Study and evaluation of ‘Dhamaka’/ ‘Kui’ Latrine ( a variant of bore hole latrine) prevalent in some districts in Rajasthan
by Dr. S.V. Mapuskar
Appa Patwardhan safai W Paryawaran Tantraniketan, Dehu village, Tal. Haveli, Dist. Pune, Maharashtra 412 109.INDIA
1. Objective :In Rajasthan State of India, predominantly in two districts, Sriganganagar and Hanumangarh districts, a design of latrine locally termed, ‘Dhamaka latrine or ‘Kui Latrine’ is prevalent and in use for the last about 30 years. Doubts had been repeatedly raised whether, (i) this design can be considered as a sanitary latrine and (ii) its suitability for the area. Therfore, it was planned to undertake a study, as regards the technical admissibility of ‘Dhamaka’ toilets as sanitary toilets and its’ appropriateness as regards local requirements. Further, in case the design was not considered sanitary, whether an alternative design could be suggested? If alternative designs were not found to be appropriate, whether any modifications would be required to convert the toilets into sanitary toilets, if these were not considered sanitary. The study was undertaken during March 2007 and April 2007. 2.
Methodology used for study:-
Prior to field visits, which were undertaken from 27th to 29th March, the basic data as regards hydrogeological conditions in the area and the data about the present drinking water sources, surface water sources as well as ground water sources were collected. The basic design concept of Dhamaka latrine was also obtained. The study team visited Sriganganagar and Hanumangarh districts from 27th to 29th March 2007. The team held detailed discussions with Rajasthan Government officials which included engineers and staff members from state water supply and sanitation mission Government of Rajasthan, engineers of PHED in two Districts and other staff members who are responsible for TSC and drinking water supply, in these two districts. The team also had detailed discussions with hydrogeologist and chemist of public health laboratories in the districts as regards hydrogeological data and the water quality monitoring from various drinking water supply schemes, from surface water sources as well as ground water sources. The data as regards microbiological and nitrate levels in ground water for the last 5 years was reviewed. The team visited 5 villages in two districts. The villages were selected on the basis of source of drinking water (that is, villages fed by canal water and villages fed by ground water as well). In addition, samples were collected from visited villages for bacteriological examinations as well as the nitrate level estimates. The team also interacted with community to discuss their perception about the use of these toilets, evolution of the use of toilets in the area, knowledge on other options of the toilet, convenience and comfort issues. 3.
Brief review of the design
The Dhamaka toilet design technologically is a type of borehole latrine. Design is locally termed ‘Dhamaka’ or ‘Dhamakedar’ because of the noise produced when the 2
night soil and water strike the bottom of the pit, which is any where between 25 to 40 ft deep. A pit of between 2 to 3 ft diameter is manually dug in the soil to the depth of 25 to 40 ft. Digging manually is possible because the soil is made up of dense clay, which does not collapse. Hole in the clay layer is dug so as to reach the sand layer below that. Digging is stopped after removing a few feet of pervious sand layer, which the experienced digger identifies from the fact that the walls of the pit in sand layer start cracking and collapsing. No lining of any kind is used as the clay layer does not crack or collapse even after several years. The pit or borehole is covered with a stone slab which is available locally and has a squatting hole of 4 to 6 inches in diameter. At some places concrete slabs are also provided as a squatting platform. Generally no pan or trap is provided in the squatting plate. The squatting plate has simply a drop hole.
Dhamaka Latrine A G shaped super structure as indicated in drawing is constructed around the squatting plate with bricks or mud blocks. Height of wall may be around 4 to 6 feet. In most of the cases, roof for the superstructure is not provided.
This pit can be used by a single family for about 15 to 20 years. When the pit gets filled up, it is closed and a new pit is dug at an adjacent suitable place for future use and it is covered with the same slab and a super structure. Old pit is closed with soil and abandoned. 4.
Villages Visited i. ii. iii. iv. v.
Masruwala village, Hanumangarh, (water sourceâ€“ground + canal water) Pucca Saharana, Hanumangarh, (water source-canal water) Village 3Y, Sriganganagar (water source-ground +canal water) Village 3G Kaliyan, Sriganganagar (water source-ground + canal water) Village 4 ML, Sriganganagar (water source â€“ canal water)
Salient features noted during field visit as regards the latrine use
In Masruwala Village, some toilets were visited. All the latrines in the village are Dhamaka type. Depth of toilet pits varied between 30ft. to 40ft. Bore wells were found to be within a distance of 10-20 ft from toilets. Toilet seats smelled badly. Plenty of hovering flies were noticed in most of the toilets. For bore wells, it was told that water table is at 27 M (about 80ft) and depth of water column in the wells about 6-7 meters. Some toilets in village have water seal traps and pans fitted for the toilet seat. Some have latrine pans without water seal trap. 50 % houses have own bore wells. Occasional incidence of infective hepatitis was reported. In one visited house, owner wanted the trap to be fitted but mason did not fit it.
In Pucca Saharana Village, again toilets and tube wells were visited. All latrines in village are Dhamaka type. Depth of toilet pits varied from 30 to 40 ft. Toilet seats smelled badly. Plenty of flies were noticed in toilet seat enclosures. In one house, for waste water management also ‘Kui’ was dug. In many places, waste water was collected in small shallow pits and twice a day, accumulated water was sprinkled on the street where it would evaporate naturally. The shallow pits could not soak water. In this village one dry dug well of about 100 ft. depth was seen. Very adjacent to the well, a large water tank or johad was present. But water from tank was not percolating to the well indicating the impervious nature of the floor of the tank. On 29.03.07, a meeting with the Collector, Sriganganagar was arranged. During discussion it was revealed that, govt. has set up a norm that in villages with less than 4000 population house hold water connections are not given. Therefore, in these villages many households depend on their own private bore wells. In Village 3 Y also all latrines in the village are Dhamaka type. In one house, as an exception, vent pipe was fixed on pit, the toilet seat being offset with pan but no trap. The latrine was clean and without flies. On enquiry, it was informed that this was suggested by the mason. This village has a dug well where water level was about 40ft deep. This water was found to be polluted during routine monitoring by PHED. Private bore wells are in use in the village. In Village 3 G (Kaliyan) Dhamaka latrines were similar type. Here, due to nearness to Sriganganagar town, tendency towards construction of septic tank toilet is increasing. Effluent from these septic tanks is let out in open surface drain. The effluent from these drains passes out to a johad formed by waste water from the village. The soil doesn’t absorb sullage from the village. The bore well adjacent to this johad was found to be heavily polluted as reported during the monitoring by PHED. Thus, septic tanks might become problematic for the village. In Village 4 ML, households have similar type of Dhamaka toilets. Here in a school, latrine with pan, trap, chamber and two ‘Kuis’, similar to twin pit latrine were constructed but was not brought into use because of apprehension and non availability of tap water connection. In this village many houses had Dhamaka toilets with latrine pan, trap and occasionally vent pipe. The percentage coverage with Dhamaka Latrines is very high. Any where between 70% to 90% households have such latrines in some villages. Pit for the toilet is dug manually by charging a labour rate at about 6 to 8 Rupees per foot of depth. Hence it is affordable for most of the families. During the field visit, it was noticed that in most of the cases the urine was getting into the drop hole in very haphazard manner as the channel for the passage of urine was very haphazard. Further, the obnoxious odour pervaded the toilet seat enclosure. The 5
smell was reduced to some extent because of the absence of roof. The odour was very marked where the roof was provided. Large amount of flies and mosquitoes were noticed in the toilets. The drop hole did not have any cover when the latrine was not in use. Squatting in such a toilet for more time would be very repulsive. It was also noticed that in many places adult males in the family prefer to go out for open defaecation. In such cases, the latrines were predominantly used by women. Hence, the head of the family was probably not interested in spending money for improving the quality of the latrine. In many places, bore wells for drinking water purposes were found to be adjacent to the latrines. In some places the distance was hardly 10 ft from the toilet. We had also discussions with some NGO representatives. It was felt that they did not have clear ideas about toilet design requirements and about various latrine technologies. 6. Status for drinking water supply in these districts. In these two districts, as revealed in Rajasthan govt. report, in Sriganganagar district, out of 2830 villages, 515 (hand pumps) villages have government drinking water supply schemes using ground water as a source. In Hanumangarh, out of 1773 villages, 470 (hand pumps) villages have govt. drinking water supply schemes based on ground water as a source. Thus, nearly 25 % villages in these two districts are using ground water for drinking purposes.
In the villages which were visited, many households had their personal bore wells. PHED does not have a record of such bore wells. Further, it was revealed that government does not provide household water tap connections in villages having less than 4000 population. In these villages only public stand posts are provided. Therefore well to do people who can afford to dig their own tube wells have their own tube wells. Thus, percentage of population using ground water is probably much more than 25%. Therefore, possibility of ground water contamination due to on site sanitation, emerges as an important issue. 7. Appropriate latrine design for on site sanitation in rural area In assessing the appropriateness of the latrine design, following points will have to be considered. A) Transfer of microbial contamination via the surface level construction of toilet seat etc. a) surface soil should not get contaminated 6
b) c) d) e) f) g)
no contamination of surface water no handling of fresh excreta excreta should not be accessible to flies and animals freedom from odour aesthetically pleasant should be simple and inexpensive
B) Risk to drinking water supply a) microbial contamination of ground water b) chemical, predominantly nitrate contamination of ground water Points related to ‘A’ above are mainly related to proper toilet seat and superstructure. These issues become significant, due to possibility of microbe spread via vectors and unhygienic behavior of user. Points related to ‘B’ above are mainly related to what happens to nightsoil and the emergent contaminants from it below the ground, from where the contamination of ground water may be possible.
The microbial contamination in ground water would depend on porosity and permeability of subsoil surface and the geohydrological environment viscinity of ground water aquifer from the absorbing surface of the pit.
The chemical contamination, predominantly due to nitrate leaching would depend on, • • •
the nature of subsurface and the geohydrological environment type of on site sanitation system which would determine the proportion of nitrate leaching viscinity of on site sanitation facility to ground water aquifer, vertically as well as laterally.
In pit latrines of any design, ablution wash water and digestive process water is supposed to be absorbed / leached in soil. While this process of absorption / leaching is taking place in the soil, the contamination attenuation processes, which control the numbers and concentrations of the contaminants, is the key to understanding the risk from on site sanitation technologies. The key processes in the attenuation of microbial contaminants could be • die off • dilution and dispersion • adsorption and filtration
In these processes travel time is an important factor. The travel time from source to ground water aquifer of around 50 days minimizes the risk. All these will depend on geological characteristics of soil layers. The processes in the attenuation of chemical contaminants like nitrates can occur where through plantations biological uptake occurs. Under aerobic conditions nitrates are mobile. However, in anaerobic conditions there is very little attenuation of nitrates. In anaerobic conditions, where nitrate load is high and is derived from large number of point sources, over an extensive area, the nitrates slowly can migrate to ground water. Once high levels of nitrates are present in the ground water, concentrations will not decrease rapidly. Thus, here also the geological structure of the soil layers remains an important factor. The liquid part of the waste in a pit latrine that infiltrates into the soil is called the hydraulic load. Where hydraulic loads are high and exceed natural attenuation potential, direct contamination of ground water is possible. As stated earlier, travel time of this hydraulic load also is important. This will, besides other factors, depend to a large extent on geological characteristics of subsoil layers. 8. Comparative evaluation of twin shallow pit latrines and borehole latrine Based on these criteria, in India, twin pit latrine with shallow pits, are being considered as the most appropriate technology for toilets. However, in some specific situations, other technologies, after reviewing pros and cons of such technologies, might turn out to be more suitable. The available field experiences and literature as regards Bore Hole latrine has thrown up some inferences as regards this technology. As the bore hole pit is deep, the possibility of ground water aquifer contamination, both bacterial and chemical is considerable. From the seat, spread of infection via flies is possible hence hygienically it may not be advisable. The presence of odour is repelling. As the pit is deep, the decomposition of night soil is anaerobic. Hence the smell of obnoxious gases like H2S will be present. Due to anaerobic digestion, methane is produced during the process. This can escape only through drop hole. Instances have been noted in other states, where similar versions of bore hole like designs are in use, that this gas has exploded due to lamp flame or smoking, causing burns to the user. Therefore twin pit latrines, with shallow pits (and water seal trap for toilet seat), where aerobic digestion takes place, possibility of ground water contamination is minimized and hygienically safe and odourless toilet seat is fixed, is considered as an appropriate technology in rural areas.
However, there may be situations where, due to technical issues, twin pit latrine with shallow pits is not feasible. In such cases, other technological options will have to be considered. Keeping these facts in view, Dhamaka toilet design will have to be evaluated. In this evaluation, the hydrogeological factors will be very important. Further it would be necessary to decide whether alternative designs are possible. If that is not possible, what modifications would be necessary to convert it to a sanitary toilet? 9. Geohydrological data for soil As seen above, the geological characteristics of soil strata would be an important criteria for the suitability of pit latrine, of any design. Aquifers transmit water, as well as store water. This is affected by two factors i. porosity ii. permeability Unconsolidated granular sediments in the soil such as sands, silt, clay etc. contain pore space between the grains. The proportion of pore spaces to the total volume of sediments is known as porosity. In sand, porosity can extend to above 30 %. The water transmitting characteristic is known as its permeability. Well connected pore spaces between the grains of sand and gravel increase their permeability. However, clays which have high porosity, but very little connection between the pores because of very small grains and compactness, transmit water very poorly, resulting into very low permeability.
Grain sizes of a range of sediment types from â€˜Guidelines for Assessing the Risk to Groundwater from Onsite sanitationâ€™ DFID 2001. Naturally, in soils with low permeability, the travel time for contaminations will increase. The greater the travel tie the greater the opportunity for contaminant attenuation. 9
Typical permeability values for various rock types Lithology
Range of likely permeability (m/d)
Silt Fine silty sand Weathered basement (not fractured) Medium sand Gravel
0.01-0.1 0.1-10 0.01-10 10-100 100-1000
The geological characteristics of the region will naturally have a bearing on the technology selection for on site sanitation. The kind of geological layers in the ground would be important. 10. Geohydrological Data for Sriganganagar and Hanumangarh While analyzing ground water trends from these districts, as shown in the maps, following facts emerge. In Sriganganagar and Hanumangarh districts, the geological strata are very significant. The soil and the strata up to about 20 to 30 ft (8 to 10 metres) is a layer of compact clay and silt with plenty of gypsum. As a result, this layer is having very low permeability for water. The travel time for water through this layer may be of several months or years. The vertical sections show that the top layer comprises of clay or clay + silt from fluvial origin in most of the areas of these two districts. The thickness (depth) of this layer varies from approx 10 to 20 ft (occasionally wind blown sand forms a thin surface layer). This layer is fairly compact and imperious to water.
Below this top layer of clay, sand layer is present. For this sand layer, the porosity may be even to the extent of 30%. This layer would be very permeable with relatively less travel time. Hence leaching of water from this layer would be better. This justifies the depth of pit in Dhamaka toilet. This sand layer is a part of aquifer, as indicated in the maps. Further, the subsoil water levels, as indicated in map, have been found in both districts to vary between 30ft to 120ft. In potable water zone, water levels are nearer the surface. In northern region of Sriganganagar District, depth of water level is less than 20 M in NW region and between 20-40 M in northern and SW region. In northern region, nitrate distribution is below 50mg/Lt. In Hanumangarh district, the depth of water level is less than 20 M in northern region and between 20-40 M in central and NW region. In the same region, nitrate distribution is below 50 mg/Lt. As far as the evaluation of Dhamaka toilets is concerned, all this geological data would be important for foreseeing the ground water contamination effects due to generalized use of Dhamaka toilets. 11. Relevance of this data in technology selection These hydrogeological conditions in these two districts (and perhaps in areas of adjacent districts in Rajasthan, Hariyana and Punjab) become an important consideration in selection of on site sanitation technology. Although twin pit latrine with shallow pit is a generally accepted technology, in these two districts, it would not be appropriate. Water from the shallow pits will not leach out because of the clay layer with very low permeability. Hence shallow pit latrine is not likely to function properly in this zone. When leaching of water from the pit is expected, deeper pit reaching the sand layer where permeability is higher, will be the only suitable technology in such situation. Septic tank technology also will not be appropriate, because the issue of management of effluent from septic tank would be problematic due to top clay layer. In one village near Sriganganagar, some families had opted for a change over from ‘Kui’ or ‘Dhamaka’ latrine to septic tank. The effluent from septic tank was let out to surface drain. This surface drain ended in a small cess pool like tank resembling ‘johad’. The bore well adjacent to this tank showed both microbial and chemical contaminations. Therefore it is felt that this kind of changeover from Dhamaka to septic tank should be discouraged.
The other possible option could be a compost toilet (ecosan). However in this case, the operation and maintenance demands very high motivation levels. As such in these districts, these may not prove to be an appropriate technology as a mass measure. Under the circumstances, bore hole latrine seems to be a desirable technology for this region. It will have to be accepted. However, the risk assessment factors stated earlier must be remembered. These risks could be i. from toilet seat and ii from contamination of ground water. We have to accept the risk, with clear mandate for increased level of monitoring and mitigation efforts. In places where shallow pit latrines are possible, this design may not be approved. While using this technology, some changes are necessary. Dhamaka toilet as it stands today cannot be termed as sanitary. However, with some modifications it can be very easily converted to a sanitary latrine. The toilet seat component needs modifications so as to minimize contaminations from surface of the seat. Further, as stated earlier, a very rigorous monitoring of ground water would be essential. 12. Modifications in toilet seat portion Avoiding microbe spread via toilet seat or drop hole can be avoided if suitable modifications are carried out. This can be done by providing latrine pan with water seal trap for the toilet seat. Goose neck pans with incorporated traps made out of C.C. mosaic material, ceramic or LLDPE plastic moulded pans can be fitted. If the toilet seat is placed offset, routine pan and trap with necessary pipeline can be fitted.
Alternatively a latrine pan without water seal, accompanied by a vent pipe of minimum 100 mm diameter can be provided. In such a case, the vent pipe should reach above the roof level and the upper end of pipe should be covered by wire gause or net to prevent passage of vectors like flies and mosquitoes. This pipe will provide ventilation as envisaged in V.I.P. toilets.
13. Possibility of ground water contamination Possibility of microbial contamination of ground water obtained from tube wells must be considered. The leachet from borehole latrine will pass vertically and laterally through sand layer for adequate distance for attenuation of this contamination. In tube wells as well as dug wells microbial contamination was noticed where multiple latrines were present within a distance of few feet from the well. It will be advisable to keep a distance of about 50ft between wells and nearest latrine, to allow for attenuation of the contamination. As far as chemical contamination from on site sanitation is concerned nitrate contamination is the most important. As per WHO prescribed standards, in potable ground water, the nitrate levels should not exceed 50mg/Lt and nitrites at 3mg/Lt. High nitrate levels give rise to methaemaglobinaemia. Further, once the nitrate levels increase, remedial measures are not possible. It has to be noted that nitrates go on increasing in aquifer very gradually. It is a continuous slow process going on over the years. Therefore, chemical contamination of ground water needs to be monitored rigorously. In case of Dhamaka toilet, the bore reaches sand layer which is a part of aquifer as indicated in geohydrological maps. Hence, these nitrates are ultimately reaching the aquifer. From the 5 villages visited by us, from two villages, namely 3Y and 3G, nitrate trends from 2001 to 2007 were available. In 3Y nitrates were 4mg/Lt in 2001 against 10mg/Lt in 2007. In village 3G nitrates were 35mg/Lt in 2001 as against 45mg/Lt in 2007. This indicates a definite trend towards rise in nitrates levels. In few more years this might reach unacceptable level. Such data from remaining three villages was not available.
In point 10 water level trends have been discussed. The premonsoon water level depths have been indicated as varying between 30ft to 120ft in the aquifers immediately underneath the top clay layer. The bore holes in Dhamaka toilets are reaching in the same aquifer to the depth of 30ft to 40ft. Naturally the vertical separation may be non existent in many cases. There, the attenuation of microbial and chemical contamination will depend only on lateral separation, increasing travel time marginally. Once nitrate levels exceed 50 mg/Lt that source has to be abandoned for drinking water purposes. Hence, continuous monitoring of these sources for microbial and chemical contamination would become very essential. Microbial contaminations can be taken care of by purification processes like chlorination. However, if nitrate levels increase the only way is to abandon the source. This monitoring will have to be done for private tube wells also, in a planned manner. 14. Observations and comments a. In the area specific situation Dhamaka latrine is a suitable design with some modifications and reservations. Bore hole latrine is generally considered as a less desirable option. However, in hydrogeological situation existing in these districts, there is no suitable alternative to borehole latrine. b. As they exist today, Dhamaka latrine canâ€™t be considered as sanitary latrine. The existing design needs to be modified. Following modifications are suggested. c. Modifications to toilet seat as indicated in point 12 are suggested. d. There are indications that in some tube wells and dug wells microbial contamination have taken place. Therefore periodical rigorous monitoring, where ground water from wells (government established or private) is used for drinking, is necessary. Public health laboratories in each district can do this. e. Similarly continuous monitoring for chemical contamination is necessary. Public health laboratories in each district can do this. f. Data about private tube wells is not available. Each Gram Panchayat and each District PHED may maintain this data.
g. Private tube wells may also be randomly monitored by microbiological and chemical examination. h. Suitably modified Dhamaka latrine may be considered appropriate only in areas where top layer of soil consists of clay which is grossly impervious to water. It is not desirable in areas with water permeable upper soil strata. Where soil conditions permit shallow twin pit latrine is advisable. i. PHED, Govt. of Rajasthan can decide on areas where only bore hole latrines are suitable, based on hydrogeological data, considering that bore hole latrine is a less desirable technology to be used only where it is inevitable. j. Changeover from Dhamaka to septic tank, in areas with low soil permeability for water should be actively discouraged by active IEC campaign. k. Modifications to existing Dhamaka toilet seat can be encouraged by IEC efforts and possibly by providing incentive from various possible sources. l. For new constructions for BPL households, modified Dhamaka should be insisted upon, for disbursement of the incentive. m. Rajasthan government, at present, has fixed the norm that in villages with less than 4000 population, house hold drinking water connections should not be given from village water supply schemes. Due to this rule, the number of private tube wells increase and the use of ground water for drinking purposes increases, irrespective of the potability state of ground water. It may be desirable to change this rule. It will be conducive to improved health status of the community. n. It was felt that grass root level functionaries of NGOs working with government for TSC work were not very conversant with merits and demerits of various on site technologies. Orientation and training of such personnel is advisable. This can be done even for grass root level personnel of PHED, involved in TSC work. o. It may be pointed out that above mentioned measures might only delay the ground water contamination. These will remain as short term risk management methods. Once nitrates increase in ground water, it is permanent. In given soil conditions and the necessity for sanitation measures, in long term, ground water is not likely to remain potable. Hence, sanitation and drinking water supply in these regions will have to be planed comprehensively by reviewing all technologies with a long term perspective.
Acknowledgements: I am thankful to Mr Kumar Alok, IAS, WASH officer, Unicef regional office, New Delhi, for his initiative and support for this study. I am also thankful to Mr. M. K. M. Joshi, ACE (Rural), PHED from state water supply and sanitation mission, Government of Rajasthan for his support during this study. This study was initiated and supported by Unicef Area Office, New Delhi. The hydrogeological maps were made available by Mr Pankaj Mathur of Unicef Jaipur office from the publications of the Government of Rajasthan. Mr Mathur was also helpful in the field study. I gratefully acknowledge the geological drawings and information from Guidelines for Assessing the Risk to Groundwater from onsite sanitation by Lawrence AR et al published by DFID in 2001. I am also grateful to various officials of the Government of Rajasthan, who very kindly provided all the necessary information and support during the study.
Published on Nov 21, 2011
Study about appropriateness of design, possibility of conversion to sanitary latrine and extent of groundwater pollution caused Dhamaka lat...