epa code of practice wastewater treatment & disposal systems

Environmental Protection Agency

Table of Contents: Part Two

List of Figures xi

List of Tables xii

PART TWO: GUIDANCE 53

Annex A Policy Background 53

Annex B Groundwater Protection Response 57

Annex C Site Characterisation 63

Annex D Discharge Options 89

Annex E Wastewater Treatment and Disposal Systems 91

Annex F Site Improvement Works 96

Annex G Operation and Maintenance 97

Annex H References and Reading Material 102

Environmental Protection Agency xi

List of Figures

Figure B.1 Relative location of wells 61

Figure C.1 Indicator plants of dry and wet conditions 66

Figure C.2 Close-up of mottling in trial hole 67

Figure C.3 Idealised cross section of the T-test holes and the proposed percolation trench 73

Figure C.4 Cross section of the P-test holes and the proposed percolation trench 75

Figure E.1 Illustration of biomat formation on the base of a percolation trench 92

Environmental Protection Agency xii

List of Tables

Table B.1 Characteristics of domestic wastewater for a single house 58

Table B.2 Response matrix for on-site treatment systems 59

Table B.3 Recommended minimum distance between a receptor and a percolation area or polishing filter 62

Table C.1 Factors to be considered during visual assessment 64

Table C.2 Factors to be considered during a trial hole examination 67

Table C.3 Subsoil classification against T-values for 400 T-tests (Jackson, 2005) 68

Table C.4 Step 3 of percolation test (T-test) procedure 73

Table C.5 Standard Method 74

Table C.6 Modified Method 75

Table C.7 Information obtained from desk study and on-site assessment 76

Table E.1 Attributes of a typical septic tank 93

Table E.2 Factors used to compare different wastewater treatment systems 94

Code of Practice: Wastewater Treatment and Disposal Systems Serving Single Houses (p.e. ≤ 10)

PART TWO: GUIDANCEAnnex A Policy Background

A.1 General

The 2006 census indicated that around 40% ofthe population of Ireland lived outside of themain cities and towns with a population of1,500 and over. Unlike other, more urbanised,European countries, around a third of thepopulation of Ireland lives in the opencountryside in individual dwellings notconnected to a public sewer. The wastewaterfrom such rural settlement patterns is disposedof to systems of various types designed to treatthe wastewater at or near the location where itis produced. Ireland enjoys a high-qualityenvironment and the conservation andenhancement of our environment is a keyobjective for the future. It is correspondinglyvital that the protection of our environment andspecifically ground and surface water quality, isa central objective in the assessment, design,installation and maintenance of newwastewater disposal systems in un-seweredareas. This code of practice (CoP) establishesan overall framework of best practice inmeeting the above objective.

The Minister for the Environment publishedplanning guidelines under Section 28 of thePlanning and Development Act 2000 onSustainable Rural Housing in 2005. Theguidelines establish an overall national-levelpolicy framework for future housingdevelopment in rural areas, which has beenadopted into the majority of countydevelopment plans. In particular, the guidelineshighlight that those sites for new houses in un-sewered rural areas must be suitable for theinstallation and operation of on-site wastewatertreatment systems and take into account localground conditions. This CoP contains anassessment methodology for the determinationof whether or not a site is deemed suitable.

The Department of the Environment, Heritageand Local Government (DoEHLG) issued aCircular Letter (SP 5/03) to planning authorities

on 31 July 2003. This Circular drew theattention of planning authorities to the vitalimportance of sound development plan policiesrelating to the protection of surface andgroundwater quality, the importance of goodlocation and design of necessary developmentin rural areas, and the then current standardsfor on-site wastewater treatment systems.

The overall regulatory and policy framework atnational level is therefore clear on the need forthe application of high standards in theassessment of, provision and maintenance ofeffective on-site wastewater disposal systemsfor new housing developments in rural areasand this CoP presents comprehensiverecommendations for the attainment of suchhigh standards in line with the regulatory andpolicy frameworks.

A.2 Planning Authorities

Under Article 22(2)(c) of the Planning andDevelopment Regulations 2006, where it isproposed to dispose of wastewater other thanto a public sewer from a development proposedas part of a planning application to a planningauthority, the applicant must submit informationon the type of on-site treatment systemproposed and evidence as to the suitability ofthe site for the system proposed as part of thatplanning application.

Planning authorities therefore have a key rolein making decisions on the suitability of sites fordevelopment, and the assessment of thesuitability of particular sites for on-sitewastewater treatment and disposal systemswill be a key element of such decision-makingprocesses in un-sewered areas. This CoPprovides the methodology for undertaking suchsite suitability assessments in accordance withthe overall regulatory and policy framework setout by the DoEHLG relating to the planningsystem.

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Assessment of site suitability under this CoPshould have regard to policies contained in thedevelopment plans as referred to above andany other relevant parallel documents such asgroundwater protection schemes (GWPSs)prepared by the Geological Survey of Ireland(GSI) and river basin management plansproduced under the Irish transposition of theEU Water Framework Directive.

Many on-site wastewater treatment systemsare available for single houses and aredesigned to:

• Treat the wastewater to minimisecontamination of soils and waterbodies

• Prevent direct discharge of untreatedwastewater to the groundwater or surfacewater

• Protect humans from contact withwastewater

• Keep animals, insects, and vermin fromcontact with wastewater, and

• Minimise the generation of foul odours.

Public health specifically and water quality ingeneral are threatened when on-site systemsfail to operate satisfactorily. System failurescan result in wastewater ponding or formingstagnant pools on the ground surface when thewastewater is not absorbed by the soil. In suchcircumstances of system failure, humans cancome in contact with the ponded wastewaterand be exposed to pathogens and also foulodours can be generated. Inadequately treatedwastewater through poor location, designand/or construction may lead to contaminationof our groundwater and surface waters, whichin many areas are also used as drinking watersupplies. In some cases, both the wastewatertreatment system and the private drinkingwater supply source are located on the onesite; therefore, it is essential that the effluent isproperly treated and disposed of. It is theresponsibility of the homeowner to ensure thatthe wastewater treatment system is installed inaccordance with the planning permission andany relevant conditions attached thereto, andthat it is properly maintained on a regular basis

to ensure that it does not cause pollution of theenvironment or of drinking waters.

A.3 Legislative Provisions

Wastewater treatment systems are designed todischarge treated effluent to waters; in Irelandmost of the small-scale on-site systemsdischarge to ground via percolation through thesoil and subsoil. In all cases, the requirementsof the water protection legislation shall becomplied with. The main water protectionlegislation includes:

• Water Services Act, 2007 (S.I. No. 30 of2007)

• Local Government (Water Pollution) Act,1977 (S.I. No. 1 of 1977).

• Local Government (Water Pollution)(Amendment) Act, 1990 (S.I. No. 21 of1990)

• Local Government (Water Pollution) Act,1997 (Water Quality Standard forPhosphorus) Regulations, 1998 (S.I. No.258 of 1998)

• Local Government (Water Pollution)Regulations, 1978 (S.I. No. 108 of 1978)

• Local Government (Water Pollution)Regulations, 1992 (S.I. No. 271 of 1992)

• Local Government (Water Pollution)(Amendment) Regulations, 1996 (S.I. No.184 of 1996)

• Local Government (Water Pollution)(Amendment) Regulations, 1999 (S.I. No.42 of 1999)

• Protection of Groundwater Regulations,1999 (S.I. No. 41 of 1999)

• Fisheries (Consolidation) Act (Amendment)1959.

In addition, the following European legalisationprovides protection to groundwater:

• Council Directive on the protection ofgroundwater against pollution caused bycertain dangerous substances (80/68/EEC)



• Council Directive concerning the protectionof waters against pollution caused bynitrates from agricultural sources(91/676/EEC)

• Directive 2000/60/EC of the EuropeanParliament and Council establishing aframework for Community action in the fieldof water policy (2000/60/EC) (commonlyreferred to as the Water FrameworkDirective), and

• Directive 2006/118/EC of the EuropeanParliament and Council on the protection ofgroundwater against pollution anddeterioration (2006/118/EC).

At European level, work is being completed onthe development of the EN 12566 series ofstandards for Small Wastewater TreatmentSystems for up to 50 PT. The EN 12566 seriesof standards is developed and published byComité Européen de Normalisation (EuropeanCommittee for Standardisation) (CEN) andadopted by the National Standards Authority ofIreland (NSAI). Their content has been takeninto account in the preparation of thisdocument.

I.S. EN 12566-1:2000/A1:2004, I.S. EN 12566-3:2005 and I.S. EN 12566-4:2007 areconstruction product standards within the termsof the Construction Products Directive and, assuch, any requirements regarding thespecification and performance of productscovered by these standards and referenced inAnnex ZA of the standard, must be based onthe content of the standard and the tests andprocedures defined in the standards. prEN12566-6 and prEN 12566-7, when adopted, willalso be construction product standards andsimilar considerations will apply.

The CoP cross-references the appropriatesections of the standard; however, the reader isreferred to the individual parts of thestandards/technical reports for full details. Thestatus of the individual parts is listed below:

• I.S. EN 12566-1:2000/A1:2004 SmallWastewater Treatment Systems for up to 50PT – Part 1: Prefabricated Septic Tanks(published by the NSAI as an IrishStandard)

• I.S. CEN/TR 12566-2:2005 SmallWastewater Treatment Systems for up to 50PT – Part 2: Soil Infiltration Systems(published by the NSAI as a Code ofPractice)

• I.S. EN 12566-3:2005 Small WastewaterTreatment Systems for up to 50 PT – Part 3:Packaged and/or Site Assembled DomesticWastewater Treatment Plants (published bythe NSAI as an Irish Standard)

• I.S. EN 12566-4:2007 Small WastewaterTreatment Systems for up to 50 PT – Part 4:Septic Tanks Assembled in situ fromPrefabricated Kits (published by CEN)

• I.S. CEN/TR12566-5:2008 Small Wastewater Treatment Systems for up to 50 PT –Part 5: Pre-Treated Effluent FiltrationSystems (published by CEN as a technicalreport)

• prEN 12566-6 Small Wastewater TreatmentSystems for up to 50 PT – Part 6:Prefabricated Treatment Units for SepticTank Effluent (in preparation)

• prEN 12566-7 Small Wastewater TreatmentSystems for up to 50 PT – Part 7:Prefabricated Tertiary Treatment Units (inpreparation).

Some of these standards apply to (or will applyto) products that are deemed to be constructionproducts for the purposes of the ConstructionProducts Directive and are know asharmonised European Standards (hENs), e.g.I.S. EN 12566-1:2000/A1:2004, I.S. EN 12566-3:2005 and I.S. EN 12566-4:2007, etc. At theend of a set co-existence period, existingconflicting national standards must bewithdrawn and all relevant products beingplaced on the market should comply with theharmonised parts of the standard and meet theperformance requirement as set out in PartOne of this CoP. The coexistence period forharmonised European Standards can be foundon the European Commissions NANDOdatabase (http://ec.europa.eu/enterprise/newapproach/nando/).

In the case of a hEN not yet being available,products should be certified (certification may



include a European Technical Approval, anAgrément Certificate or equivalent), be fit forthe purpose for which they are intended, theconditions in which they are used and meet theperformance requirements as set out in PartOne of this CoP.

The DoEHLG issued a Circular Letter(BC16/2006) in November 2006 providinginterim advice to local authorities in relation toEuropean Standards for domestic wastewatertreatment plants. It advises that I.S. EN 12566-3:2005 has been adopted by CEN andtransposed in Ireland by the NSAI as I.S. EN12566-3:2005. Wastewater treatment plantsare deemed to be construction products for thepurposes of the Construction Products

Directive (89/106/EEC) and the requirementsof that directive apply to these systems. It alsoindicates that the Second Edition of theEnvironmental Protection Agency (EPA)Wastewater Treatment Manual: TreatmentSystems for Single Houses (now the Code ofPractice: Wastewater Treatment and DisposalSystems Serving Single Houses) will provideguidance on performance levels that can begenerally applied; in their absence it refers tothe wastewater treatment performancestandards of the Irish Agrément Board (IAB).They are biochemical oxygen demand – 20mg/l, suspended solids – 30 mg/l, andammonia as NH4 – 20 mg/l.



Annex B Groundwater Protection Response

B.1 Background

The primary responsibility for groundwaterprotection rests with any person who is carryingon an activity that poses a threat togroundwater. Groundwater in Ireland isprotected under European Community andnational legislation. Local authorities and theEnvironmental Protection Agency (EPA) haveresponsibility for enforcing this legislation. In1999, the GSI, in conjunction with theDepartment of Environment and LocalGovernment (DoELG) and the EPA, issuedguidelines on the preparation of GWPSs toassist the statutory authorities and others tomeet their responsibility to protect groundwater(DoELG/EPA/GSI, 1999a,b). A GWPSincorporates land surface zoning andgroundwater protection responses (GWPRs).

This document is concerned with GWPRs forthe siting of on-site wastewater treatmentsystems for a dwelling house of up to 10 peoplewith facilities for toilet usage, living, sleeping,bathing, cooking and eating. The GWPRsoutline acceptable on-site wastewatertreatment systems in each groundwaterprotection zone (DoELG/EPA/GSI, 2001) andrecommend conditions and/or investigationsdepending on the groundwater vulnerability,the value of the groundwater resource and thecontaminant loading. It should be noted thatthese responses update the responses issuedin 2001 and relate to discharges from singlehouses to groundwater. Less stringentresponses may be appropriate for dischargesto surface waters.

In Ireland, wastewater from approximately400,000 dwellings is treated by on-sitesystems. On-site systems can be subdividedinto two broad categories: septic tank systemsand mechanical aeration systems.

A septic tank system consists of a septic tankfollowed by a soil percolation area. As analternative to a percolation area the effluent

from a septic tank can be treated by filtersystems such as:

• A soil percolation system in the form of amound

• An intermittent sand filter followed by apolishing filter

• An intermittent peat filter followed by apolishing filter

• An intermittent plastic or other media filterfollowed by a polishing filter, or

• A constructed wetland or reed bed, followedby a polishing filter.

Mechanical aeration systems include biofilmaerated (BAF) systems, rotating biologicalcontactor (RBC) systems, and sequencingbatch reactor (SBR) systems. The effluent froma mechanical aeration system should betreated by a polishing filter to reduce micro-organisms, and in some soil conditionsphosphorus. On-site wastewater systems arethe primary method used for the treatment anddisposal of domestic wastewater in rural areas.These systems are also used in urban areas,which are not connected to public sewersystems. On-site domestic wastewatertreatment systems are often located close toprivate or public wells.

When choosing the location and type of on-sitesystem, builders should have regard to anynearby groundwater source, the groundwateras a resource and the vulnerability of theunderlying groundwater. The GWPRs in thisguidance combine these factors to produce aresponse matrix.

The objectives of these GWPRs are:

• To reduce the risk of pollutants reachingdrinking water supplies

• To reduce the risk of pollution of aquifers

• To minimise pollution of domestic wells, and



• To provide advice where it is proposed tolocate domestic wells in the vicinity ofexisting wastewater treatment systems andvice versa.

The risk from on-site wastewater treatmentsystems is mainly influenced by:

• Its proximity to a groundwater source

• The groundwater vulnerability

• The value of the groundwater resource

• The depth of the water table

• The groundwater flow direction, and

• The type of on-site system and the qualityof the final effluent.

The use of these GWPRs allows decisions tobe made on the acceptability or otherwise ofon-site wastewater treatment systems from ahydrogeological point of view.

These GWPRs should be read in conjunctionwith Groundwater Protection Responses forOn-Site Wastewater Systems for SingleHouses (DoELG/EPA/GSI, 2001). Otherpublished responses in this series areGroundwater Protection Responses forLandfills (DoELG/EPA/GSI, 1999a) andGroundwater Protection Response to theLandspreading of Organic Wastes(DoELG/EPA/GSI, 1999b).

B.2 Effluent from On-siteWastewater Treatment Systemsfor Single Houses: a PotentialHazard for Groundwater

The typical characteristics of domesticwastewater are outlined in Table B.1. Particularcontaminants of concern are pathogenicorganisms and nitrates.

B.3 Pathogenic Organisms

Pathogenic organisms can causegastroenteritis, polio, hepatitis, meningitis andeye infections. Organisms such as Escherichiacoli, streptococci and faecal coliforms, with thesame enteric origin as pathogens, indicatewhether pathogens may be present or not inwastewater.

B.4 Nitrates

Nitrate in excess concentrations in water mayconstitute a risk to human health and theenvironment. Nitrogen enters on-sitewastewater treatment systems mainly asorganic nitrogen, which means that thenitrogen is part of a large biological moleculesuch as a protein. Bacteria and other microbesoxidise or mineralise the organic nitrogen toammonia, which is further oxidised to nitritesand nitrates.

TABLE B.1. CHARACTERISTICS OF DOMESTIC WASTEWATER FOR A SINGLE HOUSE.

Parameter Typical mean influent concentration (mg/l)1

Chemical oxygen demand (COD) (as O2) 956

Biological oxygen demand (BOD5) (as O2) 3182

Total suspended solids 2003

Ammonia (NH4-N) 70

Ortho-phosphorus (PO4-P) 18

Total coliforms4 (MPN/100 ml) 4.1 × 107

Escherichia coli4 (MPN5/100 ml) 7.1 × 105

1Back-calculated septic tank influent concentrations (mean) from 2000-MS-15-M1 and 2005-W-MS-15.2BOD:COD ratio of 1:3 from 2005-W-MS-15.3EPA, 2000.4Median values.5Most probable number (MPN/100 ml).



B.5 Groundwater ProtectionResponse Matrix for SingleHouse Systems

The reader is referred to the full text inGroundwater Protection Responses for On-Site Systems for Single Houses(DoELG/EPA/GSI, 2001) for an explanation ofthe role of GWPRs in a GWPS.

A risk assessment approach is taken in thedevelopment of this response matrix. Aprecautionary approach is taken because ofthe variability of Irish subsoils, bedrock and thepossibility that the treatment system may notfunction properly at all times. Where there is ahigh density of dwellings in the vicinity of public,group scheme or industrial water supplysources, more restrictive conditions may berequired or the development may need to berefused. The density of dwellings andassociated treatment systems may impact onthe groundwater because of the cumulativeloading, particularly of nitrate. This should betaken into account especially where thevulnerability of the groundwater is high orextreme.

The potential suitability of a site for thedevelopment of an on-site system is assessedusing the methodology outlined in Section 6.The methodology includes a desk study andon-site assessment (visual, trial hole test andpercolation tests). The GWPRs set out in TableB.2 should be used during the desk study

assessment of a site to give an early indicationof the suitability of a site for an on-site system.Information from the on-site assessmentshould be used to confirm or modify theresponse. In some situations, site improvementworks, followed by reassessment of thegroundwater responses, may allow a system tobe developed. Site improvements are dealtwith in Section 6.5.

Where groundwater protection zones have notyet been delineated for an area, the responsesbelow should be used in the followingcircumstances:

• Where on-site systems are proposed in thevicinity of domestic wells

• Where on-site systems are proposed in thevicinity of sources of water with anabstraction rate above 10 m3/day (e.g.public, group scheme and industrial supplywells and springs)

• Where groundwater is extremely vulnerable(based on the visual assessment and trialhole test), and

• Where there are karst features such asswallow holes, caves, etc.

The appropriate response to the risk ofgroundwater contamination from an on-sitewastewater treatment system is given by theassigned response category (R) appropriate toeach protection zone.

TABLE B.2. RESPONSE MATRIX FOR ON-SITE TREATMENT SYSTEMS.Vulnerability rating Source protection

areaaResource protection area

Aquifer category

Regionally important Locally important Poor aquifers

Inner (SI) Outer (SO) Rk Rf/Rg Lk Lm/Lg Ll Pl Pu

Extreme (X and E) R32 R31 R22 R22 R22 R21 R21 R21 R21

High (H) R24 R23 R21 R1 R21 R1 R1 R1 R1

Moderate (M) R24 R23 R1 R1 R1 R1 R1 R1 R1

Low (L) R24 R1 R1 R1 R1 R1 R1 R1 R1aFor public, group scheme or industrial water supply sources where protection zones have not been delineated, the arbitrary distancesgiven in DoELG/EPA/GSI (1999a,b) of 300 m for the Inner Protection Area (SI) and 1,000 m for the Outer Protection Area (SO) shouldbe used as a guide up-gradient of the source.Rk, Regionally Important Karstified Aquifers; Rf, Regionally Important Fissured Bedrock Aquifers; Rg, Regionally Important ExtensiveSand and Gravel Aquifers; Lk, Locally Important Karstified Aquifers; Lg, Locally Important Sand/Gravel Aquifers; Lm, Locally Important– Bedrock Aquifer which is generally moderately productive; Ll, Locally Important – Bedrock Aquifer which is moderately productive inlocal zones; Pl, Poor – Bedrock Aquifer which is generally unproductive except for local zones; Pu, Poor – Bedrock Aquifer which isgenerally unproductive.



R1 Acceptable subject to normal good practice(i.e. system selection, construction,operation and maintenance in accordancewith this CoP).

R21 Acceptable subject to normal goodpractice. Where domestic water suppliesare located nearby, particular attentionshould be given to the depth of subsoil overbedrock such that the minimum depthsrequired in Section 6 are met and that thelikelihood of microbial pollution isminimised.

R22 Acceptable subject to normal good practiceand the following additional condition:

1. There is a minimum thickness of 2 munsaturated soil/subsoil beneath theinvert of the percolation trench of aseptic tank system

or

1. A secondary treatment system asdescribed in Sections 8 and 9 isinstalled, with a minimum thickness of0.3 m unsaturated soil/subsoil with P/T-values from 3 to 75 (in addition to thepolishing filter which should be aminimum depth of 0.9 m), beneath theinvert of the polishing filter (i.e. 1.2 m intotal for a soil polishing filter).

R23 Acceptable subject to normal goodpractice, Condition 1 above and thefollowing additional condition:

2. The authority should be satisfied that,on the evidence of the groundwaterquality of the source and the number ofexisting houses, the accumulation ofsignificant nitrate and/or microbiologicalcontamination is unlikely.

R24 Acceptable subject to normal goodpractice, Conditions 1 and 2 above and thefollowing additional condition:

3. No on-site treatment system should belocated within 60 m of a public, groupscheme or industrial water supplysource.

R31 Not generally acceptable, unless:

A septic tank system as described inSection 7 is installed with a minimumthickness of 2 m unsaturated soil/subsoilbeneath the invert of the percolation trench(i.e. an increase of 0.8 m from therequirements in Section 6)

or

A secondary treatment system, asdescribed in Sections 8 and 9, is installed,with a minimum thickness of 0.3 munsaturated soil/subsoil with P/T-valuesfrom 3 to 75 (in addition to the polishingfilter which should be a minimum depth of0.9 m), beneath the invert of the polishingfilter (i.e. 1.2 m in total for a soil polishingfilter)

and subject to the following conditions:

1. The authority should be satisfied that,on the evidence of the groundwaterquality of the source and the number ofexisting houses, the accumulation ofsignificant nitrate and/or microbiologicalcontamination is unlikely

2. No on-site treatment system should belocated within 60 m of a public, groupscheme or industrial water supplysource

3. A management and maintenanceagreement is completed with thesystems supplier.

R32 Not generally acceptable unless:

A secondary treatment system is installed,with a minimum thickness of 0.9 munsaturated soil/subsoil with P/T-valuesfrom 3 to 75 (in addition to the polishingfilter which should be a minimum depth of0.9 m), beneath the invert of the polishingfilter (i.e. 1.8 m in total for a soil polishingfilter)

and subject to the following conditions:

1. The authority should be satisfied that,on the evidence of the groundwaterquality of the source and the number ofexisting houses, the accumulation ofsignificant nitrate and/or microbiologicalcontamination is unlikely

2. No on-site treatment system should be



located within 60 m of a public, groupscheme or industrial water supplysource

3. A management and maintenanceagreement is completed with thesystems supplier.

The responses above assume that there is nosignificant groundwater contamination in thearea. Should contamination by pathogenicorganisms or nitrate (or other contaminants) bea problem in any particular area, morerestrictive responses may be necessary.Where nitrate levels are known to be high ornitrate-loading analysis indicates a potentialproblem, consideration should be given to theuse of treatment systems, which include a de-nitrification unit. Monitoring carried out by thelocal authority will assist in determiningwhether or not a variation in any of theseresponses is required.

Sites are not suitable for discharge of effluent toground for very low permeability subsoils(where T > 90).

B.6 Additional Requirements forthe Location of On-SiteTreatment Systems Adjacent toReceptors at Risk, such asWells and Karst Features

Table B.2 outlines responses for differenthydrogeological situations, which may restrictthe type of on-site treatment system, andshould be satisfied in the first instance. Once aresponse has been determined for a site, thenext step is to manage the risk posed to thefeatures identified during the desk study andon-site assessment. These features includewater supply wells and springs (public anddomestic), and karst features that enable thesoils and subsoil to be bypassed (e.g. swallowholes, collapse features).

Table B.3 provides recommended distancesbetween receptors (see also Fig. B.1) andpercolation area or polishing filters, in order toprotect groundwater. These distances dependon the thickness and permeability of subsoil.The depths and distances given in this table are

FIGURE B.1. RELATIVE LOCATION OF WELLS.



based on the concepts of ‘risk assessment’ and‘risk management’, and take account, as far aspracticable, of the uncertainties associated withhydrogeological conditions in Ireland. Use ofthe depths and distances in this table does notguarantee that pollution will not be caused;rather, it will reduce the risk of significantpollution occurring.

Where an on-site system is in the zone ofcontribution of a well, the likelihood ofcontamination and the threat to human healthdepend largely on five factors:

1. The thickness and permeability of subsoilbeneath the invert of the percolation trench

2. The permeability of the bedrock, where thewell is tapping the bedrock

3. The distance between the well or springand the on-site system

4. The groundwater flow direction, and

5. The level of treatment of effluent.

TABLE B.3. RECOMMENDED MINIMUM DISTANCE BETWEEN A RECEPTOR AND A PERCOLATION AREA OR POLISHING

FILTER.T/P-value1 Type of soil/subsoil2 Depth of

soil/subsoil(m above bedrock)

(see Notes 1, 2, 3, 6)

Minimum distance (m) from receptor to percolation area or polishing filter5

Public water

supply

Karst feature

Down-gradient domestic well orflow direction is

unknown(see Note 5)

Domestic wellalongside

(no gradient)

Up-gradient domestic well

>30CLAY; sandyCLAY (e.g. clayey till); SILT/CLAY

1.2>3.0 60 15

4030 25 15

10–30Sandy SILT; siltySAND; silty GRAVEL (e.g. sandy till)

1.2>8.0 60 15

4530 25 15

<10 SAND; GRAVEL; silty SAND

2.03

2.04

>8.0460 15

604030

25 15

1The T-value (expressed as min/25 mm) is the time taken for the water level to drop a specified distance in a percolation test hole. Forshallow subsoils the test hole requirements are different and hence the test results are called P-values. For further advice see AnnexC.

2BS 5930 descriptions. 3Water table 1.2–2.0 m. 4Water table >2.0 m.5The distance from the percolation area or polishing filter means the distance from the periphery of the percolation area or polishingfilter and not from the centre.

Notes: 1. Depths are measured from the invert level of the percolation trench.

2. Depths and distances can be related by interpolation: e.g. where the thickness of sandy CLAY is 1.2 m, the minimumrecommended distance from the well to percolation area is 40 m; where the thickness is 3.0 m, the distance is 30 m; distances forintermediate depths can be approximated by interpolation.

3. Where bedrock is shallow (<2 m below invert of the trench), greater distances may be necessary where there is evidence of thepresence of preferential flow paths (e.g. cracks, roots) in the subsoil.

4. Where the minimum subsoil thicknesses are less than those given above, site improvements and systems other than systems asdescribed in Sections 8 and 9 may be used to reduce the likelihood of contamination.

5. If effluent and bacteria enter bedrock rapidly (within 1–2 days), the distances given may not be adequate where the percolationarea is in the zone of contribution of a well. Further site-specific evaluation is necessary.

6. Where bedrock is known to be karstified or highly fractured, greater depths of subsoil may be advisable to minimise the likelihoodof contamination.



Annex C Site Characterisation

The key to installing a reliable on-site systemthat minimises the potential for pollution is toselect and design a suitable treatment systemfollowing a thorough site assessment. For asubsoil to be effective as a medium for treatingwastewater, it should be permeable enough toallow throughflow and remain unsaturated,whilst capable of retaining the wastewater for asufficient length of time to allow attenuation inthe aerobic conditions.

Only after a site assessment has beencompleted can an on-site system be chosen ifthe site has been deemed suitable. Theinformation collected in the evaluation will beused to select the on-site system. The followingsections elaborate on the requirements set outin Section 6 of the code. The relevant sectionsof the Site Characterisation Form should becompleted in all cases.

C.1 Desk Study

The purposes of the desk study are to:

• Obtain existing information relevant to thesite, which will assist in assessing itssuitability

• Identify targets at risk, and

• Establish if there are restrictions relating tothe site.

A desk study involves the assessment ofavailable data pertaining to the site andadjoining areas that may determine whetherthe site has any restrictions. Informationcollected from the desk study should includeany material related to the hydrological,hydrogeological and planning aspects of thesite that may be available. The density ofexisting housing and performance of theexisting wastewater treatment systems willaffect existing groundwater quality and shouldbe noted at this stage. In addition, the locationof any archaeological or natural heritage sites(Special Area of Conservation (SAC), SpecialProtection Area (SPA), etc.) in the vicinity of the

proposed site should be identified. The LocalDevelopment Plan and planning register cancontain a wide range of planning andenvironmental information. The local authorityheritage officer should also be consulted todetermine the significance of anyarchaeological sites located in the vicinity.

The GWPSs provide guidelines for builders inassessing groundwater resources andvulnerability and for planning authorities incarrying out their groundwater protectionfunctions. They provide a framework to assist indecision making on the location, nature andcontrol of developments and activities(including single-house treatment systems) inorder to protect groundwater. GWPR zoningoutlines the aquifer classification in the generalarea and the vulnerability of the groundwater.The GWPRs will provide an early indication ofthe probable suitability of a site for an on-sitesystem. The on-site assessment will laterconfirm or modify such responses. The densityof on-site systems is also considered at thisstage. The protection responses required toprotect groundwater from on-site systemsshould be satisfied. Where no GWPS exists,interim measures, as set out in theGroundwater Protection Schemes should beadopted. If additional requirements arerequired then this should be noted in thecomments section. Also, if there are existing orproposed wells in the area then the minimumdistances set out in the GWPRs should benoted at this stage. Note, if the GWPR is R23 orhigher, the groundwater quality needs to beassessed.

C.2 On-site Assessment

C.2.1 Visual assessmentThe factors examined during a visualassessment and their significance aresummarised in Table C.1. The principal factorsthat should be considered are as follows:

Landscape position: Landscape positionreflects the location of the site in the landscape,



e.g. crest of hill, valley, slope of hill. Sites thatare on level, well-drained areas, or on convexslopes are most desirable. Sites that are indepressions, or on the bottom of slopes or onconcave slopes are less desirable and may beunsuitable.

Slope: It is more difficult to install pipework andensure that the wastewater will stay in the soilif the land has a steep slope. In some cases thepipes should be laid along the contours of theslope. Where there is surface water run-off andinterflow, low-lying areas and flat areasgenerally receive more water. This accounts tosome extent for the occurrence of poorlydrained soils in low-lying areas. Soils with poordrainage, however, may also be found on goodslopes where the parent material or the subsoilis of low permeability. Provision should bemade for the interception of all surface run-offand seepage, and its diversion away from theproposed percolation area. Mound filtersystems are prohibited on sites where thenatural slope is greater than 1:8 (12%) as this

will lead to hydraulic overloading at the toe ofthe mound down slope.

Proximity to surface features: Minimumseparation distances, as set out in the followingsections should be maintained from specifiedfeatures. The presence/location of surfacefeatures such as watercourses, includingecologically sensitive receiving waters, siteboundaries, roads, steep slopes, etc., shouldbe noted. Minimum separation distances areset out in Table 6.1. Note, distances from lakesor rivers should be measured from the highwater level or flood water level.

Existing dwellings and wastewatertreatment systems: The performance ofexisting wastewater treatment and storm waterdisposal systems should be examined and thecause of problems identified and brought to theattention of the local authority to addressremediation. Potential impacts from adjacentwastewater treatment systems should also beconsidered.

TABLE C.1. FACTORS TO BE CONSIDERED DURING VISUAL ASSESSMENT.

Factor Significance

Water level in ditches and wells Indicates depth of unsaturated subsoil available for treatment or polishing of wastewater

Landscape position May indicate whether water will collect at a site or flow away from the site

Slope Pipework, surface water run-off and seepage. Influences the design of the system

Presence of watercourses, surface water ponding

May indicate low permeability subsoil or a high water table

Presence and types of bedrock outcrops Insufficient depth of subsoil to treat wastewater allowing it to enter the groundwater too fast

Proximity to existing adjacent percolation areas and/or density of houses

May indicate a high nutrient-loading rate for the locality and/or potential nuisance problems. The location of storm water disposal areas from adjacent houses also needs to be assessed with regard to its impact on the proposed percolation area

Land use and type of grassland surface (if applicable)

Suggests rate of percolation or groundwater levels

Vegetation indicators Suggest the rate of percolation or groundwater levels. The presence of indicator plants should not be taken as conclusive evidence that the site is suitable for a drainage system, but they might indicate where any subsequent soil investigations could take place

Proximity to wells on-site and off-site, water supply sources, groundwater, streams, ditches, lakes, surface water ponding, beaches, shellfish areas, springs, karst features, wetlands, flood plains and heritage features

Indicates targets at risk



In addition, the implication of any potentialimpact due to the increased nutrient load on thegroundwater quality in the area should beassessed. This is particularly true in areas ofhigh-density housing (iPlan system) and inareas where the background nitrateconcentrations are already elevated. It isestimated that a 6 p.e. wastewater treatmentsystem (without specially designed nutrientremoval) will increase the nitrate levels by 21mg/l NO3 per hectare6.

Wells/Springs: Wells should be considered astargets at risk. The number of wells and thepresence of any springs should be noted. Theminimum distances of wells/springs fromwastewater treatment systems and percolationareas/polishing filters are set out in the GWPRfor wastewater treatment systems for singlehouses (Annex B). Wastewater treatmentsystems do not pose a risk to decommissionedwells if the wells have been properly sealed offin accordance with BS 5930 or other guidancedocument.

Groundwater flow direction: In general,groundwater flow direction can be inferred fromtopography on sloping sites and/or proximity tosurface water features such as rivers or lakes.It should be indicated on the site plan.

Outcrops and karst features: The presenceof vulnerable features such as outcrops,swallow holes, etc., should be determined andthe distance between them and the proposeddevelopment noted.

Drainage: A high density of streams or ditchestends to indicate a high water table andpotential risk to surface water. Low streamdensity indicates a free-draining subsoil and/orbedrock.

Land use: Current and previous land useshould be noted, in particular any previousdevelopment on the site should be highlightedsuch as old building foundations, etc. Housingdensity should also be noted.

Vegetation indicators: Rushes, yellow flags(irises), alders and willow suggest poor

percolation characteristics or high water tablelevels. Grasses, trees and ferns may suggestsuitable percolation characteristics. Plants andtrees suggest good drainage and poordrainage are illustrated in Fig. C.1.

Ground conditions: The ground conditionsduring the on-site investigation should benoted. Trampling damage by livestock canindicate impeded drainage or intermittent highwater tables, especially where accompanied bywidespread ponding in hoof prints. Evidence ofinfill material or made ground should also benoted which may indicate the presence of soilswith poor percolation properties beneath.

Minimum separation distances: Theminimum separation distances, as set out inSection 6 – Table 6.1, should be checked atthis stage of the assessment.

C.2.1.1 Plants indicative of drainage conditionsFigure C.1 illustrates plants that indicate dryconditions (good drainage) and others thatindicate wet conditions (poor drainage)throughout the year. Some of the photosillustrate the plants in flower – this aspectshould be ignored. Plants in flower, orotherwise, do not change their indicator status.Note that alder is a tree.

C.2.2 Trial hole assessmentThe trial hole should be located adjacent to butnot within the proposed percolation area/polishing filter, as the disturbed subsoil willprovide a preferential flow path in the finalpercolation area.

The trial hole should remain open for aminimum period of 48 h to allow the water table(if present) to re-establish itself and be securelyfenced off and covered over to prevent theingress of surface water or rainwater. If on asloping site then a small drainage channelshould be dug on the up-slope side of the holeto prevent any surface water inflow into the trialhole.

The health and safety7 aspects of placing a trialhole on the site should be borne in mind. A trialhole is a deep, steep-sided excavation, whichmay contain water and which may be difficult toexit from if improperly constructed. A risk ofcollapse of the side walls of the trial hole may

6. Section 13.2.14 Site Suitability Assessments for On-SiteWastewater Management, FÁS Course Manual, Vol. 2.



FIGURE C.1. INDICATOR PLANTS OF DRY AND WET CONDITIONS.

Thistle Bracken Ragwort

Alder Iris

Rush Willow

Dry conditions

Wet conditions



exist in some situations. All appropriate healthand safety precautions should be taken. Thedepth of the percolation test hole is dependenton the subsoil characteristics present in the trialhole.

The soil and subsoil characteristics should bedetermined as per the code and the guidancebelow and documented in the SiteCharacterisation Form.

The observations made from the trial hole andtheir significance are summarised in Table C.2.

Depth to bedrock and depth to water table:For septic tank systems a depth of 1.2 m ofsuitable free-draining unsaturated subsoil, tothe bedrock and to the water table below thebase of the percolation trenches, should existat all times to ensure satisfactory treatment ofthe wastewater. In the case of secondarytreatment systems a minimum of 0.9 munsaturated subsoil is required. Sites assessedin summer when the water table is low, shouldbe examined below the proposed invert of thepercolation pipe for soil mottling (Fig. C.2) –- anindicator of seasonally high water tables. Forfurther details see the Groundwater NewsletterNo. 45 issued by the GSI (Daly, 2006).

Soil texture: Texture is the relative proportionsof sand, silt and clay particles in a soil. Therelative proportions of these constituents aredetermined using the British Standard

BS 5930:1999 Code of practice for siteinvestigations. The rate and extent of manyimportant physical processes and chemicalreactions in soils are governed by texture.Physical processes influenced by textureinclude drainage and moisture retention,diffusion of gases and the rate of transport ofcontaminants. Texture influences the biofilmsurface area in which biochemical andchemical reactions occur. The soil textureshould be characterised using the BS 5930classification. Every significant layer

7. Trial holes fall under the definition of construction work andall activities associated with them are subject to the Safety,Health and Welfare at Work (Construction) Regulations2001 and amendments. Further information can be obtainedfrom the Health and Safety Authority, 10 Hogan Place,Dublin 2.

TABLE C.2. FACTORS TO BE CONSIDERED DURING A TRIAL HOLE EXAMINATION.

Factors Significance

Soil/subsoil structure and texture Both influence the capacity of soil/subsoil to treat and dispose of the wastewater; subsoils with high clay content are generally unsuitable

Mottling (Fig. C.2) Indicates seasonal high water tables or very low permeability subsoil

Depth to bedrock Subsoil should be of sufficient depth to treat wastewater

Depth to water table Saturated subsoils do not allow adequate treatment of wastewater

Water ingress along walls Indicates high water table or saturated layers (e.g. perched water table)

Season Water table varies between seasons (generally high in winter)

FIGURE C.2. CLOSE-UP OF MOTTLING IN TRIAL HOLE.



encountered in the trial hole should bedescribed in the Site Characterisation Form.

A guide to assist the classification ofsoils/subsoils is included in Annex C.2.2.1.Various soil/subsoil texture classificationschemes exist. Table C.3 indicates sometypical percolation rates for different subsoiltypes but it is important to realise that thesecondary constituents of the subsoil may havean effect on the percolation test results, as willstructure and compactness.

Structure: Soil structure refers to thearrangement of the soil particles into largerunits or compound particles in the soil. The soilparticles, sand, silt, clay and organic matter,are generally clumped together to form largerunits called peds. The shape and size of thepeds can have a significant effect on thebehaviour of soils. A ped is a unit of soilstructure such as an aggregate, a crumb, aprism, a block or granules formed by naturalprocesses. Soil texture plays a major part indetermining soil structure. The structure of thesoil influences the pore space, aeration anddrainage conditions. The preferred structuresfrom a wastewater treatment perspective aregranular (as fine sand), blocky, structurelessand single grain. Subsoils with extensive, largeand continuous fissures and thick lenses ofgravel and coarse sand may be unsuitable; thissuitability will be assessed in the percolationtest.

Peat soils when saturated are unsuitable fordisposal of treated wastewater because theyprovide inadequate percolation and may resultin ponding – particularly during the wintertime.

Soil compactness/density: This refers to howtightly the soil grains are packed together. It iscommonly classified from un-compact to hard.

Colour: Colour is a good indicator of the stateof aeration of the soil/subsoil. Free-drainingsoils/subsoils are in an oxidised state andexhibit brown, reddish brown and yellowishbrown colours. Many free-draining soils oflimestone origin with deep water tables aregrey at depth (due to the colour of the parentmaterial). Saturated soils/subsoils are in areduced state and exhibit dull grey or mottledcolours. Mottling (comprising a mix of grey andreddish brown or rusty staining) of the soillayers can indicate the height of the water tablein winter.

Layering (stratification): This is common insoils, arising during deposition and/orsubsequent weathering. In soils that are freedraining in the virgin state, weathering canresult in downward movement of some of theclay fraction leading to enrichment of a sub-layer with clay. In some areas a thin, hard, rust-coloured impervious layer can develop (ironpans) as a result of the downward leaching ofiron and manganese compounds anddeposition at shallow depth, which impedesdownward flow. The underlying subsoil oftenhas a satisfactory percolation rate. Such soilscan often be improved by loosening or bybreaking the impervious layer.

Preferential flow paths: Preferential flowpaths (PFPs) are formed in soils by biological,chemical and physical processes and theirinteractions. Research in recent yearsindicates that PFPs can have a significantinfluence on the movement of ponded orperched water in soil/subsoils where free (non-capillary) water is in direct contact with PFPs.The presence of PFPs should be noted duringthe trial hole assessment because theirpresence may influence the percolation rate ofthe subsoil (e.g. roots, sand fingering, wormburrows). For example, a relatively highpercolation rate (i.e. low T-value) could occur ina CLAY if it contains many/large PFPs.

C.2.2.1 Subsoil classification chart

See methodology overleaf to determine thesubsoil classification.

TABLE C.3. SUBSOIL CLASSIFICATION AGAINST T-VALUES FOR 400 T-TESTS (JACKSON, 2005).

BS 5950 soil classification T-value

GRAVEL 3–10

SAND 4–15

SILT 12–33

SILT/CLAY 15–43

CLAY >37


Code of P

ractice: Wastew

ater Treatm

ent and Disposal S

ystems S

erving Single H

ouses (p.e. ≤ 10)

Environm

ental Protection A

gency69


A: Examine Boulders and CobblesTest adapted from the British StandardsInstitution BS 5930:1999 Code of practice forsite investigations (1999).

• Using a hammer, trowel, or pick, clean off aportion of the trial pit wall.

• Examine whether the quantity ofboulders/cobbles is dominant over finermaterial. This will usually be easily done byeye. If unsure, separate boulders/cobblesfrom finer material in two sample bags andcompare weights by hand.

B and C: Preparation of Sample andApparent Cohesion TestTest taken from the British StandardsInstitution BS 5930:1999 Code of practice forsite investigations (1999).

• Collect a hand-sized representative samplefrom the cleaned-off portion of the trial pitwall.

• Remove particles larger than 2 mm, as faras possible.

• Crush clumps of subsoil and break downthe structure of the sample.

• Slowly add water (preferably as a finespray), mixing and moulding the sampleuntil it is the consistency of putty; it shouldbe pliable but not sticky and shouldn’t leavea film of material on your hands. Can thesample be made pliable at the appropriatemoisture content?

• If it can, squeeze the sample in your fist –does it stick together?

D: Thread TestTest adapted from a combination of theAmerican Society of Testing and MaterialsDesignation Standard practice for descriptionand identification of soils (visual–manualprocedure) (1984), and the British StandardsInstitution BS 5930:1999 Code of practice forsite investigations (1999).

• Ensure the sample is of the consistency ofputty. This is very important! Add extrawater or sample to moisten or dry thesample.

• Check that no particles greater than 1 or 2mm occur in the prepared sample.

• Gently roll a thread 3 mm in diameteracross the width of the palm of your hand.Remove excess material.

• If a thread can be rolled, break it and try tore-roll without adding additional water.

• Repeat until the thread can no longer berolled without breaking.

• Record the total number of threads thatwere rolled and re-rolled.

• Repeat the test at least twice per sample.Water can be added between each testrepetition to return the sample to theconsistency of putty.

E: Ribbon TestTest adapted from the United StatesDepartment of Agriculture Soil ConservationService Soil Survey Agricultural Handbook 18(1993).

PARTICLE SIZES AS DEFINED IN BS 5930:1999.

Boulder >200 mm Larger than a soccer ball

Cobble 60–200 mm Smaller than a soccer ball, but larger than a tennis ball

Gravel 2–60 mm Smaller than a tennis ball, but larger than match heads

Sand 0.06–2 mm Smaller than a match head, but larger than flour

Silt 0.002–0.06 mm Smaller than flour (not visible to the naked eye)

Clay <0.002 mm Not visible to the naked eye.



• Ensure the sample is of the consistency ofputty. This is very important! Add extrawater or sample to moisten or dry thesample.

• Check that no particles greater than 1 or 2mm occur.

• Form your moist sample into a large roll inyour hand, approximately the width of yourthumb.

• Hold your hand and arm parallel with theground. Using your thumb, press thesample over your index finger to form auniform ribbon about thumb-width and 0.5cm thick. Let this ribbon hang over yourindex finger and continue to extrude theribbon between thumb and index finger untilit breaks. Be careful not to press yourthumb through the ribbon.

• Measure the total length of the formedribbon when it breaks (i.e. from tip of thumbto end of ribbon).

• Repeat this test at least three times persample to obtain an average ribbon value.Water can be added between eachrepetition to return the sample to theconsistency of putty.

F: Dilatancy Test Test taken from British Standards InstitutionBS 5930:1999 Code of practice for siteinvestigations (1999).

• Wet the sample such that it is slightly morewet (and softer) than for a thread test, butnot so wet that free water is visible at thesurface.

• Spread the sample in the palm of one hand,such that no free water is visible at thesurface.

• Using the other hand, jar the sample fivetimes by slapping the heel of your hand orthe ball of your thumb. Take note of whetherwater rises to the surface or not, and howquickly it does so.

• Squeeze the sample, again noting if thewater disappears or not, and how quickly.

• Dilatant samples will show clear and rapidemergence of a sheen of water at thesurface during shaking, and clear and rapiddisappearance from the surface duringsqueezing. Non-dilatant samples will showno discernible sheen.

• Decide whether your sample has dilatancy.Beginners often find it quite difficult todetermine the presence of a sheen, unlessit is very obvious. It will become easier oncesamples with clear dilatancy are observed.

BS 5930:1999 CRITERIA FOR DESCRIBING DENSITY/COMPACTNESS (FINE SUBSOILS).

Term Field test

Uncompact Easily moulded or crushed in fingers

Compact Can be moulded or crushed by strong finger pressure

Very soft Finger easily pushed up to 25 mm

Soft Finger pushed up to 10 mm

Firm Thumb makes impression easily

Stiff Can be indented slightly by thumb

Very stiff Can be indented by thumbnail

Hard Can be scratched by thumbnail

BS 5930:1999 CRITERIA FOR DESCRIBING

DISCONTINUITIES.

Term Mean spacing (mm)

Very widely >2,000

Widely 2,000–600

Medium 600–200

Closely 200–60

Very closely 60–20

Extremely closely <20

Fissured Breaks into blocks along unpolished discontinuities

Sheared Breaks into blocks along polished discontinuities



C.2.3 Percolation testing The percolation test comprises themeasurement of the length of time for the waterlevel to fall a standard distance in thepercolation test hole. There are two variationsto the percolation test, i.e. the T-test and the P-test. The T-test is used to test the suitability ofthe subsoil at depths greater than 400 mmbelow the ground level. The P-test is carried outat ground level, where there are limiting factors,such as high water table or shallow bedrock orwhere the T-test result is outside theacceptable range (>50 for septic tank effluent;>75 for secondary-treated effluent) but lessthan 90.

The T-test: The T-test is used to test thesuitability of the subsoil, beneath the invert ofthe proposed percolation pipe or polishing filterdistribution system, to hydraulically transmit thetreated effluent from the treatment system. Theprecise depth at which the percolation pipe willbe located (and, by consequence, the top of theT-test percolation test hole) will depend on themost suitable subsoil layer for treatment anddisposal and the depth of topsoil at the site butwill normally be at least 450 mm below theground level, to provide adequate protection forthe percolation pipework and to ensure that thepercolation pipe is discharging into the subsoillayer. The assessor will decide the actual depthat which the percolation pipe will be located,based on the results of the visual assessmentand the trial hole investigation. This in turn willdictate the depth from ground surface to the topof the T-test percolation hole.

A T-test should be conducted at all sites wheredepth to bedrock or water table permitsbecause if a T-test is in excess of 90 then,irrespective of the P-test result, the site isunsuitable for discharge of treated effluent toground as it will ultimately result in ponding dueto the impervious nature of the underlyingsubsoil (or bedrock).

The P-test: The P-test is carried out at groundlevel to establish a percolation value for soilsthat are being considered to be used forconstructing a mounded percolation area or apolishing filter discharging at ground surface.Hence, the situation where a P-test might beconsidered is where the T-test shows that the

site is not suitable for treating effluent from aconventional septic tank (such as a high watertable or shallow bedrock or 50 ≤ T ≤ 90) andconsideration is being given to an alternativetreatment system which would dischargeeffluent at ground surface through the soilpolishing filter.

Standard and modified T and P-tests: Thestandard percolation test method (Steps 1–4)should be carried out on all sites where thesubsoil characteristics indicate that thepercolation result will be less than or equal to50. In the case of CLAY or SILT/CLAY subsoilthen a modified percolation test should becarried out. This test is outlined in Step 5 and isa modification of the Standard Method wherebyan approximation of the percolation rate forhigh T-values can be made in a shortened timeframe thus reducing the time spent on-site.

Note: Any material that falls into the bottom ofthe test holes during the carrying out of the testshould be removed prior to being re-filled.

Percolation test holes should be locatedadjacent to, but not within, the proposedpercolation area. It is important to note that thetop of the percolation hole should be located asaccurately as possible to the same level as theinvert of the percolation pipe. Further, attentionshould be given to the impact of slope andsubsoil layering on the location of the invert ofthe percolation pipe.

C.2.3.1 Percolation test (T-test) procedureThe top of the T-test holes should be at thesame depth as the invert of the proposedpercolation pipes.

Step 1: Three percolation test holes are dugadjacent to the proposed percolation area, butnot in the proposed area. Each hole should be300 mm × 300 mm × 400 mm deep 8 below theproposed invert level of the percolation pipe(Fig. C.3). The dimensions of the holes shouldbe noted in the Site Characterisation Form. Thebottom and sides of the hole should bescratched with a knife or wire brush to removeany compacted or smeared soil surfaces and toexpose the natural soil surface.

8. Change in the size of the test hole will affect the validity ofthe results.



Step 2: Each test hole should be pre-soaked4–24 h before the start of the percolation test bycarefully pouring clean water into the hole so asto fill it to the full height of 400 mm.

The water should be allowed to percolate fully(or as far as possible for the more slowlydraining subsoils) and then refilled again to400 mm that evening and allowed to percolateovernight before proceeding to Step 3 (the startof the test) the next morning.

If the water in the hole fully percolates in lessthan 10 min then repeat the pre-soakimmediately before proceeding to Step 3.

Step 3: After the hole has been pre-soaked(Step 2), it is filled once again to the full heightof 400 mm. The time that the hole is filled is

noted. The water should be allowed to drop tothe 300-mm level and the time noted (TableC.4).

There are three possible scenarios at this stageof the test, namely:

• Scenario 1 – If the initial drop from the 400-mm to the 300-mm level is greater than 5 hthis means that the T-value will be greaterthan 90. There is no requirement tocomplete the test and the site is not suitablefor discharge to ground.

• Scenario 2 – If the initial drop from the 400-mm to the 300-mm level is less than orequal to 210 min then the test should becontinued using the Standard Method(Table C.5) given in Step 4.

FIGURE C.3. IDEALISED CROSS SECTION OF THE T-TEST HOLES AND THE PROPOSED PERCOLATION TRENCH.

TABLE C.4. STEP 3 OF PERCOLATION TEST (T-TEST) PROCEDURE.



• Scenario 3 – If the initial drop from the 400-mm to the 300-mm level is greater than210 min then the test should be continuedusing the Modified Method (Table C.6)given in Step 5. This test method shouldonly be used for sites that have subsoilswith slow percolation characteristics.

Step 4: Standard Method Continue to let thelevel of water drop to the 200-mm level,recording the times at 300 mm and 200 mm.The time to drop the 100 mm is calculated (∆t).The hole is then refilled again to the 300-mmlevel and the time for the water level to drop to200 mm is recorded and ∆t is calculated(Table C.5). The hole should then be refilledonce more and the time recorded for the waterlevel to drop to 200 mm and ∆t calculated. Thismeans that three tests are done in the hole andthe hole is refilled twice. The average ∆t iscalculated for the hole. The average ∆t isdivided by 4, which gives a T-value for thathole. This procedure is repeated in each of thetest holes. The T-values for each hole are thenadded together and divided by 3 to give anoverall T-value for the site.

Step 5: Modified Method Continue to let thelevel of water drop to 100 mm, recording thetime at 250 mm, 200 mm, 150 mm and 100 mm(Tm) (Table C.6). The time factor (Tf) is thendivided by the time for each drop to give amodified hydraulic conductivity (Kfs). Theequivalent percolation value (T-value) is thencalculated by dividing 4.45 by the Kfs. Take theaverage of the four values from 300 mm to100 mm. This is repeated for each percolationhole and the T-values for each hole are addedtogether and divided by 3 to give the overall T-value for the site.

C.2.3.2 Test results

A proposed percolation area whose T-value isless than 3 or greater than 50 should bedeemed to have failed the test for suitability asa percolation area for a septic tank system.However, if the T-value is greater than 3 andless than or equal to 75, the soil may be usedas a polishing filter. T-values greater than 90indicate that the site is unsuitable for dischargeto ground, irrespective of the P-test result, andtherefore the one option available is todischarge to surface water in accordance witha Water Pollution Discharge licence.

TABLE C.5. STANDARD METHOD.



C.2.3.3 Percolation test (P-test) procedure

To establish the percolation value for soilpolishing filters and to determine the dischargeroute for secondary-treated effluent whereshallow subsoil exists, a modification of thepercolation test as described above is required.The modification relates to the depth of thepercolation test hole; the test hole is dug to 400mm below the ground surface and not at theinvert of the percolation pipes. A percolationtest carried out at the ground surface is known

as a P-test and the procedure is the same asfor the T-test outlined above except that the P-test results are expressed as P-values. FigureC.4 illustrates the cross section of the test holesand the proposed infiltration layout.

C.2.4 Integration of desk study and on-siteassessment

Table C.7 summarises the information that canbe obtained from the data collected from thedesk study and the on-site assessment.

TABLE C.6. MODIFIED METHOD.

FIGURE C.4. CROSS SECTION OF THE P-TEST HOLES AND THE PROPOSED PERCOLATION TRENCH.



TABLE C.7. INFORMATION OBTAINED FROM DESK STUDY AND ON-SITE ASSESSMENT.Information collected Relevance Factor determined

Groundwater Protection Response ZoningHydrological featuresDensity of existing housesProximity to significant sitesExperience of the areaProximity to surface features

Identifies groundwater protection requirements and targets at riskPotential cumulative nutrient loadingAdditional hydraulic loading from storm water disposalPerformance of existing systems/complaints

Site restrictions

Depth to bedrock Sufficient subsoil needed to allow treatment of wastewater

Depth to bedrock

TextureStructureBulk densityLayeringPreferential flow paths

Indicators of the suitability of the subsoil for percolation and of its percolation rate

Suitability of subsoil

ColourMottlingDepth to water table

A minimum thickness of unsaturated soil is required to successfully treat wastewater effluent

Depth of the water table

Drainage (permeability)Percolation test

Identifies suitable soils that have adequate but not excessive percolation rates

T-value or P-value



C.3 Site Characterisation Form

The following relates to an electronic form, which may be downloaded from www.epa.ie.



Annex D Discharge Options

D.1 Water Pollution Licensing

The discharge of any sewage effluent towaters9 requires a licence under the WaterPollution Acts 1977–1990. The local authoritiesprocess these licence applications. Directdischarges to groundwater of listed substancesare prohibited by the Groundwater Directive(80/68/EEC). Discharges to groundwaterreferred to in this code are discharges viaunsaturated subsoil and hence are consideredindirect discharges.

D.2 Dilution Calculations

D.2.1 Dilution calculations for indirectdischarges to groundwater

In high-density areas or where the receivinggroundwater already has relatively high levelsof nitrate or phosphorus then a simple dilutioncalculation should be carried out to assess thepotential impact of the development of thereceiving water prior to licence being granted.In all cases planning permission and adischarge licence (where required) need to bein place prior to development of the site. Thefollowing is an example of a dilutioncalculation10 to assess the impact of effluent onnitrate concentrations in water (phosphoruscalculations should be used in phosphorus-sensitive locations):

Assumptions:• Recharge (rainfall – (evapotranspiration +

run-off)) = 13.7 m3/day/ha (500 mm/year)

• Average nitrogen (N) concentrations indomestic wastewater treatment effluent = 90 mg/l N

• Average flow from septic tank (4 persons)

= 0.72 m3/day

• Average nitrogen concentration in recharge= 0.1 mg/l N

• Assume that total-N load in septic tankeffluent (in form of ammonium and organicN) is totally nitrified to nitrate in the subsoiland that no denitrification occurs11

• Nitrate concentration resulting from 1 on-site system/ha = (avg. total-N conc. in septic tank effluent ×flow) + (avg. nitrate conc. in recharge ×recharge) divided by flow plus recharge

= 6.71 mg/l N or 29.71 mg/l NO3

The only parameter that is needed to vary isrecharge, which could be reduced in the driercounties. Recharge figures may be obtainedfrom Met Éireann. This calculation can becombined with knowledge/existing waterquality data. A decision can then be made as towhether or not the increased nitrogen levels areacceptable when compared to the relevantnational standards.

D.2.2 Discharges to surface waterWhere sites are unsuitable for discharge ofeffluent to ground it is usually due to hydraulicreasons or high water tables. The failure couldbe as a result of impervious soil and/or subsoiland/or poorly permeable bedrock, which mayresult in ponding on-site. In these cases siteimprovement works are unlikely to render thesite suitable for discharge to ground and theonly possible discharge route is to surfacewater in accordance with a Water Pollution Actlicence.

Where it is proposed to discharge wastewaterto any surface waters a licence is required

9. Includes any (or any part of any) river, stream, lake, canal,reservoir, aquifer, pond, watercourse or other inland waters,whether natural or artificial.

10. Section 13.2.14.6 Site Specific Evaluation, Site SuitabilityAssessments for On-Site Wastewater Management, FÁSCourse Manual, Vol. 2.

11. ERTDI 27 – 2000-MS-15-M1 An Investigation into thePerformance of Subsoils and Stratified Sand Filters for theTreatment of Wastewater from On-Site Systems.

=(90 × 0.72) + (0.1 × 13.7)

(0.72 + 13.7)



(which is a separate procedure) and the localauthorities should risk-assess the impact of thedischarge from the on-site system on thereceiving water including the assimilativecapacity of the receiving water, the ongoingmonitoring of the system performance, and acost analysis. It should be noted that many

local authorities currently do not favourgranting discharge licences to surface watersfor single houses. For further guidance pleasesee the EPA Waste Water Discharge LicensingApplication Guidance Note (2008) (available onwww.epa.ie).



Annex E Wastewater Treatment and Disposal Systems

This section gives an overview of the maincategories of wastewater treatment systemsavailable; more detailed descriptions are givenin this CoP. Where new and innovativeproducts and technologies are proposed, thelocal authority should satisfy itself that theproducts/technologies have proven trackrecords based on good science demonstratedin other jurisdictions. In the case of treatmentsystems such new systems should comply withthe requirements of EN 12566 or equivalent.

E.1 Septic Tank System

A septic tank system (Section 7) comprises aseptic tank followed by a soil percolation area.The septic tank functions as a two-stageprimary sedimentation tank, removing most ofthe suspended solids from the wastewater.This removal is accompanied by a limitedamount of anaerobic digestion, mostly duringthe summer months under warmertemperatures. The percolation area providesadditional treatment (secondary and tertiary) ofthe wastewater and it provides the majority ofthe treatment. The wastewater from the septictank is distributed to a suitable soil percolationarea, which acts as a bio-filter. The biomat is abiologically active layer, which containscomplex bacterial polysaccharides andaccumulated organic substances and micro-organisms which treat the effluent. The biomatcontrols the rate of percolation into the subsoil(Fig. E.1). As the wastewater flows into andthrough the subsoil, it undergoes surfacefiltration, straining, physico-chemicalinteractions and microbial breakdown.Secondary-treated effluent has a lower organicloading than septic tank effluent, which leads toa reduction in lateral spread of the biomat. Afterpercolating through a suitably designed andmaintained percolation area, the wastewater issuitable for indirect discharge to ground.

Failure of a septic tank system to functionproperly is generally due to poor construction,installation, operation, lack of maintenance,installation in an area of unsuitable ground

conditions, or the use of a soakaway instead ofa properly designed percolation area.

The attributes of septic tanks are outlined inTable E.1. The following guidance on thegeneral design of conventional rectangularseptic tanks should help ensure bestperformance.

• Septic tanks should comprise twochambers and it is recommended that theyhave a minimum length to width ratio of 3:1in order to promote settlement ofsuspended solids

• Oversized rather than undersized septictanks are better because of greatersettlement of solids and larger hydraulicretention time for liquid and solids

• Properly designed baffles provide quiescentconditions and minimise the discharge ofsolids to the percolation area

• The inlet and outlet of the septic tank shouldbe separated by a long flow path for thewastewater; if the outlet is too close to theinlet, solids settlement and greaseseparation may be inadequate

• Access and inspection openings should beincorporated into the roof of the septic tank.The opening should be constructed to suchstandard and in such a manner thatunintended access (for example bychildren) cannot occur, and

• T-pieces should be installed as they preventsolids carry-over into the effluent, assist inthe formation of a surface scum layer whichtraps floating solids and grease and assistin preventing odours.

Septic tanks should:

• Be able to withstand corrosion fromwastewater and gases

• Be able to safely carry all lateral and verticalsoil pressures



FIGURE E.1. ILLUSTRATION OF BIOMAT FORMATION ON THE BASE OF A PERCOLATION TRENCH.



• Be able to accommodate water pressurefrom inside and outside the tank withoutleakage occurring

• Should be watertight to prevent wastewaterescaping to the soil outside, and to preventsurface water and groundwater fromentering the tank, and

• All septic tanks should be followed by apercolation area that is in compliance withI.S. CEN/TR 12566:2.

E.2 Secondary Treatment: On-SiteFilter Systems

Filter systems are used to provide additionaltreatment of upstream septic tank or packagedtreatment systems. These include intermittentlypumped (dosed) soil filters and sand filters(Section 8).

Soil filters comprise suitable soils placed oftenin the form of a mound (but may beunderground or part below ground/part aboveground), through which septic tank effluent isfiltered and treated.

Intermittently dosed sand filters consist of oneor more beds of graded sand underlain at thebase by a gravel or permeable soil layer toprevent outwash or piping of the sand; soil-

covered intermittent sand filters may beunderground, part underground and partoverground, or overground. The latter twoconstructions are commonly referred to asmound systems.

All intermittent filter systems should incorporatepolishing filters to provide additional treatmentof the effluent by reducing pollutants such assuspended solids, micro-organisms, andphosphorus (depending on the media).Polishing filters also provide for the hydraulicconveyance of the treated effluent to ground.

Constructed wetlands (reed beds) areconsidered to be another form of filter systemand can also be used for the treatment ofwastewater from single houses. Constructedwetlands should be underlain by either animpermeable geo-synthetic membrane or animpermeable clay liner (k = 1 × 10–8 m/s) toprevent leakage to the groundwater. Primarytreatment by a septic tank is used prior todischarge to a constructed wetland. In thewetland, the wastewater from a septic tankundergoes secondary treatment by acombination of physical, chemical andbiological processes that develop through theinteraction of the plants (reeds), the growingmedia (gravel) and micro-organisms beforedischarge of the effluent to groundwater or

TABLE E.1. ATTRIBUTES OF A TYPICAL SEPTIC TANK.

A properly constructed septic tank will:

• Retain and remove 50% or more solids

• Allow some microbial decomposition

• Accept sullage (i.e. water from baths, wash-hand basins, etc.)

• Accept water containing detergents (e.g. washing machine, dishwasher, etc.)

• Reduce clogging in the percolation area

• Not fully treat domestic wastewater

• Not work properly if not regularly maintained

• Not significantly remove micro-organisms

• Not remove more than 15–30% of the biological oxygen demand (BOD)

• Not operate properly if pesticides, paints, thinners, solvents, excess disinfectants or household hazardous substances are discharged to it

• Not accommodate sludge indefinitely

• Not operate properly if surface waters (i.e. roofs, parking areas, etc.) are discharged to it



surface water. Guidance on soil-basedconstructed wetlands can also be found inWallace and Knight (2007).

E.3 Secondary Treatment: PackagedWastewater Treatment Systems

Section 9 provides detailed descriptions ofpackaged wastewater treatment systems.These systems may be used as an alternativeto septic tank systems. Examples of thesesystems include:

• Activated sludge (incl. extended aeration)systems

• Biological/Submerged aerated filter (BAF/SAF) systems

• Rotating biological contactor (RBC)systems

• Sequencing batch reactor (SBR) systems

• Peat filter media systems

• Plastic, textile and other media systems

• Membrane bioreactor (MBR) systems.

These systems should incorporate polishingfilters before discharge of the effluent togroundwater or surface water.

E.4 Selection of a System

When selecting a wastewater treatment systema number of factors should be taken intoaccount. The range of factors to be taken intoaccount is presented in Table E.2.

TABLE E.2. FACTORS USED TO COMPARE DIFFERENT WASTEWATER TREATMENT SYSTEMS.Factor Treatment Option

No. 1Treatment Option

No. 2

Is the treatment system certified to comply with National Standards (I.S. EN 12566-1:2000/A1:2004 for septic tanks or I.S. EN 12566-3:2005 for packaged systems or other)?

Construction, installation and commissioning service is supervised

Construction of percolation area or polishing filter is supervised

Availability of suitable material for filter systems (soil/sand)

Maintenance service available

Expected life of the system

Ease of operation and maintenance requirements

Sludge storage capacity (m3)

Expected de-sludging frequency

Access requirements for sludge removal

Design criteria1

Does the system incorporate fail-safe measures to prevent it discharging untreated sewage in the event of power breaks, product defect or failure to maintain?

Capital cost

Annual running cost

Cost of annual maintenance service

Performance: % reduction in BOD, COD, TSS% reduction total P and total N% reduction total coliforms

Minimum standardBOD, SS, NH4Does it achieve the standards set out in Table 5.1?

Additional costs prior to commissioning (including site improvements)

Power requiremen ts – single phase/three phase (kw/day)1In the case of biofilm systems, the organic and hydraulic loading rates in g/m2/day and l/m2/day, respectively, should be quoted.BOD, biological oxygen demand; COD, chemical oxygen demand; TSS, total suspended solids;



a. Certification of the systemAs per Part One of this CoP.

b. Wastewater treatment performancerequirementsThe standards set in Table 5.1 (Section 5)apply to these systems.

c. Degree of environmental protectionrequiredHaving completed the site assessment asoutlined in Section 6, a decision will need tobe made on the degree of environmentalprotection required.

d. CostA single-house treatment system will entailcapital, running and maintenance costs. Inchoosing a system due regard should begiven to the overall relative costs.

e. MaintenanceA number of issues related to themaintenance of the single-housewastewater treatment system will have tobe considered such as:

R Availability of competent persons andparts for the system

R Ease of access to the system in orderto perform maintenance, e.g. de-sludging

R Frequency of maintenance required

R Capacity to sample the effluentdischarge

R Sludge storage capacity.

f. Anticipated lifetime of the system.

g. Track record of the system.



Annex F Site Improvement Works

In certain circumstances a site that is intendedfor a single-house development will presentparticular difficulties arising out of the siteassessment. Some sites may have a highwater table, may have insufficient subsoildepth, or may have unsuitable subsoil for thepurposes of treatment and percolation of thepretreated wastewater from a treatmentsystem. It may be possible in some such casesto render the site suitable for development aftercarrying out specific engineering works on thesite known as ‘site improvements’. The optionto carry out site improvements might beconsidered in circumstances where a highwater table is a problem. The conditions thatgive rise to a high water table are site specific;these include topography, nature of soils,bedrock and outfalls. Detailed designprocedures appropriate for site improvement

works are available in drainage manuals(Mulqueen et al., 1999).

In other cases, such as where the site isoverlain by insufficient depth of subsoil orunsuitable subsoil, the site may be improved bythe placement of suitable soil in lifts across thewhole site rather than just infilling in the areaaround a proposed mound system. It isnecessary to perform testing of each 300-mmlayer as the process of emplacing lifts of soilprogresses. After each lift is placed, percolationtests should be carried out. A 150-mm squarehole is excavated to a depth of 150 mm in theplaced soil. After pre-soaking to completely wetthe soil, 0.5 l of water is poured into the holeand the time in minutes for the water to soakaway is recorded. This time should be between10 min and 2 h.



Annex G Operation and Maintenance

G.1 Septic Tank Systems

The septic tank itself, the distribution systemand the percolation area all require inspectionto ensure effective operation of the system, andperiodic maintenance to ensure that the systemcontinues to work effectively over time.

G.1.1 Septic tankThe septic tank is a passive treatment unit thattypically requires little operator intervention.Regular inspections (approximately every 6months) and sludge pumping (at a minimumfrequency once every year) are the minimumoperation and maintenance requirements.

Inspections of septic tanks should includeobservation of sludge and scum accumulation,structural soundness, watertightness, andcondition of the inlet and condition of the outletfrom the tank.

G.1.1.1 Sludge and scum accumulationsAs wastewater passes through and is partiallytreated in the septic tank over the years, thelayers of floatable material (scum) andsettleable material (sludge) increase inthickness and gradually reduce the amount ofspace available for clarified wastewater. If thesludge layer builds up as far as the bottom ofthe effluent T-pipe, solids can be drawn throughthe effluent port and transported into thepercolation area, thus increasing the risk ofclogging. Likewise, if the bottom of thethickening scum layer builds downwards as faras the bottom of the effluent T-pipe, oils andother scum material can be drawn into the

piping that discharges to the percolation field.The scum layer should not extend above thetop or below the bottom of either the inlet oroutlet T-pipes. The top of the sludge layershould be at least 30 cm below the bottom ofeither tee or baffle. Usually, the sludge depth isgreatest below the inlet baffle. The bottom ofthe scum layer should not be less than 10 cmabove the bottom of the outlet T-pipe or baffle.If any of these conditions are present, there isa risk that wastewater solids will plug the tankinlet or be carried out in the tank effluent andbegin to clog the percolation area associatedwith the septic tank.

The depth of sludge can be checked using thefollowing technique or any other appropriatemethod:

• Use a 2-m pole and wrap the bottom 1.2-mwith a white rag

• Lower the pole to the bottom of the tank andhold there for several minutes to allow thesludge layer to penetrate the rag, and

• Remove the pole and note the sludge line,which will be darker than the colorationcaused by the liquid waste.

G.1.1.2 Structural soundness and watertightnessStructural soundness and watertightness arebest observed after sludge has been pumpedfrom the tank. The interior tank surfaces shouldbe inspected for deterioration, such as pitting,spalling, delamination, and so forth, and forcracks and holes. The presence of roots, forexample, indicates tank cracks or open joints.These observations can be made with a mirrorand bright light (such as a torch or flash lamp).Watertightness can be checked by observingthe liquid level (before pumping), observing alljoints for seeping water or roots, and listeningfor running or dripping water. Before pumping,the liquid level of the tank should be at theoutlet invert level. If the liquid level is below theoutlet invert, leaking is occurring. If it is above,the outlet is obstructed or the percolation areais flooded. A constant trickle from the inlet is an

Warning:In performing inspections or other maintenance,a septic tank should not be entered. The septictank is a confined space and entering can beextremely hazardous because of toxic gasesand/or insufficient oxygen. Electrical appliancessuch as mains-powered lighting should not beused near a septic tank.



indication that plumbing fixtures in the buildingserved by the tank are leaking and need to beinspected, or that infiltration of groundwaterinto the inlet pipe is taking place.

G.1.1.3 Baffles and screensThe baffles should be observed to confirm thatthey are in the proper position, secured well tothe piping or tank wall, clear of debris, and notcracked or broken. If an effluent screen is fittedto the outlet baffle, it should be removed,cleaned, inspected for irregularities, andreplaced. Note that effluent screens should notbe removed until the tank has been pumped orthe outlet is first plugged.

G.1.1.4 Septic tank pumping and de-sludgingTanks should be pumped when sludge andscum accumulations exceed 30% of the tankvolume or are encroaching on the inlet andoutlet baffle entrances. Periodic pumping ofseptic tanks is recommended to ensure propersystem performance and reduce the risk ofhydraulic failure. Septic tanks should be de-sludged at a minimum of once every year. Incases where the septic tank is at, or near, itsdesign load capacity, de-sludging should bemore often if the rate of sludge build-uprequires more frequent removal. Accumulatedsludge and scum material found in the tankshould be removed by an appropriatelypermitted contractor (in accordance with theWaste Management (Collection Permit)Regulations 2001). The local authorities have alist of permitted contractors in the area. Thepermitted contractor will arrange for thedisposal of the sludge in accordance with thenational legislation (via either disposal toagriculture or disposal to a managedwastewater treatment municipal facility).Householders obtain a certificate from thepermitted contractor each time their tank is de-sludged.

Sludge from a septic tank or a sewagetreatment system that is intended to belandspread should be managed in accordancewith the Waste Management (Use of SewageSludge in Agriculture) Regulations S.I. No. 148of 1998 (and its amendment S.I. No. 267 of2001). These regulations allow for thelandspreading of sewage sludge on agriculturalland providing that certain criteria are met and

that it is carried out in accordance with thenutrient management plan for the lands inquestion.

G.1.2 The distribution device

The effluent from the septic tank is typicallyconveyed to the percolation area through adistribution device, housed in a distribution box.The function of the device is to evenly split thehydraulic flow of partially treated effluent into anumber of approximately equal volumes foronward discharge to the individual percolationpipes in the percolation area.

The distribution box should be inspected atintervals of no greater than every 6 months.Build-up of solids in the distribution deviceshould be removed to ensure that the flowthrough the device is not obstructed, and toensure that the effluent passing through isevenly split between the outlet pipes. Thedistribution device should be checked toensure that it has not shifted on its foundationsince the previous inspection. Suchdisturbance can result from overpassing byheavy vehicles or through natural soil creep.Where such disturbance has taken place, acompetent person should reset the distributiondevice on its foundation, and the level of thedistribution device should be rechecked as partof this measure. Any damage to the box itself,its internal pipework, the jointing to the externalinlet and outlet pipes, or to the cover of thedevice should be made good as part of themaintenance procedure.

G.1.3 The percolation area

The percolation area requires little in the way ofregular maintenance in situations where aproper site assessment has been carried outprior to installation, where the system has beeninstalled correctly, and where no physicaldamage has been done to the surface afterinstallation. The percolation area should bekept free from disturbance from vehicles, heavyanimals, sports activities or other activitieslikely to break the sod on the surface. If thearea has been grassed then the excess growthof grass can be mown and removedperiodically. The use of gardening tools, whichmight break the surface, should be avoided.



The percolation area should be inspected at 6-monthly intervals to ensure that no surfacedamage has taken place. The aeration/ventpipes should be inspected to ensure that theyare still in place and intact. If possible, theinside of the vents should be examined to verifythat they are dry and free from obstruction. Thesurface of the ground in the percolation areashould be walked and examined to ensure thatit is free from surface or superficial damage andto ensure that ponding of effluent is notoccurring.

Where any damage is observed the followingprocedures should be followed:

• Where ponding of effluent is noted at thesurface it may be necessary to excavate thepercolation area to investigate the reasonfor the hydraulic failure of the distributionsystem

• Where such ponding is due to damage ofthe percolation pipework the necessaryrepairs should be carried out by acompetent person

• Any damage to aeration/vent pipes shouldbe made good, and

• The surface of the ground over thepercolation pipes should be reinstated andre-vegetated, and further damage to theground surface should be avoided bycontrolling activities on the surface.

G.2 Filter Wastewater TreatmentSystems

G.2.1 Intermittent soil and sand filtersThe main tasks are servicing of the dosingequipment (pump and distribution manifold)and monitoring of the wastewater. In the caseof sand filters, there is possible maintenance ofthe sand surface of open sand filters. When de-sludging the septic tank, the pump sump shouldalso be de-sludged. After de-sludging thechamber, the pump unit should be hosed downand the washwater and sludge be removedfrom the pump chamber. The distributionmanifold needs to be cleaned periodically (atleast once every 6–12 months) and so needs tobe designed to facilitate such an operation. The

use of backpressure gauges and zonedregions will facilitate the maintenance ofdistribution manifolds.

The performance of the pump system shouldbe checked, including the pump sump, pumpbase, the float position and operation, a checkfor blockages and volume delivered.

G.2.2 Mounded filter systemsThe most common failures in mound systemsare the granular fill material/filter materialinterface in the mound. The quantity and qualityof wastewater or the fill material can lead topotential failures. Failures due to compactionand ponding are often seen as leakage at theinterface between the soil and filter material.Hydraulic failure can occur in mounds due toexcessive ponding within the absorption areaor leaking out of the toe of the mound. Pondingcan occur where a flow rate across the granularfill/filter material interface is less than the flowrate from the dosing chamber. This may be dueto a number of causes, namely:

• Restricted clogging of the distribution pipes

• The filter material is too fine

• The loading rate is too great, or

• A combination of these factors.

Particular care should be taken to avoidcompaction or disturbance of the area over andaround the infiltration system. The dosingchamber should be kept clear of obstructionand should be checked for correct distributionand the outlets should be adjusted if necessary.All electrical and mechanical devices should beserviced in accordance with the manufacturer’sinstructions. Monitoring tubes should beinstalled to allow for the inspection of themound without unearthing the filter material orremoving the access port. These should be100-mm diameter vertical pipes with 6- to 8-mmdiameter holes (or slots) drilled down the lengthand covered with geotextile for soil filters. Anyprogressive increase in the depth of water inthe monitoring tubes may indicate a problem.The dosing chamber should be pumped out atleast once every 3–5 years or as required bythe manufacturer’s specifications. The pumpchamber (sump) should be fitted with a high-



level alarm to alert the homeowner to apossible pump failure or blocked distributionpipework. Grass and other vegetation coveringthe mound should be maintained, in order tomaximise water uptake and to prevent erosion.Trees or shrubs with extensive root systemsshould not be planted on or near the mound, asthey may clog the drainage pipes or causeshort-circuiting of the filter material.

G.2.3 Constructed wetlandsConstructed wetlands require some inspectionand maintenance to avoid the occurrence ofproblems within the system. It takesapproximately 4 weeks or so for the plants tosettle in after planting and they generallybecome fully established within the first 2years. Plants should be healthy and it ispreferable to plant before the growing season.Seedlings and rhizomes should be planted toensure early establishment and to stop thembecoming overwhelmed by weeds. Thewetland should be kept moist during periods ofdry weather especially during the first year orso, to ensure plant health. This is only neededif water is not discharging from the outlet due topercolation through clay substrates or due tohigh plant evapotranspiration rates combinedwith low summer use.

Routine inspections are necessary to ensureappropriate flows through the inlet distributorand outlet collector piping, as well as for thedetection of leakage from the pipework.Regular de-sludging of preliminary orsecondary treatment systems upstream of thewetland is needed to prevent sludge carry-overand accumulation at the wetland inlet. Grassand wetland vegetation should be checked toidentify any visible signs of plant stress ordisease. Common symptoms of plant stressare grass yellowing and leaf damage. Aspecialist or the system supplier should beconsulted if signs of plant stress are spotted.Flow distribution within the cells should beinspected from time to time in order to detectchannel formation or short-circuiting, especiallyin horizontal flow systems. The planting ofadditional vegetation or filling soil in anychannels that have formed can correct this. Allpipework and pumps should be checkedregularly to ensure that they are operatingproperly and that there are no signs of clogging.

Flow meters and timers should be checked toensure that the right amount of effluent is beingapplied to the system. In order to maximise thehealthy bacterial activity and overalleffectiveness of the treatment system, the useof bleaches and other toxic chemicals from thewastewater stream should be minimised oreliminated if possible.

G.3 Packaged Wastewater TreatmentSystems

Packaged wastewater treatment systems areconfigured in various ways and the systemmanufacturer often dictates the frequency andmethod of maintenance. When seeking specificguidance for the maintenance of such systemsthe user should consult the instructionsprovided by the manufacturer, or refer to anyinformation provided about the maintenance ofthe system in the appropriate AgrémentCertificate or standard. In some (but not all)cases, maintenance is offered by themanufacturer through a maintenance contract.Maintenance may also be availablecommercially by appropriately qualified serviceproviders.

In general, it is possible to comment on the keyitems of mechanical and electrical equipmentincluded in many such treatment systems, andsome direction in regard to maintenance can beprovided.

G.3.1 Checks that may be carried out by theuser

• The warning alarm system:

R Many of the latest packaged wastewatertreatment systems are equipped with analarm circuit. The purpose of this circuit

WarningProprietary wastewater treatment systems,which incorporate mechanical and/or electricalcomponents, are generally not userserviceable. Such units may be powered bymains electricity, and unqualified personsshould not attempt to perform maintenance onthem. To avoid serious injury or electrocution,servicing should only be carried out by qualifiedservice providers.



is to alert the user to any malfunctionthat has been diagnosed in the treatmentsystem by the built-in system monitoringdevices.

R Where the facility to do so has beenincorporated, the user shouldperiodically check the alarm circuit toensure that the system alarm is workingproperly. In most cases, it will bepossible to perform this check within theuser’s house or from a control boxoutside the house.

• Visual inspection:

R The user of a mechanical wastewatertreatment system should carry out aperiodic visual inspection of the externalelements of the treatment unit andpolishing filter.

• Odour observation:

R While carrying out the visual inspectionthe user should note any unusual odoursemanating from the mechanical aerationsystem. For example, pungent sulphide-like (bad egg) odours may indicateanaerobic conditions in the treatmentsystem. This may be indicative of abreakdown of the aeration equipmentand this should be investigatedthoroughly by a qualified serviceprovider.

• Noise:

R While carrying out the visual inspectionthe user should note any unusual noisesfrom the mechanical aeration system.For example, unusual noises comingfrom the treatment system may indicatethat there are problems with themechanical components (pump oraerator). Such problems may beassociated with partial blockages orcomponent wear and should be

investigated thoroughly by a qualifiedservice provider.

G.3.2 Proprietary filters For proprietary peat filter systems, it isadvisable that the manufacturer/competentperson assesses the quality of the media fromtime to time. The surface of the peat filtershould be examined periodically for signs ofponding and, where evident, the manufacturer/installer should be contacted. The peat mediashould not be disturbed as this may lead tochannelling of effluent or flooding. When de-sludging the septic tank, the pump chambershould also be de-sludged. After de-sludgingthe chamber, the pump unit should be hoseddown and the wash water and sludge beremoved from the pump chamber.

G.4 Polishing Filters

Where polishing filters have been installed witheither filter systems or packaged wastewatertreatment systems, these should beperiodically inspected in accordance with thegeneral principles outlined in Section 7. Inaddition, where polishing filters are situatedabove ground level, checks should be carriedout to ensure that no effluent is escaping fromthe filter above ground or at the interface withthe ground surface.

G.5 Holiday Homes

When choosing a wastewater treatmentsystem for holiday homes, considerationshould be given to the selection of a systemthat can adequately deal with periods ofinactivity (i.e. when the house is unoccupied forprolonged periods). Systems that are capableof recirculating the effluent would beappropriate. It is recommended thatbiodegradable cleaning agents be consideredfor use in holiday homes. All systems should beoperated and maintained in accordance withthe manufacturer’s instructions.



Annex H References and Reading Material

BS 5930:1999 Code of Practice for Site Investigations.British Standards Institution, UK.

BS 10175:2001 Investigation of potentially contaminatedsites – Code of Practice. British Standards Institution,UK.

Building Research Establishment (BRE) (1991).Soakaway Design. Building Research Establishment(BRE) Publications, BRE Press, UK.

Carey, C., Phelan, W. and Boland, C. (2008). Examiningthe Use of Food Waste Disposers (2005-WRM-DS-23-M1). Environmental Protection Agency, JohnstownCastle Estate, Wexford, Ireland.

CEC (1980). Council Directive 80/68/EEC of 17December 1979 on the protection of groundwateragainst pollution caused by certain dangeroussubstances. Council of the European Communities,O.J. L 20/43.

CEC (2000). Council Directive 2000/60/EC of theEuropean Parliament and of the Council of 23October 2000 establishing a framework forCommunity action in the field of water policy. Councilof the European Communities O.J. L 327.

CEN (2002). Wastewater Treatment Plants – Part 1.European Standard. I.S. EN 12255-1:2002. EuropeanCommittee for Standardization. Brussels, Belgium.

CEN (2005a). Small wastewater treatment systems forup to 50 PT – Part 2: Soil Infiltration Systems.Technical Report I.S. CEN/TR 12566-2:2005.European Committee for Standardization. Brussels,Belgium.

CEN (2005b). Small wastewater treatment systems forup to 50 PT – Part 3: Packaged and/or SiteAssembled Domestic Wastewater Treatment Plants.European Standard I.S. EN 12566-3:2005. EuropeanCommittee for Standardization. Brussels, Belgium.

CEN (2005c). Small wastewater treatment systems forup to 50 PT – Part 6: Prefabricated Treatment Unitsfor Septic Tank Effluent. European Standard prEN12566-6. European Committee for Standardization.Brussels, Belgium.

Cooper, P.F., Job, G.D., Green, M.B. and Shutes, R.B.E.(1996). Reed Beds and Constructed Wetlands forWastewater Treatment. Water Research Centre,Swindon, UK.

Daly, D. (2006). Site Suitability for On-Site WastewaterTreatment Systems – the Role of the Water Table.Groundwater Newsletter No. 45 issued by theGeological Survey of Ireland, Dublin, Ireland.

DELG (Department of Environment and Local

Government) (1992). Environmental ProtectionAgency Act, 1992. Statutory Number 7 of 1992.Government Publications Office, Dublin 2, Ireland.

DELG/EPA/GSI (Department of Environment and LocalGovernment/Environmental Protection Agency/Geological Survey of Ireland) (1999). GroundwaterProtection Schemes. Geological Survey of Ireland,Dublin, Ireland.

DoEHLG (Department of the Environment, Heritage andLocal Government) (2003). Protection of theEnvironment Act, Statutory Instrument, Number 27 of2003. Government Publications Office, Dublin 2,Ireland.

DoEHLG (Department of the Environment, Heritage andLocal Government) (2005). Safety, Health andWelfare at Work Act, Statutory Number 10 of 2005Government Publications Office, Dublin 2, Ireland.

DoELG/EPA/GSI (Department of Environment and LocalGovernment/Environmental Protection Agency/Geological Survey of Ireland) (1999a). GroundwaterProtection Responses for Landfills. GeologicalSurvey of Ireland, Dublin, Ireland.

DoELG/EPA/GSI (Department of Environment and LocalGovernment/Environmental Protection Agency/Geological Survey of Ireland) (1999b). GroundwaterProtection Responses to the Landspreading ofOrganic Wastes. Geological Survey of Ireland,Dublin, Ireland.

DoELG/EPA/GSI (Department of Environment and LocalGovernment/Environmental Protection Agency/Geological Survey of Ireland) (2001). GroundwaterProtection Responses for On-Site Systems for SingleHouses. Geological Survey of Ireland, Dublin, Ireland.

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