemical scale. The undesirable mineral deposited, usually from hard water, on or in water handling equipment. Can be found downhole on solid surfaces inside tubing, pipes, slots and perforations, and pump apertures. And, can be found above the ground in or on any equipment used for the purpose of carrying or discharging water. Usually a carbonate of calcium.

sealed reservoir: A natural reservoir containing water or other geofluid, that has finite natural boundaries by being confined within permeability barriers. The barriers can be impermeable rock of the same nature as the reservoir rock, or they can be impervious shale, carbonate beds, or salt that abuts or surrounds the reservoir. See aquifer (3) and lens.

sea water: Water from the oceans. Sea water contains many different dissolved salts. The equivalent concentration of sea water is 35,000 ppm, and has a specific gravity of about 1.025 g/cm3.

secondary recovery: See under recovery.

sediment: Solid matter, mineral and/or organic, that has been transported from its location of origin by one or more of the depositional environments. Solid matter also might be the skeletal remains and secretions of organisms that have formed in or precipitated from solutions or sea waters. See depositional environment and rock.

sedimentary: Refers to sediment deposited in any one of the depositional environments: wind, seas, and rivers. Refers to rock types such as sand, shale, limestone, conglomerates, or reworked mineral material. See depositional environment.

sedimentary basin: A basin-like geological environment suitable for the deposition of sediments. Sediments are thicker toward the center and thinning toward the perimeter.

secondary porosity: Post depositional void space in rock. Porosity created in the form of, or by, fractures, dissolution of solid materials in sediment, vugs, diagenesis, or shrinkage. Expressed as a fraction or percent of total volume.

Senate Bill 5: SB5. A 1985 Colorado legislative enactment chiefly providing for allocation of non-tributary ground water on the basis of ownership of the overlying land. The SB5 computer program has been used as the uniform standard as the most consistent criteria to quantify water under a property. For each aquifer:

(Volume of Available Water) = (Area (acres) ) × ( Thickness (ft) ) × ( Specific Yield (fraction) ) .

This equation is based on the reservoir and recovery-factor concept, and on the science in the State of Colorado, as it was known in 1985. Presently Senate Bill 5 is law and is regulatory until determined otherwise.

Technically, Senate Bill 5 applies only to reservoirs which have finite bounds. However, SB5 appears to be based on the premise that conversion of confined aquifers to unconfined aquifers will take place and thus will unlock residual water in the confined aquifer by gravity drainage. See conversion of confined aquifers to unconfined aquifers and coning (3) and (4). Also see aquifer, recovery factor, depleted, drive mechanism, pressure gradient, movable water, irreducible water, reservoir, capillarity, buoyancy, and yield. See also equity and equity determination.

senior right: A water right that has been established earlier and, therefore, is superior to any subsequent right.

shale, shaly: A descriptive property, not a mineral. A fine grained, thinly laminated or fissile rock formed by the compaction and consolidation of sediment under the weight of the overburden. The sediment consists of appreciable quantities of clay, silt, and mud. A clay shale is a shale wherein the major mineral constituent is clay.

shaped charge: Used in gun perforating operations. A high explosive with a designed, lined cavity to shape the jet used in perforating a casing. The cavity is lined and designed with a material and shape to create proper sized holes and penetrate the formation with the most efficient cavity for the production or injection of fluid.

shut in: The condition or act of shutting down all valves and pumps in a producing water well or injection well. The conditions in the well bore will be static.

shut-in pressure: Must be specific. Pressure at the wellhead, or pressure opposite the producing formation at the depth of interest, at static conditions.

silica: Silicon dioxide (SiO2). Quartz.

siliceous: Containing abundant silica derivatives or quartz.

silt: Pertains to size. Very small sized grains or particles of quartz and/or clay derivatives.

sink, sinkhole: A depression in the surface of the earth caused by dissolution and/or collapse of rock. A sink is an entry point for water into cave and spring systems. All sinks will carry water into the subsurface. GWAC.

slant hole: A hole intentionally drilled at an angle with respect to the vertical. A directional hole with a designed inclination with respect to vertical.

slots: Slices or slots in the casing placed at pre-selected locations and at specific intervals along the casing before it is run into the borehole and set in place.

soft formation: Unconsolidated or poorly consolidated sedimentary rock.

soil vapor intrusion: An intrusion into the indoor air of buildings by toxic gases that have penetrated foundations. The toxic gases might be from natural sources, manmade activity, or from contamination of the soil by volatile chemicals. Usually the expression is used to refer to intrusion by gases that have been released from toxic chemicals that found their way into the soil by an unnatural event, accident or action. Also see point source pollution.

solution gas: Usually pertains to oil and gas production. In water production, it is the gas that has been dissolved in the formation water that is released as water pressure is decreased by water production.

source: (1) Of water in an aquifer. The location or origin where natural charging or beginning takes place.

(2) Relative to crossflow, it is the place on the face of an aquifer where water emerges.

special district: A quasi-municipal corporation of the State of Colorado empowered to perform and deliver services to the owners of property located within a legally described boundary. Douglas Co.

specific conductance: A measure of the ability of water to conduct an electrical current. The inverse of electrical resistivity. Specific conductance is related to the type and concentration of ions in solution and can be used for approximating the dissolved-solids content of the water. See total dissolved solids.

specific gravity: Sometimes mistakenly referred to as density. Density is mass per unit volume (mg/liter or g/cm3). Specific gravity is a ratio of densities and, therefore, has no units.

(1) Of liquids and solids. The ratio of the density of the selected substance at standard conditions of temperature and pressure to the density of pure water at standard conditions of temperature and pressure.

(2) Of gases. The ratio of the density of the selected gas at standard conditions of temperature and pressure to the density of dry air at standard conditions of temperature and pressure.

specific retention: (1) This is the ratio of the volume of water that a given body of rock or soil will hold against the pull of gravity to the volume of the body itself. It is usually expressed as a percentage. Compare with field capacity. GWAC. Specific retention is a fraction of total volume without regard to the porosity of the aquifer. Compare with irreducible water. Also see drainage.

(2) Water adhering to the surfaces of all water-wet soils and grains. Compare in place, irreducible water, and capillarity.

specific storage: Volume of water released from or taken into storage per unit volume of the porous medium per unit change in head. It is the three-dimensional equivalent of storage coefficient or storativity, and is equal to storativity divided by aquifer saturated thickness. GWAC. See discussions under storativity.

specific yield: Of aquifers, see yield (1).

spring: A location where ground water has communication with the atmosphere and sufficient hydraulic pressure to force the water to the surface of the ground. See also artesian water.

spurt loss: Pertains to the mud filtrate loss by invasion of mud filtrate into the formation as the bit passes through the formation. This quantity of the filtrate loss is controlled by the permeability of the formation until the permeability of the mud filter cake decreases to the extent that it becomes the controlling permeable medium for all further filtrate loss.

SPWLA: Society of Petrophysicists and Well Log Analysts; 1984 Glossary, second edition, compiled and edited by Robert C. Ransom.

squeeze cementing: During or after the well completion operation, when it has been discovered that, by faulty completion practice, the annular space between the casing and the formation has not been completely filled with cement and, therefore, aquifers have not been effectively isolated, squeeze cementing sometimes is an appropriate remedial action to take. By perforating the casing at the location where a cement void or channel occurs and using appropriate plugs, squeeze cementing of the annular space to create a barrier in the annular space is performed by forcing a cement slurry under pressure to specific locations behind the casing in a well bore. The purpose is to prevent crossflow, or out-of- zone communication, and prevent contamination between aquifers, or between aquifers and the well bore.

standard conditions: STP. Standard conditions of temperature and pressure of 60o Fahrenheit and 1 atmosphere pressure of 14.7 psi.

state engineer: The state engineer is charged with the administration of the waters of the State of Colorado. In times of water shortages, the state engineer or his representative determines what water rights may divert water and in what amount. Douglas Co.

static: At rest. Immobile.

static fluid level: A misnomer. It refers to the level that liquid (water in the case of aquifers) rises in a well bore when production has been stopped or the well has been shut in.

static mud column pressure: The hydrostatic pressure of the drilling mud against the formation at the depth of interest when drilling has been stopped.

static water level: See water level (1).

stiff diagram: A rose type or polygonal diagram designed to represent specific and significant ion concentrations derived from a water analysis. The length of the radii or ribs from a central spine are scaled in the units for the concentration of each specific ion. The shape of the polygon facilitates easy recognition of the ionic profile for each water of interest. The polygonal profiles of waters provide instant recognition of changes in and comparisons of different waters at any time, time interval, and against the EPA recommended limits. See water analysis.

stimulation: Any means that will increase permeability and, thus, production or injection rate. See acid treatment and hydraulic fracturing. Also see formation damage.

storage: A finite volume with the capability to be intentionally filled and intentionally emptied. A finite volume without relief, that will maintain its pressure over time. See injection of potable water for storage purposes.

Storage coefficient: See storativity.

storage right: A right defined in terms of the volume of the water which may be diverted from the flow of the stream and stored in a reservoir or lake to be released and used at a later time either within the same year or a subsequent year. Storage water applications are submitted to the water court for adjudication and decree the same as other water rights. Douglas Co.

storativity: Coefficient of storage. Volume of water released per unit area of aquifer and per unit drop in head. Storage coefficient is a function of the compressive qualities of water and matrix structures of the porous material. A confined aquifer’s ability to store water is measured by its storage coefficient. Storativity is a more general term encompassing both or either storage coefficient and/or specific yield. GWAC.

Storativity of a confined aquifer generally is considered to be of importance when pressure is declining. As water production continues, water pressure declines. Along with this pressure decline two things can happen. Water will expand and compaction of the aquifer framework can occur resulting in the expulsion of water from the aquifer. These are not related events, but both result from a decline in water pressure. Each is an independent event, but both occur simultaneously.

For the storativity calculation, the source of the water released by either or both of these two events is the water in the aquifer itself. Storativity is the amount of change in the volume of ground water related to the surface area of the aquifer for each unit change in pressure. This is not a completely reversible process. The aquifer is not likely to rebound due to the permanency of the compaction process.

As the pressure in the aquifer reduces, so does the pressure in the surrounding clay shales. Storativity does not account for the water that is expelled from clay shales during the compaction process. This water seeks relief in porous and permeable aquifers as water production continues. See discussions in compaction (2), rebound, bulk modulus, and subsidence.

strata, stratum: A bed(s) or subdivision of the same material within a lithographic sequence or formation.

stratified: Formed, arranged, or laid down in layers. The term refers to geologic deposits. Layers in soils that result from the processes of soil formation are called horizons; those inherited from the parent material are called strata. NSSH. See strata.

stratigraphy: The branch of geology that deals with the definition and interpretation of layered earth materials, the conditions of their formation, their character, arrangement, sequence, age, and distribution; and especially their correlation by the use of fossils and other means. NSSH.

stream, streamflow: (1) In aquifers. A natural migratory stream within an aquifer. Both terms refer to the movement or migration of ground water in the permeable pathway from the geographical location of its source or natural recharge area to the geographical location of its withdrawal, production, or other form of relief. Also see pass-through aquifer.

(2) On ground surface. Refers to the commonly known tributary stream, creek, or small river.

(3) In physics. Streamflow is streamline flow or laminar flow of fluids, as opposed to turbulent flow.

(4) Discharge that occurs in a natural channel. A more general term than runoff, stramflow may be applied to discharge whether or not it is affected by diversion or regulation. GWAC.

stream depletion: In water wells. The depletion of streamflow caused by the operation of producing wells completed in the same aquifer.

stuck pipe: Drill pipe, drill collars, casing, or tubing that has inadvertently become lodged immovably in the borehole. It may occur when drilling is in progress, when casing is being run in the hole, or when the drill pipe is being hoisted. SPWLA. The problem usually occurs where the pressure in the formation is greater than the pressure in the borehole.

sublimation: The physical process by which a solid changes to a gaseous state without passing through the liquid state. See also evaporation.

subsidence: (1)  Is the sinking of the ground surface, overlying permeable strata, that results from the gradual dewatering and compaction of clay shales and other sediments overlying the strata. Depletion of water pressure in an aquifer as a consequence of excessive water production is a leading cause of subsidence. There are many examples of subsidence resulting from groundwater production due to agricultural or municipal withdrawals. Other examples where significant subsidence has taken place are: Long Beach, California resulting from oil production; and Venice, Italy resulting from industrial water production. See compaction (2) for explanation of the subsidence process. Also see rebound.

There are a number of ways to measure subsidence. Most involve methods where measurements are made at the ground surface. However, probably the best, and the method that will produce the most accurate and detailed measurements, is by the satellite method known as Interferometric Synthetic Aperture Radar, InSAR. What is InSAR? Click on the following link to go to explanations:   


(2) Sinking of the ground surface resulting from underground displacement caused by a fault, or caused by the collapse of caverns or karsts created by the dissolution of sedimentary minerals.

(3) Sinking of the ground surface resulting from surface disturbance.

suction: A generic term. Suction refers to a condition, function, or location, such as suction pump, suction line, suction cup, suction process. Suction is the artificial reduction of pressure in one of two contacting mediums, so that the higher pressure of the other medium can provide force to perform a function. That is, in a system where two communicating, but separate, pressures are balanced, suction unbalances the pressures so that the higher of the two pressures provides the force to control the function, whether it be drawing on a straw in a soda can or pumping to empty a septic tank. Suction can create neither energy nor force, and can perform no work. A vacuum is a condition resulting from perfect suction. A vacuum is the absence of matter, energy, and force; and, therefore, can perform no work. Suction creates a condition where a pressure differential provides the energy and the force to do work. The pressure differential is similar to a steep pressure gradient. See pressure gradient.

The maximum height in feet that water can be lifted by a suction-produced pressure gradient is: the quantity (prevailing atmospheric pressure in psi) divided by the quantity (0.433 times the specific gravity of the water being lifted).

supplant: Relative to water supply, to replace or to add reused or reclaimed water to the water supply system. A conservation measure to prevent waste. surface casing: In water wells. Usually a shorter length of casing to protect the hole from collapsing and isolate near surface aquifers, whereas a longer length of casing is used for the ultimate completion of the well. It is steel casing, required in all water wells, that extends at least 19 feet into the ground from the wellhead and ends at least 1 foot above the ground to prevent contaminants from entering the well. See protection casing.

surface casing: In water wells. It is a length of casing long enough to protect the hole from collapsing and to isolate near-surface aquifers. Surface casing in all water wells must extend at least 19 feet into the ground from the wellhead and end at least 1 foot above the ground to prevent contaminants from entering the well. See also protection casing. Where the surface casing in water wells is steel, a longer length of casing made of PVC or steel, run to the bottom of the borehole, often is used for the final completion of the well. Here, the longer length of surface casing also serves as the production casing.

In oil and gas wells, the overall length of the surface casing can be several hundreds of feet or several thousands of feet depending on the total thickness of the aquifers to be drilled and protected. The surface casing must be completed properly in order to isolate the aquifers from each other and protect them from contamination during the drilling process, and keep them free of contaminants throughout the completion and production processes. See completion.

surface pressure: The pressure in the well bore measured at the wellhead.

surface tension: Of liquids. It is the intermolecular cohesive force provided by the attraction of like molecules, most often observed at the surfaces of liquids, or at the interfacial contact between immiscible liquids (emulsions). The intermolecular attraction and cohesive forces act within the body of liquids, and the amount of matter gravitates to its smallest volume, resulting in the smallest surface area that can surround that volume. Examples: A rain drop; or two droplets of water that readily merge to form a single droplet containing the two volumes, but exhibiting a smaller total surface area.

Surface tension is a naturally occurring phenomenon that takes place at the interface or intersurface contact between two immiscible liquids, or a liquid and a gas. The intermolecular attraction is not a variable force dependent on its environment or surroundings, it is a property of the molecule. It is a near constant force that can be redirected by like adjacent molecules somewhat similarly as a magnetic field can be reshaped. The intermolecular attraction within a liquid is directed equally in all directions. The molecular attractions of the surface molecules have been distorted directionally toward side-to-side molecules as well as interior molecules, thus reinforcing and increasing their mutual side-to-side cohesive attractions or tensile properties.

surface water: Water on the earth’s surface, such as rivers, streams, ponds, lakes, oceans, etc.

surge irrigation: A method o irrigation using computerized valves to turn the water supply on and off to move water more uniformly down the field. CSU.


Compiled and Edited by Robert C. Ransom


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