Chapter 11: Glossary


The process by which substances in gaseous, liquid, or solid form dissolve or mix with other substances.


The attraction and adhesion of ions from an aqueous solution to the surface of solids.

air sparging

The process of injection of air below the water table to strip volatile contaminants from the saturated zone.

air stripping

A remediation process for removing VOCs from groundwater by aeration.


Pertaining to, or composed of, alluvium or deposited by a stream or running water.


A general term for clay, silt, sand and gravel, or similar unconsolidated material deposited by a river as a sorted or semi-sorted sediment in the bed of the river or on its floodplain or delta.

analytical model

A mathematical model that provides an exact or approximate solution of a differential equation (and the associated initial and oundary conditions) for subsurface water movement or transport.


The conditions under which one or more of the hydraulic properties of an aquifer vary with direction. (See also isotropy.)


A geologic formation which may contain water (sometimes in appreciable quantities), but is incapable of transmitting significant quantities under ordinary field conditions.


A geologic formation, group of formations or part of a formation that contains saturated permeable material that yields sufficient, economical quantities of groundwater.

aquifer system

Two or more permeable units separated at least locally by confining units that impede groundwater movement but do not greatly affect the regional hydraulic continuity of the system.

aquifer test (See pumping test.)


An impervious formation which neither contains nor transmits water.


A semi-pervious geologic formation which can store water but transmits water at a very low rate compared to the aquifer.

area of influence

Area surrounding a pumping or recharging well within which the water table or potentiometric surface has been changed due to the well's pumping or recharge. Also called zone of influence.

artesian aquifer

Commonly used expression, generally synonymous with (but less favored term than) confined aquifer. The term "artesian" takes its name from the basin of Artois in France.

artesian well

A well deriving its water from a confined ("artesian") aquifer.

artificial recharge

The process by which water can be injected or added to an aquifer. Dug basins, wells, or the spread of water across the land surface are all means of artificial recharge.


The process of diminishing contaminant concentrations in groundwater, due to filtration, biodegradation, dilution, sorption, volatilization, and other processes.


A tool attached to the end of the drill string and pulled through the bore to enlarge the hole and mix the cuttings with the drilling fluid.


A device used to withdraw a water sample from a small-diameter well or piezometer. It is typically a piece of pipe having a check valve in the bottom.

bail-down test

A type of slug test performed by using a bailer to remove a volume of water from a small diameter well.


That part of a stream discharge not attributable to direct runoff from precipitation or snowmelt, usually sustained by groundwater discharging into the stream.


A general term for the rock formation, usually solid, that underlies soil or other unconsolidated materials.


An absorbent aluminum silicate clay formed from volcanic ash. When thoroughly mixed with water, bentonite breaks down into small particles called platelets. The platelets plaster or shingle off the wall of the hole and form a filter cake that cuts off the flow of water into the surrounding sand or gravel.


Similar to bioremediation, but involving the introduction of organisms to affect cleanup.


A subset of biotransformation, it is the biologically mediated conversion of a compound to more simple products.


A cleanup method involving the stimulation of naturally occurring organic substances in the soil.


A process by which air is injected into the subsurface to stimulate biodegradation by microbes.


1. A hole made in the ground by drilling or pushing.

2. The act of making a hole in the ground by drilling or pushing.


A single-sack boring fluid system, which consists of bentonite, polymer, and soda ash, specially formulated by Baroid Drilling Fluids, Inc., for use in trenchless technology construction applications. Processed from premium grade Wyoming sodium bentonite with an extra high yield, enhanced to provide superior hole stabilizing properties and cuttings support with improved lubrication and torque reduction.


The female thread portion of a drill pipe.

bubbling pressure

The pressure at which air enters saturated zone (or air entry value or threshold pressure).


The potentiometric surface (or the water table) rise in the vicinity of a recharge well. It is the vertical distance between the initial and the new potentiometric surface (or the water table in the case of an unconfined aquifer) at a given point.

bulk density

The mass of a soil per unit bulk volume of soil; the mass is measured after all water has been extracted and the volume includes the volume of the soil itself and the pore volume.

cable sonde

A probe or transmitter that operates with a wire attached to the drill rack for locating purposes.

calibration of models

Refinement of estimates of the input parameters and boundary conditions of a model until model results match the field-observed data. Also known as "history matching."


A geological formation often found in the Southwestern United States that can be as hard as rock but more closely resembles very dry layered clay which becomes sticky when wet.

capillary forces

Interfacial forces between immiscible fluid phases, resulting in pressure differences between the two phases.

capillary fringe

The zone immediately above the water table within which the water is drawn by capillary forces (fluid is under tension). The capillary fringe is saturated, and it is considered to be part of the unsaturated zone.


A sediment formed by the organic or inorganic precipitation from aqueous solution of carbonates of calcium, magnesium, or iron.

carbonate rock

A rock consisting chiefly of carbonate minerals, such as limestone and dolomite.

Chinese Finger

A woven wire device used to pull product back through the bore. It is slipped over the outside diameter of the product and attached to the drill string. The harder it is pulled, the tighter it gets.


Pertaining to a rock or sediment composed principally of broken fragments that are derived from pre-existing rocks or minerals and that have been transported some distance from their places of origin.


The term used to denote sand and gravel. The use of bentonite in the drilling fluid recommended when boring in this type of soil conditions.


A reamer that enlarges the hole by compressing the soil as it is pulled through the bore.

concentration gradient

The change in concentration with distance across a fluid medium.


A clear amber liquid blend of water soluble anionic surfactant manufactured by Baroid Drilling Fluids, Inc. It can be used in conjunction with Quik-Gel~ to aid in reducing the tendency of the hole-boring tools being stuck by adhesive.

cone of depression

A depression in the groundwater table (or potentiometric surface) that has the shape of an inverted cone and develops around a discharge well.

confined aquifer

An aquifer bounded above and below by confining layers of distinctly lower permeability than the aquifer material and the one containing confined groundwater. When a well is installed in a confined aquifer, the water level in the well rises above the top of the aquifer.

confining unit

A hydra geologic unit of relatively low hydraulic conductivity, bounding one or more aquifers. (See also aquitard, aquifuge, and aquiclude.)

conservation solute

A non-reactive constituent that does not undergo chemical reaction during substance migration.


Toxic substances found in soils and groundwater.


The degradation of natural water quality as a result of man's activities. There is no implication of any specific limits, since the degree of permissible contamination depends upon the intended end use of the water.


The interaction of one or more organic contaminants that may cause them to behave differently than if they were present alone in their pure form.


Soil particles, also known as drilling spoils, created during the boring process. Use of the proper drilling fluid will help to suspend the cuttings which reduces the risk of getting stuck while boring and backreaming.

Darcy's law

An empirically derived equation for the flow of fluids through porous media. It is based on the assumptions that flow is laminar and inertia can be neglected, and states that the specific discharge, q, is directly proportional to the hydraulic conductivity, K, and the hydraulic gradient, J.

darcy, unit

A unit of intrinsic permeability, k (1 darcy = 9.87 x 10-9 cm2). The relationship between hydraulic conductivity, K, and the permeability, k, is given as K = kpg/,uwhere p is the fluid density, g is the gravitational constant, and ~ is the dynamic viscosity.


The amount of flex applied to the drill stem while steering the head.


The mass of a substance per unit volume [ML-3]. Units are pounds per cubic foot (lb/ft3), kilograms per cubic meter (kg/m3), or grams per cubic centimeter (g/cm3).


Refers to the depth of the drill head during a bore.

Resorption See adsorption, which is the reverse process.

diffusion coefficient See molecular diffusion.

discharge area

An area in which groundwater is discharged to the land surface, surface water, or atmosphere. An area in which there are upward components of hydraulic head in the aquifer. Groundwater is flowing toward the surface in a discharge area and may escape as a spring, seep, or base flow, or by evaporation and transpiration.


The spreading and mixing of chemical constituents in groundwater caused by diffusion and mixing (due to microscopic variations in velocities within and between pores).

dispersion coefficient

A measure of the spreading of a flowing substance due to the nature of the porous medium (and specific substance or fluid properties), with interconnected channels distributed at random in all directions. Also the sum of the coefficients of mechanical dispersion and molecular diffusion in porous medium.


A property of a porous medium (and the specific substance of fluid) that determines the dispersion characteristics of the contaminant in that medium by relating the components of pore velocity to the dispersion coefficient.

distribution (partitioning) coefficient

Relates the quantity of a solute sorbed per unit weight of the solid phase and the quantity of the solute dissolved in water per unit volume of water.


Dense Non Aqueous Phase Liquid. A liquid consisting of a solution of organic compounds (e.g., chlorinated hydrocarbons) and which is denser than water.

drainage basin

The land area from which surface runoff drains into a stream.


A lowering of the water table of an unconfined aquifer or the potentiometric surface of a confined aquifer caused by pumping of groundwater from wells. The vertical distance between the original water level and the new water level.

dry hole

If not enough drilling fluid is used, a dry hole occurs and the product becomes lodged in the ground.


The drilling bit that attaches to the front of the boring head. It mounts to the head at an angle and also is bent. This angle is what provides the steering capability while pushing the drill pipe.

effective grain size

The grain size corresponding to the 10% finer by weight on the grain-size distribution curve.

effective porosity

The interconnected pore space through which fluids can pass, expressed as a percent of bulk volume. Part of the total porosity will be occupied by static fluid being held to mineral surface by surface tension, so effective porosity will be less than total porosity.

effluent stream See gaining stream.

entrance pit

The area where the drill pipe enters the ground after the drill machine is set up.

entry angle

The angle at which the drill head enters the ground or the degree that the rack is set at.


The Environmental Protection Agency. The federal authority responsible for enforcing the various laws dealing with environmental standards.

equipotenffal line

A line in a two-dimensional groundwater flow field along which the total hydraulic head(the groundwater potential) is constant.

evapotranspiraffon, actual

The evaporation that actually occurred under given climatic and soil-moisture conditions.

evapotranspiration, potential

The evaporation that would occur under given conditions if there were unlimited soil moisture.

exit pit

The area where the drill pipe exits the ground and the service lines are pulled back in.

extraction well

A discharge well used to remove groundwater or air.


A premium grade, high molecular weight PHPA polymer manufactured by Baroid Company. When this is added to bentonite in the drilling fluid, it provides extended high viscosity and gel strength. It also lowers the filtration rate and increases lubrication. It is an excellent shale/clay stabilizer which minimizes swelling.

Fick's Law

The mass flux due to the molecular diffusion is proportional to the concentration gradient and the diffusion coefficient.

field capacity

The amount of moisture remaining in the soil after an extended period of gravity drainage without additional supply of water at the soil surface.

filter cake

The zone where the bentonite platelets plaster or shingle off the wall of the hole.


The water portion of the drilling fluid that seeps through the filter cake.


Term used to denote clay and shale soils. The use of polymer is recommended in these soil conditions to reduce swelling while at the same time improving lubrication and torque reduction.


When the drilling fluid moves or runs smoothly with unbroken continuity through the entire length of the bore.

Flowline or pathline

The general path that a particle of water follows under laminar flow conditions. Flowlines are perpendicular to equipotential lines in an isotropic aquifer.

flow model

A digital computer model that calculates a hydraulic head field for the modeling domain using numerical methods to arrive at an approximate solution to the differential equation c f groundwater flow.

flow, steady

A characteristic of a flow system, where the magnitude and direction of specific discharge are constant in time at any point. If the specific discharge has the same magnitude and direction at any point, the flow is uniform.

flow, unsteady (transient)

A characteristic of a flow system where the magnitude and/or direction of the specific discharge changes with time.

forged upset

The area at each end of a FIRESTICK drill stem where it tapers to a larger diameter. This larger diameter is achieved by heating the ends of the rod to temperatures in excess of 2000 F and striking it with tremendous force in a die set. To achieve this, the metal has to start out 3' longer than the desired finished length of the drill stem.

frac out

In certain conditions, the drilling fluid can build tremendous pressure in the bore. If the pressure becomes great enough, the ground will fracture to the surface. The drilling fluid escapes the bore through this rupture, and the pressure is relieved.


A general term for any break in a rock, which includes cracks, joints and faults.

fracture trace

Visible on aerial photographs, fracture traces are natural linear-drainage, soil-tonal, and topographic alignments that are probably the surface manifestation of underlying zones of fractures.

front locate point

The point in front of the drill head where the DIGITRAK locator goes from + to -. This point is also referred to as the front negative locate point.

gaining stream

A stream or reach of a stream, the flow of which is being increased by inflow of groundwater. Also known as an effluent stream.

gel strength

The ability of the drilling fluid to support and suspend the cuttings. The use of bentonite in the drilling fluid greatly increases these characteristics.


A methodology for the analysis of spatially correlated data. The characteristic feature is in the use of variograms or related techniques to quantify and model the spatial correlation structure. Also includes various techniques such as kriging, which utilize spatial correlation models.


False signals received by the locator.

glacial drift

A general term for unconsolidated sediment transported by glaciers and deposited directly on land or in the sea.

glacial outwash

Well-sorted sand, or sand and gravel, deposited by the meltdown from a glacier.

glacial till

A glacial deposit composed of mostly unsorted sand, silt, clay, and boulders and laid down directly by the melting ice.

gravitational head

Component of total hydraulic head related to the vertical position of a given mass of water relative to an arbitrary datum.

gravitational water

Water that moves into, through, or out of a soil or rock mass under the influence of gravity.

ground stake

A long copper rod with a T handle and auger bit that is screwed into the ground and attached to the boring machine to provide an additional path for electricity to flow in the event of an electrical strike.


The water contained in interconnected pores below the water table in an unconfined aquifer or in a confined aquifer.

groundwater barrier

Rock or artificial material with a relatively low permeability that occurs (or is placed) below ground surface, where it impedes the movement of groundwater and thus causes a pronounced difference in the heads on opposite sides of the barrier.

groundwater basin

General term used to define a groundwater flow system that has defined boundaries and may include more than one aquifer underlain by permeable materials that are capable of storing or furnishing a significant water supply. The basin includes both the surface area and the permeable materials beneath it.

groundwater divide

Ridge in the water table, or potentiometric surface, from which groundwater moves away at right angles in both directions. Line of highest hydraulic head in the water table or potentiometric surface.

groundwater flow

The movement of water through openings in sediment and rock that occurs in the zone of saturation.

groundwater model

A simplified conceptual or mathematical image of a groundwater system, describing the feature essential to the purpose for which the model was developed and including various assumptions pertinent to the system. Mathematical groundwater models can include numerical and analytical models.

groundwater mound

Raised area in a water table or other potentiometric surface, created by groundwater recharge.

groundwater recharge

Process of water addition to the saturated zone, or the volume of water added by this process.


A term used in the environmental industry to identify materials classified as hazardous by the EPA.


To treat metal by alternate heating and cooling in order to produce desired characteristics, such as increased hardness; temper.

Henry's Law

The relationship between the partial pressure of a compound and its equilibrium concentration in a dilute aqueous solution through a constant of proportionality known as the Henry's Law Constant.


Characteristic of a medium in which material properties vary from point to point.


Characteristic of a medium in which material properties are identical throughout. Though heterogeneity or nonuniformity is the characteristic of most aquifers, assumed homogeneity, with some other additional assumptions, allows use of analytical models as a valuable tool for approximate analyses of groundwater movement.


A situation that has been known to occur while pulling product through the bore. In this condition, the bore acts as a huge hydraulic cylinder with the product string acting as a large hydraulic ram. The drilling fluid stops flowing in the bore and pressure begins to build. The pressure continues to build to the point where the boring machine can no longer pull the product string and you have a stuck situation. Increased pullback pressure with decreased rotational pressure is an indication that hydra-lock is occurring. This most often occurs in very tight soil conditions such as dry clay and can sometimes be cured by digging a burp hole to relieve the pressure or by letting everything set for a period of time while the pressure seeps past the product string.

hydraulic barrier

Modifications to a groundwater flow system that restrict or impede movement of contaminants.

hydraulic conductivity (K)

Proportionality constant relating hydraulic gradient to specific discharge, which, for an isotropic medium and homogeneous fluid, equals the volume of water at the existing kinematic viscosity that will move in unit time under a unit hydraulic gradient through a unit area measured at right angles to the direction flow. The rate of flow of water in gallons per day through a cross section of one square foot under a unit hydraulic gradient, at the prevailing temperature (gpdlft2). In the standard International System, the units are m3/day/m2 or m/day. A coefficient of proportionality describing the rate at which water can move through a permeable medium. The density and kinematic viscosity of the water must be considered in determining hydraulic conductivity.

hydraulic conductivity

effective Rate of water flow through a porous medium that contains more than one fluid (such as water and air in the unsaturated zone), which should be specified in terms of the fluid type, content and the existing pressure.

hydraulic gradient (J)

Slope of a water table or potentiometric surface. More specifically, change in the hydraulic head per unit of distance in the direction of the maximum rate of decrease. The difference in hydraulic heads (h,-h2), divided by the distance (L) along the Towpath: J= (h1-h2)/L.

hydraulic head (h)

Height above a datum plane (such as mean sea level) of the column of water that can be supported by the hydraulic pressure at a given point in a groundwater system. Equal to the distance between the water level in a well and the datum plane.

hydrodynamic dispersion

Spreading (at the macroscopic level) of the solute front during transport resulting from both mechanical dispersion and molecular diffusion. The process by which groundwate containing a solute is diluted with uncontaminated groundwater as it moves through an aquifer (see dispersion coefficient).


Those factors that deal with subsurface waters and related geologic aspects of surface waters.

hydrogeologic parameters

Numerical parameters that describe the hydra geologic characteristics of an aquifer such as porosity, permeability, and transmissivity.

hydrogeologic pressure

Pressure exerted by the weight of water at any given point in a body of water at rest.

hydrogeologic unit

Any soil or rock unit or zone groundwater because of its hydraulic properties. that has a distinct influence on the storage or movement of groundwater because of its hydraulic properties.


The chemical property where two or more liquids or phases do not readily dissolve in one another, such as soil and water.


Characteristic of geologic materials that limits their ability to transmit significant quantities of water under the pressure gradients normally found in the subsurface environment.

impermeable layer

An area in the subsurface that has zero air flow. Limits the range of influence of extraction wells in SVE systems.


The downward entry of water into soil or rock.

infiltration rate

Rate at which soil or rock under specified conditions absorbs falling rain, melting snow, or surface water; expressed in depth of water per unit time. Also, the maximum rate at which water can enter soil or rock under specific conditions, including the presence of an excess of water; expressed in units of velocity.

influent stream See losing stream.


Latin term for "in the site," used in environmental industry to describe the treatment of contaminants without removal from their immediate location.

intrinsic permeability

Pertaining to the relative ease with which a porous medium can transmit a liquid under a hydraulic or potential gradient. It is a property of the porous medium and is independent of the nature of the liquid or the potential field.


A line connecting all points having the same time of travel for contaminant particles to move through the saturated zone and reach a well.


The condition in which the properties of interest (generally hydraulic properties of the aquifer) are the same in all directions.


Where the male and female threads of the drill stem come together.

kinematic viscosity

The ratio of dynamic viscosity to mass density. It is obtained by dividing dynamic viscosity by the fluid density. Units of kinematic viscosity are square meters per second (m2/s).

klinkenberg effect

Gas slippage along pore walls. Darcy's Law assumes that the velocity of a fluid at the pore wall surface is zero.


A weight-moving-average interpolation method where the set of weights assigned to samples minimizes the estimation variance, which is computed as a function of the variogrammodel and locations of the samples relative to each other, and to the point or block being estimated.

laminar flow

Fluid flow in which the head loss is proportional to the first power of the velocity; synonymous with streamline flow and viscous flow. Type of flow in which the fluid particles follow paths that are smooth, straight, and parallel to the channel walls. In laminar flow, the viscosity of the fluid dampens out turbulent motion.


Removal of materials in solution from rock, soil, or waste; dissolving out of soluble constituents from a porous medium by percolation of water.


Flow of water from one hydrogeologic unit to another. This may be natural, as through a somewhat permeable confining layer, or anthropogenic, as through an uncased well. It may also be the natural loss of water from artificial structures, as a result of hydrostatic pressure.

leakage coefficient

The rate of flow across a unit (horizontal) area of a semi-pervious layer into (or out of) an aquifer under one unit of head difference across this layer.

leaky aquifer

An artesian or water table aquifer that loses or gains water through adjacent semipermeable confimng units.


Lighter-than-water non aqueous phase liquid.


The unit which picks up the signal from the drill head where the transmitter is housed.

losing stream

A stream or reach of a stream that is losing water by seepage into the ground. Also known as an influent stream.


Slick or slippery as in lubricate. Polymer in the drilling fluid will increase "lubricity" in the bore.


Relatively large pores in porous medium that allow the enhanced movement of liquid and gas.


The fitting together of the pin and box sections of the drill stem.


Stainless steel wire mesh that is part of the strike alert and grounding system. The function of the mats is to equalize the voltage around the machine in the event of an electrical strike.


Solid framework of a porous material or system.

mechanical dispersion

Process whereby solutes are mechanically mixed during advective transport, caused by the velocity variations at the microscopic level; synonymous with hydraulic dispersion. The coefficient of mechanical dispersion is the component of mass transport flux of solutes caused by velocity variations at the microscopic level.

moisture content See water content.

molecular diffusion

Process in which solutes are transported at the microscopic level due to variations in thesolute concentrations within the fluid phases.

monitoring well

A tube or pipe, open to the atmosphere at the top and to water at the bottom, usually along an interval of slotted screen, used for taking groundwater samples.


Drilling fluid.

negative locate

One of two points where a Digitrak locator reading goes from + to -.


Non aqueous phase liquids.

nonpoint source

A source discharging pollutants into the environment that is not a single point.


Located on the drill head to spray drilling fluid into the bore.

observation well

A well drilled in a selected location for the purpose of observing parameters such as water levels and pressure changes. A non-pumping well used to observe the elevation of the water table or the potentiometric surface. An observation well is generally of larger diameter than a piezometer and typically is screened or slotted throughout the thickness of the aquifer.

organic carbon content

The amount of the organic carbon present in a soil. Organic chemicals in soil adsorb to soil organic carbon and the amount of adsorption can be related to the soil organic carbon content.

partial penetration

When the intake portion of the well is less than the full thickness of the aquifer. A well constructed in such a way that it draws water directly from a fractional part of the total thickness of the aquifer. The fractional part may be located at the top, the bottom, or anywhere else in the aquifer.


Chemical equilibrium condition where a chemical's concentration is apportioned between two different phases according to the partition coefficient, which is the ratio of a chemical's concentration in one phase to its concentration in the other phase.

peclet number

Relationship between the advective and diffusive components of solute transport; expressed as the ratio of the product of the average interstitial velocity and the characteristic length, divided by the coefficient of molecular diffusion. Small values indicate diffusion dominates; large values indicate advection dominates.

perched aquifer

A special case of phreatic aquifer which occurs wherever an impervious (or semi-perviousj layer of limited aerial extent is located between the water table of a phreatic aquifer and the ground surface.

perched water

Unconfined groundwater separated from an underlying main body of groundwater by an unsaturated zone.


Downward movement of water through the unsaturated zone; also defined as the downward flow of water in saturated or nearly saturated porous media at hydraulic gradients of 1.0 or less. The act of water seeping or filtering through the soil without a definite channel.

permeability coefficient

Rate of flow of water through a unit cross-sectional area under a unit hydraulic gradient at the prevailing temperature (field permeability coefficient), or adjusted to 15 degrees C.

permeability, effective

Observed permeability of a porous medium to one fluid phase, under conditions of physical interaction between the phase and other fluid phases present.

permeability, intrinsic

Relative ease with which a porous medium can transmit a fluid under a potential gradient, as a property of the medium itself. Property of a medium expressing the relative ease with which fluids can pass through it.

phreatic aquifer See water table aquifer.


A tube or pipe, open to the atmosphere at the top and to water at the bottom, and sealed along its length, used to measure the hydraulic head in a geologic unit.

piezemeter surface See potentiometric surface.


The male threads on the drill stem.


Measurement for the deviation from horizontal of the drill head.


A minute, disklikecytoplasmic body found in bentonite that plasters or shingles off the wall of the hole to form a filter cake that cuts off the flow of water into the surrounding sand or gravel. When broken down to its smallest dimension, there are enough platelets in on cubic inch of high-quality sodium bentonite to cover 66 football fields.

point source

Any discernible, confined, or discrete conveyance from which pollutants are or may be discharged, including (but not limited to) pipes, ditches, channels, tunnels, conduits, wells, containers, rolling stock, concentrated animal feeding operations, or vessels.


Any solute or cause of change in physical properties that renders water unfit for a given use.


When the contaminant concentration levels restrict the potential use of groundwater.


Any of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units, each a relatively light and simple molecule. Polymer, when used in conjunction with bentonite in the drilling fluid, enhances viscosity and gel strength, lowers filtration rate, and increases lubricity. The use of a polymer is recommended when boring in clay or shale.

pore space

Total space in an aquifer medium not occupied by solid soil or rock particles.


Ratio of the total volume of voids to the total volume of a porous medium. The percentage of the bulk volume of a rock or soil that is occupied by interstices, whether isolated or connected. Porosity may be primary, formed during deposition or cementation of the material, or secondary formed after deposition or cementation, such as fractures.


When locating with a Digitrak, this is the point directly above the drill head where the locator readout changes from + to

potable water

Suitable for human consumption as drinking water.

potenffometric surface

A surface that represents the level to which water will rise in wells penetrating a confined aquifer. If the head varies significantly with depth in the aquifer, then there may be more than one potentiometric surface. The water table is a particular potentiometric surface for an unconfined aquifer.


A hole dug to expose underground utilities crossing the proposed bore path.

pressure aquifer

Also known as confined aquifer. (See confined aquifer.)

pressure head

Hydrostatic pressure expressed as the height (above a measurement point) of a column of water that the pressure can support.

pressure, static

Pressure exerted by a fluid at rest.


An electronic device that fits inside the drill head and sends out a signal used to locate the head, read pitch and roll, and determine depth.


Potential responsible parties. Waste generators who are responsible for the ultimate fate of toxic wastes. Includes property owners, industries, government agencies, etc. The current federal laws make the PRPs liable in perpetuity for these wastes.


The specific gravity of water

public water supply system

System for provision to the public of piped water for human consumption. Such a system has at least 15 service connections or regularly serves at least 25 individuals daily or at least 60 days out of the year. The term includes any collection, treatment, storage, and distribution facilities under control of the operator of such system and used primarily in connection with the system, and any collection or pretreatment storage facilities not under such control that are used primarily in connection with the system.

pumping test

A test that is conducted to determine aquifer or well characteristics. A test made by pumping a well for a period of time and observing the change in hydraulic head in the aquifer. A pumping test may be used to determine the capacity of the well and the hydraulic characteristics of the aquifer. Also called aquifer test.


Plastic pipe that can be used as well casing material.


A step in the heat treating process to cool hot metal which causes it to harden. The most common quench mediums are brine, water, oil, and air. The greatest hardness and strength for most materials are obtained by brine or water quenching. However, this also produces the most distortion and cracking. Oil or air quenching will produce less distortion and cracking but also less strength and hardness.


Highest-grade sodium bentonite manufactured by Baroid Drilling Fluids, Inc. This drilling fluid mix develops a cost-effective low solids slurry with high viscosity, high gel strength, and controlled filtration rate to provide formation and hole stabilization.


A white granular pure grade polymer manufactured by Baroid Drilling Fluids, Inc. When added to a premixed bentonite slurry, it improves clay/shale stabilization and enhances all properties of a bentonite slurry used in boring.


The actual boring machine which includes drive head, controls, vise' etc.

radial flow

The flow of water in an aquifer toward a vertical well.

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.

range of influence

The area that can be remediated by an extraction well in an SVE system.

Raoult's Law

A physical law which describes the relationship between the vapor pressure of a component over a solution, the vapor pressure of the same component over pure liquid, and the mole fraction of the component in the solution.


Any of various tools attached to the end of the drill string and pulled through the bore to enlarge the hole and mix the cuttings with the drilling fluid.

rear locate point

The point behind the drill head where the readout on a Digitrak locator switches from + to -. This is also called the rear negative locate point.


an electronic unit that receives information from the transmitter. This is also referred to as the locator.


The addition of water to the zone of saturation; also, the amount of water added. Can be expressed as a rate (i.e., in/yr) or a volume.

recharge area

An area in which there are downward components of hydraulic head in the aquifer. Infiltration moves downward into the deeper parts of an aquifer in a recharge area.

recharge basin

A basin or pit excavated to provide a means of allowing water to soak into the ground at rates exceeding those that would occur naturally.

recharge boundary

An aquifer system boundary that adds water to the aquifer. Streams and lakes are typicalrecharge boundaries.

remedial construction

The business of implementing the methods for cleanup. Includes firms that specialize in underground storage tank removal and soil vacuum extraction.


The methods of cleanup used for contaminated soils and groundwaters.


An auxiliary electronic readout that displays information received from the receiver.

residual saturation

Saturation below which fluid drainage will not occur.


The movement of a solute through a geologic medium at a velocity less than that of the flowing groundwater due to sorption or other removal of the solute.

Reynolds number

Dimensionless number expressing the ratio of inertial to viscous forces acting on the fluid, Re=pVd. The number can be used to determine whether the flow is laminar or turbulent.


The most commonly used method for determining the hardness of a metal.


A section of drill stem.

rod wiper

A donut-shaped neoprene disk that fits around the drill stem to help clean it during the pullback. The rotational position of the drill head as it relates to a clock face.


The speed of the drill stem turning in the ground. It also relates to how fast the reamer turns.


That part of precipitation flowing to surface streams. The total amount of water flowing in a stream. It includes overland flow, return flow, interflow, and baseflow.

safe yield

The amount of naturally occurring groundwater that can be withdrawn from an aquifer on a sustained basis without impairing the native groundwater quality or lowering water levels.


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

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.

seepage face

Whenever a phreatic surface approaches the downstream external boundary of a flow domain, it always terminates on it at a point that is above the water table of the body of open water present outside the flow domain. The segment of the boundary above the water table and below the phreatic surface is called the seepage face.


An aquifer that has a "leaky" confining unit and displays characteristics of both confined and unconfined aquifers. (See leaky aquifer.)

sewer probe

This transmitter is designed to bore sewer pipe by allowing the bore to be on grade. The probe works on a 0. 1% readout.

site characterization

The process of determining the geology, hydrology, type of contaminants and area of contamination. Done by engineering and consulting firms.

skin effect

The damage to the permeability in the proximity of a well due to drilling fluids.

slug test

A test for estimating hydraulic conductivity of an aquifer in which a rapid water-level change is produced in a piezometer or monitoring well, usually by introducing or withdrawing a "slug" of water or a weight. The rise or decline in the water level is monitored.

slurry wall

A subsurface wall constructed by digging a trench and backfilling it with a slurry and designed to prevent groundwater flow.

soda ash

Sodium carbonate in powdery white form used to increase the PH level of hard water. This makes the mixing of bentonite and polymers into the drill fluid much easier.

soil venting, soil vapor extraction, soil vacuum extraction, "SVE"

All describe the process of using extraction wells as a means to deliver a vacuum in the subsurface, thereby pulling toxic vapors to the surface to be treated by an incineration, catalytic or absorptive process.

solute transport

Net flux of solute through a hydrogeologic unit, controlled by the flow of subsurface water and transport mechanisms.

solute transport model

Mathematical model used to predict the movement of solutes (generally contaminants) in an aquifer through time.


An electronic device that fits inside the drill head and transmits a signal used for locating purposes. Also referred to as a transmitter or probe.


Processes that remove solutes from the fluid phase and concentrate them on the solid phaseof a medium; used to encompass absorption and adsorption.


A method of forcing VOCs from the saturated zone into the vadose zone by pushing air into the groundwater.

specific capacity

The rate of discharge of water from the well divided by the drawdown within the well.

specific discharge

The volume of water flowing through a unit cross-sectional area of an aquifer.

specific drawdown

The drawdown within a well divided by the discharge rate of water from the well (inverse of specific capacity).

specific gravity

The ratio of a substance's density to the density of some standard substance, usually water.

specific retention

As water is being drained from the interstices of soil, after drainage has stopped, the volume of water retained in an aquifer per unit area and unit drop of the water table.

specific storage

The amount of water released from or taken into storage per unit volume of a porous medium per unit change in head.

specific surface

The amount of surface area of a dispersed system per gram or per unit volume of the dispersed phase.

specific yield

The volume of water that a saturated rock or soil will yield by gravity (often used as a synonym for effective porosity or storage coefficient of unconfined aquifers).

spiral reamer

A specially designed back reamer that resembles a huge wood screw. This long tapered spiral design is well suited for pushing hard obstacles out of the way.


Discrete place where groundwater flows naturally from rock or soil onto the land surface or into a surface water body.

stagnation point

A point in a groundwater flow field at which the groundwater is not moving. The magnitude of vectors of hydraulic head at the point are equal but opposite in direction.

static water level

The level of water in a well that is not being affected by withdrawal of groundwater.


A section of drill pipe.

step potential

Describes the electrical voltage differential between two points.

strike alert

A warning system on all NAVIGATORs that is set off by contact with an electrical power source.

storage coefficient

The amount of water released from or taken into storage per porous medium column with a unit surface area per unit change in head. (See also storativity.)


A dimensionless term representing the volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head. It is equal to the product of specific storage and aquifer thickness. In an unconfined aquifer, the storativity is equivalent to the specific yield.


The commonly used name for a federal law called "CERCLA," This act designated a portion of funds to be put away by generators of certain wastes for the research and implementation of remediation processes.


Principle used for linear problems, such as confined groundwater flow, that allows equation solutions to be added to form new solutions. For example, if within a well field, pumping rates of the pumped wells are known, the composite drawdown at a point can be determined by summing the drawdown caused by each individual pumped well.


A soap based substance which acts as a wetting agent to reduce the tendency of clay cutting to stick together. It also reduces the tendency of boring tools becoming stuck by adhesion.


Attaches between the back reamer and the product being pulled back to keep the product from twisting.


Metal that is reheated after quenching for the purpose of making it more stress-free, crack free, distortion-free and slightly softening it.


The instrument used for measuring the capillary pressure in an unsaturated zone.

thread compound

Used to lubricate the thread and shoulder area of the drill joint. Suitable thread compound should have a zinc base of 40-60% by weight to withstand the pressures and torque that is applied to the drill stem joints. Sometimes mistakenly referred to as grease.


This occurs when you push the drill stem into the ground without rotating.

time of travel (TOT)

The time required for a contaminant to move in the saturated zone from a specific point to well.


The rotational force applied to the drill stem joints.


Rate at which water of the prevailing kinematic viscosity is transmitted through a unit width of the aquifer under a unit hydraulic gradient. It is equal to an integration of the hydraulic conductivities across the saturated part of the aquifer perpendicular to the flow paths. The rate at which water is transmitted through a unit width of an aquifer under a unit hydraulic gradient. Transmissivity values are given in gallons per minute through a vertical section of an aquifer one foot wide and extending the full saturated height of an aquifer under a hydraulic gradient of one in the English Engineering System; in the Standard International System, transmissivity is given in cubic meters per day through a vertical section of an aquifer one meter wide and extending the full saturated height of an aquifer under a hydraulic gradient of one. It is a function of properties of the liquid, the porous media, and the thickness of the porous media.


An electronic device that fits inside the drill head and transmits a signal used for locating purposes. Also referred to as a sonde or probe.

turbulent flow

Water flow in which the flow lines are confused and heterogeneously mixed. It is typical of flow in surface water bodies (2). That type of flow in which the fluid particles move along very irregular paths. Momentum can be exchanged between one portion of the fluid and another. Compare with laminar flow.


Conditions in which the upper surface of the zone of saturation forms a water table under atmospheric pressure.

unconfined aquifer See water table aquifer.

unconsolidated aquifer

An aquifer made up of loose material, such as sand or gravel, that has not undergone lithification.

unsaturated flow

Movement of water in porous medium in which the pore spaces are not completely filled with water.

unsaturated zone

The zone between the land surface and the water table. It includes the root zone, intermediate zone, and capillary fringe. The pore spaces contain water, as well as air and other gases at less than atmospheric pressure. Saturated bodies, such as perched groundwater,may exist in the unsaturated zone, and water pressure within these may be greater than atmospheric. Replaces the older terms "zone of aeration" and "vadose zone."


Underground storage tanks used for the storage of fuels and other liquids. Most have leaked contaminants into the ground around them. A program to remove all old USTs is in place by the EPA and is scheduled to be completed by 1998.

vadose zone

The area immediately beneath the surface of the earth. Usually made up of soils, small rocks, gravels, clays, etc. Above saturated zone.


The process of determining the degree to which a model is an accurate representation of the real world from the perspective of the intended uses of the model.

velocity, average interstitial

Average rate of groundwater flow in interstices expressed as the product of hydraulic conductivity and hydraulic gradient (specific discharge) divided by the effective porosity. It is synonymous with average linear groundwater velocity or effective velocity.


The examination of the numerical technique in the computer code to ascertain that it truly represents the conceptual model and that there are no inherent problems with obtaining a solution.


The internal friction within a fluid that causes it to resist flow.


Volatile organic compounds, typically with a high vapor pressure and a tendency to evaporate rapidly.


The transfer of a chemical from liquid to the gas phase. Solubility, molecular weight, and vapor pressure of the liquid, and the nature of the air-liquid interface, affect the rate of volatilization.

water budget

An evaluation of all the sources of supply and corresponding discharges with respect to an aquifer or drainage basin.

water table

Upper surface of a zone of saturation, where that surface is not formed by a confining unit; water pressure in the porous medium is equal to atmospheric pressure. The surface between the vadose zone and the groundwater; that surface of a body of unconfined groundwater at which the pressure is equal to that of the atmosphere.

water table aquifer

An aquifer in which the water table forms the upper boundary.

well field

An area containing two or more wells supplying a public water supply system.

well, fully penetrating

A well drilled to the bottom of an aquifer, constructed in such a way that it withdraws water from the entire thickness of the aquifer.

well interference

The condition occurring when the area of influence of a water well (the cone of depression) overlaps that of a neighboring well or wells, as when the wells are pumping from the same aquifer.

well screen

A filtering device used to permit the flow of liquid or air but prevents the passage of sediments or backfill particles.

well yield

The volume of water discharged from a well per unit time.


The physical structure, facility, or devise at the land surface from or through which groundwater flows or is pumped from subsurface, water-bearing formations.

wellhead protection area (WHPA)

The surface and subsurface area surrounding a water well or well field, supplying a public water system, through which contaminants are reasonably likely to move toward and reach such water well or well field.

wetting agent

A substance that reduces the surface tension of a liquid, causing the liquid to spread across or penetrate more easily the surface of a solid. A soap-based wetting agent reduces the tendency of clay cuttings to stick together. It also reduces the tendency of boring tools becoming stuck due to adhesion.

wilting point

The soil-moisture content below which plants are unable to withdraw soil moisture.

wing cutter

A backreamer specially designed to cut, mix, and change the form of the material that is being pulled through to make it into a passable or manageable form.

zone of capture

Area surrounding a pumping well that encompasses all areas of features that supply groundwater recharge to the well.

zone of contribution (ZOC)

The area surrounding a pumping well that encompasses all areas or features that supply groundwater recharge to the well.

zone of influence (ZOI)

The area surrounding a pumping well within which the water table or potentiometric surfaces have been changed due to groundwater withdrawal.

zone of transport (ZOT)

The area surrounding a pumping well, bounded by an isochrone and/or isoconcentration contour, through which a contaminant may travel and reach the well.




American Petroleum Institute


Applicable or Relevant and Appropriate Rquirements


American Society for Testing and Materials


Comprehensive Environmental Response, Compensation, and Liability Act


Code of Federal Regulations


Clean Water Act


Department of Defense


Department of Transportation


Environmental Protection Agency


Federal Emergency Management Agency


Maximum Contaminant Level


Maximum Contaminant Level Goal


National Contingency Plan


National Pollutant Discharge Elimination System


National Priority List


Occupational Safety and Health Act


Potential Responisiblity Part


Resource Conservation and Recovery Act


Remedial Investigation/Feasability Study


Record of Decision


Superfund Amendments and Reauthorization Act


Superfund Innovative Technology Evaluation


Toxicity Characteristic Leaching Procedure


US Geological Survey


Underground Storage Tank


Vacuum Extraction System