2001 MAL: Small Bore Sewerage System Monitoring: 1) Rakheedhoo, Vaavu Atoll; 2)Komandoo, Shaviyani Atoll
Author: Fathaha, A. A.; Miles, L.; Musthafa, M.; Sajidha, A.; Mubarik, M.; Latheef, A.; Amir, A.; Aliyya, M.
This study contributes to a programme being carried out to assess the effectiveness of sewerage systems installed by the Government of Maldives (GoM) over the past seven years. The programme is being funded by UNICEF. Seven such systems have been installed since 1994 and, by comparing the effectiveness of these systems under the comparatively different settings on each of the islands concerned, it is hoped that lessons can be learned and improvements made to the design and management of these (or similar) systems in the future. The study follows on from the work carried out by Riyan Design and Management Consultants and detailed in the July 1999 report, "Environmental Evaluation of Small Bore Sewer Systems at Lh. Hinnavaru and K. Gulhi" and an MWSA report on the system installed in V. Rakheedhoo in May 2001.
Purpose / Objective
The objective of the work carried out in Sh. Komandoo was to investigate the performance of the system installed after six years of operation, and to evaluate its impact on the community and on the natural environment.
An inspection of the installed system was carried out (with particular reference to its physical condition) and photographs taken for future reference. Levelling surveys were carried out in critical parts of the system in order to determine the gradients of the installed sewers. Dye tracer experiments were conducted to measure the flow rates in different parts of the system. Groundwater and seawater samples collected in and around the island were analysed and used to produce maps of groundwater quality so as to assess the impact of the system upon the surrounding environment. Photographs were taken of the lagoon around the island in order to document its condition for future reference.
A household survey was conducted using a comprehensive questionnaire to gather information on the performance of the system, its maintenance, possible groundwater pollution problems and possible marine pollution problems. Discussions were carried out with the island community to find out their views on the present system and to learn something about its performance over the past seven years. Plans for future development and for land reclamation were also discussed.
Key Findings and Conclusions
The sewerage system installed in V. Rakheedhoo in 1994 appears to have been working to the satisfaction of the island community. It has become clear that this is not so much because the system has been operating perfectly, but rather because the community is managing the system themselves. Problems are reported to the island office, and blockages and minor repairs are dealt with by co-operation between the householders and the island office. This community management is something that should be encouraged with the implementation of any new schemes through awareness programmes and appropriate information, education and communication (IEC) initiatives. Where necessary, training ought to be carried out and equipment/technical assistance for maintenance provided.
The impact of the system is difficult to gauge from data collected over such a short period, which can only provide a snapshot of the situation. However, the relatively high quality of the groundwater on Rakheedhoo indicates that the system is not allowing sewage to enter the underlying aquifer. The majority rely on collected rainwater for drinking, but use well water for cooking and washing. The fact that the sewerage system excludes pathogens from the island's groundwater is, therefore, important in safeguarding the health of the community. The fact that the island health centre reports no problems either with diarrhoeal disease or with skin infections is testament to this.
The most significant negative impact the system has had seems to be upon the lagoon environment. This is because the system is being operated in such a way that the lagoon and reef are subject to acute shock loads every few months. The four outfalls are sealed and only opened when the septic tanks are full. Because the septic tanks are unable to provide any form of treatment in this mode of operation, largely untreated sewage is released to the lagoon in large quantities. MWSA has advised the island office against this practice, suggesting they leave the outfalls open to enable the septic tanks to work as they were designed to.
The study described in Rakheedhoo offers some valuable lessons that can help in the design and management of similar systems for other islands in the Maldives. Perhaps most significant is the fact that the system installed is more akin to "shallow sewerage" than "small bore sewerage". Shallow sewerage is generally employed in areas with higher population densities than that found in Rakheedhoo and, in fact, relies on the high wastewater flows generated by these high population densities for its effective operation. Despite the low flows and gradients discovered in Rakheedhoo during this study visit, however, the system was performing satisfactorily. This suggests that shallow sewerage may be appropriate for the more densely populated islands in the Maldives (not least because it is especially applicable where groundwater levels are high, where heavy vehicular loads are absent and where there is limited space for household septic tanks).
It should be noted, however, that the most important factor in the success of the system in Rakheedhoo has been the willingness of the island community to take ownership of the system and to carry out repairs and maintenance, as necessary. This is something which MWSA and the Government of Maldives should encourage and facilitate on future schemes. This might mean conducting information, education and communication (IEC) campaigns, and/or carrying out training, if necessary.
There are three main problems with the sewerage system in Sh. Komandoo. The first of these, and of most concern to the community themselves, is the degree to which the system has been corroded by hydrogen sulphide. Second, the community perceives the system to have increased the salinity of the groundwater. Third, many members of the community consider the system provided by GoM to be inferior to the one they had themselves installed and are, therefore, reluctant to take ownership of the system.
Fortunately, the corrosion appears to have affected the inspection chambers only. Unless action is taken in the next six months, however, it is possible that corroded material washed into the sewer lines will cause frequent blockages that could be difficult to remove without excavation of the affected lines. Therefore, in order to protect the considerable investment that GoM has made in the system, repair work should be carried out. MWSA is of the opinion that the removal of the corroded material and the reconstruction of the inspection chambers are necessary. The structure can be rebuilt using normal cement, but a 10mm layer of plaster using sulphate resistant cement should be added to all surfaces. In addition, the benching should be built up to an angle of 45o. The benching is currently almost horizontal and this could be encouraging the aerobic conditions in these chambers by reducing flow velocities.
The increased salinity of the groundwater reported by members of the community is likely to be related to the fact that all wastewater, including most grey water (from kitchens and laundry) is disposed of to the sewer and discharged to the sea. As a result, there is limited recharge of the aquifer during the dry months. As groundwater has been extracted, saltwater intrusion will have occurred. The quality of the groundwater in Komandoo could be returned in the long term by the increased disposal of grey water to the ground (perhaps through small filter beds) and by strategies for groundwater recharge. The main concern then will be whether the reduced flows in the sewerage system are more prone to becoming anaerobic or whether blockages are more likely to occur. This is a matter for discussion among MWSA, MoH and Komandoo's Island Office.
The community was not involved in the design of the system installed on Komandoo. As such, they are reluctant to take ownership and to operate and maintain the system. Many are of the opinion that the system they had built themselves previously, was superior. A key component of any scheme to be built in the future ought to be a demand on behalf of the community. Where this is not present, there are likely to be problems. Community ownership of infrastructure is something that should be encouraged with the implementation of any new schemes through awareness programmes and appropriate information, education and communication (IEC) initiatives.
The impact of the system is difficult to gauge from data collected over such a short period, which can only provide a snapshot of the situation. However, the relatively high quality of the groundwater on Komandoo indicates that the system is not allowing sewage to enter the underlying aquifer. The fact that the sewerage system excludes pathogens from the island's groundwater is therefore important in safeguarding the health of the community. The fact that the island health centre reports no problems with diarrhoeal disease is testament to this. The problems reported with skin disease could be related to the pollution of the lagoon or to the salinity of the groundwater, discouraging people, especially children, from washing properly.
The system in Komandoo, like that in Rakheedhoo, is better described as shallow sewerage than small bore (see Rakheedhoo report for discussion of these terms). Despite carrying unsettled sewage, the gradients measured were adequate to provide self-cleansing flows, despite low velocities. This, like the evidence gathered from Rakheedhoo, suggests that lower gradients are adequate in similar situations in the Maldives.
It is suggested that, along with measures to explain how to repair the corroded inspection chambers, information, education and communication activities are carried out to get the community to understand not only how the corrosion has taken place, but also the effect of grey water being discharged to the sewer on the salinity of the aquifer. Strategies for the recharge of the aquifer can be introduced and practical measures suggested. In the long term, it is hoped that an increased understanding of the system will encourage greater ownership on the part of the community.
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