Water Movement in Water Movement in SoilSoil

James L. Anderson, PhDDavid Gustafson

Aziz Amoozegar, PhDDavid Lindbo, PhD

Model Decentralized Wastewater Practitioner Curriculum

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CitationCitationGustafson, D., J. Anderson, A. Amoozegar, and Gustafson, D., J. Anderson, A. Amoozegar, and

D.L. Lindbo. 2005. Water Movement in SoilD.L. Lindbo. 2005. Water Movement in Soil––Power Point Presentation. Power Point Presentation. inin (D.L. Lindbo and (D.L. Lindbo and N. E. Deal eds.) Model Decentralized N. E. Deal eds.) Model Decentralized Wastewater Practitioner Curriculum. National Wastewater Practitioner Curriculum. National Decentralized Water Resources Capacity Decentralized Water Resources Capacity Development Project. North Carolina State Development Project. North Carolina State University, Raleigh, NC. University, Raleigh, NC.

Water movementWater movementWhy is this important?Why is this important?How Systems workHow Systems workFlow patternsFlow patterns

UnsaturatedUnsaturated•• BiomatBiomat

SaturatedSaturated•• Darcy’s LawDarcy’s Law

Flow directionFlow directionLateral movementLateral movementVertical movementVertical movement

Soil impactsSoil impacts

Why is it important?Why is it important?

Keys to where it goesKeys to where it goesKeys to how it movesKeys to how it moves

Unsaturated Unsaturated SaturatedSaturated

Identifies potential problemsIdentifies potential problems

Hydrologic CycleHydrologic Cycle

ET

Regional water table

Well

Unsaturated flow

Restrictive layer

Saturated flow

Precipitation

Hydrology ComponentsHydrology ComponentsPrecipitationPrecipitationEvapotranspirationEvapotranspirationInfiltrationInfiltration

Surface flow (runSurface flow (run--off)off)Subsurface flow Subsurface flow

•• lateral flow, interflow, shallow groundwater flowlateral flow, interflow, shallow groundwater flowVertical seepage Vertical seepage

•• deep percolation, groundwater rechargedeep percolation, groundwater recharge

Unsaturated Zones"Unsaturated Zones"Capillary fringeCapillary fringe

Water tableWater tableSaturated Saturated

RAINFALL(48-54 Inches/Year)POTENTIAL ET(36-40 Inches/Year)

SURFACE RUNOFF SURFACEWATERINFILTRATION

WATER TABLE

GROUND WATER FLOW

CONFINED AQUIFERAQUIFER RECHARGE

(1/2 TO 2 Inch/Year)

CONFINED LAYER AQUTARD

CROPLAND FORESTLAND

Direction and rate of ground-water movement.

Recharge area Dischargearea

Water table

Days

Decades

Years

Centuries

MillenniaFlow lines

GR

OU

ND

WA

TER

SYST

EM

Impermeable Layer

Ground WaterSlow Moving

Lateral FlowDeep Percolation

Slowly Permeable layer

Stream

Water Table

Ground WaterMounding

Vadose Zone

Septic System

WastewaterInput Runoff

Infiltration

Precipitation

Evapotranspiration

Well

Impermeable Layer

Ground Water

Slow Moving

Lateral Flow

Deep Percolation

Slowly Permeable layer

Stream

Water Table

Ground WaterMounding

Vadose Zone

Septic System

WastewaterInput Runoff

Infiltration

Precipitation

Evapotranspiration

Well

Water thru the Water thru the Soil Treatment AreaSoil Treatment Area

What is waterWhat is waterWhat is sewageWhat is sewageOnsite systemsOnsite systems

System geometrySystem geometryFlow patternsFlow patternsIdealized system Idealized system

WaterWater-- What is it ?What is it ?

Water is a Water is a didi--polar, “charged” moleculepolar, “charged” moleculeThe charges create bondsThe charges create bondsThese bonds create adhesive and These bonds create adhesive and cohesive forces among molecules and cohesive forces among molecules and surroundingssurroundings

105 o+

-Oxygen atom

Hydrogen atom

H-bond

++ --

--

++

++

--

BONDSAND WATER DIPOLES

SewageSewageWhat is it?What is it?

WaterWaterBacteria foodBacteria food

•• BODBOD•• NutrientsNutrients

TSSTSS•• SolidsSolids

PathogensPathogensSolutes Solutes Others

How much is How much is Produced?Produced?

120120--150 gpd 150 gpd per bedroom*per bedroom*5050--75 gpd 75 gpd per personper person

Where is it Produced?Where is it Produced?Bathroom [60%]Bathroom [60%]

•• Toilet 40%Toilet 40%•• Bathing 20%Bathing 20%

Kitchen [20%]Kitchen [20%]Laundry [20%]

Others

Laundry [20%]

Flow to the SystemFlow to the SystemAmountsAmounts

DailyDaily•• DesignDesign

MonthlyMonthly•• AverageAverage•• 6060--70% of Design70% of Design

AnnuallyAnnually•• 5050--60% of Design

Variation in flowVariation in flowDaily totalsDaily totalsComes in SHOTSComes in SHOTS

Waste strengthWaste strengthBiomat developmentBiomat development

60% of Design

System definitionSystem definitionUse

Pretreatment

Final treatment & dispersalSoil treatment area [SAT]

System geometrySystem geometry

Infiltrative surface

Infiltrative surface

System GeometrySystem Geometry

Influences:Influences:Longer areaLonger area

Smaller Smaller loadingloading

Shorter lengthShorter lengthGreater Greater down slope impactdown slope impact

Long Short

Contour LinesDrainage

Direction of Ground water Flow

Drainfield

Contour LinesDrainage

Direction of Ground water Flow

Drainfield

DRAINFIELD

Contour LinesDrainage

Direction of Ground water Flow

Drainage

Direction of Ground water Flow

Drai

nfie

ld

Flow pattern in subFlow pattern in sub--surface surface trenchtrench

Mounded Groundwater

Unsaturated flow

Saturated Conditions

Unsaturated flow

Saturated flow

Unsaturated vs. Saturated Unsaturated vs. Saturated flowflow

UnsaturatedUnsaturatedPores: Air availablePores: Air available

Slower:Slower:Next to particlesNext to particles

AerobicAerobic

SaturatedSaturatedPores: Volume filled Pores: Volume filled with waterwith waterFaster:Faster:In large poresIn large poresNon aerobicNon aerobic

Saturated ConditionsSaturated Conditions

Pores are filled with

water

Unsaturated ConditionsUnsaturated Conditions

Pores are filled with air & water along the soil

particles

Least Permeable

Slowly Permeable Layer

Ground Water Mounding andFormation of a Saturated Zone

HYDROLOGY OF A SEPTIC SYSTEM

Infiltration fromTrenches

Vertical Movementthrough the Unsaturated Zone

Lateral Movementin the Saturated Zone

Flow pattern in subFlow pattern in sub--surface surface trenchtrench

Least Permeable

Slowly Permeable Layer

Ground Water Mounding andFormation of a Saturated Zone

Soil termsSoil termsTopsoilTopsoil

SubsoilSubsoil

Parent MaterialParent Material

Soil HorizonSoil HorizonSoil ProfileSoil Profile

TextureTextureStructure Structure ConsistenceConsistence

MineralogyMineralogyPore sizePore sizeSoil colorSoil color

10/2/200310/2/2003 Soil and Site. Lindbo et al. DRAFTSoil and Site. Lindbo et al. DRAFT 55

What is unsaturated flowWhat is unsaturated flowMatricMatric potentialpotential•• TensionTension•• SuckicitySuckicity factorfactor

Capillary attractionCapillary attraction•• AdhesionAdhesion•• CohesionCohesion

How does this happenHow does this happenVertical movementVertical movementLateral movementLateral movement

MatricMatric potentialpotential

TensionTensionSuctionSuctionHighHigh--toto--lowlowPotentialPotential

ImpactsImpacts

Pore size & unsaturated flowPore size & unsaturated flowLarge pores Large pores water will water will movedmovedpredominantly predominantly by gravityby gravitySmall poresSmall poreswater will move water will move in all directions in all directions better & further

Large Pores

Small Pores

better & further

Capillary AttractionCapillary Attraction

Adhesion Adhesion –– attraction between dissimilar attraction between dissimilar materialsmaterialsCohesion Cohesion ––attraction between similar attraction between similar materialsmaterials

Capillary FringeCapillary Fringe

Unsaturated zone above the water tableUnsaturated zone above the water tableWater held in this zone by tension (matric Water held in this zone by tension (matric potential, adhesive and cohesive forces)potential, adhesive and cohesive forces)This zone is generally not important to us, This zone is generally not important to us, and is difficult to measureand is difficult to measure

How does unsaturated flow in How does unsaturated flow in the soil treatment area happen?the soil treatment area happen?Unsaturated flow is the keyUnsaturated flow is the keyBiomatBiomat formationformation

BODBODOxygen relationshipOxygen relationshipTSSTSS

Pressure distributionPressure distribution

Flow pattern in a gravity Flow pattern in a gravity trenchtrench

Biomat Growth (t = 0 = start )Biomat Growth (t = 0 = start )

Flow pattern in a gravity Flow pattern in a gravity trench trench

Biomat Growth (t = growth)Biomat Growth (t = growth)

Flow pattern in a gravity Flow pattern in a gravity trench trench

Biomat Growth (t=mature)Biomat Growth (t=mature)

Flow pattern with Flow pattern with Pressure DistributionPressure Distribution

Pressure distributionPressure distribution

BiomatBiomat & sidewalls & sidewalls BiomatBiomat develops along the bottom and then around the develops along the bottom and then around the trenchtrenchPondingPonding levels use sidewallslevels use sidewallsExcessiveExcessive pondingponding depths may create saturated flowdepths may create saturated flowNarrower allows more surface areaNarrower allows more surface areaNarrower allows better O2 transferNarrower allows better O2 transfer

Soil treatment area sizingSoil treatment area sizing

Sewage effluent characteristics Sewage effluent characteristics Soil propertiesSoil properties

TextureTextureStructureStructureConsistence/ MineralogyConsistence/ Mineralogy

TheThe biomatbiomatHydraulic conductivity?Hydraulic conductivity?

Long Term Acceptance Rate Long Term Acceptance Rate LTARLTAR

The biomat controls the ability of the soil to The biomat controls the ability of the soil to accept effluent: this is the LTARaccept effluent: this is the LTARGenerally State codes dictate LTARsGenerally State codes dictate LTARsCONFUSION CONFUSION

On the relationship of LTAR & KsatOn the relationship of LTAR & Ksat•• Hold on we will get thereHold on we will get there

on the relationships between texture/structure on the relationships between texture/structure Constance and the Perc rateConstance and the Perc rate

LTARLTAR

Texture/ StructureTexture/ StructureOther testsOther tests--Saturated conductivitySaturated conductivityPercolation ratesPercolation rates

Soil Characteristics and Soil Sizing Factor (> 3' separation)Percolation Rate Soil Sizing Factorminutes per inch Soil Texture square feet/ gallon(mpi) per day(sqft/ gpd)

faster than 0.1* Coarse sand 0.830.1 to 5 Medium sand 0.83

Loamy sand0.1 to 5** Fine sand 1.676 to 15 Sand y loam 1.2716 to 30 Loam 1.6731 to 45 Silt loam 2.00

Silt46 to 60 Clay loam 2.20

Sandy clay Silty clay

over 61 to 120*** Clay 4.20 Sandy clay Silty clay

slower than 120****

*Use systems for rap id ly permeable soils:pressure d istribution or serial d istribu tion withno trench >25% of the total system.**Soil having 50% or more fine sand p lus very fine sand .***A mound must be used .****An other or performance system must be used

Influencing theInfluencing the Biomat Biomat GoodGood

DesignDesignLoadingLoading

HydraulicHydraulicOrganicOrganic

Resting Resting Depth of coverDepth of cover

Oxygen availability

BadBadPeroxidePeroxideAcidAcid

Oxygen availability

Saturated soils contain free Saturated soils contain free waterwater

Free water is not under a suction, and flows in response to gravity.

What is SaturationWhat is Saturation

A horizon is saturated when the soil water A horizon is saturated when the soil water pressure is zero or positivepressure is zero or positiveThis water has a pressure greater than This water has a pressure greater than atmospheric pressure, and pushes air out atmospheric pressure, and pushes air out of holes in the groundof holes in the ground

In layman's termsIn layman's termsWater flows from the soil into a holeWater flows from the soil into a hole

Auger hole in soil is filledwith air just after digging

Water tableWater table Air

Auger hole in soil is filledwith air just after digging

Water tableWater table

Air14 psi

Water tableWater table

Water pushes air out of holeWater pushes air out of hole

Air

Water below water table has pressure greater that air pressure

Eventually hole fills with water to the level of the water table where

water pressure=air pressure

Air

Saturated soilSaturated soil(water pressure(water pressure>air pressure)>air pressure)

Unsaturated soilUnsaturated soil(water pressure(water pressure< air pressure)< air pressure)

Finding saturation in Finding saturation in soilssoils

Identifying saturation by looking for free Identifying saturation by looking for free water is easy to do in the field with water is easy to do in the field with pits or auger holes.pits or auger holes.

Percolation

GroundwaterWell

Evaporation

Gradient

Onsite SystemSaturated flowSaturated flow

GravityGravitySlopeSlope•• Hydraulic gradientHydraulic gradient

RestrictionsRestrictions•• SoilSoil

Darcy’s lawDarcy’s lawFlow (Q)/At = Ksat x dH/dL

Saturated FlowSaturated FlowKsatKsatSlopeSlopeApplicationsApplications

14

7

0.7

0.07

<1.4 x 10-5

1 x 10-2

5 x 10-3

5 x 10-4

5 x 10-5

<1 x 10-8

Typical of beach sand.

Typical of very sandy soil,too rapid to effectivelytreat pollutants in wastewater.

Typical of moderatelypermeable soils.

Typical of fine-textured,compacted or poorlystructured soils.

Extremely slow; typicalof compacted clay.Ksat of 10-5 may be requiredwhere nearly impermeablematerial is needed.

Ksat Ksat Comments(cm/s) (in/h)

Some approximate values ofSaturated Hydraulic Conductivity & comments

CalculatingCalculating KKsatsat

Double ring infiltrometerIn lab processIn lab processDouble ring Double ring infiltrometerinfiltrometerAmoozemeter readingAmoozemeter readingPerc tests?Perc tests?

Elevation 102

Elevation 98

Sand Ksat = 10 in/hr

Q (1 sqft) = Slope x Ksat x Area= (102’- 98’)/ 40’ x 10 in/hr x 1 sqft= 4’/40’ x 10 in/hr x 1sqft x ft/12”= .083 cuft/hr x 7.5 gal/cuft x 24 hr/day= 15 gpd per sqft

40’ apart

Calculation of QCalculation of QA = 1 ftA = 1 ft22

Ksat = 10 in/hrKsat = 10 in/hrConvert Ksat to ft/hrConvert Ksat to ft/hr10 in/hr X 1ft/12in 10 in/hr X 1ft/12in = 0.83 ft/hr= 0.83 ft/hrGradient = Gradient = dHdH//dL dL = (102’= (102’--98’)/40’ = 4’/40’98’)/40’ = 4’/40’= 0.1= 0.1

Calculation of QCalculation of Q

Q = K x Q = K x dHdH//dLdL x Ax A= 0.83 ft/hr x 0.1 x 1 ft= 0.83 ft/hr x 0.1 x 1 ft22

Q = 0.083 ftQ = 0.083 ft33/hr/hrCalculate GPD Calculate GPD 7.5 gal/ft7.5 gal/ft33 x 0.083 ftx 0.083 ft33/hr x 24 hr/d/hr x 24 hr/d7.5 gal/7.5 gal/ftft33 x 0.083 x 0.083 ftft33//hrhr x 24 x 24 hrhr/d/dQ = 15 gal/day Q = 15 gal/day

Linear Loading RateLateral movementLateral movement

Overall system issueOverall system issueControlled by “smallest window”Controlled by “smallest window”Related to:Related to:

Over all lengthOver all lengthOver all [Compounding] flowOver all [Compounding] flow

Slope ConsiderationsSlope Considerations

Horizontal Flow

1

2 3

BoumaBouma StudyStudy

BiomatBiomat = LTAR= LTARBUT Be CarefulBUT Be CarefulRelationship toRelationship to biomatbiomat {crusting} rates{crusting} ratesLimits are different for sand:clayLimits are different for sand:clay

Where the two flows meetWhere the two flows meetTrenchesTrenches

BiomatBiomat: Flow control: Flow controlUnsaturated zoneUnsaturated zone

SeparationSeparationTreatmentTreatment

MoundingMoundingRaising of saturated levelsRaising of saturated levels

Ground waterGround waterSaturated flowSaturated flow

Putting it togetherPutting it together

NOT TO SCALEUnsaturated Zone

Water Table or an Impermeable layer

DistributionPipe

Air Space

SaturatedZone

Soil Surface

Wastewater

BackfilledSoil

Water FlowPath

Gravel

Groundwater MoundingGroundwater MoundingWhat is itWhat is it

The raising of the saturated zone above a The raising of the saturated zone above a restriction orrestriction or watertablewatertable

Calculation?Calculation?Simple (Darcy’s law)Simple (Darcy’s law)Complex (e.g., Complex (e.g., ModflowModflow))

Tough to applyTough to applyThe closer you are to the water the more The closer you are to the water the more important mounding becomesimportant mounding becomes

Summary of Influences on Summary of Influences on System performanceSystem performance

Saturated conditionsSaturated conditionsLack of treatmentLack of treatmentPreferential flowPreferential flow

Too high a LLRToo high a LLRDown slope surfacing [blow out]Down slope surfacing [blow out]

ExcessiveExcessive biomatbiomat growthgrowthOrganic loadingOrganic loading

Construction soil damageConstruction soil damage

ConclusionsConclusions

Flow above/through the Biomat is Flow above/through the Biomat is saturatedsaturatedFlow into the soil from the biomat is Flow into the soil from the biomat is unsaturatedunsaturatedBiomat reduces/controls the flow from a Biomat reduces/controls the flow from a system system Flow is generally verticalFlow is generally verticalMore research is necessaryMore research is necessary

Hydrologic cycleHydrologic cycle

Impermeable Layer

Ground Water

Slow Moving

Lateral Flow

Deep Percolation

Slowly Permeable layerStream

Water Table

Ground WaterMounding

Vadose Zone

Septic System

WastewaterInput

Runoff

Infiltration

Precipitation

Evapotranspiration

Well

HomeworkHomework

QuestionsQuestionsTrench example Trench example

Calculate downward movementCalculate downward movementLateral movementLateral movementBiomatBiomat impactsimpacts

Darcy’s LawDarcy’s Law