BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

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the harbour water body. This mirrors the suspended sediment concentration distributions. CMS (1995b) point out that the measured nitrogen concentrations (ammonium plus nitrates) in the Port of Cape Town water body do not depart much from those measured in Cape West coast nearshore waters and eutrophication of the overall water body cannot be considered to have occurred yet. This is borne out by dissolved oxygen levels that appear to be mostly near saturation levels with only isolated instances of super saturation or hypoxia (CMS 1995b). The flow of water from Duncan Dock into the Alfred Basin may assist in keeping the system oxic by preventing or lessening the development of stagnant water bodies. 5.2.2.3 Dissolved trace metal concentrations CSIR (unpublished data) measured dissolved trace metal concentrations in surface water samples taken from locations in the harbour at approximately 3 month intervals in 2005 and 2006. Trace metals such as cadmium, cobalt and lead were consistently below the detection limit. The measurements of those trace metals that were consistently above detection limits are summarised in Table 10. Table 10: Mean dissolved trace metal concentrations (µg/l) in surface water samples taken from the entrance to Ben Schoeman Dock (BSE), the Ben Schoeman lay up Basin (BSL), the entrance to Duncan Dock (DDE), the Duncan Dock intake (DDI), the Victoria and Alfred Basin synchro-lift (VAS) and the Royal Cape Yacht Club (RYC) at four occasions at approximately 3 monthly intervals in 2005 and 2006. Trace Statistic Site metal BSE BSL DDE DDI VAS RYC (µg/l) n 10 5 11 5 11 5 Chromium Mean 4.08 1.10 4.67 1.16 17.09 0.73 Std Dev 3.49 0.50 3.77 0.42 158.2 0.23 Copper Mean 1.24 1.72 1.97 1.38 5.51 1.02 Std Dev 1.02 1.28 1.44 2.17 2.94 0.22 Nickel Mean 1.10 - 2.12 0.71 7.59 - Std Dev 0.84 - 1.67 0.17 18.14 - Zinc Mean 7.87 7.07 6.75 5.26 18.23 7.80 Std Dev 5.01 5.34 3.92 3.80 14.99 7.71 Statistical comparisons between the sites (one way ANOVA and Tukey's multiple comparison test; Sokal and Rohlf 1995) show that copper and zinc were elevated (p0.05) throughout the harbour. Mean concentrations for these trace metals were higher in the Victoria & Alfred site but were also highly variable (standard deviation>mean). The high trace metal concentrations are probably attributable to ship repair activities at the synchro-lift. This is a semi-enclosed area and probably weakly flushed leading to low dilution of dissolved material washing out of the repair facility. Given the configuration of the Port of Cape Town it is arguable whether trace metals released from this area have any influence on the wider areas of the harbour. If the Victoria & Alfred site values are excluded the mean dissolved trace metal concentrations in the harbour are: chromium 2.98 (+/- 3.19)µg/l, copper (1.52 (+/- 1.12)µg/l, nickel 1.33 (+/- 1.13)µg/l and zinc 7.05 (+/- 4.83)µg/l; n = 36 in all cases. Cadmium, cobalt and lead are below detection limits, there are apparently no recent data available for arsenic or mercury. 37
The mean values calculated above are all well within the RSA water quality guideline concentrations for the maintenance of marine ecosystems (DWAF 1995). This is despite the fact that the harbour receives contaminants from a range of sources such as stormwater, ship cargo handling and shipping itself. 5.2.2.4 Biological indicators of pollution Biological indicators of pollution in the harbour area comprise the harbour wall biofouling and sediment benthos community surveys of CMS (1995a), mussel watch measurements of trace metal concentrations at sites in the outer harbour (CSIR unpublished data) and harbour water toxicity tests (CMS 1995b). The CMS (1995a) benthos surveys have been discussed above and showed that the harbour wall biofouling community declined into the harbour and was depauperate at the head of the Victoria and Alfred Basins. CMS (1995a) note that this was consistent with gross indicators of hydrocarbon pollution. However, it is also consistent with reducing water exchange rates and so the observed biological distributions cannot be unequivocally linked to pollution with the data at hand. Similar to the biofouling community soft sediment benthos was generally depauperate and completely absent from sediments in the inner harbour areas. CMS (1995a) recorded that sediments in these areas were black and anoxic and that there was also a degree of hydrocarbon contamination. This is stronger circumstantial evidence of pollution effects on the harbour biological communities. Mean trace metal body burdens in mussels (Mytilus galloprovincialis) from sites on the seaward side of the eastern breakwater and the outer extremities of Duncan and Victoria Docks are listed in Table 11. There are no clear gradients evident in the data; cadmium is elevated on the outer harbour breakwater compared to the two sites in the harbour and copper is elevated on the Duncan Dock. Further, the mean values for all of the trace metals measured are approximately similar to those measured at Llandudno, on the Atlantic coast south of Cape Town, over the period 1985-1995 (Brown and Warrington, 1995). As this site is remote from any industrial activity it can be considered to be unpolluted. The observed concentrations are also well within the published limits for human consumption (Staatskoerant 1994). From this it is concluded that the mussel trace metal body burdens presented here do not signal significant pollution by trace metals. Table 11: Mean trace metal body burdens (µg/g dry weight) in mussels collected from three locations in the Port of Cape Town over the period October 2000 to April 2006. The collection sites were the seawall of the eastern breakwater (BSC) and the outer ends of Duncan Dock (DD) and Victoria Dock (VD). The data were supplied by CSIR, Stellenbosch. Trace metal Site BSC DD VD Mean Std Dev Mean Std Dev Mean Std Dev Cadmium 3.11 0.66 2.28 0.36 1.70 0.54 Chromium 1.11 0.33 1.12 0.66 0.90 0.27 Copper 5.38 1.35 7.09 1.43 5.84 0.55 Mercury 0.13 0.12 0.28 0.14 0.17 0.07 Lead 3.04 0.78 3.03 1.23 2.99 1.59 Zinc 302.8 93.3 347.7 125.3 257.3 38.8 38
Page 1 and 2: BEN SCHOEMAN DOCK BERTH DEEPENING S
Page 3 and 4: the test organisms. The EC 5 is usu
Page 5 and 6: Turbidity Upwelling Vulnerable Wrac
Page 7 and 8: Another important issue is the poss
Page 9 and 10: 6.2.1.3 Settlement of material susp
Page 11 and 12: 2 METHODOLOGY For the assessment tw
Page 13 and 14: The proposed deepening of the Ben S
Page 15 and 16: 4.3 Cumulative effects Table Bay re
Page 17 and 18: undetectable in 80% of the measurem
Page 19 and 20: 5.1.3 Biological communities The ma
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Page 23 and 24: Niambia sp. Coleoptera Diptera Tylo
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Page 31 and 32: Table 2: Common whales and dolphins
Page 33 and 34: Table 3: Site, time, mean count (co
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Page 37 and 38: sensitive because of its conservati
Page 39 and 40: Schoeman Dock occurred in 1971 (Pro
Page 41 and 42: Table 7: Hydrocarbon distributions
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Page 45: SS mg/l Boxplot for TSS 80 60 40 20
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Page 53 and 54: Table 12a: London Convention Annex
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Page 67 and 68: Impact Assessment Table No Mitigati
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Page 73 and 74: considered to be low. Further, the
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suspended sediment concentrations i
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Figure 28a: Dredge spoil dump site
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6.2.3.6 Elevated water column turbi
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The evaluation with mitigation is:
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Figure 29a: Predicted exceedance in
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6.3 Cumulative Impacts The proposed
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Impact summary Table (cont.) Impact
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Impact summary Table (cont.) Impact
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mitigated by ensuring that the Cutt
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operations at Coega Port. Prepared
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Glassom D., K. Prochazka and G.M. B
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Protekon 2006. Port of Cape Town co
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