Definition of Terms

A
Action level TheconcentrationestablishedbytheU.S.Environmental
ProtectionAgencyofcopperorleadwhich,ifexceeded,triggerstreatment
orotherrequirementsthatawater-supplysystemmustfollow.
Acute criteria Anestimateofthemaximumconcentrationofaconstituent
towhichaquaticlifecanbeexposedforshortperiodsoftimewithoutdetri-
mentaleffects.
Algorithm Asystematicprocedure(usuallyrepetitive)forsolvinga
problem.
Alluvium Ageneraltermforunconsolidatedsedimentaryaccumulations
depositedbyriversorstreams.Itincludessedimentdepositedinriverbeds
andfloodplains.
Anhydrite Acalciumsulfatemineral(CaSO
4
)thataltersreadilyto
gypsum.
Anticline Afoldinwhichthestratadipawayfromtheaxis.Aftererosion,
theoldestrocksareexposedinthecentralcoreofthefold.Seefigure17.
Aquatic-life criteria Water-qualitystandardsdesignedtoprotectaquatic
life.
Aquifer Anundergroundbodyofporousmaterials,suchassand,gravel,or
fracturedrock,filledwithwaterandcapableofsupplyingusefulquantities
ofwatertoawellorspring.
Artesian aquifer Anaquiferthatcontainswaterthatwouldriseabovethe
topoftheaquiferinapenetratingwell;alsoconfinedaquifer.
Artesian well Awellinwhichthewaterwillriseabovethetopofthe
aquifer.Whenthewaterlevelisabovelandsurface,waterwillflowfromthe
well.
Axial plane Withreferencetofolds,suchasanticlinesandsynclines,an
imaginaryplanethatintersectsthecrestortroughofafold.Seefigure17.
B
Basal Locatedatthebottomofageologicunit.
Base flow Thatpartofstreamflowthatissustainedprimarilybyground-
waterdischarge.Itisnotattributabletodirectrunofffromprecipitationor
meltingsnow.
Basin yield Theannualyieldofabasin(expressedininches),whichis
obtainedbydividingannualflowbydrainagearea.
Bedrock aquifer Anaquifercomposedofconsolidatedmaterialsuchas
limestone,dolomite,sandstone,siltstone,shale,orfracturedcrystallinerock.
Beneficial-use criteria Water-qualitystandardsestablishedbytheStateto
protectbeneficialusesthatareassignedtostreamsegments,lakes,and
aquifers.
Breccia Arockcomposedoflarge,angularfragmentscementedintoa
solidmass.
Brine Waterhavingadissolvedsolidsconcentrationgreaterthanthatof
seawater(35,000milligramsperliter).
Capillary fringe Thelowersubdivisionoftheunsaturatedzone,immedi-
atelyabovethewatertable,inwhichthevoidsarefilledwithwaterunder
pressurelessthanthatoftheatmosphereandheldbysurfacetension.
Carbonate rocks Rocksconsistingmainlyofcarbonateminerals,which
containthecarbonateradical(CO
3
-2
)combinedwithotherelements.Exam-
plesarelimestoneanddolomite.
Cenozoic Themostrecentofthefourerasintowhichgeologictimeis
divided.ItextendsfromtheendoftheMesozoicEratothepresent.
Chronic criteria Anestimateofthemaximumconcentrationofaconstitu-
enttowhichaquaticlifecanbeexposedforextendedperiodsoftimewithout
detrimentaleffects.
Clay Anearthy,extremelyfine-grainedsedimentorsoftrockcomposed
primarilyofclay-sizedorcolloidalparticles,havinghighplasticityanda
considerablecontentofclayminerals.
Colluvium Ageneraltermappliedtounconsolidatedmaterialdepositedby
rainwashorslowcontinuousdownslopecreep,usuallycollectingatthebase
ofhillsides.
Common ions Thegroupofconstituentsthatincludescalcium,magnesium,
sodium,bicarbonate,sulfate,andchlorideandcollectivelyconstitutemore
than95percentofthedissolvedsolidsformostnaturalwaters.(Anionisan
electricallychargedparticle.)
Concentration Theamountofaconstituentpresentinagivenvolumeof
sample.Usuallyexpressedasmilligramsperliterormicrogramsperliterfor
awatersample.
Conceptual model Aworkingmodelorhypothesisdescribingaphenome-
nonorprocessthatisdifficultorimpossibletoobservedirectly.
Confined Saidofgroundwaterthatisunderpressuregreaterthanthatof
theatmosphere.Whenanaquiferiscompletelyfilledwithwater(fullysatu-
rated)andisoverlainbyaconfiningunit,thewatercanbeconfinedunder
pressure.
Confined aquifer Anaquiferthatcontainswaterthatwouldriseabovethe
topoftheaquiferinapenetratingwell;alsoartesianaquifer.Seefigure7B.
Confining unit Arelativelylowpermeabilitygeologicunitthatimpedesthe
verticalmovementofwater.
Conglomerate Acourse-grainedsedimentaryrockcomposedofrounded
fragmentsofpebbles,cobbles,orboulderscementedintoasolidmass.
Constituent Achemicalsubstanceinwaterthatcanbemeasuredbyanalyt-
icalmethods.
Consumptive use Permanentremovalofwaterfromawaterbodybydiver-
sions,evaporation,ortranspiration.Fornonconsumptiveuses,wateriseven-
tuallyreturnedtothewaterbody.
Cross section Adiagramordrawingthatshowsfeaturestransectedbya
givenverticalplane.Seefigure20.
Crystalline rock Igneousormetamorphicrock.
Cubic foot per second Therateofwaterdischargerepresentingavolume
of1cubicfootpassingagivenpointduring1second;approximatelyequal
to7.48gallonspersecond,448.8gallonsperminute,or0.02832cubicmeter
persecond.
D
Depression storage Accumulationofwaterfromprecipitationindepres-
sionsinthelandsurface.
Dip Theslopeofatiltedlayerofrock.
Direct runoff Therunoffreachingstreamchannelsimmediatelyafterrain-
fallorsnowmelt.
Discharge Rateoffluidflowpassingagivenpointatagivenmomentin
time,expressedasvolumeperunitoftime,suchascubicfootpersecond.
Dissolution Processbywhichmineralsandrockmaterialsaredissolvedby
afluid.
Dissolved solids Thetotalofalldissolvedmineralconstituents,usually
expressedinmilligramsperliter(mg/L).Thedissolvedsolidsconcentration
commonlyiscalledthewaterssalinityandisclassifiedasfollows:fresh,
0-1,000mg/L;slightlysaline,1,000-3,000mg/L;moderatelysaline,3,000-
10,000mg/L;verysaline,10,000-35,000mg/L;andbriny,morethan35,000
mg/L.
Dolomite Asedimentaryrockcomposedprimarilyofcalcium-magnesium
carbonate,CaMg(CO
3
)
2
.
Dome Anupliftthatiscircularorellipticalinmapview,withbedsdipping
awayinalldirectionsfromacentralarea.Seefigure17.
Drainage area Thetotalareaofawatershedupstreamofagivenlocation,
suchasastreamflow-gagingstation.
Drainage basin Theareadrainedby(orcontributingwaterto)astream,
lake,orotherbodyofwater;alsowatershed.
E
Effective porosity Theporosityconsistingofinterconnectedvoids.
Erosional remnant Atopographicfeaturethatremainsorisleftstanding
abovethegenerallandsurfaceaftererosionhasloweredthesurrounding
area.
Evaporation Theprocessofliquidwaterbecomingwatervapor,including
vaporizationfromwatersurfaces,landsurfaces,andsnowfields,butnot
fromleafsurfaces.
118 AtlasofWaterResourcesintheBlackHillsArea,SouthDakota
C
Evaporite mineral Amineralprecipitatedasaresultofevaporation,such
ashalite.
Evapotranspiration Lossofwaterfromalandareathroughevaporation
fromthesoilandsurface-waterbodiesandtranspirationbyplants.
F
Fault Asurfacealongwhicharockbodyhasbrokenandbeendisplaced.
Seefigure17.
Flowpath Thedirectionofmovementofgroundwater,andanycontami-
nantsthatmaybecontainedtherein,ascontrolledbythehydraulicgradient
andothergeologicfactors.
Fold Abendorflexureinarock.Seefigure16.
Formation Thefundamentalunitinthelocalclassificationofrocksinto
geologicunitsbasedonsimilarcharacteristicsinlithology,whichisthe
descriptionofrocksonthebasisofsuchcharacteristicsascolor,mineralogic
composition,andgrainsize.Formationsmayrepresentrocksdepositeddur-
ingshortorlongtimeintervals,maybecomposedofmaterialsfromseveral
sources,andmayincludebreaksindeposition.Formationstypicallyare
namedaftergeographiclocalitieswheretheywerefirststudiedordescribed.
Fracture Acrackinarock.Alsoincludesjointsandfaults.
Fresh water Waterthathasadissolvedsolidsconcentrationsoflessthan
1,000milligramsperliter.
G
Geographic information system (GIS) Acomputerprogram(andassociated
databases)thatpermitsgeographicinformationtobedisplayed,manipu-
lated,andanalyzed.
Geologic time scale Anarbitrarychronologicarrangementofgeologic
events,commonlypresentedinachartformwiththeoldesteventandtime
unitatthebottomandtheyoungestatthetop.
Ground water Waterbeneaththelandsurfaceinthesaturatedzone.
Ground-water level Thelevelofthewatertableinanunconfinedaquifer
orofthepotentiometricsurfaceinaconfinedaquifer.
Group Ageologicclassificationconsistingoftwoormoreformations.
Gypsum Themineralformofhydratedcalciumsulfate,CaSO
4

2H
2
O.
H
Halite Amineralcomposedofsodiumandchloride,NaCl(salt).
Hogback Asteep,elongateridge;commonlyprotectedfromerosionbya
steeplydippingresistantstratum.
Hydraulic connection Existswhenchangesinhydraulicheadinadjacent
aquifersorsurface-waterbodiesinfluenceeachother.
Hydraulic gradient Therateofchangeintotalheadperunitofdistanceof
flowinagivendirection.Waterwillflowfromhigherhydraulicheadto
lowerhydraulichead.
Hydraulic head Inanaquifer,thealtitudetowhichwaterwillriseinaprop-
erlyconstructedwell.Thisisthealtitudeofthewatertableinanunconfined
aquiferorofthepotentiometricsurfaceinaconfinedaquifer.
Hydrogeology Factorsthatdealwithgeologicinfluencesonwater.
Hydrograph Agraphshowingflowratesorwaterlevelswithrespectto
time.Astreamhydrographcommonlyshowsrateofflow;awellhydrograph
commonlyshowswaterlevel.
Hydrologic budget Anaccountingoftheinflowto,outflowfrom,and
storagechangeinahydrologicunitsuchasanaquiferordrainagebasin.
Hydrologic cycle Theconstantcirculationofwaterfromthesea,through
theatmosphere,totheland,andbacktothesea.
I
Igneous rocks Rocksthatsolidifiedfrommoltenorpartlymoltenmaterial,
suchasmagma.Graniteisanexampleofanigneousrock.
Infiltration Movementofwaterfromthelandsurfaceintothesoilorporous
rock.
Interflow Therunoffinfiltratingintothesurfacesoilandmovingtoward
streamsasshallow,perchedgroundwaterabovethemainground-water
level.
Intrusion Theprocessofemplacementofmagmainpre-existingrock.
Isotope Oneoftwoormorespeciesofthesamechemicalelementthatdif-
ferfromoneanotherbyhavingadifferentnumberofneutronsinthenucleus.
Theisotopesofanelementhaveslightlydifferentphysicalandchemical
propertiesduetotheirmassdifference.
K
Karst Atypeoftopographythatisformedoverlimestone,dolomite,or
gypsumbydissolution.Itischaracterizedbysinkholes,caves,andunder-
grounddrainage.
L
Laminated Saidofarockcontainingverythinlayers;platy.
Limestone Asedimentaryrockconsistingmostlyofcalciumcarbonate,
CaCO
3
,primarilyintheformofthemineralcalcite.
Loss threshold Maximumrateofwaterlostbystreamstounderlyinggeo-
logicunits.Untilstreamflowupstreamfromalosszoneexceedstheloss
threshold,theentireflowofthestreamislosttounderlyinggeologicunits.
Loss zone Astreamzone,orsegment,whereflowislosttounderlying
geologicunits.
M
Massive Saidofrocksthatoccurinverythickbedsthatareuniformin
structureandcompositionthroughout.
Maximum Contaminant Level (MCL) Maximumpermissiblelevelofacon-
taminantinwaterthatisdeliveredtoanyuserofapublicwatersystem.
MCLsareenforceablestandardsestablishedbytheU.S.Environmental
ProtectionAgency.
Mean Thearithmeticaverageofaseriesofvalues.
Median Thevalueofthemiddlenumberinasetofdataarrangedinrank
order.The50thpercentile.
Mesozoic TheeraofgeologictimefromtheendofthePaleozoicEratothe
beginningoftheCenozoicEra.
Metamorphic rock Derivedfrompre-existingrocksinresponsetochanges
totemperature,pressure,orstressthatresultinchangesinthemineralogy,
chemistry,orstructureoftherock.Examplesofmetamorphicrocksareslate
andschist.
Mineralized areas Areaswherethelocalgeologyisknowntohaverela-
tivelyhighconcentrationsoftraceelements,suchasarsenic,copper,gold,
lead,silver,andzinc.
Monocline Astep-likebendorfoldinotherwisehorizontalorgently
dippingbeds.Seefigure17.
N
Nutrients Nitrogenandphosphorus,whichareessentialtoplantgrowth.
O
Observation well Awellconstructedforcollectionofhydrologicdata,
suchaswaterlevelsandwaterquality.
Orogeny Theprocessoftheformationofmountains.
Orographic Pertainingtomountains.Climatically,theliftingofaircurrents
causedbypassageupandovermountains.
Outcrop Thatpartofageologicformationthatisexposedattheland
surface.
Overland flow Thatpartofrunoffflowingoverlandsurfacestoward
streamchannels.
P
Paleozoic TheeraofgeologictimefromtheendofthePrecambrianErato
thebeginningoftheMesozoicEra.
Perched ground water Unconfinedgroundwaterseparatedfromanunder-
lyingmainbodyofgroundwaterbyanunsaturatedzone.
Perched spring Aspringwhosesourceofwaterisabodyofperched
groundwater.
Perennial Referstoastreamthatflowsthroughouttheyear.
DefinitionofTerms 119
Permeability Thecapacityofaporousrock,sediment,orsoilfortransmit-
tingafluid.
Porosity Thepercentageofthesoilorrockvolumethatisoccupiedbypore
space,voidofmaterial;definedbytheratioofvoidstothetotalvolumeofa
specimen.
Potential evaporation Themaximumamountofwaterthatwouldevapo-
rateundernaturalconditionsifunlimitedmoisturewasavailable.
Potentiometric surface Asurfacerepresentingthehydraulicheadof
groundwater;representedbythewater-tablealtitudeinanunconfinedaqui-
ferorbythealtitudetowhichwaterwillriseinaproperlyconstructedwell
inaconfinedaquifer.
Precambrian Theoldestgeologictimeperiod,whichoccurredbeforethe
beginningofthePaleozoicEra.ThePrecambrianEraconstitutesabout
90percentofallgeologictime.
Public water supply Watersupplyprovidedtothepublic;definedinSouth
Dakotaashavingatleast15serviceconnectionsorregularlyservingatleast
25individualsdailyforatleast60daysoutoftheyear.
R
Radioactive decay Spontaneousemissionofparticles(alphaorbeta)and
gammaraysfromthenucleusofanunstablenuclide.Theresultingproduct
nucleusmaybestableorunstable,inwhichcasedecaycontinuesuntila
stablenuclideisformed.
Radioactive decay series Aseriesorsuccessionofnuclides, eachofwhich
becomesthenextintheseriesbyradioactivedecay,untilastablenuclideis
formed.
Radioactivity Theemissionofenergeticparticlesand/orradiationduring
radioactivedecay.
Radionuclide Aradioactivenuclide.(Anuclideisaspeciesofatomschar-
acterizedbythenumberofneutronsandprotonsinitsnucleus.)
Recharge Theprocessinvolvedwherebyinfiltrationreachesthesaturated
zone.Alsotheamountofwateradded.
Residence time Ingroundwater,thelengthoftimewaterremainsunder-
groundbeforeitisextractedordischarged.
Return flows Inirrigationwaters,theexcesswaterreturningtoastream
channel.
Runoff Thatpartofprecipitationcontributingtostreamflow.Runoffcan
originateasdirectrunofforbaseflow.
S
Saline water Saltywater.Classifiedbythedissolvedsolidsconcentration
inwater.
Sandstone Asedimentaryrockcomposedofabundantroundedorangular
fragmentsofsandsetinafine-grainedmatrix(siltorclay)andmoreorless
firmlyunitedbyacementingmaterial.
Saturated Theconditioninwhichtheporesofamaterialarefilledwith
water.
Secondary Maximum Contaminant Level (SMCL) Maximumlevelestab-
lishedbytheU.S.EnvironmentalProtectionAgencyforcontaminantsthat
canadverselyaffecttheodororappearanceofwaterandmayresultindis-
continuationofuseofthewater.SMCLsarenonenforceable,generallynon-
health-basedstandardsthatarerelatedtotheaestheticsofwateruse.
Secondary permeability Thepermeabilitydevelopedinarockafterits
deposition,throughsuchprocessesasweatheringandfracturing.
Secondary porosity Theporositydevelopedinarockafteritsdeposition,
throughsuchprocessesasdissolutionorfracturing.
Sedimentary rock Rocksresultingfromtheconsolidationofloosesedi-
mentthathasaccumulatedinlayers.Examplesofsedimentaryrocksare
sandstone,siltstone,limestone,andshale.
Semiconfining unit Unitthatmaytransmitsomewatertoandfromadja-
centaquifers.
Shale Afine-grainedsedimentaryrock,formedbytheconsolidationof
clay,silt,ormud.
Signature Acharacteristicorcombinationofcharacteristicsbywhicha
materialorobjectmaybeidentified.
Sill Atabularigneousintrusionthatparallelsthebeddingofthesurround-
ingsedimentaryormetamorphicrock.
Solution opening Anopeninginarockmaterialresultingfromthedissolu-
tionofcalciumcarbonateinlimestoneorchalk.
Spring Anynaturaldischargeofwaterfromrockorsoilontotheland
surfaceorintoasurface-waterbody.
Stable isotope Anisotopethatdoesnotundergoradioactivedecay.
Stratigraphic column Thevertical(orchronological)sequenceofrock
unitsportrayedinacolumnfromoldest(bottom)toyoungest(top).See
figure15.
Streamflow Theflowofwaterinastreamchannel.Derivedfromallcon-
tributingsources,includingbaseflow,directrunoff,andothersourcessuch
asdiversionsorwelldischarges.
Streamflow depletions Lossofwaterfromsurface-waterresources.Inthe
BlackHillsarea,theprimarystreamflowdepletionsarestreamflowlossesto
outcropsoftheMadisonandMinnelusaaquifers,consumptivewithdrawals,
andreservoirevaporationassociatedwithirrigationoperations.
Streamflow-gaging station Aparticularsiteonastream,canal,lake,reser-
voir,orotherbodyofwaterwheresystematicobservationsofstreamdis-
chargeandotherhydrologicdataareobtained.
Structural feature Afeatureproducedbydeformationordisplacementof
therocks,suchasafoldorfault.
Superfund AprograminitiatedbytheU.S.EnvironmentalProtection
Agencytodefine,study,andaidincleanupactivitiesforlocationsthatare
environmentalhazards.
Surface water WaterontheEarthssurface.
Syncline Afoldinwhichthestratadiptowardtheaxis.Aftererosion,the
youngestbedsareexposedinthecentralcoreofthefold.Seefigure17.
T
Trace element Anelementfoundinonlyminoramountsinwater,gener-
allylessthan1.0milligramperliter.Includesarsenic,copper,iron,lead,
mercury,manganese,selenium,andzinc.
Tracer Asubstance,suchasdye,usedintracingflowpathsordetermining
traveltimes.
Transpiration Processbywhichwaterthatisabsorbedbyplants,usually
throughtheroots,isevaporatedintotheatmospherefromtheplantsurface,
suchasleafpores.
Tributary Astreamfeeding,joining,orflowingintoalargerstreamorlake.
Tritium Aradioactiveisotopeofhydrogen(
3
H)havingtwoneutronsand
oneprotoninthenucleus.
U
Unconfined Saidofgroundwaterthathasawatertable;thewaterisnot
confinedunderpressure.
Unconfined aquifer Anaquiferinwhichthewatertableisexposedtothe
atmospherethroughopeningsintheoverlyingmaterials.
Unconsolidated aquifer Anaquifercomposedofmaterialthatisloosely
arrangedorwhoseparticlesarenotcementedtogether,suchassandsand
gravels.
Unsaturated Theconditioninwhichtheporesofamaterialcontainatleast
someair.
W
Watershed Theareadrainedby(orcontributingwaterto)astream,lake,
orotherbodyofwater;alsodrainagebasin.
Water table Thetopofthewatersurfaceinthesaturatedzoneofanuncon-
finedaquifer.
Water year The12-monthperiod,October1throughSeptember30,thatis
designatedbythecalendaryearinwhichitends.
Y
Yield efficiency Theratioofbasinyieldtoannualprecipitation,which
indicatesthepercentageofannualprecipitationthatisyieldedasstreamflow
(orrecharge).
120 AtlasofWaterResourcesintheBlackHillsArea,SouthDakota