Groundwater Protection Code: Septic Tanks
Contents
1. Sys tems that provide some treatment this does not include cesspools operate best with a steady input If your system is used intermittently for example holiday ac commodation you may need to take additional precautions to prevent pollution Specific precautions will depend on the nature of the system consult the opera tors manual or maintenance company but might include dosing the system with proprietary organisms 2 3 Regular checks It is important that you regularly check the operation of the system This might include e a fortnightly or monthly visual check on the discharge from system to the drainage field or discharge point Building regulations require an inspection chamber between a septic tank treatment plant and discharge for this pur pose The discharge from other forms of non mains drainage should also be regularly checked e regular monthly checking of the level of liquid and solid in tanks e ensuring the mechanisms are all working correctly such as rotating contac tors and air lift pumps e checking that sewage or effluent is not saturating the ground or flowing over land into a stream or onto another property In order to show that you have carried out the checks properly it is recom mended that you keep records of items such as e the design manufacturer and installer age location of system and drainage field monthly water levels in the distribution chamber other items you might include in your2. non mains sewerage systems must comply with relevant water protection legislation Failure to do so could result in long term contamina tion of valuable groundwater and as a consequence may result in serious penal ties costs and liabilities The code gives advice to help avoid these sorts of problems 1 2 What sort of code The code is made under Regulation 21 of the Groundwater Regulations 1998 and approved by Ministers with the aim of providing practical guidance on pro tecting groundwater in England amp Wales Not complying with the code is not an offence in itself but following the advice in the code will help to ensure that rele vant water legislation in particular the Groundwater Regulations are complied with In enforcing such compliance the Environment Agency will consider whether or not the guidance in the code has been or is likely to be followed A summary of the legal requirements to protect groundwater is provided at Annex A Chapter 2 sets out advice relevant to persons owning operating or maintaining a non mains system Chapter 3 contains advice for persons installing a new sys tem or taking a system out of service It is up to such persons to make use of the guidance appropriately If in doubt you should contact your local Environment Agency office a list of contacts is provided at Annex B It is important to emphasise that the code relates specifically to the protection of groundwater and is not intended to a
3. the Environment Agency further powers specifically to control activities in or on the land which could lead to groundwater pollution They also allow ministers to approve codes of practice aimed at helping persons engaged in activities in or on the land com ply with the Regulations Although domestic effluent discharged from certain isolated dwellings outside drinking water abstraction areas are excluded from the scope of the Regulations the advice in this code will still be relevant to such dwellings since they are within the scope of the Water Resources Act Owners of non mains sewerage systems may require an authorization or dis charge consent from the Environment Agency if their system is designed to dis charge to land or controlled waters ie surface waters or groundwaters The ad vice in this code will be relevant whether or not an authorization or discharge consent is required Section 101A of the Water Industry Act 1991 places a duty on sewerage under takers to provide a public sewer for those premises where the existing arrange ments are giving or are likely to give rise to adverse environmental or amenity effects and it is considered appropriate to resolve the difficulties by providing a public sewer This means that for example if a septic tank can no longer func tion properly because of rising groundwater the owner of the premises may be able to apply to the undertaker to be connected to the mains sewerage network ANNE
4. 1 The need for control Inappropriate operation and maintenance of your system will present a serious risk to groundwater even if the system is appropriately sited designed and in stalled A general overview of the risks is given in Annex C To avoid pollution problems you must e be careful what you put into the system e take time to check the system regularly e ensure that the system is regularly maintained to keep it functioning This chapter provides advice on these issues 2 2 Caring for your system In order to maintain the operation of your system you need to take some simple precautions A number of household chemicals and cleaning products can kill the helpful or ganisms in septic tanks package plants and other non mains systems that rely on biological action to treat the sewage Oil and grease etc can also impair the treatment process This may result in a poor quality effluent and the need to empty the tanks more often Some of these chemicals are very polluting and their discharge to groundwater is prohibited To avoid these problems do not put the following down sinks toilets or other drains that go to the septic tank treatment plant excess amounts of bleach solvents e g white spirit cellulose thinners some cleaning products oil grease or fats pesticides Biologically based cleaning products which are less harmful to sewage treatment processes are available and may be more suitable to non mains systems
5. Drainage field Private water supplies Soakaway from borehole to this Not a recommended 1 or another property means of discharge Min 50m preferably not downstream of discharge Bottom of Sewage treated in unsatu tank dam rated zone ie above the wa aged and ter table Produces a less leaking polluting discharge to Tank never groundwater needs emptying Little or no treatment Raw sewage enters groundwater Little attenuation once below the water table Groundwater is at risk of pollution by sewage passing down through the ground and reaching the water table Non mains sewerage systems that discharge to ground are intended to do so in a controlled way via a properly designed shallow drainage field with an adequate depth of unsaturated soil between the base of the drainage field and the water table In such systems the gradual percolation of effluent through the unsaturated soil is an intrinsic vital and probably the most important component of the treatment process The most common causes of increased risks to groundwater from such systems arise when 1 A system is located in an area where the water table is too near to the ground surface to allow adequate treatment of the sewage effluent before reaching the groundwater table A system is connected to a a means of rapid infiltration such as a deep soakaway or borehole These bypass the soil layer again causing a risk of inadequate treatment of the effluent
6. Groundwater Protection Code Use and construction of septic tanks and other non mains sewerage Groundwater Protection Code Use and Construction of Septic Tanks and other Non Mains Sewerage CHAPTER 1 The aim of the code 1 1 Why a code 1 2 What sort of code 1 3 What types of non mains sewerage systems does this code cover CHAPTER 2 Operating your system 2 1 The need for control 2 2 Caring for your system 2 3 Regular checks 2 4 Maintenance CHAPTER 3 Design installation and decommissioning 3 1 The need for control 3 2 Overview of process for obtaining permission 3 3 Pre design considerations 3 4 Design 3 5 Installation 3 6 De commissioning ANNEX A Legal requirements to protect groundwater ANNEX B Environment Agency contacts ANNEX C Principal Risks to Groundwater from non mains sewerage systems ROW o oO AAA 14 15 17 CHAPTER 1 The aim of the code 11 Whya code Non mains sewerage systems can pollute groundwater all water lying below the water table or in aquifers if they are poorly located built or operated This can impact public and private space water supplies other groundwater abstractions and surface water in rivers streams and lakes Such pollution can make water unusable for drinking water and toxic to aquatic life Once contaminated groundwater is very difficult and expensive to make good and for this reason there are UK and EC laws to protect it Persons involved with
7. X B Environment Agency contacts ENVIRONMENT General Enquiry Line Tel 08459 333 111 AGENCY Emergency Hotline Tel 0800 807060 Head Office Rio House www environment Waterside Drive agency gov uk Aztec West Almondsbury Bristol Tel 01454 624400 BS32 4UD Fax 01545 624 409 Anglian Region Kingfisher House Goldhay Way Orton Goldhay Peterborough Tel 01733 371811 PE2 5ZR Fax 01733 231840 Southern Region Guildbourne House Chatsworth Road Worthing West Sussex Tel 01903 832000 BN11 1LD Fax 01903 821832 Midlands Region Sapphire East 550 Streetsbrook Road Tel 0121 7112324 Solihull Fax 0121 7115824 B91 1QT South West Region Manley House Kestrel Way Exeter Tel 01392 444000 EX2 7LQ Fax 01392 444238 North East Region Rivers House 21 Park Square South Leeds LS1 20G Tel 0113 2440191 Fax 0113 2461889 Thames Region Kings Meadow House Kings Meadow Road Reading RG1 8DQ Tel 0118 953 5000 Fax 0118 950 0388 North West Region Richard Fairclough House Knutsford Road Warrington WA4 1HG Tel 01925 653999 Fax 01925 415961 Environment Agency Wales Cambria House 29 Newport Road Cardiff CF24 OTP Tel 01222 770088 Fax 01222 798555 ANNEX C Principal Risks to Groundwater from non mains sewerage systems Figure 3 Illustration of risks to groundwater wells and surface water from septic tank pakage plant systems
8. al authority 3 6 De commissioning Decommissioning is likely to occur when mains sewerage is made available or when buildings are demolished In some instances cesspools are permitted by the Environment Agency on the basis that they will be de commissioned when mains sewerage becomes available Drainage fields may need to be decommis sioned where the performance has deteriorated as a result of clogging or com paction or because new building requires the sewage facilities to be moved The principal dangers to groundwater from decommissioning are likely to arise where not all connections are directed to the new system and remain live and where tanks are not emptied Thorough decommissioning should ensure that all connections to the drainage pipework are removed and that all necessary steps are taken to ensure that the pipework cannot be used for other purposes All tanks should be emptied by a specialist contractor and made safe by infilling ANNEX A Legal requirements to protect groundwa ter The Water Resources Act 1991 and the Groundwater Regulations 1998 are the primary legislation protecting groundwater in England and Wales The Act makes it an offence to cause or knowingly permit pollution of groundwater and provides the Environment Agency with powers to address pollution The Regula tions put in place a regime specifically aimed at controlling both direct and indi rect discharges of listed substances to groundwater and give
9. before reaching the water table The effluent discharged from the system retains an unacceptably high concentration of potential pollutants This may result from any or all of the following poor design poor maintenance overloading deterioration leakages within the system caused accidentally during installation through time due to a range of factors such as settlement tree roots and other building work or deliberately for example by holing a cess pool in an attempt to reduce tanker removal costs poor decommissioning i e pipework is still active o
10. could be the cause as they are releasing raw sewage Investigate identify and resolve the problem with the help of profes sional specialist services if required Your rights to main sewerage If existing arrangements are causing or may cause risks to the environment you may have rights to mains sewerage under s 101A of the Water Industry Act 1991 Annex A provides further details CHAPTER 3 Design installation and decommission ing You should read this chapter if you are installing a new sewage treatment system for yourself or having it installed for you 3 1 The need for control The location of a non mains sewage system is an important element in prevent ing or minimising pollution and correct design and construction are essential for its effective performance De commissioning of redundant systems needs care ful consideration to avoid on going threats to groundwater This chapter sets out essential considerations including key statutory controls in carrying out any of these activities but you should also familiarise yourself with the principal groundwater risks set out in Annex C 3 2 Overview of process for obtaining permission Before the system can be installed planning permission and building control ap proval must be obtained Similarly before the system may be operated a dis charge consent from the Environment Agency may be required Hence contact should always be made with the planning officer at the local aut
11. ddress matters relating to health and safety or non groundwater environmental issues since these are the subject of other regimes codes and guidance Neither is the code intended to be a comprehen sive design or user manual for non mains sewerage systems A general overview of the principle risks to groundwater from non mains sewer age systems is at Annex C You may find this helpful when following the advice in the code 13 What types of non mains sewerage systems does this code cover The code is targeted at persons who own install operate empty maintain or decommission small non mains sewerage operations serving individual proper ties and small developments The type of systems covered include septic tank systems in which partial treatment of the sewage occurs within the tank with additional treatment of the effluent within a shallow drainage system package treatment plants the effluent discharged to the shallow drainage system is of a higher quality than that discharged from septic tanks cesspools sealed tanks with no discharge outlet alternative or additional treatments e g reed beds and waterless toilets and all the drainage connecting the property to the means of treatment The general groundwater principles in the code will also be relevant to larger non mains sewerage systems CHAPTER 2 Operating your system You should read this chapter if you own or manage your own sewage treatment system 2
12. hare the responsibility and costs of maintenance Troubleshooting If you notice any of the following you may have a problem with your system The ground around your drainage area is saturated or water effluent is flowing across the ground This may imply that the soil has become saturated either because of rising groundwater levels poor natural drainage of the soil or the soil has become clogged either by the discharge from the drainage pipes or due to bio fouling You should investigate the cause of the problem and put re medial measures in place This may require the use of professional specialist services Sewage is backing up in the drains or sinks and toilets are draining slowly The tank may be clogged with solid material and need emptying Alternatively the drains connecting to the system maybe blocked This could result in damage to the pipes and loss of sewage from the pipes into the ground This can lead to pollution If the tank becomes too full access covers maybe pushed off and sew age released onto the ground The tank must be emptied immediately No outflow from the system The tank may need emptying see above the in fluent drains to the tank maybe blocked see above or the tank is leaking Es tablish the reason and effect a remedy Odour or unexpected fungal or bacterial growths in nearby stream or water course This may mean that poorly treated or raw effluent is discharging to sur face water Damaged pipes or tank
13. hority the local authority building control department and the local Environment Agency office before designing and installing a new or modified system Environment Agency contact details are given at Annex B Planning permission is obtained either through the submission of a planning application or deemed planning permission granted in accordance with the Town and Country Planning General Permitted Development Order 1995 De tailed planning guidance on the selection of appropriate drainage is given in Cir cular 3 99 in Wales circular 10 99 applies A fundamental question you will need to answer is why connection to a main sewer is not proposed Building Control approval is required to ensure adequate drainage to meet the requirements of the Building Regulations prior to construction of a non mains sewerage system The Regulations require as a minimum that building work be notified to the local authority and for certain larger works the applicant must de posit full plans with the local authority Building Control or an Approved Inspector The Building Regulations set out minimum standards for building work and par ticular requirements with respect to non mains sewerage are given They pro vide for local authority inspection of foul drainage and give periods of notice for covering up drainage systems They also require that foul drainage should be connected to public foul sewer or combined sewer wherever reasonably practi cal Polluti
14. isposal system and water table e they provide additional wastewater treatment The disadvantages are e they may be more expensive to construct e they require a relatively large land area dedicated to wastewater application only e they are only suitable for gently sloping sites of less than 7 e they are likely to require pumping equipment with additional costs Figure 2 Drainage Mound Drainaae field p L ZTN GINA a agi a gn TETA E he Nee A Mound 3 5 Installation During the installation stage care should be taken to ensure that the tank is struc turally sound to prevent leaks or ingress of groundwater Tanks should have third party certification confirming their structural integrity and that they are fit for purpose Glass fibre and thermoplastic tanks should have an Agr ment Certifi cate British Board of Agr ment BBA and pre cast concrete tanks should satisfy the appropriate British Standard Septic tanks should be constructed in accor dance with BS EN 12566 prefabricated tanks or BS6297 1983 built in situ Package treatment plants should meet the requirements of BS7781 Building control inspection of the installation should be carried out to ensure that it meets requirements of the Building Regulations Alterations to existing drainage systems is a controlled service under Regulation 3 and 4 of the Building Regulations 2000 and section 61 of the Building Act 1984 You must notify such work must to the loc
15. ly on the number of us ers and is not sensitive to location The design of the drainage field however will have an important impact on the risk to groundwater Drainage design Good drainage design is a key to ensuring that sewage does not end up in groundwater The scope for the design and siting of the drainage field will de termine the suitability of a site The British Standard BS6297 gives advice on ensuring that drainage fields are appropriate However the following points are emphasised from the point of view of groundwater protection 1 A drainage field should generally be located a minimum of 50 metres from a potable water supply borehole or spring 2 Soakaways should be avoided particularly borehole soakaways because they are designed for rapid inflow below the soil layer and thus provide little or no opportunity for the vital stage of additional treatment of the sewage effluent within the soil layer 3 Use of drainage mounds see figure 2 should be considered carefully A drainage mound is an engineered structure to allow secondary treatment of sep tic tank effluent where the subsoil is occasionally waterlogged but where drain age fields would otherwise be suitable They cannot be used to overcome poor percolation conditions in the subsoil since they will simply result in seepages around the ground surface The advantages of drainage mounds are e they increase the separation distance between the d
16. monthly inspection dates of tank desludging emptying other maintenance and servicing activities recommended by the manufacturer any problems and remedies applied 2 4 Maintenance Routine Septic tank treatment plant This should be emptied regularly If it does not need emptying every year this may be because it is leaking and further investiga tion will be required Cesspool This will need emptying on average once a month If the cesspool never or infrequently needs emptying or if the intervals between emptying are increasing there is likely to be a leak in the tank or pipework that should be in vestigated and repaired see figure 1 If you have a cesspool this is probably because the ground conditions are unsuitable for the discharge of effluent This may be due to a number of factors but in general it is because of an increased risk of pollution of surface or groundwater or public health risk So a leaking cesspool is potentially a serious problem and needs rectifying quickly Figure 1 Damage to Cesspool Cesspool Very inten sive maintenance monthly emptying If gt Pe damaged can have SS ing discharge of raw release of raw sewage Api DN a ze sewage and poten with little signs initially a ted cs tially polluting oe groundwater Systems that involve pumps or moving parts These will need regular main tenance If you are connected to a shared system it is good practice to have a formal agreement to s
17. on control Written permission from the Environment Agency is required in many cases before effluent can be disposed of to controlled waters rivers and streams coastal waters groundwater and some lakes or to land In addition no tices can be served on anyone who is doing something or failing to do some thing such that pollution of controlled waters is likely to occur The aim of this code is to avoid the need to serve notices specifically under the Groundwater Regulations in respect of unsatisfactory sewerage systems nevertheless this good practice will help to protect all controlled waters 3 3 Pre design considerations Before deciding on an appropriate design for the system you should consider your sewage disposal requirement and the options presented by the site It will be necessary to carry out some investigation and testing as part of the scheme development Those aspects that are of particular importance in protecting groundwater are confirm that connection to public sewer is not an option this will be the first check for acceptability applied by the local authority estimate or measure the volume of the sewage that will need to be managed and assess it s nature inspect the proposed site to assess the practicality of constructing the system and to identify any features that may count against a non mains sewerage system e g water supply well investigate to determine whether ground conditions are appropriate for the con
18. struction of a drainage field This will involve an understanding of the percolation capacity of the ground the minimum and typical depths to the water table and the direction of flow of the groundwater Non mains sewerage systems often rely on gravity drainage and therefore locations at a low point within a site will be preferred however the low point may be associated with a higher risk of flooding and a thinner unsaturated zone high groundwater table Where such risks are unacceptable then alternative locations may require consideration You should also be aware of the right to main sewerage under s 101A of the Water Industry Act 1991 as outlined in Annex A 3 4 Design Guidance on the design of a non mains sewage treatment system is provided in the British Standard BS6297 soon to be superseded by BS EN 12255 amp 12566 and Part H of the Building Regulations 2000 Compliance with the require ments of these documents will be taken as compliance with the design require ments of this code though you should take particular note of the groundwater protection considerations set out in this section If as a result of reading this section there are areas of uncertainty you should refer to the Environment Agency for advice The design of a non mains sewerage system can be divided into design of the septic tank package treatment plant and design of the drainage field The for mer should be fairly straightforward depending principal
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