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DRAINAGE & SEWERAGE CHAPTER VI A. DRAINAGE & SEWERAGE (iii) Manual on Sewerage and Sewage Treatment - Ministry of Urban...

DRAINAGE & SEWERAGE CHAPTER VI A. DRAINAGE & SEWERAGE (iii) Manual on Sewerage and Sewage Treatment - Ministry of Urban Development, New Delhi. 601 General (iv) Regulations issued by Municipal Reference may be made to the following Corporations or local Public Health for provisions not contained in this Chapter. Departments should also be In case of any variation, the latter shall prevail. referred. (i) National Building Code of India 1983 602 Preparation of Schemes of - Part IX Plumbing Services, Sewerage- Drainage and Sanitation. Definitions of some common terms are (ii) Relevant BIS Codes as mentioned given below:- below :- (i) Drain : A conduit/channel for the IS 1172: 1983 Code of basic carriage of storm water requirements for water or other used water supply drainage and sanitation. (ii) Drainage : A system for removal of any unwanted liquid IS 1726: 1974 Specifications for cast iron manhole covers (iii) Sewer : A pipe/conduit used and frames. generally for carrying sewage or other water- IS 1742: 1983 Code of practice for borne wastes building drainage. (iv) Sewerage : A system for the collection and conveying IS 2470: 1985 Code of practice for sewage to the point of installation of septic disposal tanks. (v) Manhole : An opening by which a IS 4111: 1986 Code of practice for man may enter and leave ancillary structures in a drain, a sewer or other sewerage system. closed structure for inspection, cleaning IS 5329: 1983 Code of practice for and other maintenance sanitary pipeworks operations fitted with a above ground for suitable cover buildings. 155  DRAINAGE & SEWERAGE (vi) Soil Waste : The discharge from e) availability of piped water supply water closets, urinals, in the area, present and anticipated sinks, cattle sheds, per capita water supply gullies etc. f) the nature of sewage, total sewage (vii) Sewage : It includes all kinds of flow - present and prospective liquid wastes of a community or industry. It g) discussion of different possible is classified as follows: - disposal points and their (a) Storm sewage, comparative merits (b) Sanitary sewage, (c) Industrial waste. h) review of different possible methods of treatment B. WATER-BORNE SEWERAGE i) engineering features and economical aspects of the sewer 603 Adherence to Regulations - system, an index and a general layout plan with contours at In the preparation of under-ground intervals of 2m alongwith a sewerage schemes, the Drainage Regulations schematic diagram. Sub-soil in regard to the installations of all sanitary conditions including level of water equipments and construction of drains and table and location of other services sewers shall be followed. - their positions, size etc. basis for computation of surface run-off, 604 Sewerage Schemes - drainage area and silting of storm sewage and overflow, wherever Reports of sewerage schemes should necessary include- j) number and location of pumping a) a historical retrospect leading to the stations with hydrostatic heads and justification of the project frictional loss of heads on pumps and on mains b) description of existing facilities, if any k) a comparison of total costs (recurring and non-recurring)of the c) population studies, analysis and alternatives involved under major prediction based on a critical subheads appraisal of available data l) the most satisfactory alternative d) location of the water supply scheme for the project, as headwork for the area and the recommendedprobable stages of neighbouring communities construction, procurement of proprietary material for the project 156  DRAINAGE & SEWERAGE and any special problems relating standard tables are available which thereto may be referred. 605 Designing of Sewers - 607 Alignment of Sewer- Sanitary sewer system and storm water The alignment of the sewer is determined drainage system should be designed from a survey plan which should be prepared separately. to a scale of 100 metres to a cm. The proposed sewer-lines are shown on a plan alongwith the The size of sanitary sewer depends on ground levels and soil conditions, necessary quantity of sanitary sewage, variation in peak for establishing grades and estimating the cost and average flows, limiting velocities of flow, of the work. In the profiles, the invert and topography of the area, construction material crown gradient lines should be shown. etc. 608 Velocity of Flow - The limiting The size of storm water sewer depends velocities for existing conditions should be on storm water run-off, Self Cleansing Velocity, determined and gradients decided accordingly. construction material etc. Normally, a minimum velocity of 1 metre per second and a maximum of 2 metres per Sanitary sewers are not expected to second, are allowed. On steep slopes, one or receive storm water. It should be ensured more drop manholes may be provided. that proper design and construction of sewers and manholes are provided. a) Self Cleansing Velocity - It is necessary to maintain a minimum 606 Quantity of Sewage - velocity or self-cleansing velocity in a sewer to ensure that suspended The factors which influence the quantity solids do not deposit and cause of sewage are population and per capita blockage. Self cleansing velocity sewage. Population estimates should cater is determined by considering the for future requirements. particle size and specific weight of the suspended solids in sewage. A a) Generally 80% of the water minimum velocity of 0.8 mps at supplied may be considered to design peak flow in the sanitary reach the sewers. sewers is recommended subject to a minimum velocity of 0.6 mps for b) The lean and peak flows of sewage present peak flow. will be about 50 and 150 percent of the average respectively. The sewer b) Velocity at Minimum Flow - To avoid should be designed for the maximum steeper gradients which will require flow rate, after allowing for seasonal deeper excavations, it is the fluctuations. For design purposes 157  DRAINAGE & SEWERAGE practice to design sewers for the mm except for hilly areas where steep slopes self cleansing velocity at ultimate are available. In those areas minimum size peak flows. This is done on the may be 100 mm. assumption that although silting might occur at minimum flow, the 611 Storm Water silt would be flushed out during the peak flows. However, the problem Quantity of storm run-off is dependent of silting may have to be faced in on intensity and duration of rainfall, the early years, particularly for characteristics of catchment area and time smaller sewers which are designed required for such flow to reach the sewer. to flow half- full, as the actual depth of flow then is only a fraction of the Storm water flow for this purpose may full depth. Transport of suspended be determined by using rational methods, solids should be achieved in such hydrograph methods or empirical formulae. a manner that deposition and odour nuisance therefrom are kept to a 612 Manholes - A manhole is an opening minimum. Sewers are normally constructed on the alignment of a sewer to designed for flows with free water facilitate a person to access the sewer for surface and self-cleansing the purpose of inspection, testing, cleaning velocities. Pressure sewers, and removal of obstructions from the sewer including siphons, should be line. avoided as far as practicable. According to IS:4111 - spacing of c) Maximum Velocity - Erosion of manholes is designed with reference to sewer sewers is caused by sand and other diameter as given below: gritty material in the sewer at excessive velocity. Velocity of flow Sewer dia in mm Upto 300 301 to 500 501-900 in a sewer is recommended not to Spacing in metres 45 75 90 exceed 2.0 mps. When silt and grit loads are heavy, 609 Ventilation in Sullage - catchpits may be provided at suitable intervals depending on local conditions and as approved From consideration of ventilation in by the Divisional Engineer. wastewater flow, sewer should not be designed to run full. Sewers upto 400 mm dia may be 613 Choice of Material for Sewers designed to run at half depth, 400-900 mm diameter at two third depths and larger sewers a) Salt glazed stoneware pipes - For all at three fourth depth at ultimate peak flows. sewers and drains in all soils except where supports are required, glazed stoneware pipes 610 Size of Sewer - shall be used. They are particularly suitable where acid effluents or acid sub-soil conditions Minimum diameter of sewer shall be 200 are likely to be encountered. 158  DRAINAGE & SEWERAGE b) Cement Concrete Pipes - These can Authority, the width at bottom of trenches be used as an alternative to glazed stoneware for pipes of different diameters laid at pipes of over 150 mm diameter. These shall different depths shall be as given below: not be used to carry acid effluents or sewage under conditions favourable for the production 1) For all diameters, upto an average of hydrogen sulphide and shall not be laid in depth of 120 cm, width of trench in those sub-soils which may affect the strength cm = diameter of pipe+30 cm of concrete. 2) For all diameters for depths above c) Cast Iron Pipes - These shall be used 120 cm, width of trench in cm = in unstable or made-up grounds or where diameter of pipe+40 cm. sewer is laid at insufficient depth. These are particularly useful where pipes are suspended 3) Not withstanding (1) and (2), the in basements or similar situations or for total width of trench at top should crossings of water courses. These pipes are not be less than 75 cm for depth suitable where the velocity is more than 2.4 exceeding 90 cm. m/s. iii) All pipes, ducts, cables, mains or other d) Asbestos Cement Pipes - These pipes services exposed in the trench shall be are commonly used for house drainage effectively supported by timber and/or systems and are not recommended for chain or rope-slings. underground situations. They are not suitable to carry acid effluents or sewage under iv) All drainage sumps shall be sunk clear conditions favourable for the production of of the work outside the trench or at the hydrogen sulphide. sides of manholes. After the completion of the work, any pipes or drains leading e) PVC Pipes - Unplasticised PVC pipes to such sumps or temporary sub-soil may be used for drainage purpose. drains under permanent work shall be filled in properly with sand and 614 Laying of Sewer Pipes consolidated. a) Excavation - The safety precautions b) Laying of Pipes - Laying of pipes shall required as per construction practices shall be done in accordance with good practice i.e. be ensured. unloading of pipes should be by using mechanical means to avoid damages, (i) Excavation shall proceed to within about adjusting to proper levels, minimum thickness 7.5 cm of the finished formation level. of lead at the face of socket not to reduce This final 7.5 cm is to be trimmed and less than 6mm, alignment to be repeatedly removed as a separate operation checked and refilling of trenches etc. immediately prior to the laying of the pipes or their foundations. c) Jointing - All soil pipes, waste pipes, ventilating pipes and other such pipes above (ii) Unless specified otherwise by the ground, shall be gas-tight. All sewers and 159  DRAINAGE & SEWERAGE drains laid below the ground shall be water rammed on both sides of the pipe with a tight. Jointing shall be done in accordance wooden hammer. On no account shall with specification prescribed for particular type material be tipped into the trench until of pipes. the first 15-cm of fil-ling has been completed. The process of filling and d) Connection to Existing Sewers - tamping shall proceed evenly so as to maintain an equal pressure on both sides (i) The connection to an existing sewer of the pipeline. shall, as far as possible, be done at the manholes. The work of connection with (v) Filling shall be continued in layers not the existing sewerage system shall be exceeding 15cm in thickness, each layer carried out by the Authority owning the being watered and well rammed. system or under its supervision. (vi) In roads, surface materials previously ii) Connection with the sewer shall be excavated shall be replaced as the top affected by the cautious enlargement of layer of the filling, consolidated and a small hole and every precaution shall maintained satisfactorily till the be taken to prevent any material from permanent reinstatement of the surface entering the sewer. No connection shall is made. be formed in such a way as to constitute a projection into the sewer or to cause (vii) In gardens, the top soil and turf, if any, any diminution in its effective size. shall be carefully replaced. e) Back-Filling - f) Pipes should preferably be laid with the socketted ends against the direction of (i) Filling of the trench shall not be flow and in straight lines. commenced until the length of pipes therein has been tested and passed g) In manholes, no pipes should project. Pipes should be laid flush with the inside face (ii) All timber may be withdrawn safely as of the manhole walls. Where a pipe passes filling proceeds. through the manhole wall, an arch should be built round the pipe to carry the weight of the (iii) Where the pipes are unprotected by masonry above it. concrete haunching, the first operation in filling shall be carefully done to hand- 615 Sewage Disposal - pack and tamp selected fine material around the lower half of the pipes so as Standard flushing systems are meant to buttress them to the sides of the primarily to transport human waste from the trench. toilet to the treatment plant located a few kilometres away or to connect the railway (iv) The filling shall then be continued to 15 sewerage system to the municipal sewers. cm over the top of the pipe using selected Therefore, this standard sewerage system is fine hand-packed material, watered and appropriate only where underground sewerage 160  DRAINAGE & SEWERAGE system exists. A comparative estimate of is not permitted, as the effluent from the septic cost should be prepared for the connection tank is hazardous from the point of view of with the municipal sewerage system vis-a-vis health and pollution. Since, it is usually not an independent sewage disposal plant. possible to provide soak pit/filter bed in built up urban areas, septic tank system would not Where water-borne sewerage is not be appropriate in such areas. possible, septic tank system of disposal of sewage is normally adopted. The capacity of the septic tank should be such as to take care of the variations in 616 Septic Tanks - the flow. A detention period of 24 to 48 hrs. for tanks serving less than 50 persons and a Modern septic tank system is an on a period of 10 to 18 hrs. for tanks serving more site disposal method, which uses standard than 50 persons are generally adopted. flushing. The septic tank acts as sedimentation-cum-digestion tank. Anaerobic The size and shape of the septic tank digestion of the settled sludge occurs in its shall be generally in agreement with the bottom zone and the supernatant liquid has minimum dimensions given in the table to undergo treatment in a soak pit/filter bed. below:- Use of septic tank without follow-up treatment 161  DRAINAGE & SEWERAGE Table 6.1 _________________________________________________________________________________ No. of Users Length Width Liquid Depth _________________________________________________________________________________ metres metres metres _________________________________________________________________________________ Domestic tanks 5 1.5 0.75 1.0 10 2.0 0.90 1.0 15 2.0 0.90 1.3 20 2.3 1.10 1.3 50 4.0 1.40 1.3 Tanks for Housing Colonies 100 8.0 2.6 1.0 150 10.6 2.7 1.0 200 12.4 3.1 1.0 300 14.6 3.9 1.0 Tanks for Hostels and Boarding Schools 5.0 1.6 1.3 100 5.7 2.1 1.4 150 7.7 2.4 1.4 200 8.9 2.7 1.4 300 10.7 3.3 1.4 _________________________________________________________________________________ The septic tank should be constructed disinfectants should be used in latrines in 2 compartments to facilitate cleaning of one attached to septic tanks as they kill the while the other is in use. A bottom slope of 5 organisms, which digest sewage. to 10% towards inlet is recommended. For providing any soakpit/filter bed with Septic tanks should be cleaned when a septic tanks the water table must be well below large quantity of sludge has collected in the their depth and the rain water from surface bottom of the tank. The interval of cleaning also should not interfere with their functioning. should not normally exceed 12 months. After Hence, these are not usually suitable where cleaning 3 or 4 shovelful of surface earth water tables are high or where ground slopes containing grass roots and decaying vegetable are flat. matter should provide a good start. No 162  DRAINAGE & SEWERAGE 617 Aqua Privy Latrines - distance. The latrine will usually consist of an under 6. The flow from the toilet to digesters is to ground masonry tank on top of which are fixed be by gravity. the latrine pans. The outlet of the pans are dipped 7.5 to 10 cm below the flow line in the 7. When combined digesters are used, the tank. The pans may be fixed with or without sewage will first get collected in a traps to the outlet pipe. The excreta will get chamber attached to each water closet digested in the masonry tank below and will and then flow to a combined digester. The be cleared at intervals through manhole left slope of the pipe lines from the collection for this purpose. The effluent may be then chamber to the digester should not be absorbed by sub-surface irrigation process or flatter than 1 in 20 so as to allow for easy by other alternative means. flow. 618 Bio-Latrines - 8. A water seal of 50mm above the crown level of the inlet pipe at the inner face of These are improved aqua privies used the digestion tank wall, shall always be for sewage ranging from very small quantities maintained in the digestion tank. to comparatively larger quantities. They need 1.5 to 2 litres/capita of water for flushing. 9. The plinth level of the latrines should be Standard drawings are available from RDSO. decided working backwards from the The following points should be taken care of invert level of the outlet pipe of the in bio-latrines. digestion tank. 1. No water tap should be provided in the 10. The sludge settled at the bottom of the water closet to prevent flooding of digestion tank may be cleared once in digesters, which will prevent efficient two years. anaerobic action. 11. Satisfactory working of the anaerobic 2. Excessive water should not be used in digesters in the tank, is indicated the water closet. i) if the effluent is odourless 3. The pan in the bio-latrines should have a ii) if the effluent does not attract flies slope not less than 40 degrees with and mosquitoes; and horizontal. iii) if the pH value of the effluent is not 4. No foreign matter e.g. garbage, soap less than 7.0. water etc. should be thrown into the water closet pan. 12. Outlet drains should have proper slope and rounded corner. 5. The digesters should be linked directly to the toilet with least possible inter 13. Adequate ventilation should be provided in bio-latrines. 163  DRAINAGE & SEWERAGE 14. In case of public or community type of maximum extent possible and that it is not toilets, users are likely to throw rags, polluted and the waste disposal systems stones etc. into the toilets. In such cases should be designed with these ends in view. an inspection chamber with 25-50mm This applies to both ground water and surface spaced grating should be provided just water. In case of non-residential toilets at before the entry of water into the digesters stations etc., and community toilets provided to arrest any such material. with 'standard flushing' arrangements, instead of flushing cisterns of 13.5 litres capacity, the 15. A minimum retention of 30 days is use of 'coach' handles should be preferred so required for anaerobic digestion, while that only the required amount of water is used. a septic tank provides retention only for In case of urinals, instead of automatic flushing 2-7 days and hence the effluent from the cisterns, dripping ferrules may be used to septic tank must have its main treatment conserve water. in a soakpit/filter while effluent from a digester can be discharged directly in a 620 Recommended Toilet Systems drain system. Based on the above rationale, directions 619 Conservation of Water - for selecting appropriate toilets system are summarised below:- There is a general shortage of water (i) Where an underground sewerage supply in India and in some parts even the system can be connected, use a 'flush' drinking water is scarce. Therefore, it has to type toilet as under:- be seen that water is conserved to the _________________________________________________________________________________ Residential With no water Cistern flushing, (use good qualitycisterns, preferably Toilets shortage the newer Models using less than 3 gallons Water). Residential With water 'Coach' handle flushing toilets shortage Non-residential - 'Coach' handle flushing. However,for toilets in retiring toilets rooms, rest houses same type as for residential toilets. _________________________________________________________________________________ (ii) Where an underground sewerage system is not available: _________________________________________________________________________________ In built-up areas or in all Bio-latrines other areas where soakpits or filter beds are not feasible On roadside stations-do- In sparsely inhabitedstations Bio-latrines or septic tank system (coach handle type flushing should be used) 164  DRAINAGE & SEWERAGE (iii) In case of urinals, automatic Sewers may be flushed by firehose from flushing cisterns should not be used and only the nearest fire hydrant if conveniently located dripping ferrules may be used. if the stoppage is too stubborn to respond to flushing, it may be removed by rodding from All toilets on the Railways must be the next manhole or it may be necessary to sanitised on top priority program basis. Thus dig down to the point where the trouble exists. only flush toilets with underground sewerage, flush toilets with septic tank systems (with (b) Records of the location and depth of soakpit/filter-bed for the septic tank effluent) all sewers and house connections should be and bio-latrines (also acquaprivy) are the kept in sufficient detail and accuracy for approved sanitised toilet systems for use on locating any sewer in case it becomes the Railways. Hence - necessary to dig it up. Connections of house drainage to the sewer should be permitted to - all 'dry' (Service type) toilets must be be done only by competent and experienced sanitised. labour. - all septic tanks, if not provided with (c) Sewer line gangs, if under the prescribed soakpit/filterbed, must be Engineering Department, should attend to the provided with these or if possible, cleaning and flushing of all sewers at least converted into digesters by minimising twice every month. Manholes should be left the flushing so that the same tank can open for few hours for gases to escape, before provide clear minimum 30 days any man enters into it. retention (in addition to the space for digestion at the bottom). 623 Open Sullage Drains C. MAINTENANCE OF SEWERAGE Open sullage drains should be AND DRAINAGE maintained in a thoroughly satisfactory condition; cleaning and flushing should be done 621 General - at least twice a month or more often, as considered necessary. Soak-pit should be dug Due consideration shall be given to up and cleaned at least once a month or as maintenance requirements at the time of required and fresh broken stones, broken designing sewerage system. Provision of bricks or cinder filled in. openings, staircases and due provisions for eliminating gas hazards, should be ensured. 624 Storm Water Drains 622 Sewer Lines Special examination should be made of storm water drains, particularly before the a) Maintenance of sewers involves commencement of monsoon, to ensure correct removal of stoppages and clearing out the grades. Out falls should be particularly deposits. Clogging may be due to grit examined with a view to ensure satisfactory deposition, penetration of roots from adjoining disposal of the storm water. trees, growth of fungi or stagnation of sewage. 165  DRAINAGE & SEWERAGE 625 Disposal Works sulphide is detected using lead acetate paper and that of oxygen by safety All sullage disposal works should be lamps) examined once a quarter and their sanitary condition ensured. When an appreciable e) If the atmosphere is normal, workmen extent of silting has taken place, septic tanks may enter with a safety belt attached and should be cleaned in co-ordination with the with two men available at the top. For Medical Department whose responsibility lies extended jobs, the gas tests shall be in either doing it on contract or departmentally. repeated at frequent intervals depending on circumstances 626 House Connections Surface drains should be examined f) If oxygen deficiency or noxious gas is frequently and there should be no stagnation found, the structure shall be ventilated of sullage near the premises. Gully traps with with pure air by keeping open at least gratings should be examined wherever one manhole cover each on upstream installed and prompt action taken for renewal and downstream side for quick exit of and replacements necessary. toxic gases or by artificial means. The gas tests shall be repeated and the 627 Conservancy and Sanitary atmosphere cleared before entering. Arrangements Adequate ventilation shall be maintained during the work and the test repeated Conservancy arrangements will be in the frequently charge of either the Medical, or Operating or Engineering Department. Any irregularity g) If the gas or oxygen deficiency is present noticed in their working should be promptly and it is not practicable to ventilate reported to the officials concerned. adequately before workers enter a manhole, mask shall be worn and 628 Maintenance of Sewerage System extreme care shall be taken to avoid all While assisting sewer maintenance sources of ignition. Workers should be crews entering a deep manhole or sewer taught how to use the oxygen hose where dangerous gas or oxygen deficiencies equipment. In these cases, they shall may be present, the following precautions always use permissible safety lights (not should be taken: ordinary flashlights), rubber boots or non- sparking shoes and non-sparking tools a) allow no smoking or open flames and guard against sparks h) Workmen descending a manhole shaft to inspect or clean sewers, shall try each b) erect warning signs ladder step or rung carefully before putting the full weight on it to guard c) use only safe gas-proof electric lighting against insecure fastening due to equipment corrosion of the rung at the manhole wall. When work is going on in deep sewers, d) test for noxious gases and oxygen deficiencies (presence of hydrogen 166  DRAINAGE & SEWERAGE at least two men shall be available for obstruction found shall be removed with lifting workers from the manhole in the suitable drain cleaning tools and the event of serious injury system thereafter shall be flushed with clean water. i) Portable air blowers, for ventilating sewer manhole are recommended for all tank, d) The covers of access plates to all gullies, pit or manhole work where there is a shall be removed and the traps plunged question of the presence of noxious and flushed out thoroughly with clean gases, vapours or oxygen deficiency. water. Care shall be taken not to flush The motors for these shall be of weather the gully deposit into the system. proof and flame-proof types; compression ignition-diesel type (without e) Any defects revealed, as a result of sparking plug). When used, these shall inspection or tests shall be made good. be placed not less than 2m away from the opening and on the leeward side f) The covers or inspection chambers and protected from wind, so that they will not gullies shall be replaced, bedding them serve as a source of ignition for any in suitable grease or other materials; and inflammable gas which might be present. Provision should be made for ventilation g) Painting of ladders/rings in deep and it should be of the forced type which manholes and external painting of can be provided by a blower located at manhole covers shall be done with ground level with suitable flexible ducting approved paints. to displace out air from the manhole 630 Covered Stormwater Drains - All 629 Periodical Cleaning of Drainage stormwater drains shall be periodically rodded System - The following operations shall be by means of drain rods and a suitable rubber carried out during periodical cleaning of a or leather plunger. After rodding, they shall drainage system:- be thoroughly flushed with clean water. Any obstruction found shall be removed with a) The covers of inspection chambers and suitable drain cleaning tools. manholes shall be removed and the side benchings and channels scrubbed 631 Subsoil Drains - All subsoil drains shall be periodically examined for obstruction b) The interceptive trap, if fitted, shall be at the open joints due to the roots of plants or adequately cleaned and flushed with clean other growth. water. Care shall be taken to see that the stopper in the rodding arm is securely 632 Responsibilities of the Assistant replaced. Engineer and Staff - The Assistant Engineer and the Section Engineer (Works) should c) All lengths of main and branch drains inspect all drainage systems in their charge shall be rodded by means of drain rods and ensure their maintenance in an efficient and a suitable rubber or leather plunger. condition. Complaints from residents should After rodding, the drains shall be be promptly attended to. thoroughly flushed with clean water. Any 167