BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

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Figure 7: Chartlet of the Ben Schoeman Dock in the Port of Cape Town. The proposed dredge area is demarcated by the purple line (from Protekon drawing # BDC009V). Grey circles indicate the positions of sediment samples taken in 2005 and black squares those taken in 2006. The green nav marker shows the position of sediment sample BS1B. Table 5: Gross distribution of sediment particle sizes in the soft sediments in the proposed dredge area (from Schoonees 2006) Particle size fraction (µm) Classification % Approximate volume to be dredged* (m 3 ) >2000 Gravel 4 37 980 >63 -
Schoeman Dock occurred in 1971 (Protekon 2006) and therefore the muds, silts and clays in the surficial sediments in the Basin have probably been accumulating since this period. 5.2.1.2 Surficial sediment contaminant distributions Contaminant concentrations in the surficial sediment (top ~20cm) in the Port of Cape Town have been routinely measured since 1999 (CSIR data). In 1999, 2000, 2001 and 2004 coverage in the Ben Schoeman Dock Basin was limited to three stations (eg CSIR 2004). In 2005 this was extended to 10 stations (CSIR, 2005). This series of measurements identified high levels of contamination at the head (south eastern side) of the dock Basin which was further investigated in 2006 through 11 sampling stations distributed mainly in this area. Figure 7 shows the distribution of the 2005 and 2006 sampling stations that were located within the proposed dredge area. The trace metal concentrations measured in 2005 and 2006 are listed in Table 6. London Convention 'special care' concentration ranges and 'prohibition' thresholds (DEA&T 1998) are listed to show sites and trace metals non-compliant with these, and the BCLME (2004) sediment quality guideline values are listed to show the probability of in situ adverse biological effects. Table 7 lists hydrocarbon concentrations measured in the Ben Schoeman Dock Basin surficial sediments in 2005 (no measurements were made in 2006). Table 7 includes screening level thresholds to show whether the measured levels constitute any appreciable risks of generating adverse environmental impacts. Table 6 shows that individual and combined LC Annex 2 trace metal concentrations were in the special care range at all sampling locations except that of BS5 in 2005. Further, cadmium (Cd) and mercury (Hg), LC Annex 1 contaminants, exceeded the special care (action level) threshold at three and seven of the 18 sites sampled respectively. Most of the exceedances were close to the lower end of the defined ranges except for combined Annex 2 trace metals at sampling location BS1B which was slightly above the prohibition threshold. This sampling point is actually located ~11m outside of the specified dredge area (Figure 7) and is thus technically also outside of this evaluation. However, it is possible that sediments at this site could be disturbed during the proposed dredging which merits its inclusion in this assessment. All of the sampling locations had trace metal concentrations that exceeded TEL thresholds while at two of them mercury exceeded the PEL threshold. This indicates that modifications to the soft sediment benthic community in the harbour Basin was possible at most sample sites and probable at BS5 and BS1M. However, other extrinsic factors such as water exchange and food availability would probably also play roles in structuring the benthic community as would the in situ effects of anoxia etc. There are essentially two possible sources that could explain the observed trace metal concentrations in Port of Cape Town surficial sediments: o Erosion of (terrestrial) clay minerals and deposition in the harbour, ie a lithogenic source, and o Anthropogenic sources. 30
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
Page 21 and 22: Supralittoral fringe (Littorina zon
Page 23 and 24: Niambia sp. Coleoptera Diptera Tylo
Page 25 and 26: Midlittoral zone - The intertidal o
Page 27 and 28: Fish - Nearshore and in the sandy b
Page 29 and 30: 2000 at Robben Island revealed furt
Page 31 and 32: Table 2: Common whales and dolphins
Page 33 and 34: Table 3: Site, time, mean count (co
Page 35 and 36: 150000 125000 100000 Kg 75000 50000
Page 37: sensitive because of its conservati
Page 41 and 42: Table 7: Hydrocarbon distributions
Page 43 and 44: care concentration ranges for cadmi
Page 45 and 46: SS mg/l Boxplot for TSS 80 60 40 20
Page 47 and 48: The mean values calculated above ar
Page 49 and 50: o o possibility of the dredge spoil
Page 51 and 52: The gravel sized component of the s
Page 53 and 54: Table 12a: London Convention Annex
Page 55 and 56: Benthos distributions in Block #1 -
Page 57 and 58: 40 40 30 Site 1A 30 Site 1B % Speci
Page 59 and 60: 2 Cluster Dendrogram and MDS ordina
Page 61 and 62: the well developed ripples in the c
Page 63 and 64: 6 IMPACT IDENTIFICATION AND ASSESSM
Page 65 and 66: Accordingly the potential environme
Page 67 and 68: Impact Assessment Table No Mitigati
Page 69 and 70: are summarised in the table and it
Page 71 and 72: Figure 21b: Predicted number of day
Page 73 and 74: considered to be low. Further, the
Page 75 and 76: A A B B B Figure 23a and b: Predict
Page 77 and 78: dependent on these include the harm
Page 79 and 80: structures. The apparent lack of su
Page 81 and 82: Diving birds such as cape cormorant
Page 83 and 84: Figure 24: The predicted worst case
Page 85 and 86: Figure 25 depicts the simulation mo
Page 87 and 88: 6.2.3.2 Alteration of benthic biolo
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Impact Assessment Table No Mitigati
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Nature of impact - Turbid plumes of
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Figure 26b: Predicted worst case ex
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Figure 27b: Predicted worst case ex
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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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BEN SCHOEMAN DOCK BERTH DEEPENING Specialist ... - Transnet

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