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FOREWORD Over the past centuries, Bhutan has been able to keep its environment intact and preserve its rich natural resources for future generations. However, decelopment of the country has resulted in new threats to the environment. In particular, rapid urbanisation in recent years has become one of the major concerns for the Royal Government. In 1999, the National Environment Commission issued six environmental sectoral guidelines for Bhutan, namely, Hydropower, Power Transmission Lines, Highways and Roads, New and Existing Industries, Forestry, Mining and Mineral Processing. In addition, a Strategic Environmental Assessment and Ambient /Discharge standards and Environmental Sampling Manual were also produced. However, no guideline for the urban sector was drafted. In view of the importance accorded to the development of the urban sector and with the aim to promote and facilitate sound development in the urban environment, the National Environment Commission Secretariat started development of suitable urban environmental guidelines. Specific sectors in urban development were targeted and prioritised, and codes of practice for these activities were developed. These codes of practice aim to promote basic environmental procedures and criteria that should be followed to ensure sound development in the urban environment. As the first Environmental Codes of Practice for the urban sectors, these have been kept simple and easy to follow. They are not overly technical, as specifications have already been detailed in other documents that are referred to in these booklets. On behalf of the National Environment Commission, I would like to take this opportunity to express my gratitude to all the Departments, Ministries and other relevant organisations that extended their co- operation, help and timely contribution. I would also like to thank the DANIDA funded Environment Sector Programme Support (ESPS) for its assistance. This contribution and technical assistance has been of immense help in producing these Environmental Codes of Practice. Tashi Delek. Nado Rinchhen Deputy Minister National Environment Commission ACKNOWLEDGEMENTS This report is one of a series of Environment Codes of Practice prepared with Technical Assistance and funding provided by DANIDA under the Environment Sector Programme Support (ESPS). Environmental Codes of Practice were also prepared for Solid Waste Management and Urban Roads and Traffic Management. Other activities in the urban sector, also require/have similar Environmental Codes of Practice. These activities along with the relevant organisations for preparing them have been identified. These Environmental Codes of Practice have been produced after numerous meetings with the relevant organisations, which have provided invaluable input in the form of materials, assistance and comments on the early drafts. In particular, NEC would like to thank the Department of Urban Development and Housing (DUDH), Thimphu City Corporation (TCC), Phuentsholing City Corporation (PCC) and the Department of Roads (DOR). We would like to acknowledge all who were involved in this project, especially Mr. Richard Allen from NIRAS (Consulting Engineers and Planners A/S), the primary author of these Environmental Codes of Practice and Mr. Thinley Dorji (civil engineer and intern at the NEC) who worked very closely with Mr. Richard Allen in developing these booklets. Mr. Grant Bruce (DANIDA Chief Technical Expert, NEC) has been very supportive and we would like to thank him for his assistance. There are also a number of people in Nepal who the author would like to thank for their assistance. Finally, we would like to express our appreciation and gratitude to the Deputy Minister of Environment, Dasho Nado Rinchhen, and the rest of the staff at NEC for their enthusiasm and support for the project. These Environmental Codes of Practice will be subject to peroidic review and suggested improvements will be carefully considered by the NEC and relevant ministries, with a view to ensuring that the document remains relevant and practical. TABLE OF CONTENTS Foreward Acknowledgement Abbrevation I. Introduction II. Purpose of the Code III. Legal Aspects IV. The Code of Practice for Sanitation and Sewage Management 1. Research and Surveys 2. Technical Options 3. Septic Tanks 4. Disposal of Effluent 5. Soakpits (or Soakaways) 6. Dispersion or Drainage Trenches 7. Disposal of Effluent into A Mains Sewerage System 8. Disposal of Sludge Waste 9. Disposal of Sludge Waste from Latrine Pits 10. Disposal of Sludge Waste from Septic Tanks 11. Main Sewerage Systems for Urban Areas 12. Wastewater Standards 13. Management of Toxic Waste 14. Public Toilets 15. Health Aspects 16. The Groundwater Pollution Risk 17. Education and Awareness Raising 18. Glossary of Terms 19. References for Further Technical Information 20. Websites Annex A: Pit Latrines and Other Alternative Sanitation Systems I. INTRODUCTION Environmental Codes of Practice (ECOP) for sanitation and sewage management in urban areas were prepared in collaboration with a number of resource persons in Bhutan, Kathmandu and Europe, together with the use of document and Website references. This code forms part of the Urban Environmental Assessment Guidelines prepared by the National Environment Commission (NEC) for the Royal Government of Bhutan (RGoB). Although best practices aim to achieve an ideal situation, common sense and realism must play an important part in the Bhutanese planning and implementation process. Present rules and regulations pertaining to sewage and sanitation in Bhutan are found in the RGoB Water and Sanitation Rules, July 1995, prepared by the Public Works Division of the Ministry of Communications (see reference 1, Section 19A). This Code provides support on environmental issues to these important current rules and regulations. Urban authority engineers will provide technical specifications for structures concerned with sewerage and sanitation management (see also, Section 19C); they are not covered in this code unless they pertain directly to environmental risks. It is not expected that all principels described in the following sections can be achieved immediately; they do, however, represent goals that should be worked toward and ultimately attained in the not-too-distant future. II. PURPOSE OF THE CODE a) To promote sound environmental sanitation practices and management of sewage in the urban areas of Bhutan. b) To specify and list key environmental terms, one or more of which may be attached to the environmental clearance issued for a relevant project or activity under the Environmental Assessment Act 2000. c) To assist the regional and national competent authorities in assessing the environmental impact of a sanitation and sewage management project or activity. III. LEGAL ASPECTS The Code describes environmental terms and conditions for sanitation and sewage management and should be considered as a guideline. However, where the competent authority issuing an environmental clearance deems it necessary, quotes from sections within this Code may be extracted and included in the clearance for a project under Chapter 3 of the Environmental Assessment Act 2000. Furthermore, the language of the extracted section/s may be altered in order to make the relevant activity, procedure or practice mandatory. IV. THE CODE OF PRACTICE FOR SANITATION AND SEWAGE MANAGEMENT 1. RESEARCH AND SURVEYS 1.1 Sanitation and sewage management problems in urban and peri-urban areas can arise for a number of reasons, thus, it is essential that sound planning occurs and appropriate regulation is in place before design and construction. It is important, therefore, that sufficient research occurs in Bhutan to identify the main problems and constraints in both larger centres and satellite towns. 1.2 The most appropriate sanitation and sewage system for each urban area and sub- area will be based on household size, population and expected growth rates, water availability, rate and volume of sewage discharge, economics, cultural aspects and other technical details, such as soil characteristics and percolation rates. 1.3 For purposes of planning individual household, communal and urban sewage systems, comprehensive surveys are therefore necessary to collect the above data and other technical information. 1.4 Provision of an appropriate sanitation and sewage system depends upon co- operation between providers and beneficiaries, which happens through dialogue and the exchange of information. 1.5 Planners, providers, communities and users in the urban areas need to review all options on the basis of health risk and benefit, economy, social acceptability, simplicity of design and construction, operation and maintenance, and local availability of appropriate materials and skills. 1.6 All involved in planning, surveying and constructing sanitation and sewerage systems must strictly follow the rules and technical instructions listed in the RGoB Water and Sanitation Rules, July 1995 (see Section 19A, reference 1). The relevant section is entitled “Drainage and Sanitation Requirements,” from Page 14. 1.7 It should be remembered that individual users are the ultimate decision-makers in the acceptance or rejection of technology, whether existing or new; it is they who determine the final success of the project. 1.8 Equally important in improving sanitation are awareness and education campaigns (see Section 17). Individuals and communities need to be convinced that the benefits of improved sanitation, and the improved technology with which it is associated, outweigh the costs and efforts of construction, implementation and management. 1.9 During the research, surveys and investigations, it is therefore imperative that providers appreciate the social context and the constraints within which individual decisions are made. They must learn from the communities about why improved sanitation may elicit negative responses and also the positive features of community values, beliefs and practices (including those associated with religion) which can be harnessed to promote change. 2. TECHNICAL OPTIONS 2.1 In the two largest Bhutanese urban areas, Thimphu and Phuentsholing, main sewerage systems connect individual households, institutions or septic tanks via an arrangement of interconnected sewers to a treatment centre. There, excreta and liquid waste decompose to harmless materials that can be disposed of safely in a designated area. 2.2 In the long term, a main sewerage system is recommended for all Bhutanese urban areas. 2.3 Main sewerage systems have several advantages over on-plot sanitation: easier for the users to operate; little or no nuisance and health risk from odours and insects; and sullage and approved industrial wastewater can be discharged into sewers. 2.4 Establishment of a main sewerage system incurs heavy costs; thus, an appropriate charge must be levied on the user for such service. 2.5 For reasons of economy and size, other sewage systems may need to be identified in the short term for smaller urban areas and areas lying outside the sewerage system in peri-urban situations, especially for those areas without a piped water supply (see Section 3 and Annex A). 2.6 Alternative sanitation systems must provide the same health benefits as a sewerage system but: Should remain affordable; Should be able to operate with or without piped water; Should provide the greatest convenience possible for users; Should provide minimal access to animals and insects; Should have no/minimal contact between human and fresh excreta; Should result in minimal pollution of water; Should result in minimal contamination of soil; Sholud provide minimal offence (sight, smell, flies); Should be simple and reliable to operate and maintain; Should be accessible to people of all ages. 2.7 Individual septic tanks for each household or building are the recommended alternative system for those urban areas that at present do not have a mains sewerage system (see Section 3). 2.8 Pit latrines are not permitted in urban areas in Bhutan and, where they currently exist, they should be phased out. However, construction and use of such systems may be unavoidable in exceptional circumstances (e.g., in schools and other institutions situated in peri-urban areas and in temporary labour camps). Refer to Annex A for further details. 3. SEPTIC TANKS A septic tank (see Figure 3.1) is an underground, watertight settling chamber into which raw sewage and all liquid wastes, including kitchen and bathroom waste are delivered through a pipe from plumbing fixtures inside a house or other building. The sewage is partially treated in the tank by separation of solids to form sludge and scum. Effluent from the tank infiltrates the ground through a soakpit (see Section 5) or drainage trenches (Section 6), or can be led directly to a nearby main sewerage system (Section 7). Septic tanks can serve single dwellings, communities or institutions. 3.1 Septic tanks are the recommended alternative to a mains sewerage system: In all areas not linked to a mains sewerage system; In smaller urban centres where a mains sewerage system is not yet an economic option; Where a piped water supply exists. 3.2 Property owners and building contractors in urban areas have various responsibilities in terms of tank construction and the various responsibilities in terms of tank construction and the management of sewage. These are listed in the RGoB rules (reference 1, Section 19A) and should be strictly adhered to. 3.3 The following points should be considered during pre-construction surveys, site selection, the detailed design phase, construction, operation and maintenance in order to promote efficiency and reduce potential public health hazards. 3.4 Septic tanks must be sited in locations where they are accessible for both maintenance and de-sludging by a vacuum tanker. 3.5 Septic tanks should be located as far as possible away from buildings and should not be located in swampy areas or areas prone to flooding. 3.6 On no account should roof drainage or surface water drainage be allowed to enter the septic tank system. 3.7 Tanks should be designed with adequate capacity to ensure: a) Proper settling of incoming sewage; b) Proper digestion of the settled sewage; and c) Storage of digested sludge until it is removed. 3.8 Tanks should be provided with a free board of at least 30cm to prevent flooding. 3.9 Tanks should be provided with ventilation pipes and cowls at a suitable height to take out foul smells. 3.10 Effluent from the septic tank should not be discharged into an open drainage system because it poses a health hazard, creates bad smells and encourages mosquito breeding. 3.11 It is important that the sludge is removed as frequently as required to ensure that it does not occupy too great a proportion of the tank capacity (see ection 10). 3.12 Surveys need to take into proper account the soil characteristics of areas where septic tanks are planned. Septic tank systems only work well when the soakpit area is permeable so that liquid effluent drains away safely and efficiently. 3.13 It is important that there is no risk of flooding or waterlogging in the soakpit area since such occurrences will overload the system and create a surface health hazard. 3.14 In case of clayey non-porous soil or where houses are closely spaced, special advice must be sought from the relevant urban authority. 3.15 If a mains sewerage system is or becomes available, a connection should be established to the main system after consultation with the concerned urban authority. 3.16 A general design of a typical septic tank is shown in Figure 3.1. Sanitation Engineers, familiar with rules and regulations in force in Bhutan and representing the concerned urban authority should be contacted for advice, assistance and approval of a proposed site and design for a septic tank. Technical design specifications are available from the relevant urban authorities (see Section 19C). Figure 3.2 3.17 On commissioning a septic tank, the tank should be filled with water. As the tank fills with solids and effluent, this water is displaced to the soakaway area. 3.18 It is recommended that a few bucketfuls of sludge from an established septic tank are added to a new tank in order to accelerate the start of biological action. 3.19 Three main causes of septic tank failure must be guarded against: a) If insufficient water is added at the commissioning stage, the water seals fail (because of evaporation), bad smells occur and no effluent is discharged; b) If tanks are not de-sludged at the proper time, sludge can discharge with the effluent and cause blockages in soak pits. Neglect of sludge disposal can result in whole systems clogging and overflowing, causing severe nuisance and health hazards; c) Effluent disposal in soak pits or drainfields is improperly designed, systems that are too small or are sited in impermeable soil will inevitably clog and overflow. 4. DISPOSAL OF EFFLUENT Effluent is the liquid that flows from a latrine or tank or, at a main sewerage system, from the treatment works. Effluent may contain pathogens; thus, safe disposal is essential to ensure that disease is not spread. 4.1 From all types of latrine: All latrines, except compost latrines, are unsealed pits, and thus effluent percolates into the subsoil and is safely treated by soil microbial action. The only risk occurs where the groundwater table is too high, making subsequent pollution possible (see Section 16). 4.2 From septic tanks, aqua-privies and compost latrines:The three main methods of handling and disposing of effluent are; via soakpits (Section 5), via drainage trenches (Section 6), and via a mains sewerage system (Section 7). S 5. SOAKPITS (OR SOAKAWAYS) Soakpits provide an economical method for disposal of effluent from septic tanks as well as aqua-privies and compost latrines. 5.1 Design of a soakpit is a specialist’s task, since the effectiveness of disposal depends on the porosity and percolation characteristics of the soil, level of the groundwater table, climatic conditions, presence or absence of vegetation, aeration of the soil and the concentration of suspended solids in the effluent. 5.2 It is therefore essential to obtain as much of the above data as possible as well as specialist advice from the sanitation engineers of the responsible urban authority before designing and constructing a soakpit. 5.3 Soakpits (see Figure 5.1 for typical arrangement) should be located near septic tanks but at least 5 metres away from any building or structure, and in permeable soils (see Section 5.5). Figure 5.1 5.4 Soakpits must be of adequate size, and care must be taken to ensure that no flooding by surface runoff and subsequent saturation occurs. 5.5 Soakpits should be constructed in permeable soils only, and no single pit should deal with more than 5000 litres of effluent per day. A simple test for permeability can be made by digging a pit about 1 metre diameter and 2 metres deep. The pit should be filled with clean water. In suitable soil, all water should seep away within 24 hours. 5.6 Design criteria and technical specifications are available from many sources (e.g., Section 19C, reference 5, A Guide to the Development of On-Site Sanitation, Franceys et al, WHO). 5.7 It is good practice to protect these areas by fencing to prevent entry by children and digging by scavengers, and to plant trees and shrubs around the perimeter. 5.8 If the required infiltration area is large, it may be more economical to provide drainage trenches (see Section 6). 6. DISPERSION OR DRAINAGE TRENCHES Drainage trenches are recommended for disposal of large quantities of effluent from septic tanks. These trenches disperse the effluent into the subsoil through an underground network of open-jointed pipes over a large area, reducing the risk of overloading at one place. This is a land-hungry technique, however, hence the alternative term drainage field. Figure 6.1 6.1 The permeability of the soil is a key criterion in the design and size of drainage trench areas. Specialist design and construction advice is necessary and should be sought from the responsible urban authorities. 6.2 A risk in drainage trenches is that soil around the pipes becomes clogged and impermeable after some time. It is important to check on any change of appearance in the moisture and vegetation condition that might suggest soil is beginning to clog. 6.3 The area around these trenches must be fenced to prevent entry by children and digging by dogs, pigs nad so forth. 6.4 Abandoned trench areas can be safely used for cropping after two years. 7. DISPOSAL OF EFFLUENT INTO A MAINS SEWERAGE SYSTEM Effluent from septic tanks may be collected periodically with vacuum trucks (where available) and then disposed of using sewer outlets such as inspection holes. Where septic tanks are not connected to either soakpits or drainage trenches, this is the only safe and recommended method for emptying effluent from septic tanks. 7.1 Ideally, effluent should be disposed of into a mains sewerage system through a piped connection. 7.2 For those urban areas not connected to an existing mains system, a vacuum truck should be used to collect the effluent, which is then disposed of down an inspection hole of the mains system. 7.3 Where there is no mains sewerage system in the urban centre, effluent should be collected by a vacuum truck and disposed of at a designated treatment centre or other site approved by the responsible urban authority. 7.4 Emptying of effluent from a septic tank in this manner should be carried out as and when needed, and no later than when the tank effluent has reached to within 50cm of the top of the tank. 8. DISPOSAL OF SLUDGE WASTE Several ways exist for disposing of solid waste excreta, ranging from cheap and simple to complex and expensive. All have inherent advantages, disadvantages and health risks. 8.1 Emptying of sludge waste from pits and septic tanks and its subsequent cartage and disposal is an inherently risky operation in terms of the spread of disease, and every care should be taken to ensure minimal health hazards to operators and the general public. 8.2 All sludge waste needs to be properly covered during collection and cartage to avoid flies coming into contact with excreta. 8.3 Where vacuum tanks are not available, special precautions need to be taken – e.g., the use of covered buckets and containers and covering the surface of excreta with sawdust, ash, soil or dry cow dung. 8.4 Protective clothing is required for all coming into close contact with excreta, e.g., good-quality gloves, masks, boots and overalls. 8.5 Special training -- in everything from frequent washing of hands, through methods of fly control, to safe and proper operation of the vacuum truck -- is required for those dealing with excreta. 8.6 Excreta must be disposed of in a safe and proper manner at an approved and officially designated site. Preferably, it should be taken directly to the treatment plant; alternatively, where there is no treatment plant, it might be buried in the ground. 8.7 Specialist advice should be sought and taken at all stages during this process. 9. DISPOSAL OF SLUDGE WASTE FROM LATRINE PITS Latrine pits (see Annex A) gradually fill with accumulated solids and with liquid if the soil is not sufficiently permeable. 9.1 When the pit is nearly full, there are three options: The pit can be topped up with soil and abandoned. Trees and even fruits (e.g., banana) can be planted on top of the pit. Ideally, the floor slab and superstructure have been designed and constructed in such a way that they can be moved to a new site; Figure 9.1 The full pit can be emptied. This is not recommended, since manual emptying of a recently filled pit is hazardous because the material is likely to carry live pathogens. Proper protective clothing, boots, masks, equipment and covered handcarts must be provided to those involved in emptying pits where this is absolutely necessary. Emptying such pits with a vacuum tanker is rarely efficient since the pump can have difficulty with thicker sludge (pipes block) and access is often difficult; The full pit can be rested for about two years. The contents can then be dug out without presenting any significant health hazards and used as fertilizer on grain crops. 9.2 In many cases, some problems of pit filling are overcome by either having very big pits or using double or twin pits. 9.3 Manual methods of emptying pit latrines are hazardous, and great care and sensible precautions should be taken. Scoops and buckets suitable for the more fluid type of waste are employed while thicker sludge has to be dug out by hand. 10. DISPOSAL OF SLUDGE WASTE FROM SEPTIC TANKS Septic tanks that are not connected to the main urban sewerage system may be empted periodically using vacuum trucks. 10.1 Every effort should be made to cause minimum nuisance and health risk at the site of the septic tank during truck movement and at the treatment plant. 10.2 It is essential that septic tanks are designed so that access to the tank for the vacuum tanker is good. Frequency of sludge removal should be ensured every 3 to 5 years, subject to local conditions. 10.3 It is important to annually check on the depth of sludge waste in the septic tank. De-sludging (emptying) of septic tanks should take place when the sludge depth has reached 2/3 of the liquid depth. The need for de-sludging is urgent when the level of sludge determined with a sounding rod rises to within 10 to 15cm of the connecting aperture between the two chambers of the tank. 10.4 When de-sludging septic tanks, some sludge should be allowed to remain and the tank refilled with water in order to promote the essential microbial activity in the cleaned tank. 10.5 The sludge should be disposed of carefully in the sludge drying beds at the sewage treatment plant or another designated treatment location and later disposed of at a suitable approved landfill. 10.6 Sludge should not be deposited down the manholes or inspection holes of existing sewerage systems. 10.7 De-sludging with the vacuum tanker by the municipal authority involves time and money. The costs should be borne in part by the user; for example, Phuntsoling City Corporation provides one free- empty-per year, after which the cost is Nu. 1,000 per empty. 10.8 Although sewage undergoes treatment in a septic tank, both solid matter and effluent still may contain pathogenic organisms and should be considered unsafe. Great care and strict safety precautions (e.g., masks, protective clothing, boots and rigorous training) must be provided to those authorised to carry out such tasks. 11. MAIN SEWERAGE SYSTEMS FOR URBAN AREAS In sewage systems such as those existing in Thimphu and Phuentsholing, discharge from flush toilets (water closets, WCs) and other liquid household waste (sullage) flows along a system of pipes (sewers) to a treatment works. The main advantages are: the user has no concern after emptying the toilet; the system deals efficiently with effluent and solid excreta; there is little to no nuisance from flies, mosquitoes or bad odour; health risks are significantly minimised; the sludge and effluent are safely and efficiently treated; and the treated effluent can be safely reused for some purposes (e.g., irrigation). The main disadvantages are that the systems are expensive to establish and require a piped and reliable water system. 11.1 Because these systems are very expensive and cause considerable disruption to the urban environment during the construction phase, it is essential to seriously consider the need and the economics of construction and operation before venturing further. 11.2 To minimise disruption to urban life and limit damage to existing infrastructure (e.g., roads, drinking water pipelines, power and TV cables), it is essential to undertake planning and design with all relevant urban authorities and community groups. 11.3 Sewerage systems from collection through transport to treatment are complex and thus require efficient infrastructure for safe construction, operation and maintenance. It must not be forgotten that trained manpower is an essential and expensive part of installing and efficiently managing an urban sewerage system. 11.4 To operate, sewerage systems require a minimum supply of piped water, around 70 litres per person per day. 11.5 Pre-design surveys and estimates must take into account that the treatment plants are complex and require quite extensive areas of flat land as well as efficient day- to-day management. 11.6 Adequate treatment of effluent is essential when it is discharged to a watercourse in order to avoid downstream pollution (see Section 12). 11.7 During the design and planning phase for main sewage systems, including the treatment works, the following points should be considered: Capacity and flexibility to meet growth in demand; Availability of land; Local nuisance, e.g., odours, flies; Quality of effluent required, e.g., ratio of river flow to effluent flow (8:1 minimum dilution); flow (8:1 minimum dilution); Quality of receiving water; Re-use of receiving water downstream, which can determine the importance of pathogen removal; Climatic conditions accommodating hydraulic and organic shock loads; Capacity required to remove Biochemical Oxygen Demand; Capacity to stabilise nutrient pollution; Capacity to stabilise chemical pollution; Effectiveness in reducing suspended solids from effluent to acceptable levels; Cost-capital investment and operation and maintenance; Chemicals, mechanical and electrical parts that require importing from abroad which causes extreme difficulties with suppliers; Highly trained staff requirements; Simplicity of construction and operation and maintenance to reduce the strain on human and financial resources. 11.8 Treatment plants are designed to treat certain, but not all, waste products. It is essential, therefore, that the sewerage system is isolated from industrial and other sources of toxic and hazardous waste that the designed treatment plant cannot process (see Section 13). 11.9 Storm water from roads, roofs and other public areas (e.g., parks, sports grounds, commercial and public service areas) must not enter the sewer. It is common practice to join rainwater down-pipes to the sewerage network; this should be strictly prohibited, because it causes flooding of the network following heavy rain, even resulting in manhole covers being blown off. Building owners should be made responsible for ensuring that a) this practice does not occur and b) that all junction boxes are covered. Fines might be considered for persistent neglect. 11.10 It is imperative that the sewerage system is properly designed and built to ensure that contamination of the drinking water supply does not occur. Inadvertent pipe breakages and leaks can cause serious health risks if the sewerage system runs too close to or crosses the drinking water lines. 11.11 It is important that sewers have an adequate design for over capacity to prevent overfill, flooding and blockage. It is common for systems to be designed without adequate capacity for future urban growth. Systems are often at full capacity during peak hours of domestic use in the morning (7 to 9 a.m.) and in the evening (7 to 10 p.m.), as well as during holiday periods. 11.12 Bearing in mind the constraints of the Bhutanese terrain, sewers should be laid at a gradient that minimises scoring and siltation and potential damage to the system. Scoring occurs when the design gradient is too high, resulting in high velocities of sewer flow that erodes the pipes. Silting action takes place when the velocity is too low because of low gradient with subsequent in-pipe deposition. 11.13 Damage to the sewerage system should be reported immediately to the competent authorities and repairs undertaken speedily, especially if the damage poses any threat to public health (e.g., leakage of sewage into drinking water systems or onto public places or agricultural land). 11.14 Users need to be made aware of the importance of prompt reporting of faults and leaks in the sewerage system. Community groups responsible for solid waste management and general sanitation should be established in each ward to ensure prompt action when problems and emergencies arise. 11.15 In addition, sanitary inspectors employed by the responsible urban authority need to make frequent checks on the system during routine inspection rounds within their wards. 11.16 The treatment of sewage at the plant will be designed specifically for the urban situation and site. Secondary treatment of raw sewage and sullage is essential before discharge into a watercourse, and this may be undertaken in a series of ways: removal of gross solids, this may be undertaken in a series of ways: removal of gross solids, sedimentation, anaerobic stabilisation ponds, aerobic stabilisation ponds, and percolating filters. 11.17 Design, construction and management of such sewage systems is a specialised task, and consultation with experienced engineers is essential, especially during the planning phase. 12. PUBLIC TOILETS Public toilets are essential for all busy urban centres. 12.1 Public toilets should be conveniently located in the busy areas of town to simplify and encourage use: for example, bus, truck and taxi terminals, sports centres and swimming pools, parks and playgrounds, main shopping and commercial areas, and industrial and administration centres. 12.2 Ideally, public toilets should be constructed where they can be connected to the main urban sewerage network, if one exists. 12.3 Where a mains sewerage system does not exist, septic tanks connected to soakpits are appropriate. 12.4 Sufficient numbers of toilets for both males and females should be provided to avoid queues at busy periods. 12.5 Proper hand-washing facilities also should be provided to encourage good sanitation. 12.6 The concerned urban authority should adopt a pay-and-use system in all public toilets to facilitate upkeep and maintenance. 12.7 An attendant in charge should be appointed to care for and maintain the toilets and washrooms in a clean, sanitary condition. 12.8 The toilets and baths should be washed and disinfected at least twice a day. 12.9 Public toilet areas should be fenced and well-lit, and women and children should feel it is a safe environment for them to enter, especially at night. No gambling, drinking of alcohol or general loitering should be permitted in the vicinity, especially within the fenced area. The attendant should be given the responsibility and the authority to ensure that the public toilets are safe and to call the police in the event of trouble. 12.10 The urban authority should ensure that a sound revenue system is established, and the entire service (including responsibilities for revenue collection, 24-hour staffing, maintenance, security and hygiene) may be leased out to a service contractor. Figure 12.1 13. MANAGEMENT OF TOXIC WASTES In Bhutan, toxic wastes can be generated by both institutions and the existing small to medium-sized industrial plants (e.g., hospitals, slaughterhouses, veterinary clinics, autoworkshops, carbide producers, dyeing and wood factories, dry cleaners, photo labs). Wastes generated by some of these facilities can seriously damage general sewerage networks and treatment plants. Toxic wastes are sometimes discharged directly into the main sewer because the wastes are usually produced in very small amounts. This is, however, not good general practice. Special attention needs to be given to wastes from such industries and public service institutions; this is covered in greater detail in the ECOP on Management of Hazardous Waste. In terms of sewage and sanitation practices, it is necessary toIn terms of sewage and sanitation practices, it is necessary to define those wastes that can and cannot be accepted by the present and future main urban sewerage systems. Some details are provided in the RGoB, Sanitation and Water Rules, July 1995 (see Section 19, reference 1, Pages 17 to 22); these are summarised in the table below. 14. WASTE WATER STANDARDS The following four tables have been extracted from Ambient/Dis charge Standards and Environmental Sampling Manual, published by NEC in February 1999 (see Section 19B). The tables provide guideline criteria for the following: Table 14.1 Criteria for Raw water supply (1) - mg/L, unless otherwise stated (1) Raw water Supplies refers to waters used as the intake source of water for public use and can include surface water and groundwater. Ref: Canadian Water Quality Guidelines (1978, updated 1996). Prepared by the Task Force on Water Quality Guidelines of the Canadian Council of Ministers of the Environment. Inland Waters Directorate, Environment Canada. (2) Recommended by the National Environment Commission until more relevant information becomes available. Table 2 (Criyera for raw water supply) Table 14.2 Bacteriological drinking water quality criteria develle 14.2 Bacteriological drinking water quality criteria developed by WHO (1) (1) WHO: Guidelines for drinking water quality (second edition), Vol. 2., Pages 174- 181. Immediate investigative action must be taken if either E. coli or total coliform bacteria are detected. The minimum action in the case of total coliform bacteria is repeat sampling; if these bacteria are detected in the repeat sample, the cause must be determined by immediate further investigation. (2) Although E. coli is the more precise indicator of faecal coliform pollution, the count of thermotolerant coliform bacteria is an acceptable alternative. If necessary, proper confirmatory tests must be carried out. Total coliform bacteria are not acceptable indicators of the sanitary quality of rural water supplied, particularly in tropical areas, where many bacteria of no sanitary significance occur in almost all untreated supplies. (3) It is recognised that in the great majority of rural water supplies in developing countries, faecal coliform contamination is widespread. Under these conditions, the national surveillance agency should set medium-term targets for the progressive improvement of wa Table 3 (Bacterilogical drinking water quality) Table 14.3 Criteria for drinking water supplies (1) - maxmun acceptable concentration in drinking water - mg/L, unless otherwise stated (1)Drinking water guidelines apply to “treated” or “finished” water as it comes from the tap and are not intended to be applied directly to surface water. (2) Recommended by the National Environmental Commission until more relevant information becomes available. These guidelines are based on the criteria prepared by WHO (1996), the Canadian Water Quality Guidelines (1978, updated 1996), (USEPA) the United States Environment Protection Agency (1990-1993 series), and PESCOD (Pollution Environmental Standard Control Organisation and Development, (obtained from Asian Institute Technology, Bangkok, July 1997). Table 4 (Citeria for drinking water supplies) Table 14.4 Water quality criteria for agricultural uses (mg/L) Table 14.4 Water quality criteria for agricultural uses (mg/L) (1) Recommended by the National Environment Commission until such time as local data sources are available. Present criteria based on the Canadian Water Quality Guidelines (1978, updated 1996) and the Indian Environment Protection Rules.(1986). (2) ID = insufficient data to develop a guideline. (3) Maximum residues in irrigation water, or 1,000 total coliforms per 100ml. Table 5 (Water quality for agricultural use) The NEC document Ambient/Discharge Standards and Environ- mental Sampling Manual, (Section 19B) provides further informa- tion on such issues, including criteria for the protection of fresh- water aquatic life. It also describes detailed standard operating procedures for environmental sampling and analysis in order to monitor the quality of the waters for different purposes. Thus, an important reference document for the authorities responsi ble for environmental monitoring. 15. HEALTH ASPECTS Many insects are attracted to excreta because they provide rich organic material and water, both of which are essential for the insect’s development. The risk of high insect populations and subsequent disease transmission is far greater in latrine-type systems than in septic tanks and main sewerage systems, especially where management of the former is poor. 15.1 The most important groups of insects in terms of public health risk are mosquitoes, houseflies, blowflies and cockroaches. 15.2 Pools of polluted water must be controlled because some forms of mosquitoes breed in polluted water, including that found in some pit latrines. Unlike flies, mosquitoes are not deterred by low light levels. 15.3 The three larval stages of house- and blowflies are found in excreta or mixtures of excreta and decaying vegetable matter. Flies commonly transmit pathogens from the excreta to food intended for human consumption. Contact between flies and excreta, effluent and sludge waste should be prevented through the use of fly- screen netting, seat and latrine covers, and spring doors. 15.4 Cockroaches are attracted to latrines by the moisture and organic matter and are then likely to transmit disease by carrying pathogens on their bodies. Cockroach numbers should be controlled by maintaining clean and sanitary conditions within the house, esby maintaining clean and sanitary conditions within the house, especially in the kitchen and food storage areas. 15.5 Whether a latrine pit, soakpit or area surrounding a septic tank is dry or wet makes no difference to fly breeding, but for mosquitoes wet pits are essential as the larvae need water to swim in and a free liquid surface for the breathing siphon. Wet conditions therefore require extra vigilance in order to control mosquito populations. 15.6 In latrines and toilets without a water seal, it is possible to reduce the mosquito risk by covering the surface of the liquid in the pit with a film that prevents the mosquito larvae from breathing. Oil and proprietary chemicals have been used effectively but they may pollute the groundwater and thus are not recommended unless approved by the relevant urban authorities. Alternatively, small plastic balls that float on the surface can be used. 15.7 In many latrines, however, the period during which there is free liquid on top of the sludge is limited to short periods immediately after starting up or before emptying. Normally, a layer of scum forms on the water surface, preventing further mosquito breeding. When users or communities complain of increased mosquito populations after a pit latrine system has been installed, prompt attention should be given to this issue by the district health and sanitation officials. 15.8 Latrines pits must be kept dark to reduce the fly population. However, this may not be considered safe and user-friendly for certain members of the community, especially children. Thus, ideally an electric light powered by the mains electricity with a switch might be provided; alternatively, a candle plus a box of matches might be provided, but this also is not safe for younger, unsupervised children. 15.9 Any ventilation holes in either pit or latrine house must be screened, because flies use both sight and smell to find food materials. 15.10 Open pit latrines are ideal breeding places for flies, and all such latrines need prompt attention from the urban authorities. 15.11 Pit latrines, soakpits and drainage trenches should be sited as far as possible from where food is stored and prepared in order to prevent migration of cockroaches to and from latrine and food source. 15.12 Rats also can be a problem because they look upon excreta as food. If they come into contact with excreta and then with food intended for human consumption, disease may be transmitted. Rats have also been reported to burrow into latrine pits (e.g., in Nepal). This creates a disease transmission route as well as causing large volumes of soil to fill up the pit. 15.13 Where such rat problems occur, it is important to line the top 0.5 to 1.0 metre of the pit with bricks or stone and cement. In urban areas, it is recommended that a 500mm sanitary seal should be standard practice. 15.14 For good control of all insects, the following pit latrine design features are mandatory: Tight-fitting lids to the latrine (not applicable to VIP latrines); Tight-fitting doors or privacy screen to the privy; Closed systems with a water seal; All holes and gaps in the privy sealed; Screened ventilation spaces in the privy; Pit and privy should be kept as dark as possible; All latrines should be fitted with a screened air vent. 15.15 To further reduce risk of bad odours, insect breeding and disease transmission, a number of important management strategies should be considered.These inculde such as pay-to-use systems and employment of an assistant in larger communal or public toilets, fines for those improperly using the latrines, and public awarenessfines for those improperly using the latrines, and public awareness and education campaigns. 15.16 It is essential that the squat pans of a pit latrine are cleaned after each use and thoroughly cleaned with a brush and water at least once a week. Figure 15.1 15.17 All toilets should be fitted with hand-washing facilities in order prevent spread of pathogens. 15.18 When unsanitary latrines occur in schools, children acquire poor hygiene habits that may be difficult to break. Educational establishments thus need to be at the forefront of promoting improved hygiene habits. Well-built and operated pit latrines at schools are generally far safer and of greater fundamental value than a porcelain and tile WC that is allowed to become dirty and a home to insects. 16. GROUNDWATER POLLUTION RISK Liquid percolating into the soil from latrine pits, soakpits and drainage trenches may contain large numbers of microorganisms of faecal origin, including pathogens, nitrates and other salts. Therefore, groundwater under or near to, or downslope from, the pits may create a pollution risk, especially when close to watercourses or where wells and boreholes exist. 16.1 Table 14.2 records the permitted levels of feacal coliform in drinking water. Where sampling and analysis of a water drinking source shows excessive coliform, it may be caused poor sanitation and subsequent contamination. Possible causes include leakage of sewage from a mains system of sewers, a broken septic tank, a collapsed pit latrine, and blocked or poorly maintained soakpits and drainage trenches. 16.2 Avoidance of groundwater pollution is essential. 16.3 It is important to ensure that groundwater level is lower than two metres below the bottom of the pit or drainage trenches throughout the year. Where this is the case, virtually all bacteria, virus and other faecal organisms are removed. 16.4 Where this is not the case, it is important to insert a 2-metre sand or loam layer between the bottom of the pit and the groundwater. 16.5 Wells can be safely sited 8 metres from a latrine pit, soakpit or drainage trench if the soil is fine. 16.6 Chemical pollution extends much further from the pit or drainage trenches than does pollution by microorganisms. With high pit latrine and septic tank densities, nitrate concentrations may build up to levels in excess of those recommended in the national drinking water guidelines. In urban areas of high concentration of such methods of waste storage, this needs to be monitored at least twice a year. 16.7 In some urban areas, overloading of soakpits can also occur, resulting in overflow and surface flow; this is a more serious risk in the monsoon season, when groundwater tables are naturally higher. This too needs monitoring during sanitary inspectors’ normal inspection rounds. 16.8 In areas where drinking water supply systems occur near sewage disposal systems, water in leaky pipes also may be contaminated if the pressure drops and polluted groundwater levels are above those in the pipes. Sanitary inspectors together with community watch groups also need to monitor this through observing sudden the appearance of wet soil areas and puddles. 17. EDUCATION AND AWARENESS RAISING 17.1 It is mandatory that the responsible urban authority designs, schedules and carries out regular education and awareness raising camules and carries out regular education and awareness raising campaigns to promote sound sanitation. These campaigns should ensure that all groups in the urban population are made aware and retain awareness of the importance of good sanitation practices in terms of environmental health and safety. The campaigns should target different groups on a ward-by-ward basis – residential, commercial, industrial, hospitals, educational establishments and other institutions (e.g., big office blocks and army and police barracks). 17.2 It is strongly recommended that public servants, especially those involved in health services, take an active part or be recruited during these sanitation campaigns. 17.3 Campaign schedules and annual programmes should be strictly followed as a matter of priority. Improving sanitation practices will proceed only slowly, but will be even slower without such annual campaigns. Schools are a key target group. 17.4 Different methods for communicating with the public should be used, including: radio, TV, video, documentaries and advertisements, newspaper cartoons, pamphlets/leaflets, dance groups, national theatre troupes, song and the Internet. 17.5 Respected members of the community should be used as key resource to promote awareness. 17.6 Materials may be prepared in all relevant languages. 18. GLOSSARY OF TERMS Aqua-privy: latrine in which excreta fall directly through a submerged pipe into a water tight settling chamber below the floor and from which effluent overflows to a soakaway or drain. Biochemical oxygen demand: The mass of oxygen consumed by or ganic matter during aerobic decomposi tion under standard conditions, usually measured in milligrams per litre during five days; a measure of the concentration of sewage. Excreta: Faeces and urine. Compost latrine: In this type of latrine, excreta fall into a watertight tank to which ash or vegetable matter is added. Dry latrine: A latrine where users defecate into a bucket, basket or other receptacle that is regularly emptied. Latrine: Place or building, not normally within a house or other building, for retention and sometimes decomposition of excreta. Overhung latrine: Latrine sited such that excreta falls directly into the sea or other body of water. Nightsoil: Human excreta, with or without anal cleaning material, which are deposited in a bucket or other receptacle for manual re moval (often taking place at night). Offset pit: Pit that is partially or wholly displaced from its superstructure. On-plot sanitation: sanitation systems contained within the plot occu pied by the dwelling. On-plot sanitation is associated with household latrines but also includes facilities shared by several households together on the same plot. On-site sanitation: Includes communal facilities that are self-contained within the site, in contrast to sewage and dry latrines, where excreta is removed from the site. Pathogens: Organisms that cause disease. Percolation rate: The rate at which liquid moves through soil. Pit latrine: Latrine with a pit for accumulation and decomposition of excreta and from which liquid infiltrates into the surrounding soil. Pour-flush latrine: Latrines into which a small quantity of water is poured to flush excreta through a water seal into a pit. Sanitation: The means of collecting and disposing of excreta and commu nity liquid waste in a hygienic way so as not to endanger the health of individuals or the community as a whole. Septic tank: Watertight chamber for the retention, partial treatment and discharge for future treatment of sewage. Sewage: Wastewater that usually includes excreta and that is, will be or has been carried in a sewer. Sewer: Pipe or conduit through which sewage is carried. Sewerage: System of interconnected sewers. Soakaway: Soakpit or drainage trench for subsoil dispersion of liquid waste. Soakpit: Hole dug in the ground serving as a soakaway. Sullage: Wastewater from bathing, laundry, preparation of food, cook ing and other personal and domestic activities that does not contain excreta. Superstructure: Screen or building of a latrine above the floor that pro vides privacy and protection for users. Vent pipe: Pipe provided to facilitate the escape of gas from a latrine or septic tank. VIP latrine: Ventilated Improved Pit latrine or pit latrine with a screened vent pipe and a partially dark interior to the superstructure. Water seal: Water held in the U-shaped pipe or hemispherical bowl con necting a pan to a pipe, channel or pit to prevent the escape of gas and insects from the sewer or pit. Wastewater: Sewage or sullage. Y-junction: Chamber in which liquid may be directed along either of two pipes or channels. 19. REFERENCES FOR FURTHER TECHNICAL INFORMATION A) Relevant Bhutanese and Regional Legislation 1. Public Works Division, Ministry of Communications, RGoB (July 1995), Water and Sanitation Rules. 2. Department of Works, Housing and Roads, Ministry of Communications (1996), Bhutan Building Codes. These are under review; see new RGoB Building and Plumbing Rules, at present under preparation by the Urban Development and Housing Division of the Ministry of Communications. 3. RGoB Urban Land Administration Act (final draft dated 22 July 1998) 4. Indian Codes of Practice for Plumbing, Section 1, Water Supply. 5. Ministry of Foreign Affairs, Danida and RGoB (March 1996), Operation and Maintenance Manual, Wastewater Treatment Plants. 6. Ministry of Foreign Affairs, Danida and RGoB (January 1996), Operation and Maintenance Manual, Sewer Network. 7. RGoB (1999), The Bhutan Municipal Act. 8. RGoB (1996), Land Compensation Rate. 9. RGoB (2000), Environmental Assessment Act. B) Relevant Bhutanese and Regional Reports B) Relevant Bhutanese and Regional Reports 1. NEC/RGoB (February 1999), Ambient/Discharge Standards and Environmental Sampling Manual. 2. NEC/RGoB (1993), Health Care in Industry, a background paper for Bhutan’s National Environment Strategy by Dr Pem Namgyal. 3. PT Hatfindo Prima for NEC (May 1999), Wastewater and solid waste codes of practice. 4. GTZ for HM Government of Nepal (1992), Urban Environmental Guidelines for Nepal. 5. DANIDA/RGoB (Draft, May 2000), Environmental Sector Support Programme: Draft Final Report on Urban Environmental Guidelines. 6. NEC/RGoB (Draft, June 2000), Manual for the Environmental Clearance of Projects. C) Other Relevant Literature 1. WEDC (Water, Engineering and Development Centre), Loughborough University, for ODA (1995), On-Plot Sanitation in Low-Income Urban Communities; A Review of Literature, A.Cotton et al. 2. HT Mann and De Williamson (1982), Water Treatment and sanitation: Simple Methods for Rural Areas, Intermediate Technology Publications. 3. Waste (advisers on urban environment and development), for Environmental Systems Information Centre (AIT, 1997), The Collection of Husehold Excreta: the operation of services in Urban Low-Income Neighbourhoods. Urban Waste Series 6, Maria S. Muller. 4. World Bank (1980), Appropriate Technology for water Supply and sanitation: a sanitation field manual, JM Kalbermatten et al. 5. WHO (1992), A Guide to the Development of On-site Sanitation,R Franceys et al. 6. WHO (1996), Fact Sheets on Environmental Sanitation: cholera and other epidemic diarrhoeal diseases control: prepared by the Robens Institute, University of Surrey. 7. UNDP/World Bank Water and Sanitation Programme, South Asia (Andrew Fang, July 1999), On-site Sanitation, an international Review of World Bank Experience, a study carried out by the East Asia Environmental and Social Development Unit of the World Bank. 8. Garg SK, Sewage Disposal and Air Pollution Engineering. 9. Fair GM, Elements of Water Supply and Waste Water Disposal. 10. Hardenbergh WA, Water Supply and waste Disposal. 11. Isaac PSG, Public Health Engineering. 12. Hammer HJ, Water and waste water technology. 13. Ehlers VM, Municipal and Rural Sanitation. 14. Birdie GS and Birdie JS, Water Supply and Sanitary Engineering. 15. UNEP Environmental Management Guidelines No. 14 (Nairobi, 1988), Environmental Guidelines for Domestic Wastewater Management. 16. UNDP Project Management (INT/82/002), Report Number 1, Volume 1: Guidelines, Water Supply and Sanitation Project Preparation Handbook. 20. WEBSITES There are hundreds of Websites concerning sanitation and sewage management. The most comprehensive are those sites maintained by governments and international organisations. Those worth visiting include: World Health Organisation United Nations Development Programme World Bank US, UK, Danish and Australian government sites. InFind is a good search engine for this purpose; go to www.infind.com and type in a keyword such as sanitation, sewage, sewerage systems or health. Utilise the search engine of the particular site you enter by using a more specific word, which will lead to the required information (e.g., water criteria, septic tankslead to the required information (e.g., water criteria, septic tanks or latrines). V ANNEX A Pit Latrines and Other Alternative Sanitation Systems: There are several types of pit latrine, all of which have the following advantages: relatively low cost, simple design and construction, acceptance of excreta and different anal cleansing materials in a simple hole in the ground.Under good management, they can pro vide satisfactory long- term use. However, no type of latrine other than those employing septic tanks are permitted in urban areas in Bhutan for the following reasons: Unlike septic tanks, they cannot be upgraded through connection to a sewerage system; Management good enough to maintain a high degree of sanitation cannot be guaranteed; Pit latrines pose an unacceptable serious health risk in crowded urban areas. However, latrines may have to be considered in some circumstances, and some basic codes are listed in the following sections. A1. Open Defecation When there are no latrines or sanitation system, people resort to defecation in the open; this may be indiscriminate or in special places generally accepted by the community (e.g., defined areas, rubbish and manure heaps, or under trees). Open defecation encourages flies, which spread faeces-related diseases, and in moist ground the larvae of intestinal worms develop. In addition, surface water runoff from defecation areas results in water pollution and a distinct health risk to those downstream. Open defecation should not be tolerated in urban areas of any size. There are better options (listed below) that confine excreta in such a way that the cycle of re-infection from excreta-related disease is broken. Fines for those repeatedly defecating in open areas will be established and enforced. A2. Pit latrines Pit latrines come in a variety of forms, as listed below: A2-1 Dry latrines, where users defecate into a bucket, basket or other receptacle that is regularly emptied. Poor operation and spasmodic or infrequent collection result in bad smells and cause an insect nuisance, which the collection process results in a health hazard to collectors. A2-2 Overhung latrines, which are built over water into which the faeces fall. They should not be used in urban areas for clear and obvious health risks to downstream users. A2-3 Shallow pits or small holes about 30 cm deep may be dug near places of work (e.g., near construction sites or on farms) into which people defecate; the faeces should then be covered with soil. Decomposition in shallow pits is rapid because of the large bacterial population in topsoils, but flies breed in large numbers and hookworm larvae spread around the holes. Although there is no cost involved in shallow pit construction and maintenance, the fly nuisance and health risks are serious disadvantages. Shallow pits should not be permitted in any urban areas. A2-4 Borehole latrines are excavated by hand or by machine, often with a diameter of about 400mm and a depth 6 to 8 metres. They can be excavated quickly when boring equipment is available (eg., construction sites and road maintenance sites).However disadconstruction sites and road maintenance sites).However disadvantages include the sides tend to be fouled by excreta, producing a subsequent fly nuisance; they have a short life owing to a small cross sectional area; and there is a greater risk of groundwater pollution given the depth of the hole. Borehole latrines should not be permitted in urban areas. A2-5 Compost latrines (refer Figure 12.1) where excreta fall into a watertight tank to which ash or vegetable matter is added. If the moisture content and chemical balance are controlled, the mixture will decompose to form a good soil conditioner in about four months. Pathogens are killed in the dry alkaline compost, which can be removed for application to farmland as fertilizer. The disadvantages, however, outweigh the benefits of this recycling process.Careful operation is essential, lack of an adequate composting period has resulted in high levels of worm infection, urine should be collected separately, and ash and vegetable matter must be added regularly. Because of high management skills required, compost latrines are not recommended for urban situations. However, where they may exist in farming areas in peri-urban environment with a requirement for soil conditioner, sanitation officers should ensure that management is optimal and there is minimal risk of worm and pathogen infection. Strict rules apply concerning production of crops on kitchen gardens or farmland that has received either decomposed or fresh excreta because no sanitation system can guarantee that all pathogens have been killed. Crops that can be grown on or within 25 metres of land treated with excreta include groundnuts, grains, tobacco, sugar-cane, cotton, orchard and tree crops. Crops eaten raw or without any skin removal should not be cultivated because sewage effluent is a potential carrier of pathogens that are likely to cause diseases such as typhoid, cholera, dysentery and worm infections. It is strongly recommended that sanitary officers ensure that gumboots are worn by those farming land on which treated effluent has been spread. A2-6 A Simple Pit Latrine consists of a slab over a pit that may be 2m or more in depth (refer Figure 15.1). The advantages of simple pit latrines are that they are low cost, can be built by householders, need no water, and operation, management and maintenance are easily understood. Disadvantages include: a) Risk of groundwater pollution that can result from percolation of the liquid from all types of pit latrine; b) Odour and insects that can cause great nuisance and health risk, ( see Section 15); c) Risk of poor management, because good operation and maintenance of latrines are essential to ensure a long life and sound sanitary conditions. If poorly managed and maintained, pit latrines provide a level of sanitary hygiene little above open defecation. Management, education and awareness are therefore crucial; d) Risk of improper operation and maintenance; householders need to be trained by sanitation officers in proper methods. Under sound construction and management, excreta in the pit should undergo decomposition to innocuous, humus-like solids, water and gases. The remaining water and gases should dissipate into the ground or air, leaving a solid residue in the pit. During decomposition, disease-causing pathogens should be killed, but this process may take up to two years; e) Difficult in poor ground conditions. Although not recommended for urban areas, pit latrines may be necessary in some situations, in which cases the following codes apply: They should be sensibly designed in collaboration with the user household or community; The floor of the latrine (a slab made of wood or cement) should be firmly supported on all sides and raised above the surrounding ground so that surface water cannot enter the pit; rounding ground so that surface water cannot enter the pit; If the sides of the pit tend to collapse, they should be lined. In urban situation with heavier foot and vehicular traffic than normal, there is a tendency to say that in urban areas they should all be lined; A squat hole in or above the slab or a seat is provided so that excreta fall directly into the pit; The latrine should be fitted with a door for privacy; If specialist input suggests that there may be a risk of groundwater pollution, 2 metres of sand or loam should be inserted between the bottom of the pit and the groundwater table - this removes most micro-organisms of faecal origin; Pit latrines should receive only small amounts of water, and since the pit is not sealed this liquid seeps from the pit into the surrounding ground; It is essential that all types of latrine are designed and fitted with a tight fitting cover over the squat hole when the latrine is not in use. This is the most important management factor to be learnt by the user, and in public places fines should be imposed to those who repeatedly do not replace the cover after use; All pits should be rested when they are filled to within half a metre of the slab; It is safe to empty them after two years but precautions should still be taken (e.g., protective clothing, laboratory testing and safe disposal). A2-7 Ventilated Improved Pit (VIP) latrines (refer Figure 9.1) are more sanitary than a simple pit latrine and should be used wherever necessary and approved by urban authorities. VIP latrines have better control of fly and mosquito populations and there is much less odour in the latrine due to ventilation through a pipe extending above the latrine roof with fly proof netting over the top. The inside of the superstructure is kept dark which may be a problem for children, who can be frightened by entering a dark toilet. Another disadvantage is that the top of the pipe should be 500mm above the nearest structure ( to allow good airflow across the pipe), and thus the VIP latrine is suitable only in low density urban areas. A2-8 Pour-flush atrines, a pit latrine fitted with a trap providing a water seal that is cleared of faeces by pouring in sufficient quantities of water to wash the solids into the pit and replenish the water seal (see Figure 3.1). Important advantages of this system are that the water seal prevents flies, mosquitoes and odours reaching the latrine from the pit and the pans are cheap and can be manufactured locally. The pit may be directly underneath the latrine or offset somewhat by providing a short length of pipe or covered channel from the pan to the pit. Offset latrines, however, require more water and are more expensive to construct. Disadvantages include the following: Pour-flush latrines can be used only where a reliable water supply is available; Water is a part of the sanitation system, mosquito breeding may be increased. It is therefore more important that a tight- fitting lid remains an essential part of this type of latrine in order to minimise fly and mosquito breeding (see section 15). Advantages include the fact that this type of system can be upgraded by fitting a flush toilet to the latrine (although these tend to use more water) as well as through connection to an urban sewerage system when this becomes available. A2-9 Other forms of latrine include double or community pit latrines, which may be appropriate in some situations in low-density urban areas and peri-urban situations. Single large pits have some advantages and can be used in order to minimise maintenance in terms of the frequency of emptying. Research has shown that pits with a volume of 1cubic metre per user last 30 to 50 years. A3. Aqua Privies A3. Aqua Privies An aqua-privy has a water-tight tank located immediately beneath the latrine floor so that excreta fall directly into the tank through a pipe. The bottom of the pipe is submerged in the liquid in the tank forming a water seal to prevent escape of flies, mosquitoes and smell. The tank functions like a septic tank, but are less expensive to construct. Effluent usually infiltrates into the ground through a soakpit (see Section 5). Accumulated solids (sludge) must however be removed regularly, most appropriately via a vacuum tanker. Aqua-privies are not generally recommended for urban areas as they have a reputation for poor operation, but may be suitable for some situations.