Environmental impact assessment for the proposed water and sewerage system in Dhiffushi, Kaafu Atoll, Maldives

Abstract

This report discusses the findings of an environmental impact study under the proposed water and sewerage system project at K. Dhiffushi. The project is proposed by the Secretariat of Dhiffushi Council. The project entails establishment of a proper island-wide water supply and sewerage system. The proposed project will involve installing a pipe network to collect sewage and wastewater from all the households on the island and necessary pumping stations. Currently, raw sewage and wastewater is disposed to the lagoon via multiple outfalls polluting the nearshore environment while there are a few house-level soak-pits polluting groundwater. The proposed outfall will pump wastewater beyond the house-reef at over 7m depth. The proposed water supply network will be an integrated system consisting of harvested rainwater from roofs of community buildings with desalinated water which will be treated and distributed to households through the water supply network. Rainwater is the main source of potable water used in the island as each house has a 2500 litre tank. For other uses groundwater is used which is either pumped out by electric pump or rarely by manually using a handcrafted bucket (dhaani). Water intake will be by using boreholes. The boreholes will be drilled and installed according to the Borehole Drilling Guidelines administered by the Environmental Protection Agency. The brine discharge will be inside the harbour. It is important to provide adequate supply of potable water and provide appropriate wastewater disposal systems to provide safe and adequate supply of water and to minimize faecal contamination and foul smell in the groundwater, which the community is highly dependent upon. Furthermore, the small water storage facilities at household level presents water shortage issues during the dry season while contamination of the groundwater lens with wastewater effluent and salinization of the lens has become an increasingly important issue. Several alternatives to the proposed project components have been identified in this report. Some of these alternatives consider alternative means of wastewater disposal including treatment, alternative means of water supply and alternative outfall locations. Since groundwater wells are fixed with electric pumps to draw water which has been the main reason for excessive drawdown and subsequent salinization of the freshwater lens, alternatives involving sustainable groundwater use such as skimming wells have been recommended. Wastewater treatment is considered as a favourable option while it has been argued that if the effluent can be disposed of at an appropriate location, there would not be a need for treatment since there will be good mixing and flushing in such areas. It has also been recommended to use solar desalination technologies since the initial demand would be low. Environmental impacts were assessed for both the construction and operational phase of the project. Most of the environmental impacts identified for the construction phase of the project were minor negative; these include excavation and related difficulties to road uses, sedimentation from installing the outfall and temporary salinization of groundwater from dewatering to lay out the pipe network and pump stations. However, the impacts identified for the operational phase of the project were mostly moderate to major positive; improvement of groundwater quality and nearshore environment from stopping the current sewage disposal practise and reduction of related health hazards. Disposal of sewage via a sea outfall is considered as minor negative impact while the lack of multiple lagoon outfalls will help to improve the quality of the lagoons which is a primary recreational area of the island. The main mitigation measures for this project during the construction phase are similar to other water supply and sewerage projects such as dust control plans, working during low-tide during pipe installation and rigorous supervision. In case of deterioration of groundwater quality due to potential dewatering during construction of lifting stations in residential area, measures to water plants in the area that may be affected due to dewatering shall be in place. The design shall also ensure that dewatering is minimized. As for the operational phase trained maintenance staff to service the sewerage system and regular check-ups have been suggested in addition to monitoring water quality as well as reef health for potential impacts. Increasing awareness on groundwater conservation and promoting sustainable groundwater aquifer management, especially the skimming well technology has been suggested. The Proponent is willing to undertake monitoring during and after the construction phase in addition to undertaking the mitigation measures proposed by the consultants. In conclusion, it appears justified from a technical, administrative and to some extent environmental point of view, to carry out the proposed water supply and sewerage system development project. The alternative of wastewater treatment will involve greater operational costs; therefore, it is recommended to proceed with the project as proposed while keeping the option open for future wastewater treatment, as and when required.