Environmental impact assessment for the proposed sea water cooling system in Addu City, Maldives

Abstract

This report discusses the findings of an environmental impact study under the proposed sea water cooling system for the electrical generator sets in the central power station of Addu city. Central Power House at Addu City requires Engine cooling by using saline water. The system will require installing three boreholes with multi stage submersible pumps, supply line for pressure header and feeding lines with valves and flanges. The proponent of this project is Fenaka Corporation Ltd. Rotary-mud drilling will be employed for the construction. The depth of borehole will be determined in accordance with the existing guidelines; i.e. if electrical conductivity of discharge water has reached 50-60mS/cm before reaching 30m depth, drilling will continue until it has reached 30m. Furthermore, if electrical conductivity of discharge water at 30m depth is measured less than 50-60mS/cm, drilling will be continued until electrical conductivity reaches to 50-60mS/cm. The extracted earth and saline water from drilling activities will be deposited on a purpose-built plastic sheet and water will be separated from the solids. The water extracted from this is proposed to be disposed off into the lagoon via the reject line in the operational phase. The most significant impact from the proposed project would be temporary deterioration of local freshwater quality during borehole installation and seawater quality at the disposal site. The impact on groundwater during borehole construction is of low magnitude and temporary. The impact is also of little significance. The impact of seawater quality at discharge location is almost negligible given that the discharge water has similar characteristics to the lagoon water in terms of salinity although the water would be hot at the time of discharge. Since the discharge location is a reef flat area with no coral the impact is negligible. Furthermore, the area gets dry at low tide and there is no recreational value in this area as it is the rim reef flat. Alternatives have been identified in the EIA, however it is seen that the best method to carry out the project is the proposed method of using boreholes. The alternative is to use a seawater intake, however, due to the distance of a feasible intake location with the rim reef closest to the location, boreholes are considered to be more suitable. The consultations with the Council also revealed that the proposed route for the discharge pipeline is not suitable, as there is no road in the proposed route. Therefore, as per the Council’s recommendation, it is proposed to consider the alternative route that would dispose at the same location as the existing brine discharge pipe. Since there were no significant environmental impacts identified for the proposed project, mitigation measure were general construction phase guidelines such as dust control measures and appropriate waste management. The alternative route for the discharge pipe may also mitigate some social concerns and is recommended to consider the alternative route. There would not be additional costs associated with this alternative route, and even if there is, there would not be a considerable cost difference. Environmental monitoring is not considered necessary for this project. However, monitoring has been proposed for about one year to assess and examine changes to the environment, if any. It covers the monitoring of marine water quality at the discharge location for temperature and salinity only at 3-monthly intervals for a maximum of 2 years. This can be integrated within a monitoring programme for the powerhouse. Water quality testing that may be necessary to be performed upon completion of the borehole, which has been indicated in the Borehole Guidelines shall also be performed. In conclusion, it appears justified from a technical and environmental point of view to carry out the proposed project to construct a cooling water system for the existing powerhouse in Hithadhoo, Addu City. However, it is recommended to consider the alternative route for discharge pipeline, as recommended by Addu City Council.