land capability assessment · 2018-06-14 · land capability assessment lot 1 ps624473 cemetery...

Land Capability Assessment Lot 1 PS624473 Cemetery Road Bethanga

1 of 21

LAND CAPABILITY ASSESSMENT Lot 1 PS624473 (Cemetery Road Bethanga)


This report has been prepared for:

Brett Martin

C/- GeoPlan Consulting

PO Box 92

Tawonga Sth

3698

This report has been prepared by:

Simon Hollis

MSc (Geoscience)

GeoPlan Consulting

PO Box 92

Tawonga Sth

3698

GeoPlanReferenceNumber 1708ReportDate August2017(revisedJune2108)Preparedby SimonHollisAssessors Academic and ProfessionalQualifications

BachelorAppliedScience(EnvironmentalManagement)AdvancedDiplomaSpatialInformationandSurveyingGraduateDiplomaLandRehabilitationGraduateDiplomaRuralandRegionalPlanningMasterofScience(Geoscience)

LIMITATIONSThe findingscontainedwithin this LandCapabilityAssessmentarederived frommethodologiesprovidedby relevantCodeofPracticeandAustralianStandardanddueregardhasbeengiventoundertakeallaspectsofthestudy inaccordancewiththerequirementswith best practice and relevant standards.Whilst the findings contained in this report represent a reasonableinterpretationofsiteconditions,itdoesnotindicatethatthesefindingsrepresenttheactualstateofthesiteatallpoints.TheInformationcontainedinthisdocumenthavebeenproducedbyGeoPlanConsultingfortheuseofthepersonororganisationforwhichithasbeenpreparedandGeoPlanundertakesnodutytooracceptsanyresponsibilitytoanythirdpartywhomayrelyonthisdocument.


Contents TABLE OF CONTENTS EXECUTIVESUMMARY..................................................................................................................................3

INTRODUCTION............................................................................................................................................5

METHODOLOGY...........................................................................................................................................5

PUBLISHEDSOILINFORMATION...................................................................................................................6

TOWONGPLANNINGSCHEME......................................................................................................................6RURALACTIVITYZONE(RAZ)..................................................................................................................................6

SITEASSESSMENT.........................................................................................................................................6

SOILASSESSMENT........................................................................................................................................8Overview.......................................................................................................................................................8SubsoilSodicity,EmersonClass,SalinityandpH..........................................................................................8Nutrients.......................................................................................................................................................8PermeabilityandAS/NZ1547:2012SoilCategory........................................................................................9

SITERISKANALYSIS......................................................................................................................................9LANDCAPABILITYASSESSMENT..............................................................................................................................10

WASTEWATERMANAGEMENT...................................................................................................................11BUFFERDISTANCESANDLANDAPPLICATIONAREASITING...........................................................................................11THEORETICALWASTEWATERFLOWANDORGANICMATERIALLOADINGRATECALCULATIONS............................................11SEPTICTANKCAPACITY.........................................................................................................................................11TREATMENTANDLANDAPPLICATIONOPTIONS.........................................................................................................11

LandApplicationAreaSizingCalculations..................................................................................................12

CONCLUSIONANDRECOMMENDATIONS...................................................................................................13KEYSITECONSTRAINTSANDDESIGNRESPONSE........................................................................................................13SYSTEMMANAGEMENTRECOMMENDATIONS...........................................................................................................14

REFERENCES...............................................................................................................................................16

Appendices: AppendixA-SitePlanAppendixB–SoilProfilesAppendixC–WaterandNutrientBalanceAppendixD–NorthEastLandResourceAssessmentSoil-LandformDataAppendixE–LaboratorySoilAnalysis


Executive Summary

EXECUTIVESUMMARYSITEANDSOILASSAYSUMMARYSOILDEPTH SoildepthsacrossLot1PS624473aregreaterthan1.0metres–

impermeablelayernotencounteredDEPTHTOWATERTABLE Groundwaternotencountered

AccordingtoVisualisingVictoria’sGroundwaterwebsitedepthtowatertableis<20m:http://maps.cerdi.com.au/vvg.php?agreement=Agree+and+Continue

GEOLOGY/SOILGROUP Ordoviciangneissandgneissicpegmatite

NorthEastLandResourceAssessmentLandUnit:

HGn;HillsonGneiss

NorthEastLandResourceAssessmentLandelement:Moderateslopes(HGn2)Soils(Major):BrownloamgradationalsoilsandreddishtexturecontrastsoilsAustralianSoilClassificationGroup:BrownKurosol

TOPOGRAPHY Moderateslope(10-15%)Waxingdivergent

COARSEFRAGMENTS(%)(SUBSOIL)

<5%.Therewasanabsenceofsubsoilcoarsefragments

SUBSOIL-B1HORIZON Brownish-greylightclayB1horizonsatdepths300mm-500mm

SUBSOILSTRUCTURE(B1HORIZON)

YellowishbrownsandyclayB2horizonsatdepths500mm–1000mm

EMERSONCLASS B1-2B2–2

pH˟(1:5Water)

B1–6.7B2–7.1

ELECTRICALCONDUCTIVITY(1:5WATER)˟dS/m

B1–0.02B2–0.04

EXCHANGEABLESODIUM%(ESP)˟

B1–0.92%B2–1.2%

SUBSOILSOILPERMEABILITY(Ksat)(m/day

<0.06m/daySoilpermeabilitywasdeterminedusingtheTalsma-Hallammethodandthevisual/tactilemethod

SOILCATEGORY(AS/NZ1547:2012)

5c

DESIGNLOADINGRATE(TRENCHES&BEDS)(mm/day)

PrimaryTreatment-Refertonotes2and3toTableL1inAustralianStandardAS/NZS1547:2012

DESIGNIRRIGATIONRATE(mm/day)

3

DESIGNLOADINGRATE(EVAP/TRANS)(mm/day)

5

˟DeterminedbyNutrientAdvantageLaboratories


LandapplicationAreaSummary

IndicativeGeneralSiteDesignRecommendationsSummary(CoPDayFlowRateandCoPBOD)

TreatmentStandard

SepticTank

Capacity(Litres)

LandApplicationMethod ConstructionRequirements

(RelevantAS/NZS

1547/2012ConstructionDiagram)

CalculatedLength(m)

IndicativeLAAArea(m²)

PrimaryorSecondaryTreatment(AWTSorSandFilter)

3000L(3BR)

4000L(4BR)

4500L(5BR)

ETA/ETS⁺^ L6&L 205m(3BR)

257m(4BR)

309m(5BR)

510m²

660m²

750m²

Subsurfaceirrigation* M1 320m²(3Bedroom)

400m²(4Bedroom)

475m²(5Bedroom)^UsingtheformulaatAppendixL4.2ofAS/NZS1547/2012*UsingwaterbalanceasshownatAppendixC(9thDecilewetyearrainfall–AlburyAirport&standardfixtures)⁺Where:Trenchlengthdoesnotexceed30mTrench/BedWidth=0.7mTrench/BedSpacing=2mPerimeterLandApplicationAreaBuffers-2m


Introduction AninvestigationhasbeenundertakentoassesstheoverallcapabilityLot1PS624473,CemeteryRoadBethanga for the purpose of on-site wastewater management and to investigate the merits ofundertakingun-sewereddevelopmentontheland.

Thisreportprovidesinformationabout:• Soilconditions;• Siteconstraints;• General indicative advice about appropriate wastewater treatment system and land

applicationmethodsinresponsetooverallsiteandsoilcharacteristics;and• Indicativewastewaterlandapplicationareasizing;

Thefindingsofthisreporthavebeenmadeincontextofprioritisingpublicandenvironmentalhealthwith generic design recommendations framed on achieving sustainable wastewater disposal withacceptableresidualenvironmentalandpublichealthrisk.

Methodology Thefieldcomponentofthelandcapabilityassessmentwasundertakenon8July2017employingthemethodologyofVictorianEPApublicationNo.746.1LandCapabilityAssessmentforOnsiteDomesticWastewater Management and Publication 891.4 Victorian Code of Practice – Onsite WastewaterManagement 2016 (CoP). It was also undertaken in accordance withAustralian Standard AS/NZS1547:2012On-siteDomesticWastewaterManagement. The indicativewastewaterdisposal systemdimensionshavebeencalculatedusingtheCodeofPracticeandwaterbalancemodelling.

Thestudymethodologyhascomprisedthefollowing:• Adesktopstudyofrelevantgeological,topographical,climateandsoilreferences.• Soilandsiteassessment;

This included thedrilling, loggingandsamplingof three investigationboreholesacross thesubjectlandinordertoestablishsoilprofileconditionsandidentifyspatialvariationsacrossthesubjectland.A75mmhandaugerwasusedtodrilltheboreholes;

• Soil permeability derived using the Talsma-Hallammethod and the visual / tactilemethodwhichincludedanassessmentofsub-soiltextureandstructure;

• Waterandnutrientbalanceanalysisbasedonthe9thdecilewetyearrainfallderivedfromthemeanmonthly rainfalldata for theAlburyAirportWeatherStation (BureauofMeteorologyStationNo.072160);and

• Analysisoffindingsandreportwriting.


Published Soil Information TheprincipalsoillandformstudyintheareaistheNorth-EastLandResourceAssessment1.Itprovidesthefollowingassessmentofthesite:

GeomorphicUnit:1.3.1EasternUplands;RidgesandHills;HighDissectedRidgesandValleyRelief

Geology:OrdoviciangneissandgneissicpegmatiteSoilLandFormMapUnit:HGn;HillsonGneiss(Tallangatta/Leneva/Bethanga)

LandElement:Moderateslopes Soils:Brownloamgradationalandreddishtexturecontrastsoils AustralianSoilClassification:BrownKurosol

Towong Planning Scheme Rural Activity Zone (RAZ) ThesubjectlandisincludedintheRuralActivityZone(RAZ).PursuanttoClause35.08-2oftheTowongPlanning Scheme, a lotmaybeused for oneor twodwellings provided allwastewater fromeachdwellingistreatedandretainedwithinthelotinaccordancewiththeStateEnvironmentProtectionPolicy(WatersofVictoria)undertheEnvironmentProtectionAct1970.Thepurposeofthisstudy,interalia,istoprovideinformationtodemonstratecompliancewithClause35.08-2oftheTowongPlanningScheme.

Site Assessment Table 1

Site Summary Response

SiteAddress Lot1PS624473(CemeteryRoadBethanga)Zone RuralActivityZone(RAZ)Overlays SignificantLandscapeOverlay–Schedule1(SLO1)CatchmentStatus LakeHumePWSCWaterSupply ReticulatedsupplyExistingDevelopment Clearedandgiventopasture

AshedislocateddownslopefromthestudyareaAspect NortherlyVegetation Pasturegrasses

Minoroccurenceofhydrophilicspecies(Juncussp)atthestudysiteLandform Waxing-divergentGeology OrdoviciangneissandgneissicpegmatiteSlope ~10%Fill Noneevident-naturalprofilesobservedRocksandRockOutcrop Limitedoutcropping

1Reynardetal.NorthEastVictoriaLandResourceAssessment(2002),DepartmentofSustainabilityandEnvironment.


SurfaceWater ThearenofeaturesforwhichCodeofPracticesetbackswillapply.

FloodPotential <1:100ARIStormwater run-onandupslopeseepage

Thestudyislikelytoexperiencelimitedstormwaterrun-onandtheriskof

effluenttransportoffsiteviaoverlandflowisminimalDepthtoGroundwater Groundwaternotencountered,novisiblesignsofshallowwatertableor

groundwaterdischarge,nohydrophilicplantsobservedAccordingtoVisualisingVictoria’sGroundwaterwebsitedepthtowatertableis<20m:http://maps.cerdi.com.au/vvg.php?agreement=Agree+and+Continue

Site Drainage andSubsurfaceDrainage

Somemottlingwithintheobservedprofilesisindicativeofasoilmoistureregimethathassomefluctuation.Thegreyishcolourthatisprevailsthroughouttheobservedsubsoilprofileistypicallyindicativeofslowdrainage

Photo 1: NW view across study site Photo 2: SE view across study site


Soil Assessment Overview Threeassessmentboreholesweredrilledwithin the studyarea (AppendixA). Thiswas sufficient toadequatelycharacterisethesoilsoftheimmediatelandscapeandsubjectlandforthepurposeoftherezoningproposal.ExcavationlogsareprovidedatAppendixB.Thesoilsarecharacterisedby:

• GreyishBrown,FineSandyClayLoamA1horizonstoadepthof100mm;• GreyishBrown,moderatelystructuredClayLoamA2Horizonstoadepthof200-300mm;• BrownishGrey,moderatelystructuredLightClayB1horizonsatdepths200/300–400/500mm;• Yellowish-brown,weaklystructuredSandyClay,atdepths400/500mm-1000+• Allprofilesdemonstratedanabsenceofcoarsefragments(<5%);• Limitedmottlesthroughtheprofileindicatelittlefluctuationsinthesoilmoistureregime.

Subsoil Sodicity, Emerson Class, Salinity and pH

Soil particle flocculation is important because water moves mostly in large pores between soilaggregates. SoilswithahighExchangeable SodiumPercentage (ESP)will have reducedpermeability(Ksat). Aggregate stability is also impacted by the amount of soluble salts (EC) in the soils. Class 2EmersonClassratingsinplacessuggestthatsoilmanagementwillneedtoincludemeasurestoreducesoildispersion.Table2:SodicityEmersonClassSalinityandpH*Horizon B1 B2ElectricalConductivity(1:5Water)d/Sm 0.02 0.03

pH(1:5Water) 6.7 7.1

EmersonClass 2 2Sodium%ofcations 0.92% 1.2%

*DeterminedbyNutrientAdvantageLaboratory

Nutrients Clay-richsoilssuchasthosefoundonthissitecanfixlargeamountsofphosphorous.Phosphate-richeffluentseepingthroughthesesoilswilllosemostofthephosphorouswithinafewmetres.Thelimitingnutrientforthis site is nitrogen and no phosphorous balance is required. Nitrogen, that is contained in organiccompoundsformsnitrate-Nwhenprocessedinanaeratedtreatmentplant.Alternateperiodsofwettinganddrying,withthepresenceoforganicmatterpromotesreductiontonitrogengas(denitrification).Plantrootsabsorbnitratesatvaryingratesdependingontheplantspecieshoweverafeatureofnitrateisthatitismobileandcanbereadilyleached.Accordingly,itcanentergroundwaterviadeepseepageandsurfacewatersviaoverlandflowandnear-surfacelateralflow.IndicativesitelandapplicationsizinghasbeenmadewithreferencetoanitrogenbalancesshownatAppendixCandTable5.


Permeability and AS/NZ1547:2012 Soil Category Saturatedhydraulicconductivityofthesitewasmeasuredusingaconstantheadpermeameterintestholesacrossthesite(AppendixA).Threepermeametertestswereconductedonthesiteto identifyspatial variations inpermeability across thepotential landapplicationarea.A summaryof results isprovidedinTable3.PursuanttoEPApublication891.4(CoP)theindicativepermeabilityofsoilsinthesouthofthesubjectlandwas0.06mm/day(Category5csoil).Thesepermeabilityrateswereconfirmedusingthe‘visual-tactile’soilclassificationmethod.

Site Risk Analysis Land Capability Assessment Arangeofsitefeatureshavebeenassessedintermsofthedegreeoflimitationtheypresentforarangeofonsitewastewatermanagementsystems(Table4).Referenceismadetotheratingscaledescribedin Table 1 of EPA Publication 746. Land Capability Assessment for On-site Domestic WastewaterManagement.

Table3:Permeability,AS/NZS1547:2012SoilCategoryandDesignRatesTestHole Ksat(cm/min) Ksat(m/day)

1 0.0033 0.052 0.0042 0.063 0.0045 0.06

SiteMean 0.0040 0.06DESIGNLOADINGRATE(TRENCHES&BEDS)

(mm/day)

Seenotes2and3TableL1AustralianStandardAS/NZS1547:2012

DESIGNIRRIGATIONRATE(mm/day)

3(Category5cSoils)

DESIGNLOADINGRATE(EVAP/TRANS)(mm/day)

5(Category5cSoils)


LANDFEATURES

TABLE4-LANDCAPABILITYCLASSRATING

Low Medium High Limiting/unsuitable AmeliorativeMeasures&RiskReduction

AvailablelandforLandApplicationArea(LAA)

LotsizeexceedsLAAandduplicateLAArequirements

MeetsLAAandduplicateLAArequirements

MeetsLAAandpartialduplicateLAArequirements

InsufficientLAAarea Provide minimum lotsizeswithsufficientLAAand commensuratereserve. Provide CoPsetbacks

Aspect North,north-eastornorth-west

East,west,orsouth-west

Southorsouth-east South–fullshade

ExposureFullsunand/orhighwindorminimalshading

Partialshade Limitedlight,littlewind,heavilyshadedarea

Perpetualshade

SlopeForm Convexordivergentsideslopes

Straightsidedslopes Concaveorconvergentsideslopes

Locallydepressed

SlopeGradientTrenches&beds

<5% 5–10% 10–15% >15% MonitorerosionandseepageDiscourageaccess

SlopeGradientSubsurfaceIrrigation

<10% 10–30% 30–40% >40%

SitedrainageRunoff/runon

LowLikelihood

Moderatelikelihood Highlikelihood Cutoffdrainnotpossible

Landslip* LowPotentialModPotential

HighPotential Existing

ErosionPotential Low ModerateHigh

Nopracticalamelioration

Flood/inundation Never <1AEP 5%AEP >5%AEP

Distancetosurfacewaters(m)

BufferdistancesexceedsallCoderequirements

BufferdistancescomplieswithallCoderequirements

Bufferdistancesdonotcomplywithall/someCoderequirements

<40m

Distancetogroundwaterbores(m)

Noboresonsiteorwithinasignificantdistance

BufferdistancescomplywiththeCode

BufferdistancesdonotcomplywiththeCode

Nosuitabletreatmentmethod

Vegetation Plentiful/healthyvegetation

Moderatevegetation Sparseorlimitedvegetation

Propagationnotpossible

Depthtowatertable(potentiometric)(m)

>2m 2–1.5m 1.5m 1.5m-Surface

Depthtowatertable(seasonalparched)(m)

>1.5m <0.5m 0.5–1.5m0.5m-Surface

Rainfall**(9thdecile)(mm)

<500mm500–750mm

750–1000mm >1000mm Landapplicationareasizingbasedonwaterbalance

Panevaporation(mean)(mm)

1250–1500mm 1000–1250mm 750–1000mm <750mm

SoilProfileCharacteristicsStructure High or moderately

structured Weakly structured Structureless,

massive or hardpan ApplicationofGypsum

Fill materials Nil or mapped good quality topsoil

Mapped variable depth and quality materials

Variable quality and / or uncontrolled filling

Uncontrolled poor quality / unsuitable filling

Thicknessofsoil(m)atthelocationof:Trenches&beds >1.4m >1.4m <1.4m <1.2m Subsurfaceirrigation >1.5m 1–1.5m 0.75m <0.75m PermeabilityPermeability *** (limiting horizon) (m / day) Measured in situ

0.15 – 0.3 0.03 – 0.15 0.3 – 0.6

0.01 – 0.03 0.6 – 3.0

> 3.0 < 0.03

MinimisedomesticwateruseMinimisedischargeofsodiumsaltstoLAAAlternatebetweendifferentpartsofLAALargerLAA


Wastewater Management ThisLandCapabilityAssessmenthasbeenpreparedtoprovidegeneraladviceastothemostappropriatetreatmentandlandapplicationsystemsatLot1PS624473giventheintrinsicsiteandsoilcharacteristicsofthestudysite.Thefollowingsectionsprovideanoverviewofsuitablesystemsatthesubjectland,withgeneraladviceaboutsizinganddesignconsiderations,andtheirjustificationforselection.Buffer Distances and Land Application Area Siting Asageneralrule,thefuturelandapplicationareasshallbesitedsothat:

• Wherepractical,theyareexposedtoprevailingwindsandnotshadedfromsunlight,orareplacedwherenearbyplantscanhelpevapotranspirationoftheeffluent;

• Theydonotaffect,orarenotaffectedbyandcomplywithrequirementsforsetbackdistancesfrombuildings,propertyboundaries,retainingwallsandembankments;and

• Sufficient setbacks from surface water buffer distances are provided to prevent humancontact,maintainpublicamenityandprotectsensitiveenvironments.

Theseprincipleswillberequiredtoinformlandapplicationareasitingaswilltheprescribedsetbackswithin Publication 891.4Victorian Code of Practice – OnsiteWastewaterManagement July 2016.Giventheexistingfarmdamwillberemovedtofacilitatethesubdivisionofthe land,therearenoothersurfacefeaturesthatrequiretheapplicationofCoPsetbacks.

Theoretical Wastewater Flow and Organic Material Loading Rate Calculations Tocalculateatheoretical landapplicationareasizeappropriateforthesiteandforthepurposeofdeterminingaminimumlotsizeriskthreshold,theassumptionsofSection3.4.1andTable4oftheCodeofPracticehavebeenadopted.Calculationshavebeenbasedonthreescenarios-three,four-bedroomandfivebedroomdwellings.Redundancyisbuiltintothecalculationsbyassumingon-goingoccupationbymaximumnumbersofresidents,9thdecilewetyearrainfallandusingstandardwaterfixturesinwaterbalancecalculations.

Septic Tank Capacity PursuanttoTableJ1ofAS/NZS1547:2012,theminimumoperationalcapacityforanall-wasteseptictankinthisinstanceisrecommendedtobe:• 3000L(3Bedroom)• 3500L(4Bedroom)• 4000L(5Bedroom)

These capacities provide for sludge storage capacity providing for a maximum interval prior todesludging/pumpoutof5years(basedonscumandsludgeaccumulationratesinAS/NZS1547:2012).

Treatment and Land Application Options AppendixKofAS/NZS1547:2012providesguidanceonsystemselection.Itsummarizescommonsiteand soil constraints and provides advice on land application systems that are best suited to theprevailing conditions.As a general rule, themore severeandnumerous the constraints the feweroptions,theriskierthesystemandgreatermaintenanceandinstallationcosts.


AS/NZS 1547:2012 requires, inter alia, the selection of the land application system to take intoaccount:

(a)Thevolumeofwastewaterproduced;(b)Thequalityoftheeffluentdischargingfromthewastewatertreatmentunit;(c)Thenatureofthesoilprofileandresultingsoilcategory;(d)TheDLR/DIRassociatedwiththesoilcategory,(basedonbestavailableknowledgeoftheLTAR);(e)Therequiredspacingbetweentrenches/beds/irrigationlinesorsprays;(f)Surfacewaterandgroundwaterlevelsandmovements;and(g)Localclimate.

Thechiefconstraintatthestudysiteisrelativelylow-permeabilityCategory5csubsoilsandtosomeextentpotentiallydispersive(EmersonClass2)soilsinplaces.TableK2ofAS/NZS1547:2012makesthefollowingrecommendationstoaddressandmitigatetheseconstraints:

§ Employalargerapplicationarea;§ Reducewastewaterflowusingwater-savingdevices;§ Mounds,ETAbeds,trenchesorirrigationsystems,designedusingwaterbalance;§ Doseeffluentsowetthesoilmorethanonceaday;§ PlacesoilofgoodpermeabilityaroundabsorptiontrenchesandETAbedsandtrenches;§ Installwhensoilsaredryoronlyslightlymoist;§ Avoidheavyequipmentonapplicationareawhensoilsaremoistorwet;§ Avoidsmearingsidesandbottomsoftrenchesandbeds;§ Minimisedomesticwateruse;§ Minimisedischargeofsodiumsaltstoapplicationarea;§ Alternatebetweendifferentpartsofthelandapplicationarea.§ ApplyGypsumtoreceivingsoil(min1kg/m2)toalldisturbedsoilsurfaceareas;§ Avoidconstructionduringwetweather;§ Fillandclosetrenchesasrequiredandcoverwithgoodtopsoilassoonaspossible;and§ Avoidsoapsanddetergentswithhighsodiumcontent.

Given the low Ksat of the subsoil, it is also recommended that consideration be given to treatingwastewater to a secondary standard via anAeratedWastewater Treatment System (AWTS)or sandfilter. On-site wastewater disposal systems designed, constructed, operated and maintained inaccordance with the recommendations of AS/NZS 1547:2012 with appropriate regard to the siteconstraintsisunlikelytoimpactonthebeneficialuseofsurfacewatersandgroundwaterinthearea.

Land Application Area Sizing Calculations SubsurfaceIrrigationWithin Lot 1 PS624473, subsurface irrigation would be an appropriate land application method,particularlygiventheCategory5csubsoils.Thepreferredapproachtocalculatesubsurface irrigationarealandapplicationareasizingistoundertakeawaterandnutrientbalancecalculationusingAS/NZS1547:2012. This method takes into account rainfall, evaporation and soil porosity to calculate theappropriatelandapplicationarea.

Thewaterbalanceseekstofindtheminimumdisposalareaforagivenwastewaterdischargerateinthisinstance.TheCoPindicatesthattheappropriateDesignIrrigationRate(DIR)asbeing3mm/dayintheCategory5csubsoilsand3mmfortheCategory5bsubsoilsobservedinthesouthernpartofthesubjectland.Thewaterandnutrientbalancealsoassumes30mg/litreNintheeffluent,adenitrificationrateof20%,withNuptakeof220kg/ha/yearforapasturecomprisingarye/clovermixandsequentialzoneddosingof the irrigationarea, providing a conservativeestimateof thenitrogen content in thedeepseepageandlateralflow.


Without taking into account further expected denitrification below the root zone and in thegroundwater(reportedtobeinthevicinityof80%),denitrificationinthelateralflow(externaltotheirrigation areas but within the curtilage of the allotment) and plant uptake in the lateral flow, theirrigationarea is shown inTable5using9thdecilewetyear rainfall fromthenearbyAlburyAirportweatherstationwithintheCategory5csubsoils.

Evapotranspiration(ETA)TrenchesandSecondaryTreatmentThe Australian Standard provides scope for the use of Evapotranspiration (ETA) trenches as a landapplicationsystemoption.Suchsystemsaredesignedtoreducerelianceonsoilabsorptiononly.ETAland application systems function in amanner that is similar to absorption trenches and bedswithtrenchesandbedsplantedoverwithvegetationsothattheprocessoftranspirationassistsineffluenttreatment.Theycanhelppromoteaerationandbiologicaltreatmentofeffluent.Likewise,secondarytreatmentappliedtotrenchandbedsystemcouldbeavalidsystemoption.

GuidelinesforthedesignoftrenchsystemsareoutlinedintheStandardAS/NZS1547:2012.PursuanttoAppendixL4.2ofAS/NZS1547/2012, trench,bedandETAdimensionsshallbedetermined fromtherelationship:

L= Q

DLRxW

Where: L=Lengthinmetres

Q=DesigndailyflowinL/day

DLR=DesignLoadingRateinmm/day

W=Widthinmetres

Table5:SubsurfaceIrrigationLAASizing

3Bedroom 4Bedroom 5Bedroom

LandApplicationArea 320m² 400m² 475m²AreaforNitrogenUptake* 287m² 358m² 430m²*UsingwaterbalanceusingCodeofPracticehydraulicload,9thdecilewetyearandstandardwaterfixtures


Table6

IndicativeLandApplicationDesignRecommendations

TreatmentStandard

SepticTankCapacity(Litres)

LandApplicationMethod

AreaCalculationMethod

ConstructionRequirements

(RelevantAS/NZS


CalculatedLength(m)^

IndicativeLAAArea(m²)⁺

Primary /SecondaryTreatment

3000L(3BR)

4000L(4BR)

4500L(5BR)

ETA/ETS

(AppendixL4.2ofAS/NZS1547/2012)

L6&L 205m(3BR)

257m(4BR)

309m(5BR)

510m²

660m²

750m²

^UsingtheformulaatAppendixL4.2ofAS/NZS1547/2012andDLRof5mm/dayforbothprimaryandsecondarytreatment.⁺Where:Trenchlengthdoesnotexceed30mTrench/BedWidth=0.7mTrench/BedSpacing=2mPerimeterLandApplicationAreaBuffers-2m


Conclusion and Recommendations Summary Thisstudyhasconcludedthat:• Thesiteislargelyclearofsurfaceandgroundwaterfeaturesandthatsurfaceandgroundwaters

shouldnotbeimpactedifCoPsetbacksareapplied.Thestatutorysetbackshaveconsiderableredundancy built in and if surface and groundwater features are afforded the appropriatesetbackswaterqualityimpactsshouldbenegligible.

• Thestudyareaissufficientlyclearofotherenvironmentalconstraintstoassumesuccessfulon-sitedomesticwastewatermanagement.Thewaxing-divergentlandapplicationareacoupledwithanorthernaspectprovidesasuperiorcontextforwastewatermanagementandonethatfacilitateswatersheddingandwindandsolarexposure;

• Thelotsizeissubstantiallylargerthantheindicativelandapplicationareasizingcalculatedbythisstudy,therebysupportingthenotionthatallwastewatershouldbeabletobetreatedandretainedwithintheboundsofthelot.Using9thdecilewetyearrainfall,thecalculationsofthisreportsuggestanindicativelandapplicationareasareasfollow:

• AS/NZS1547:2012providessystemselectionanddesignmodificationsthatcaterforspecific

siteconstraintsandservetoreducerisktoanacceptablelevelinsuchsituations.ManyinherentsitelimitationsmaybeovercomebyapplyingAS/NZS1547:2012systemselectionanddesignadvice though the site-specific land capability assessment process. The low permeabilitysubsoilsandpotentiallydispersivesoilscanbeaddressedviasystemdesignandmanagementinaccordancewithAS/NZS1547:2012.

Table7:LandapplicationAreaSummary

IndicativeGeneralSiteDesignRecommendationsSummary(CoPDayFlowRateandCoPBOD)

TreatmentStandard

SepticTank

Capacity(Litres)

LandApplicationMethod ConstructionRequirements

(RelevantAS/NZS


CalculatedLength(m)^

IndicativeLAAArea(m²)⁺

PrimaryorSecondaryTreatment(AWTSorSandFilter)

3000L(3BR)

4000L(4BR)

4500L(5BR)

ETA/ETS L6&L 205m(3BR)

257m(4BR)

309m(5BR)

510m²

660m²

750m²

Subsurfaceirrigation* M1 320m²(3Bedroom)

400m²(4Bedroom)

475m²(5Bedroom)^UsingtheformulaatAppendixL4.2ofAS/NZS1547/2012*UsingwaterbalanceasshownatAppendixC(9thDecilewetyearrainfall–AlburyAirport&standardfixtures)⁺Where:Trenchlengthdoesnotexceed30mTrench/BedWidth=0.7mTrench/BedSpacing=2mPerimeterLandApplicationAreaBuffers-2m


Key Site Constraints and Design Response Asidentifiedanddiscussedinthisreport,thechiefconstraintsatLot1PS624473are:

• LowpermeabilityCategory5csubsoils.

PursuanttoTableK2ofAS/NZS1547/2012thefollowingarerecommendedtoaddressmitigatethisconstraint:

o Uselargeapplicationarea;o Reducewastewaterflowusingwater-savingdevices;o Mounds, ETA beds, trenches or irrigation systems, designed using water balance

(AppendixD);o Doseeffluentsoastowetthesoilmorethanonceaday;o Placementof soil of goodpermeability around absorption trenchesor aroundETA

bedsandtrenches;o Installwhensoilsaredryorslightlymoist;o Avoidheavyequipmentonapplicationareawhensoilsaremoistorwet;o Avoidsmearingsidesandbottomsoftrenchesandbeds;o Minimisedomesticwateruse;o Minimisedischargeofsodiumsaltstoapplicationarea;ando Alternateapplicationbetweendifferentpartsofthelandapplicationarea.

• Potentiallydispersive(EmersonClass2)soils.

PursuanttoTableK2ofAS/NZS1547/2012thefollowingarerecommendedtoaddressmitigatethisconstraint:

o Avoidsmearingbottomsoftrenchesandbeds;o Fillandclosetrenchesasrequiredandcoverwithgoodtopsoilassoonaspossible;o Avoidssoapsanddetergentswithhighsodiumcontent;o Minimisedischargescontainingsodiumsalts;o ApplyGypsumtoreceivingsoil(min1kg/m2)toalldisturbedsoilsurfaceareas;o Avoidconstructionduringwetweather;

SecondaryTreatmentGiventhelowKsatofthesubsoil,itisrecommendedthatconsiderationbegiventotreatingwastewateronthesubjectlandtoasecondarystandardviaanAeratedWastewaterTreatmentSystem(AWTS)orsandfilter.LandApplicationSizingTable7providesanindicativelandapplicationareasizingbasedonobservedsubsoilKsatandmaximumdwellingoccupancy.The lot sizewillbe sufficient toaccommodatea LandApplicationArea sized tomatchlow-permeabilityCategory5csubsoilsusing9thdecilewetyearrainfall.


System Management Recommendations ReserveAreasAlthough reserve areas are not required for subsurface irrigation by the CoP they are neverthelessrecommendedastheyprovideanadditionalsafetymeasure.Areserveareaof100%ofthedesignareashouldbeconsideredaspartoftheriskmanagementprocesstobeavailableatthesiteforexpansion,for restingof the land application system,or for duplicationof the land application system if othercircumstances require this at some future time. The reserve area needs to be protected from anydevelopmentthatwouldpreventitbeingusedinthefuture.SoilRenovationToimprovesoilstructureandimprovethestabilityofpedsafterreceivingsalinewastewater,gypsumapplication is recommended.Gypsummay be broadcast over the land application area at a rate of1kg/m2andcanberebroadcastoverthelandapplicationareaatthesamerateatarecurrenceintervalof5years.LoadBalancingAloadbalancingmechanismenablesshort-termstorageandsustainableflowstothedistributionareaoverextendedtime.Surgeflowsarepossibleduetospecialeventsorgatheringsandsuchsituationscancausethesystemmaybecomeoverwhelmedforaperiod.Thispotentialproblemcanbeeliminatedbyinstallingaplantwithaloadbalancingfacility(orequivalentfunction)whichenablesshort-termstorageandsustainableflowstothedistributionareaoverextendedtime.Anotherbenefitoftheloadbalancingfacilityisthatitcanalsoprovidetemporarystorageshouldtheplantfailorifthereisapoweroutage.AsConstructedPlansUponcompletionofsysteminstallation,‘asconstructed’plansshouldbeprovidedtoCouncilandkeptonfile.

ZoneDosingFuture land application areas should be irrigated sequentially by zones to promote the creation ofalternating and transient aerobic and anaerobic soil conditions. The nominated indicative site landapplicationareaissizedconservativelyfornitrogenattenuation,usingpasturegrass(rye/clovermix),whichhasanitrogenuptakeof220kg/ha/year.Abenefitofzoneddosingisthatitwillincreasetheefficiencyofthelandapplicationareaforremovingnitrogenfromthesoil.Theprincipleriskofundersizedlandapplicationareaisthattheyareatriskofbecominganaerobicforlongperiods, with the risk of microbial build-up. Microbial build-up leads to secretion of microbialpolysaccharides, which cover soil particles and restrict the ability of the soil to absorb nutrients andultimatelyattenuatepathogens.Overtimepolysaccharidescancoattheinteriorofpipesandblockdrainageholes if drainage is slow due to an overloaded land application area. This in turn can lead to effluentsurchargefromtheendsofthedrainagepipes,formingpreferentialflowpathsthroughoverlyingsoilanddrainingtonearbysurfacewaters.Alternatingaerobicandanaerobicconditionscreatedbyzoneddosingassistsinthepreventionofthebuild-upofmicrobialpolysaccharides,enhancingeffluentrenovation.

PressureCompensatedSubsurfaceDisposalPressure compensated subsurface disposal is recommended by this study. This systemdelivers effluentdirectly into the soil and fora surface flowcontainingeffluent tooccur, theeffluenthas to riseagainstgravity,throughatleast150mmofsoil.Toensureproperfunctioningthereisarequirementforthepressurecompensateddistributionnetwork tobeplacedparallel to contours and/orhorizontal for eveneffluentdistribution.


StormwaterControlWastewatersystemsshouldbeprotectedfromrainfallrun-offusingmethodssuchastheinstallationand use of bunds, cut-off drains, or improved surface drainage to prevent systems from hydraulicoverloading.Inaddition,thelandapplicationsystemshallbeshapedtoshedrainfall.

WaterReducingFixtures

It is recommended that future residenceswithin Lot1PS624473be fittedwith fullwater-reductionfixturesincludingthecombineduseofreducedflushtoilets,shower-flowrestrictors,aeratorfaucets,front-loadwashingmachinesandflow/pressurecontrolvalvesonallwater-useoutlets.

Landuseactivity

Activitieswithin the land application areas such as recreation activities, or grazing animals shall becontrolledorprohibitedsothatsoilcompactionorinterferencewiththefunctionofthelandapplicationsystemisminimisedandpeopleavoidpotentialcontactwitheffluentresidues.

Unlessallowedforinthedesign,futurelandapplicationareasshallnot:• Bepavedorsealed;• Besubjecttovehiculartraffic(otherthanapedestrian-controlledlawnmower);• Besubjecttoregularfoottrafficsuchaspathways;• Havestructuresorbuildingserectedonit.Withregardtothelandapplicationsystemthefollowingarealsorecommended:• Regularlymowingofvegetationwithinthelandapplicationarea;• HeavyequipmentshouldbeavoidedonLAAwhensoilsaremoistorwet;• The operation and maintenance of the treatment and disposal system in accordance with

manufacturer’srecommendations.


References EnvironmentProtectionAuthority (2003a).Publication746.LandCapabilityAssessment forOn-siteDomesticWastewaterManagement

Environment Protection Authority (2016) Publication 891.4 Victorian Code of Practice – OnsiteWastewaterManagementFebruary2013.

McDonaldRC.Isbell,R.F.,Speight,J.G.,Wlker,.JandHopkins,M.S.,(1990).AustralianSoilandLandSurveyFieldHandbook2ndedition,InkataPress,Melbourne,Sydney.

Reynardetal.NorthEastVictoriaLandResourceAssessment(2002),DepartmentofSustainabilityandEnvironment.

StandardsAustralia/StandardsNewZealand(2012).AS/NZS1547:2012OnsiteDomesticWastewaterManagement

land capability assessment · 2018-06-14 · land capability assessment lot 1 ps624473 cemetery...

Documents