Government ServicesGovernment Services

Private Sewage DisposalandWater SupplyStandardsGovernment Services

ForewardThe preparation of this document was madepossible due to the contributions from a varietyof people with expertise in public health,engineering and waste disposal.In particular, the efforts of the people involvedin the preparation of the “Draft SewageDisposal Technical Guidelines: Newfoundlandand Labrador” and the “Standards of AcceptedPractise for the Location, Design andConstruction of Private Sewage DisposalSystems” was invaluable in the drafting of thisdocument.i


Table of ContentsIntroductionA1SECTION AA31.Overview of On-site Sewage SystemsA3The Septic TankDistribution BoxAbsorption TrenchesSeparation DistancesA3A4A4A5Approved DesignersA6Approved Designer DesignationApproved Designer ExaminationConflict of InterestSuspension of Approved DesignersA6A6A7A7Application ProcessA8Areas in MunicipalitiesUn-serviced SubdivisionsApplicationComponents of a SubmissionCertificates of ApprovalA8A8A8A9A 10Building Site EvaluationA 11Lot Size and SuitabilityLand Area and Lot WidthSeasonal Site EvaluationsSoil CharacteristicsSoil TextureSoil StructureSoil DepthSoil ColourSoil DensityTest PitsPercolation TestA 11A 11A 12A 12A 13A 13A 14A 14A 15A 15A 162.3.4.iii

Table of ContentsSlopeSite UpgradingA 18A 18SECTION BB11.Septic Tank StandardsB1Construction/Installation RequirementsSeptic Tank SizingResidentialCommercialB2B3B3B3Absorption Field StandardsB5Distribution BoxesAbsorption TrenchesResidential DwellingsResidence with ApartmentDuplexesCommercial BuildingsAbsorption Field/Construction Installation RequirementsDosing DeviceB5B6B6B7B7B7B8B 11Fill SystemsB 13DescriptionSite ConsiderationsDesignSizing of the Filled AreaFill SelectionConstructionSettling of FillOther RequirementsOperation and MaintenanceB 13B 13B 14B 14B 14B 14B 14B 14B 15Seepage or Leaching PitsB 16Construction/Installation RequirementsDry Wall Constructed PitRock Filled PitB 16B 16B 17Ocean OutfallsB 18Construction RequirementsLegal EasementsB 18B

Table of Contents6.Pit PriviesB 20Construction RequirementsB 20Vault PrivyB 23Construction RequirementsB 238.Composting, Incinerating and Chemical ToiletsB 259.Holding TanksB 26Construction RequirementsSizing of Holding TanksDisposal of Holding Tank WasteB 26B 26B 26Grey Water DisposalB 27Construction RequirementsB 27Decommissioning Septic SystemsB 29Septic Tanks & D-BoxesAbsorption FieldsB 29B 2912.Water Service Hook-upsB 3013.Private Water SuppliesB 31Water SuppliesConstruction RequirementsWater Quality TestingWell Liners/CasingsAbandoned Dug WellsProtection from Road SaltB 31B 31B 34B 34B 34B 34Backfill InspectionsB 35Water TestB 35Septic System MaintenanceB 367.

Table of Contents16.GeneralWater Treatment UnitsB 36B 37Alternate SystemsB 38SECTION CAppendixviC1

IntroductionIndividual on-site sewage systems have been, andcontinue to be, an important part of wastemanagement in many communities in Newfoundlandand Labrador. Providing adequate sewage disposal isan important component in the protection of publichealth and the protection of groundwater andsurface water from pollution. Many ruralcommunities, due to their size and populationdensity, cannot provide the traditional engineeredsanitary sewer system. Where this is the case, on-sitesewage disposal systems have been employed as apractical solution to servicing individualdevelopments. For people in un-serviced areas (e.g.,municipal sewage services not available), on-sitesewage treatment is often the only practical solutionfor domestic sewage waste. The septic tank andsubsurface absorption field (septic tank system)remains the method of choice. A well designed andproperly maintained system installed on anacceptable site can provide long term, safe andeffective treatment of domestic sewage.On-site sewage disposal refers to disposal into thesoil and groundwater environment of all domesticsewage, produced by a home, commercial or otherestablishments. The conventional method for newdevelopment is the subsurface disposal system (i.e.,the septic tank and soil absorption field). Propersiting, installation and maintenance are the keys toensuring that a septic system functions properly forthe long term. Not every proposed building site canbe approved for private sewage disposal and watersupply systems. There are minimum requirementswith respect to size, location in relation to otherphysical structures or activities, soil conditions, etc.,that must be met. A thorough site evaluation isrequired to determine if a proposed building lotmeets these requirements.The site evaluation must be performed by anApproved Designer registered with the GovernmentService Centre (GSC). The results of the evaluation,along with a detailed sewage disposal system designThe Government of Newfoundland & Labradorand water supply design (signed by the designer), athrough the Sanitation Regulations under the Healthcompleted application (signed by the applicant), andand Community Services Act regulate onsite sewageMunicipal Approval (in a letter from thedisposal systems with a daily sewage flow of less thanmunicipality) must be submitted to the GSC to be4546 litres. The regulations govern the design,considered for issuance of a “Certificate ofconstruction and installation of such systems. ThisApproval”. No construction or excavation, otherdocument outlines the minimumacceptable standards for privatethan that necessary for site evaluation,(household) sewage treatment systemsshould commence until a “Certificate ofMaximum Dailywith sewage flows of less than 4546Sewage Flow underApproval” has been issued for the site.litres/day.the Sanitation Regulations An inventory of approved designers isof the Health andmaintained at the local GovernmentCommunity Services ActService 4546 L/day.For flows greaterthan 4546 L/daythe Water ResourcesAct applies.A1


Section A1.OVERVIEW OF ON-SITESEWAGE SYSTEMSFigure 1: Septic TankThe typical on-site sewage system referred to in theseStandards includes the following components:···the building sewer, after it leaves the building;the treatment unit (e.g., septic tank); andthe soil absorption system (e.g., absorptiontrenches).The building sewer is simply a water tight pipe thatcarries the sewage from the building to the treatmentunit. The treatment unit processes raw wastewater toremove solids, fats and greases.The soil is recognized as a key component of any onsite sewage system. The degree to which a treatmentunit processes the building sewage will determine thedesign of the system within the soil.The size and layout of a soil absorption system (e.g.,absorption trenches) varies according to type oftreatment system, site conditions and anticipatedloads. Typically, perforated pipe and gravel distributethe effluent over the absorption area. Gravel orcrushed rock provides storage for peak effluent flows;a large infiltration surface between the effluent andunderlying soil or sand, provides a bed for the pipeand protection over it.1.1 The Septic TankThe septic tank provides primary treatment byseparating the solids from the domestic sewage waste.The lighter solids float to the top and the heaviersolids settle to the bottom. This leaves a relativelyclarified liquid effluent between the layers.Anaerobic bacterial activity (bacterialactivity without the presence of oxygen)partially breaks down the waste in theseptic tank. The liquid effluent from the tank isdistributed to the absorption field through adistribution box.As mentioned, the primary function of a septic tankis to retain fats, greases, and other solids. Primarytreatment of sewage takes place within the tank,where anaerobic bacteria digest these materials. Theun-digestible portion remains in the tank and isdisposed of when the tank is pumped. The effluentwhich leaves the tank for secondary treatment in theabsorption field is, ideally, free of suspended fats,greases, and other solids. However, it does containorganic materials, bacteria, and viruses.Those solids that are stabilized settle to the bottomof the septic tank where they form a sludge blanket.Fats and greases rise to the top of the septic tankforming a scum blanket. The sludge and scumblankets must be removed periodically to preservethe liquid capacity necessary for satisfactory solidsremoval.A typical septic tank removes about 40 to 50% of the5-day biochemical oxygen demand, 50 to70% of the total suspended solids, 20 to30% of the nitrogen, and up to 30% ofthe phosphates. Disease organisms doSeptic tank contentsnot multiply in the septic tank; theymust be pumpedsurvive or are reduced.out regularly.A3

1.2 Distribution BoxThe distribution box and the absorptiontrenches form the absorption field.The distribution boxmust be water tightand level.The distribution box has an outlet toeach absorption trench. The effluentfrom the septic tank flows into the box and throughthe different outlets to the absorption trenches.Because the outlets are level with each other, eachline should receive an equal volume of effluent. Thedistribution box must be level; if not, the flow to theabsorption trenches will be uneven.1.3 Absorption TrenchesThe absorption trenches, through a series ofperforated pipes laid in a bed of crushed stone, filtersand distributes the effluent throughout the field byallowing the effluent to slowly trickle from theperforated pipe into the crushed stone and downthrough the soil. The crushed stone and soil act asbiological filters.Unlike the septic tank where treatment isfacilitated through the activity ofanaerobic bacteria, waste in theabsorption trenches is broken down byaerobic bacteria. Aerobic bacteriarequires oxygen to be present forsurvival.Oxygen, therefore, is essential to the efficientoperation of the absorption field. Since oxygendiminishes with the depth of soil, it is importantthat the depth of absorption trenches not exceed themaximum set out in the standards. Exceeding therequirements increases the likelihood of the systemmalfunctioning.Evapotranspiration, the uptake of moisture throughevaporation and through transpiration by vegetation,contributes to the effective functioning of thedisposal field. Evapotranspiration reduces theabsorption load on the soil. Ensuring that thedisposal field does not exceed recommended depthsis again important since the deeper the trenches, theless evaporation that occurs and the lesstranspiration since the effluent is farther away fromthe roots of vegetation. To ensure the systemreceives the full benefits from transpiration, seedingor sodding of the disposal field should be done soonafter the system is installed.Continuous or frequent ponding of septic tankeffluent on the bottom of the absorption field resultsin the growth of a biological layer that filters out moreand more solid particles and dissolved pollutants fromthe septic tank effluent. A clogging mat is formed atTotal coliforms concentrations of 57,000 colonies perthe point of infiltration into the soil. This matmilliliter within the absorption field are typicallynormally penetrates 1/2 to 6 centimeters into the soil.reduced to less than 200 colonies per milliliter at orIt consists of a slimy mass of septic tank effluentbeyond a foot of the clogging mat. Fecal coliformssolids, mineral precipitates, microorganisms, and theconcentrations of 19,000 colonies per milliliter withinby-products of decomposition. Microorganisms in thethe disposal field are typically reduced to less than 2mat feed on septic tank effluent nutrients to producecolonies per milliliter at or beyond a foot of theslimes, polysaccharides, carbon dioxide, etc. Filteredclogging mat. Fecal streptococci concentrations ofout cellulose, undigested food residues, etc.,1,600 colonies per milliliter within the disposal fieldhydrolyze and biodegrade slowly. Mineralare typically reduced to less than 2 colonies perprecipitates, such as ferrous sulfide, etc.,milliliter at or beyond a foot of thealso contribute to the clogging mat. Asclogging mat. The clogging mat typicallythe effluent filters through the soil,removes approximately 10% of theorganisms present in the soil act toSeed or sodnitrogen but is less effective in removingremove harmful bacteria, viruses andabsorption fieldsphosphates.other facilitate transpiration.A4

1.4 Separation DistancesThe distance that septic tanks and absorption fieldshave to be separated from bodies of water, propertyboundaries, drilled and dug wells, etc., is provided inthe Sanitation Regulations and these Standards. Withrespect to separation from bodies of water, considerthe following information related to what would beconsidered a surface water body.A stream that is on a topographic map is astream. The fact that a stream doesn’t showup on a map does not mean it is not a stream.If there’s flowing water then it is a stream. Ifthere is only flowing water at certain times,then it is an intermittent stream.Ditches are man-made conveyances and itdoes not matter if there is water in them ornot. Usually ditches are dry and are meant tocarry storm water runoff only. However, allstreams and ditches lead elsewhere andeventually join up with larger streams,brooks, rivers, ponds, lakes and the ocean.It might be wiser to determine if the septicsystem will have an impact on the water bodyand if that impact will carry downstream. Onthat basis, it would not matter what it is. Allthat is required is occasional flowing water.If there is insufficient separation from theseptic system, then there could be adverseimpacts. In other words, separation from anysource of flowing water ought to bedetermined by the properties of the ground(slope and permeability) rather than whattype of water body might be adjacent.(Source: Water Resources Division, Department of Environment and Conservation)A5

2.APPROVED DESIGNERSUnder the Approved Designer policy of theDepartment of Government Services the initialinspections/assessments of building lots withproposed on-site sewage services can be carried outby individuals registered with Government ServiceCentre as Approved Designers.2.1 Approved DesignerDesignationThe evaluation of a site for on-site sewage systemsmust be performed by an Approved Designerregistered with the Government Service Centre(GSC). Persons who are Certified Public HealthInspectors, Professional Engineers, CertifiedEngineering Technicians or Certified EngineeringTechnologists generally can be expected to havesufficient expertise to provide proper assessments,designs and construction drawings for the proposedsystems. Individuals holding these designations areautomatically considered Approved Designers andmay apply for registration as an Approved Designerwithout any requirement, other than the submissionof an application. Applicants must provide proof oftheir certification or professional designation.Alternatively, these individuals may simply request inwriting or by fax to be listed by the GovernmentService Centre as an Approved Designer. Aregistration number will be issued to the qualifiedapplicant. No fee is required for registration.It is recognized, however, that there are contractorsand others who have the necessary expertise but lackthe designations as aforementioned. These personscan be recognized as Approved Designers of on-siteseptic systems by:··A6submitting an application to become anapproved designer; andsuccessfully completing a written examdesigned to test knowledge in the area of on-site sewage systems and private watersupplies.The exam is to be written in the presence of anofficial of the Government Service Centre. Theresults of the exam will be reviewed by anEnvironmental Health Officer and, if a satisfactorymark is obtained, the Environmental Health Officerwill recommend to his/her supervisor that thesuccessful applicant be registered as an ApprovedDesigner and that a registration number be given toidentify the person on the Approved Designer listing.2.2 Approved DesignerExaminationCandidates who wish to become Approved Designersmust have the ability to communicate satisfactorilythrough writing and documentation. Candidates forApproved Designer status must successfully completea written exam. The exam will be administered by theGovernment Service Centre at its various locationsthroughout the province. Three Approved Designerexams exist. They must be written in sequence: ExamA is to be written first followed by exam B, ifnecessary, and then exam C, if necessary.To successfully pass the exam, a minimum mark of75% must be attained overall. A candidate mustreceive a minimum of 20 out of a possible 30 markson Section IV of the exam.If a candidate is unsuccessful in obtaining ApprovedDesigner status after the first exam, a candidatecannot re-write the exam for a two (2) month period.If after the second writing the candidate isunsuccessful s/he cannot re-write the exam for a six(6) month period. A candidate who is unsuccessfulafter writing the third exam, will not be consideredagain for Approved Designer status, without proof ofeducation in the area of lot assessment/on-sitesewage disposal and successful completion of the

Approved Designer exam.2.3 Conflict of InterestTo avoid a conflict of interest situation, persons whohold a CPHI(C), P. Eng., CET or CTech designationand are currently employed by the GovernmentService Centre, Regional Health and CommunityServices Boards or Department of Health andCommunity Services are not to prepare designs forsubmission for approval, unless they haveappropriate approval per the Conflict of Interest Act.2.4 Suspension of ApprovedDesigner StatusThe designation of an individual as an ApprovedDesigner may be suspended due to reoccurringdeficiencies in submissions. Examples ofdeficiencies include repeated submission of flaweddesigns which are incomplete or based upondeficient or incorrect field data. Individuals mayapply for reinstatement after a period of ninemonths. At that time, individuals, includingCPHI(C)’s, P.Eng’s, CET’s, etc. will be required tosuccessfully complete the Approved Designer to comply with these Standards or are based onfalse or misleading information, his/her ApprovedDesigner status shall be revoked. For the purposes ofremoving an Approved Designer’s status, a deficiencyshall include: Actively facilitates installation of a watersupply/or a sewage disposal system withoutsubmission of plans and receipt of approvalfrom the GSC for the system(s). Submission of a design based on inaccurate orinsufficient information. Repeated submission of plans in contraventionof good design practice. Failure to identify existing elements ofdevelopment and maintain the requiredseparation distances for wells and sewagedisposal systems. Any other issue found to be significant in theeffective operation of the sewage disposalsystem or the water supply or which couldresult in a risk to the health or safety of thehomeowner or the adjacent property owners.When an Approved Designer submits designs whichNOTEDesign submissions that contain “deliberate misinformation” or are part of an “illegal activity” may resultin the immediate lifetime removal of an individual’s Approved Designer status.Approved Designers who are inactive for a period of greater than two years must reapply to theGovernment Service Centre to obtain Approved Designer status.A7

3.APPLICATION PROCESSThe decision to approve the development of landmay be subject to input from various governmentdepartments/agencies dependant on the location ofthe land and the type of development proposed. TheGovernment Service Centre will continue to requirethat an applicant demonstrate a site is suitable forinstallation of a septic system prior to approvingdevelopment of a particular lot even in cases wherean applicant may only intend to install a pit privy.The only exception to this is remote sites. Thefollowing are some of the points that should be notedduring the application process.3.1 Areas in MunicipalitiesThe decision whether or not a particular site may bedeveloped rests with the Municipality in accordancewith the Municipalities Act. Generally, municipalitiesrely on the GSC to determine the suitability of landfor private sewage systems. For those municipalitiesthat issue an occupancy permit, we will be requestingthat this permit not be issued until the municipalityreceives from the GSC a Final Approval Certificateof the private sewage and water system.3.2 Un-serviced SubdivisionsA subdivision for the purpose of this policy shall bedefined as a development of five lots or greater.Professional Engineers, only, can preparesubmissions for subdivisions.Subdivisions of between five and fifteen lots, with theexception of the Professional Engineer requirement,will require submissions for each lot in accordancewith the procedure outlined in this document.Proponents wishing to develop subdivisions ofgreater than fifteen lots in un-serviced areas will berequired to submit an engineering study of theA8overall development to the Government ServiceCentre which should form in part the basis for theconsultant's recommendation about the suitability ofthe sites for individual water supplies and sewagedisposal systems. The Government Service Centrewill review for consideration of conceptual approvalof the overall development.Reference can be made to the document "Guidelinesfor Assessment of Un-serviced Subdivisions” (SeeAppendix) for items that should be addressed in theengineering study and report. Apart from the overallengineering assessment, each site will requireevaluation and design data as outlined in Section 3.4of these Standards. Any Approved Designer mayevaluate and design onsite services for lots deemed tobe suitable for development in the overallengineering assessment.3.3 ApplicationThe applicant, or Approved Designer acting onbehalf of the applicant, must provide theGovernment Service Centre with two complete copiesof the water and/or sewage system design(application and building site evaluation). Uponapproval, one copy will be retained by theGovernment Service Centre and the second copy willbe forwarded to the appropriate municipal authority.All applications pertaining to building sites requiringinstallation of private water and/or sewage systemsrequire the approval of the Government ServiceCentre, Department of Government Services.A water and/or sewage system design submission ismade as one complete package. If a submission isreceived from an Approved Designer and allrequired information (including municipal approvaland completed application form) has not beenprovided at that time, the incomplete package will bereturned to the Approved Designer, and will benoted as an incomplete submission. No submissionswill be processed whereby it is stated that furtherinformation will be sent at a later date. Specifically,no submissions will be processed pending municipalapproval.

3.4 Components of aSubmissionThe applicant or approvedrepresentative must submit thefollowing:1. A GSC “Application to DevelopLand” completed and signed by theapplicant;Submissions withincomplete or erroneousinformation will bereturned to theApproved Designerfor correction andre-submission and maylead to suspensionof design privileges.3. A floor plan for the proposed dwelling/establishment, including basement and belowground level pipes/plumbing, if applicable;4. Municipal Approval;8. Design calculations for design of theseptic system;9. Detailed drawings showing allconstruction details required to installthe septic tank, distribution box,absorption trenches and proposedwater supply;10. A profile of the land which accuratelydescribes the grade of the land in thegeneral area where the septic systemis to be installed;2. A detailed diagram of the lot (see Figure 2) withdimensions indicating:lot boundaries (property lines)lot sizelocation of adjacent wells and sewage systemsseparation distancesexisting and proposed buildingsditchingbrooks & streams, ponds and other naturalwater coursesmunicipal or private water servicesdrivewayslivestock operations;7. Depth of ground water table;11.A description of the general groundconditions in the area where the system is tobe installed. The applicant should note thepresence of rock, topsoil, gravel, bog, etc. Aphotograph of the site would be helpful;12.If imported fill is to be used to compensatefor a depth of good soil that is less than the161 centimetre minimum requirement, thenthe following is required for designsubmission:the source (location) of the imported fill;the soil type of the imported fill;in situ percolation rate of theimported fill*; andcharacteristics (e.g., type and strata)of the soil present at the site to bedeveloped.5. Results of a percolation test indicating the date* the in situ percolation rate of thethe test was performed as well as theimported fill must be determined eachname,Ifthebuildinglotiswithintime fill is removed from the site (i.e.address and phone number of theamunicipalauthority,gravel pit).person responsible for performing theMunicipalApprovalistest;required to be included13. Additionally, dependant on siteat the time of the water6. Information regarding soil strata andconditions, adjacent developments,type in the area proposed forand/or sewage systemetc., the applicant may be required toinstallation of the system. Thedesign submission. If not,provide additional informationapplicant should have test pits dug tothe submission will berequested by the Environmentaldetermine this information;returned to theHealth Officer such as:Approved Designersieve analysis data,without processing.water table monitoring.A9

Figure 2: General Layout of Private Sewage Disposal SystemNOTE: “Surface water” includes all bodies of water such as lakes, streams, ponds and wetlands.3.5 Certificates of Approval1. Certificate of Approval2. Final Approval CertificateAll applications for approval of a private sewagedisposal system and water supply shall be reviewedand assessed by an Environmental Health Officerwith the Government Service Centre. A Certificateof Approval will be completed and provided to theapplicant if the application and building siteevaluation submission are considered satisfactoryfollowing a review by an Environmental HealthOfficer. A copy of the Certificate of Approval and acopy of the Approved Designer’s submission will beforwarded to the appropriate municipal authorityand/or controlling agency. Applicants will be notifiedin writing if their building site evaluation submissionis unacceptable.A final inspection must be conducted by anEnvironmental Health Officer on all newly installedsewage disposal systems. A Final ApprovalCertificate will be issued to the applicant when theinstallation is in compliance with the building siteevaluation submission, these Standards and theSanitation Regulations. A copy of the certificate willbe submitted to the municipal authority and/orcontrolling agency and may be provided to theApproved Designer.A10

SITE EVALUATION4.BUILDING SITEEVALUATIONpercolation ratesoil characteristicsground water tableslopeseparation distancesbuilding lot sizeThe assessment/evaluation of buildinglots which require on-site sewage is to becarried out by Approved Designersregistered with the Government ServiceCentre. This section provides details onseveral elements of the building site evaluation that arerequired to be submitted with the GSC “Application toDevelop Land”.The site evaluation will include:identifying the location for the proposed sewagedisposal system and water supply that satisfies theminimum separation requirements set out in thisdocument;determining the absorption rate of the soil byperforming a minimum of three percolation tests;conducting a soil evaluation which may requireexamination of a test pit that is a minimum of 1.8metres deep;ensuring that the slope is within acceptable limits;and,where a municipal water supply is not available,identifying a suitable location for a well.4.1 Lot Size and SuitabilityThe land area in which an on-site subsurface sewagesystem is to be installed must be: adequate to permit the installation of a welland septic tank with soil absorption on-site. sufficient to allow the appropriate separationdistances between wells, springs, existingbuildings, inland waters, property boundaries,embankments, etc. sufficient enough to accommodate a completereplacement system, should the first onemalfunction and require replacement.4.2Land Areaand Lot Width1. Un-Serviced Building LotsFor un-serviced building lots (lots wherewater and sewage disposal services will beprovided on-site), a minimum lot size of 1860 squaremetres is required. A minimum lot width of 30metres is required throughout the entire area inwhich the absorption field (distribution box to end ofabsorption trenches) is to be installed. This areamust be able to accommodate the septic system whilemaintaining separation distances and have sufficientspace for the installation of a replacement system.2. Semi-Serviced Building LotsFor semi-serviced building lots (lots where water orsewage disposal services will be provided off-site), aminimum lot size of 1400 square metres is required.A minimum lot width of 23 metres is requiredthroughout the entire area in which the absorptionfield (distribution box to end of absorption trenches)is to be installed. This area must be able toaccommodate the septic system while maintainingseparation distances and have sufficient space for theinstallation of a replacement system.NOTE1. Some municipalities may have minimum lotfrontage requirements. Please check with themunicipality to determine if minimum lotfrontages exist.2. For lots where duplexes are proposed the lotsize will be two times the size required for a2single family residence (e.g., 2 X 1860 m 23720 m ).A11

3.Rural Infilling VarianceWhere land is surrounded by development whichprohibits expansion and where an approval cannot beawarded beca

A typical septic tank removes about 40 to 50% of the 5-day biochemical oxygen demand, 50 to 70% of the total suspended solids, 20 to 30% of the nitrogen, and up to 30% of the phosphates. Disease organisms do not multiply in the septic tank; they survive or are reduced. Section A Figure 1: Septic Tank Septic tank contents must be pumped out .