Effluent Conveyance

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Effluent ConveyanceEffluent Conveyance

Paul Trotta, P.E., Ph.D.Paul Trotta, P.E., Ph.D.

Justin Ramsey, P.E.Justin Ramsey, P.E.

Chad CooperChad Cooper

University Curriculum DevelopmentUniversity Curriculum Development

for Decentralized Wastewaterfor Decentralized Wastewater

ManagementManagement


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NDWRCDP DisclaimerNDWRCDP DisclaimerThis work was supported by the National Decentralized WaterThis work was supported by the National Decentralized Water

Resources Capacity Development Project (NDWRCDP) withResources Capacity Development Project (NDWRCDP) withfunding provided by the U.S. Environmental Protection Agencyfunding provided by the U.S. Environmental Protection Agency

through a Cooperative Agreement (EPA No. CR827881through a Cooperative Agreement (EPA No. CR827881--0101--0)0)

with Washington University in St. Louis. These materials havewith Washington University in St. Louis. These materials havenot been reviewed by the U.S. Environmental Protectionnot been reviewed by the U.S. Environmental Protection

Agency. These materials have been reviewed byAgency. These materials have been reviewed by

representatives of the NDWRCDP. The contentsrepresentatives of the NDWRCDP. The contentsof these materials do not necessarily reflect the views andof these materials do not necessarily reflect the views and

policies of the NDWRCDP, Washington University, or the U.S.policies of the NDWRCDP, Washington University, or the U.S.

Environmental Protection Agency, nor does the mention of tradeEnvironmental Protection Agency, nor does the mention of trade

names or commercial products constitute their endorsement ornames or commercial products constitute their endorsement orrecommendation for use.recommendation for use.


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CIDWT/University DisclaimerCIDWT/University Disclaimer

These materials are the collective effort of individuals fromThese materials are the collective effort of individuals fromacademic, regulatory, and private sectors of theacademic, regulatory, and private sectors of the

onsite/decentralized wastewater industry. These materials haveonsite/decentralized wastewater industry. These materials havebeen peerbeen peer--reviewed and represent the current state ofreviewed and represent the current state of

knowledge/science in this field. They were developed through aknowledge/science in this field. They were developed through aseries of writing and review meetings with the goal of formulatiseries of writing and review meetings with the goal of formulatingnga consensus on the materials presented. These materials do nota consensus on the materials presented. These materials do not

necessarily reflect the views and policies of University ofnecessarily reflect the views and policies of University ofArkansas, and/or the Consortium of Institutes for DecentralizedArkansas, and/or the Consortium of Institutes for Decentralized

Wastewater Treatment (CIDWT). The mention of trade names orWastewater Treatment (CIDWT). The mention of trade names orcommercial products does not constitute an endorsement orcommercial products does not constitute an endorsement or

recommendation for use from these individuals or entities, norrecommendation for use from these individuals or entities, nordoes it constitute criticism for similar ones not mentioned.does it constitute criticism for similar ones not mentioned.


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CitationCitation

Trotta, P.D., and J.O. Ramsey. 2005. EffluentTrotta, P.D., and J.O. Ramsey. 2005. Effluent

ConveyanceConveyance -- PowerPoint Presentation.PowerPoint Presentation. inin (M.A.(M.A.Gross and N.E. Deal, eds.) UniversityGross and N.E. Deal, eds.) University

Curriculum Development for DecentralizedCurriculum Development for Decentralized

Wastewater Management. NationalWastewater Management. NationalDecentralized Water Resources CapacityDecentralized Water Resources Capacity

Development Project. University of Arkansas,Development Project. University of Arkansas,

Fayetteville, AR.Fayetteville, AR.


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Conveyance OverviewConveyance Overview


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Section Objectives:Section Objectives:

Provide introduction to Conventional SewerProvide introduction to Conventional SewerSystemsSystems

Introduce design limitations ofIntroduce design limitations ofConventional Sewer SystemsConventional Sewer Systems

Discuss Vacuum SewersDiscuss Vacuum Sewers Discuss Grinder PumpsDiscuss Grinder Pumps

Compare and contrast Pressure andCompare and contrast Pressure andGravity Flow Effluent Sewer SystemsGravity Flow Effluent Sewer Systems


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Overview of Onsite andOverview of Onsite and

DecentralizedDecentralizedAll aspects of Onsite and Decentralized wastewaterAll aspects of Onsite and Decentralized wastewater

treatment and dispersal involve the movement oftreatment and dispersal involve the movement ofeffluents of varying qualities. This includes transferseffluents of varying qualities. This includes transfersfrom:from:

Individual homes to cluster or community collectionIndividual homes to cluster or community collectionsystems.systems.

Individual homes to onsite treatment facilities.Individual homes to onsite treatment facilities.

Onsite treatment facilities to onsite disposal facilitiesOnsite treatment facilities to onsite disposal facilities


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Design Constraints of LargeDesign Constraints of Large

Scale SystemsScale SystemsLargeLarge--scale municipal gravity flow sewer systems arescale municipal gravity flow sewer systems are

generally designed with the following constraints ingenerally designed with the following constraints inmindmind::

Flow velocitiesFlow velocities

Average, low, or high flowsAverage, low, or high flows Inverted siphonsInverted siphons

Minimum sewer diametersMinimum sewer diameters

Minimum and maximum sewer depthsMinimum and maximum sewer depths

Access facilities (manAccess facilities (man--holes)holes)Minimum horizontalMinimum horizontaland vertical separationsand vertical separations


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Additional Design Issues ofAdditional Design Issues of

Large Scale SystemsLarge Scale SystemsLargeLarge--scale municipal gravity flow sewerscale municipal gravity flow sewer

systems are generally designed with thesystems are generally designed with thefollowing constraints in mindfollowing constraints in mind::

Lift StationsLift Stations CleanoutsCleanouts

Air Relief ValvesAir Relief Valves


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Decentralized Sewer SystemsDecentralized Sewer Systems

The onsite counterparts or alternatives toThe onsite counterparts or alternatives to

municipal sewer system include:municipal sewer system include: Septic Tank Effluent PumpSeptic Tank Effluent Pump

EnhancedEnhanced--Flow STEP systemsFlow STEP systems

Low Pressure Pipe/Low Pressure DistributionLow Pressure Pipe/Low Pressure Distribution

Septic Tank Effluent GravitySeptic Tank Effluent Gravity

Grinder PumpGrinder Pump

Vacuum SystemsVacuum Systems


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STEP and GP SystemsSTEP and GP Systems

Compared below are the basic features of STEP and GPCompared below are the basic features of STEP and GPsystems.systems.


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Pressure Flow vs. Gravity FlowPressure Flow vs. Gravity Flow

Pressure Flow hydraulics most often makesPressure Flow hydraulics most often makes

use of a pump to provide the energyuse of a pump to provide the energynecessary to overcome friction, providenecessary to overcome friction, provide

velocity, and/or change elevation. Gravityvelocity, and/or change elevation. Gravity

Flow hydraulics always make use of gravityFlow hydraulics always make use of gravity

as the source of force necessary to overcomeas the source of force necessary to overcome

friction and provide velocity. There are,friction and provide velocity. There are,however, situations in which the distinctionhowever, situations in which the distinction

can be blurred.can be blurred.


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Wastewater DesignWastewater DesignFlowsFlows


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Cover community sewer systems DesignCover community sewer systems DesignFlows and Peak FactorsFlows and Peak Factors

Introduce STEP and STEG Design FlowsIntroduce STEP and STEG Design Flows Design process for STEP Design Flow andDesign process for STEP Design Flow and

Peak Flow EstimationPeak Flow Estimation


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Community Sewer System DesignCommunity Sewer System Design

Flows and Peaking FactorsFlows and Peaking FactorsThe design of all wastewater collection systems, weatherThe design of all wastewater collection systems, weather

they are centralized, decentralized or individual onsitethey are centralized, decentralized or individual onsite

systems, are affected by the daily variation of the wastewatersystems, are affected by the daily variation of the wastewater

or treated effluent that they are designed to carry.or treated effluent that they are designed to carry.

D i Fl f STEP & STEGD i Fl f STEP & STEG


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Design Flows for STEP & STEGDesign Flows for STEP & STEG

SystemsSystemsShown is a typical diurnal flow pattern for a single residenceShown is a typical diurnal flow pattern for a single residencewith gravity flow discharges, the average per housewith gravity flow discharges, the average per house

discharge from five homes and the average per housedischarge from five homes and the average per housedischarge from 61 homesdischarge from 61 homes


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Flow Modulation from MultipleFlow Modulation from Multiple

Contributors to a STEP systemContributors to a STEP systemThere are several additional hydraulic featuresThere are several additional hydraulic features

of the pump systems used within STEPof the pump systems used within STEPsystems that can either increase or decreasesystems that can either increase or decreasethe peak flows that reach it. The factors to bethe peak flows that reach it. The factors to be

considered include:considered include:

The discharge characteristics of the pumpThe discharge characteristics of the pump

chosenchosen The tank dimensionsThe tank dimensions

The control floats set pointsThe control floats set points

STEP Di l Fl St fSTEP Di l Fl St f


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STEP Diurnal Flow Stream from aSTEP Diurnal Flow Stream from a

single homesingle homeShown is a simulated typical STEP diurnal flow pattern for aShown is a simulated typical STEP diurnal flow pattern for a

single residencesingle residence


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Design Flow and Peak FlowDesign Flow and Peak Flow

Estimation for STEP SystemsEstimation for STEP SystemsIt should be apparent that joining theIt should be apparent that joining the

discharges from several homes anddischarges from several homes anddeveloping a reasonable design flowdeveloping a reasonable design flow

presents a challenging problem. Twopresents a challenging problem. Twofundamental approaches to developing afundamental approaches to developing a

design flow have been identified:design flow have been identified:

Probability MethodProbability Method

Rational MethodRational Method


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Pressure DistributionPressure Distribution

S ti Obj tiS ti Obj ti


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Understand and calculate Friction LossesUnderstand and calculate Friction Losses Calculate Minor losses with EquivalentCalculate Minor losses with Equivalent

Lengths and Loss CoefficientsLengths and Loss Coefficients Compute the total head required to pumpCompute the total head required to pump

water from a tank to a disposal field for awater from a tank to a disposal field for a

given flow rate.given flow rate.

Interpret pump performance curvesInterpret pump performance curves

Compare pump performance curves toCompare pump performance curves to

system requirements and select thesystem requirements and select the

appropriate pump for a system.appropriate pump for a system.

T f P Di t ib tiT f P Di t ib ti


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Types of Pressure DistributionTypes of Pressure Distribution

Pressure delivery to a distribution box forPressure delivery to a distribution box forsubsequent gravity flow to individualsubsequent gravity flow to individual

disposal trenchesdisposal trenches

Pressure delivery to the laterals within thePressure delivery to the laterals within theindividual disposal trenches, which is oftenindividual disposal trenches, which is often

referred to as Low Pressure Pipe or LPP.referred to as Low Pressure Pipe or LPP.

Pressure delivery to the common communityPressure delivery to the common community

pressure line of a STEP systempressure line of a STEP system

Pressure delivery to the common communityPressure delivery to the common communitygravity line of a STEG systemgravity line of a STEG system

F i ti LFriction Losses


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Friction Losses are generated as the flow slidesFriction Losses are generated as the flow slidesalong the pipe and bumps into obstacles (turns,along the pipe and bumps into obstacles (turns,

bends, expansions and contractions) and thebends, expansions and contractions) and the

energy that is used up in the water as it slidesenergy that is used up in the water as it slides

around itself in turbulence.

Friction LossesFriction Losses

around itself in turbulence.

Generally losses are related to these variables:Generally losses are related to these variables:

Pipe LengthPipe Length Water VelocityWater Velocity

Pipe DiameterPipe Diameter Water ViscosityWater Viscosity

Pipe MaterialPipe Material


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Head Loss EquationsHead Loss Equations

Hl = f * L/D * V2/2gDarcy Weisbach

Hazen Williams

Head loss/100 ft of pipe = 100 * (Q/(0.285 * C * D2.63))

1.85

Q = flow in gallons per minuteD = pipe diameter in inches

C = smoothness coefficient

H d LH d L


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Head LossHead Loss

TableTable

If it is desired to use theHazen Williams Formuladirectly, use a C valueof 140 (for plastic pipe).

If it is desired to use theDarcy Wesibach H

l

= f*(L/D)*V2/(2g) be sureto use the actual insidepipe diameter and afriction factor f equalto 0.021


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Minor LossesMinor Losses

Impacts of Minor Losses: losses resultingImpacts of Minor Losses: losses resultingfrom changes in direction, changes infrom changes in direction, changes in

flow area and changes in friction due toflow area and changes in friction due to

fittings.fittings.

Equivalent lengths or loss coefficientsEquivalent lengths or loss coefficients

are used to calculate minor losses.are used to calculate minor losses.

E i l t L th d LEquivalent Length and Loss


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Equivalent Length and LossEquivalent Length and Loss

CoefficientsCoefficientsEquivalent lengths (LEquivalent lengths (Lee) assume each fitting or flow variation) assume each fitting or flow variation

produces a head loss that is equal to the losses caused by anproduces a head loss that is equal to the losses caused by anequivalent length of the pipe.equivalent length of the pipe.

For example, a 2For example, a 2--inch gate valve may produce the same amountinch gate valve may produce the same amount

of friction as 1.5of friction as 1.5--feet of 2feet of 2--inch pipe. Therefore the equivalentinch pipe. Therefore the equivalent

length of the gate valve is 1.5length of the gate valve is 1.5--feet.feet.

Each fitting has a loss coefficient, K, associated with it. ThiEach fitting has a loss coefficient, K, associated with it. Thiss

coefficient is multiplied by the kinetic energy to get the assoccoefficient is multiplied by the kinetic energy to get the associatediated

lossloss

Head Loss:Head Loss:


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Head Loss:Head Loss:Continuous versus PerforatedContinuous versus Perforated

Hl multiple orifices along a pipe = 1/3 * Hl total pipe carrying the total flow

Pump & Pipe SystemPump & Pipe System


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Pump & Pipe SystemPump & Pipe SystemA simple diagram of a sample Pump and Pipe SystemA simple diagram of a sample Pump and Pipe System

System Curve ComponentsSystem Curve Components


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System Curve ComponentsSystem Curve ComponentsThe system curve is defined as the total of the static lift (theThe system curve is defined as the total of the static lift (the

change in elevation) plus the friction loss in the pipingchange in elevation) plus the friction loss in the piping

system.system.

Hydraulic MachineHydraulic Machine


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Hydraulic Machineyd au c ac eFor each pound of water lifted one foot, one footFor each pound of water lifted one foot, one foot--pound ofpound of

work is done. If 550 footwork is done. If 550 foot--pounds of work are done perpounds of work are done persecond we call that 1 HP {0.746 kW}.second we call that 1 HP {0.746 kW}.

Ideal versus Actual Pump CurveIdeal versus Actual Pump Curve


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Ideal versus Actual Pump CurveIdeal versus Actual Pump CurvePumps have efficiencies somewhat less than 100% andPumps have efficiencies somewhat less than 100% and

exhibit different efficiencies at different flow rates. Thisexhibit different efficiencies at different flow rates. Thisresults in the typical pump curve departing more and moreresults in the typical pump curve departing more and more

from the ideal curve as the flow departs more and more fromfrom the ideal curve as the flow departs more and more from

its optimum design point.its optimum design point.

Family Of Pump CurvesFamily Of Pump Curves


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Family Of Pump CurvesFamily Of Pump CurvesMultiple pump curves from a manufacturer are needed priorMultiple pump curves from a manufacturer are needed prior

to selecting a pump best suited for a design.to selecting a pump best suited for a design.

System Curve & Pump CurveSystem Curve & Pump Curve


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System Curve & Pump CurveSystem Curve & Pump CurveIllustrated is a system curve superimposed upon a series ofIllustrated is a system curve superimposed upon a series of

pump curves that will determine which operating point ispump curves that will determine which operating point isused for a design.used for a design.

Determining Flows Along The LineDetermining Flows Along The Line


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Determining Flows Along The LineDetermining Flows Along The Line

The first step in the design of a community STEP system isThe first step in the design of a community STEP system isthe application of pump hydraulic considerations to thethe application of pump hydraulic considerations to the

common line serving the entire community.common line serving the entire community.

Establishing the Hydraulic GradeEstablishing the Hydraulic Grade


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g yg yLineLine

The design starts with the required elevation and exitThe design starts with the required elevation and exitpressure or head and adds the head losses in each sectionpressure or head and adds the head losses in each section

of pipe based upon the computed design flow for that sectionof pipe based upon the computed design flow for that section

of pipeof pipe

From Septic Tank To Common LineFrom Septic Tank To Common Line


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From Septic Tank To Common LineFrom Septic Tank To Common Line

The second step inThe second step in

the design of a STEPthe design of a STEPsystem is thesystem is the

application of pumpapplication of pump

hydraulichydraulicconsiderations to theconsiderations to the

pressure line from thepressure line from the

individual pump to theindividual pump to thecommon transportcommon transport

system.system.

From Septic Tank To DispersalFrom Septic Tank To Dispersal


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p pp pSystemSystem

One of the more common applications of pump hydraulics inOne of the more common applications of pump hydraulics inthe onsite/decentralized arena is the use of pumps to deliverthe onsite/decentralized arena is the use of pumps to deliver

effluent to a dispersal field.effluent to a dispersal field.


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Gravity Conveyance inGravity Conveyance inOnsite & DecentralizedOnsite & Decentralized



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Section Objectives:Sect o Object es

Understand the basics of gravity flow andUnderstand the basics of gravity flow andits uses in Onsite designits uses in Onsite design

Understand and be able to use ManningsUnderstand and be able to use Manningsequation in Onsite designequation in Onsite design

Become familiar with the basics in GravityBecome familiar with the basics in Gravity

Sewer designSewer design

Understand some basic designs andUnderstand some basic designs and

examples for wastewater distributionexamples for wastewater distribution

Overview of Gravity Flow inOverview of Gravity Flow in


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Overview of Gravity Flow inOverview of Gravity Flow in

Individual Onsite SystemsIndividual Onsite SystemsThe primary system components of a OnsiteThe primary system components of a Onsite

Gravity Flow system are as follows:Gravity Flow system are as follows: ConveyanceConveyance

TreatmentTreatment DistributionDistribution

DispersalDispersal

Gravity Collection and ConveyanceGravity Collection and Conveyance


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Gravity Collection and ConveyanceG a ty Co ect o a d Co eya ce

in Decentralized Systemsin Decentralized SystemsDecentralizes systems tend to serve smaller communities orDecentralizes systems tend to serve smaller communities or

groups of homes and/or businesses.groups of homes and/or businesses.

STEG/VGS Vs. ConventionalSTEG/VGS Vs. Conventional


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STEG/VGS Vs. ConventionalS G/ GS s Co e t o a

Sewage Collection SystemsSewage Collection SystemsSTEG/VGS sewer systems, while still relying uponSTEG/VGS sewer systems, while still relying upon

gravity to move the effluent along are different ingravity to move the effluent along are different in

several significant ways from the moreseveral significant ways from the more

conventional municipal sewer system.conventional municipal sewer system.

Shallow DepthShallow Depth DiameterDiameter

Inverted SiphonsInverted Siphons

Lack of SolidsLack of Solids

VelocitiesVelocities

ScourScour

STEG/VGS V STEP S tSTEG/VGS V STEP S t


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STEG/VGS Vs. STEP SystemsSTEG/VGS Vs. STEP Systems

STEG/VGS systems may be a more costSTEG/VGS systems may be a more cost

effective solution to effluent transfer ineffective solution to effluent transfer inareas where a predominant downhill pathareas where a predominant downhill pathcan be developed. STEG/VGS systemscan be developed. STEG/VGS systems

differ from STEP systems in the followingdiffer from STEP systems in the followingways:ways:

PumpsPumps

GradesGrades

DiameterDiameter

Flow EqualizationFlow Equalization

Gravity Conveyance Hydraulics InGravity Conveyance Hydraulics InO i & D li d


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Onsite & DecentralizedOnsite & Decentralized

As the sewer pipeAs the sewer pipes grade and elevation follow the naturals grade and elevation follow the natural

contours there are sections of the pipe which flow full undercontours there are sections of the pipe which flow full under

slight hydrostatic pressure and there are areas which flowslight hydrostatic pressure and there are areas which flowwith a free water surface as open channels.with a free water surface as open channels.

Important hydraulic considerationsImportant hydraulic considerations


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p yp y

for gravity flowfor gravity flowIn gravity sewer design there are four majorIn gravity sewer design there are four major

design factors to be considered:design factors to be considered: SlopeSlope

DiameterDiameter RoughnessRoughness

Velocity {Min/Max}Velocity {Min/Max}


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Flow Depth versus PipeFlow Depth versus Pipe


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p pp p

Diameter.Diameter. The hydraulic radius isThe hydraulic radius is

divided by the wetteddivided by the wettedperimeter.perimeter.

Determining the hydraulicDetermining the hydraulicradius for circular pipesradius for circular pipesflowing partially full canflowing partially full canbe extremely difficult.be extremely difficult.

This figure can be usedThis figure can be used

to solve a variety ofto solve a variety ofunknowns based on theunknowns based on theratio of the flow depth toratio of the flow depth tothe pipe diameter.the pipe diameter.

the crossthe cross--sectional areasectional area

Design Process for GravityDesign Process for Gravity


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g yg y

Sewer SystemsSewer Systems Gravity flow can be used where there is aGravity flow can be used where there is a

sufficient elevation difference between thesufficient elevation difference between the

treatment outlet and the disposal plumbing.treatment outlet and the disposal plumbing. Gravity flow systems are simple, passive andGravity flow systems are simple, passive and

inexpensive, but are the least efficient method ofinexpensive, but are the least efficient method of

distribution.distribution.

Distribution is very uneven over the infiltrationDistribution is very uneven over the infiltrationmediamedia

Maximum and minimum flow variations areMaximum and minimum flow variations arenecessary factors in properly sizing andnecessary factors in properly sizing anddesigning system components.designing system components.

Design Limitations For GravityDesign Limitations For Gravity


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g y

Flow SewersFlow SewersSewer lines must be placed at a sufficient depth to preventSewer lines must be placed at a sufficient depth to prevent

freezing and to receive wastewater from the lowestfreezing and to receive wastewater from the lowest

fixture unit location.fixture unit location.

DistributionDistribution


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DistributionDistribution

Gravity dispersal systems are used to disperseGravity dispersal systems are used to disperse

treated wastewater back into the environmenttreated wastewater back into the environment For percolating systems the gravity distributionFor percolating systems the gravity distribution

system is located in permeable, unsaturatedsystem is located in permeable, unsaturated

natural soil or imported fill materialnatural soil or imported fill material

Perforated pipe is installed to distribute thePerforated pipe is installed to distribute the

wastewater into the distribution systemwastewater into the distribution system

Typical Soil Absorption TrenchTypical Soil Absorption Trench


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yp pyp pThough both the sidewalls and the bottom of the trench mayThough both the sidewalls and the bottom of the trench may

act as infiltrative surfaces, most design guidelines call foract as infiltrative surfaces, most design guidelines call forthe area of the drain field to be based only on the area ofthe area of the drain field to be based only on the area of

the bottom of the trench.the bottom of the trench.

Uneven FlowUneven FlowEven with careful attention paid to keeping the distributionEven with careful attention paid to keeping the distribution


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p p gp p g

pipes level or with a constant grade, the effluent distributionpipes level or with a constant grade, the effluent distribution

will concentrate at the beginning of the pipe.will concentrate at the beginning of the pipe.

Unfortunately, often due to less than perfect installation, theUnfortunately, often due to less than perfect installation, the

actual discharges between orifices is more unpredictable.actual discharges between orifices is more unpredictable.

Serial Loading TrenchSerial Loading Trench


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Instead of dividing theInstead of dividing the

flow equally amongflow equally among

the trenches as in athe trenches as in a

system usingsystem using

DDboxes, theboxes, the

highest trench ishighest trench is

loaded untilloaded until

completely floodedcompletely floodedbefore the nextbefore the next

(lower) trench(lower) trench

receives effluentreceives effluentand so on downand so on down

slope.slope.

Application of a diversion valveApplication of a diversion valve


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With diversion valves individual lines or entire sections ofWith diversion valves individual lines or entire sections of

drain fields can bedrain fields can be restedrested as considered necessary.as considered necessary.

Distribution Example 1Distribution Example 1


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Distribution Example 1Distribution Example 1Given:Given: A four bedroom residence generating 600 gallons perA four bedroom residence generating 600 gallons per

day wastewater from typical family activities is dischargedday wastewater from typical family activities is dischargedafter treatment to a disposal field. The system willafter treatment to a disposal field. The system will

discharge into soils with a soil application rate of 0.4 gpd/sf.discharge into soils with a soil application rate of 0.4 gpd/sf.Due to soil conditions at deeper levels and regulatoryDue to soil conditions at deeper levels and regulatoryconstraints the trenches can only be 48constraints the trenches can only be 48 deep. Localdeep. Localregulations allow trenches with a maximum width of 24regulations allow trenches with a maximum width of 24 andanda minimum cover of 12a minimum cover of 12. The regulations also allow. The regulations also allowabsorption area to include the bottom of the trench and theabsorption area to include the bottom of the trench and thesidewalls up to the invert of the 4sidewalls up to the invert of the 4 dispersal pipe.dispersal pipe.

Find:Find: Total length of trenches.Total length of trenches.

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Effluent Conveyance