State of the Bay Report 2011-Final.pdf - Anchor Environmental

State of Saldanha Bay & Langebaan Lagoon 2011
Activities & discharges
Onshore construction issues: human activity, air, noise and vibration pollution, dust, blasting
and piling driving, disturbance of coastal flora and fauna);
Construction and installation of a water discharge and intake pipeline issues: construction
site, pipe lay-down areas, trenching of pipeline(s) in the marine environment and
consequent disturbance of subtidal biota); and
Construction and installation of intake boreholes.
The issues associated with the operational phase included:
altered flows at the discharge resulting in ecological impacts (e.g. flow distortion/changes at
the discharge, and affects on natural sediment dynamics);
the effect of elevated salinities in the brine water discharged to the bay;
biocidal action of non-oxidising biocides such as dibromonitrilopropionamide (DBNPA) in the
effluent;
the effects of co-discharged waste water constituents, including possible tainting effects
affecting both mariculture activities and fish factory processing in the bay;
the effect of the discharged effluent having a higher temperature than the receiving
environment;
direct changes in dissolved oxygen content due to the difference between the ambient
dissolved oxygen concentrations and those in the discharged effluent; and
indirect changes in dissolved oxygen content of the water column and sediments due to
changes in phytoplankton production as a result of altered nutrient dynamics (both in terms
of changes in nutrient inflows and vertical mixing of nutrients) and altered remineralisation
rates (with related changes in nutrient concentrations in near bottom waters) associated
with near bottom changes in seawater temperature due to the brine discharge plume.
The marine specialist report assessed the impacts of RO plants with several different designs
at three sites. It was expected that the impacts of construction at the authorized site would be very
low as these construction activities would have utilized existing infrastructure as their basis and
construction activities would not have been extensive. Operational impacts associated with the
intake of water through boreholes were expected to be insignificant to low. All potential impacts
associated with the discharge of brine through a pipeline at Caisson 3 (the authorized site) were
expected to be of a low to very low level, with the exception of the use of oxygen scavengers with no
mitigation measures, which was expected to have a medium level impact. A monitoring programme
was outlined in the marine specialist report. Aspects of the environment which require monitoring
include the benthic macrofauna communities, dissolved oxygen levels in the near bottom waters in
the immediate vicinity, trace metals and tainting substances in the RO plant effluent, toxicity of the
effluent, and temperature, salinity and suspended solids in the near-field. Monitoring activities
commenced during the second half of 2010 in order to establish a baseline prior to the RO plant
coming into operation. Follow-up monitoring is planned when the plant is finally brought on line.
3.3.6.2 West Coast District Municipality Desalination Plant
The West Coast District Municipality (WCDM) has proposed the construction of an additional
RO plant in the Saldanha Bay area. The West Coast has limited water resources (due to its semi-arid
nature) but yet is required to supply 22 towns and 876 farms across the region with potable water.
Currently water is supplied by the Voelvlei Dam, Misverstand Dam and the Langebaan road aquifer,
however the volume allocated from these sources for this is close to the maximum possible. During a
feasibility study in 2007 to assess the most viable solution to the water scarcity issue in the WCDM,
several sources of additional water were considered. These included:
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