Environmental impact assessment : for the proposed sewerage system Henbadhoo, Noonu Atoll, Maldives

Abstract

This report discusses the findings of an environmental impact study under the proposed sewerage system project at N. Henbadhoo. The project is proposed by the Secretariat of the Henbadhoo Council. The project entails establishment of a proper island-wide sewerage system with sea outfall. The proposed project will involve installing a pipe network to collect sewage from all the households on the island and necessary pumping stations. Currently raw sewage is disposed onto the ground via house-level soak-pits; polluting groundwater greatly. The proposed outfall will pump wastewater beyond the house-reef at over 7m depth. A number of alternatives to the proposed project components have been identified in this document. Of these, one of the alternative outfall locations is indicated to be as suitable as that proposed or better considering the overall effluent plume movement. However, the proposed option is also considered appropriate given that the location has no significant negative environmental impacts. It is also proposed to consider a treatment plant in the design, though the consultants are of the opinion, proposed system without a treatment plant is more than appropriate given the cost of treatment for such as small population and that the sewage is well diluted while salinity helps in minimizing the impacts of faecal coliforms. 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 sedimentation from installing the outfall and temporary salinization of groundwater from de-watering 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 from stopping the current sewage disposal practise and reduction of related health hazards. Disposal of sewage via proposed sea outfall is considered to have a minor negative impact. The main mitigation measures for this project during the construction phase are similar to other sewerage projects such as dust control plans, working during low tide as much as possible 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 desig shall also ensure that dewatering is minimized. As for the operational phase trained maintenance staff to service the sewerage system and regular check-ups has 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. The monitoring programme will involve testing the groundwater quality at different locations and seawater quality at outfall location as well as ocean currents at the outfall location. This monitoring programme may be carried out for no more than 5 years. In conclusion, it appears justified from a technical, administrative and environmental point of view, to carry out the proposed sewerage system development project. The alternative of wastewater treatment will involve greater operational costs; therefore, it is recommended to proceed the project as proposed while keeping the option open for future wastewater treatment, as and when required