Issues to be Addressed Describe the impacts of the proposed RO Plant on the marine biology of the project area during the construction and operational phases; Assess all factors resulting from the construction and operation of the RO plant and associated infrastructure that may influence the marine and coastal environments in the region, based on existing information; and Recommend mitigation measures.
Abstraction and discharge of water from and into the sea : Permit under Sections 32 and 56 of the Water Resources Management Act (No. 24 of 2004). The discharged water (and associated co-discharges) is classified as “industrial effluent” : License under the Water Resources Management Act (No. 24; 2004). A combined licence to abstract and use water and to discharge effluent is covered under Section 38 of the Act. Licenses provided through the Ministry of Agriculture, Water Affairs and Forestry. Legal & Permitting Requirements: National Standards
Legal & Permitting Requirements: International Standards RSA Department of Water Affairs & Forestry (DWAF 2007): “Guidelines for the evaluation of possible environmental impacts during the development of seawater desalination processes” gives general guidance on the assessment procedure, lists possible environmental impacts which can be expected during implementation of seawater desalination, and provides recommendations for specialist and monitoring studies. International Finance Corporation: Environmental, Health, and Safety Guidelines applicable to projects discharging industrial wastewater. Water Quality Guidelines providing recommended target values: South African Water Quality Guidelines for Coastal Marine Waters (1995) World Bank guidelines (1998) ANZECC guidelines (2000) US Environmental Protection Agency guidelines (2006).
Overlap with other Studies Numerical Modelling Study: Effluent plume modelling results used to assess magnitude of impact on marine communities i.e. “footprint” of the discharge Hydrographical and Geophysical Survey: Bathymetry and sub-bottom profiling results used in description of affected subtidal environment and associated communities Coastal Physical Processes and Dynamics: Predicted accretion, sedimentaion and erosion rates used to assess impacts on affected marine biota
Impact on the Marine Environment Key Sources for Potential Impacts on the Marine Environment: Construction of intake and brine disposal structures Permanent presence of these structures Discharge of high-salinity brine Both Atlernatives (pipelines and stilling basin) considered in EIA but only impacts associated with pipelines presented here
Main Findings Construction of Intake and Discharge Pipelines: Disturbance and destruction of beach macrofauna through vehicular traffic, jetty and pipeline construction and excavations Accidental spillage or leakage of fuel, chemicals, or lubricants Disturbance and destruction of subtidal macrofauna through excavations, blasting, jetty construction and pipeline laying Increased turbidity and resettling of sediments during excavation Disturbance of surf-zone fish, seabirds and marine mammals through contruction noise Effects of blasting on marine mammals and turtles Significance Ranking: Low Medium High
Main Findings Operational Phase: Permanent presence of pipelines Permanent loss of habitat under intake and discharge pipelines Intake and discharge structures provides new artificial reef habitat Impingement and entrainment of marine organisms Changes in water circulation at the inlet structure due to the abstraction of large volume of seawater Flow distortion at the discharge, and effects of pipeline on natural sediment dynamics Significance Ranking: Low Medium High
Main Findings Operational Phase: Discharge of hypersaline brine Increased salinity in porewater and mixing zone affects marine biota Increased in temperature in mixing zone affects marine biota Effects of biocide plume on marine biota in mixing zone Reduction in dissolved oxygen due to dechlorination Effects of discharged co-pollutants on marine biota Effects of discharged anti-scalants on marine biota Effects of discharge cleaning solutions Effects of bacterial regrowth in brine Effects of heavy metals in brine due to corrosive processes Significance Ranking: Low Medium High
Mitigation Measures Good house-keeping during construction, including oil spill contingency plan for accidental spills Reduce impingement and entrainment by inclusion of appropriate screens and velocity caps at intake structure Dechlorinate the feed-water with sodium bisulfite (SBS) Check the brine for bacterial re-growth and treat with SBS shock dosing SBS is an oxygen scavenger and can deplete dissolved oxygen in the brine if overdosed; consider installation of a permanent aeration system Avoid polyphosphate antiscalants - use antiscalant with relevant eco-toxicological testing Treat backwash sludge in sludge handling facility and remove solids (i.e. the insoluble ferric hydroxide precipitate) Neutralize acidic cleaning solutions before discharge
Monitoring Recommendations Diffuser Performance Monitoring to ensure that the diffuser is performing to specifications and achieving the required level of dilution ( validates model results) Whole Effluent Toxicity (WET) testing Continuous monitoring of the residual chlorine and dissolved oxygen levels in the brine. Periodical monitoring of heavy metal content from corrosion processes Periodical monitoring of bacterial re-growth in the brine Contingency plan that examines the risk of contamination and procedures to mitigate any unanticipated impacts (e.g. mixing zone larger than expected) Annual inspection program to check the physical integrity of the pipelines and diffuser