Main Operational Impacts 6.
5.15 Potential impacts arising through the operational phase of the Qatalum Project include the following: • Impacts associated with the seawater scrubber effluent discharge (i.e. increased temperature, low pH and increased COD)• Entrainment of marine organisms/fish/mammals within the seawater intake; and• Impacts associated with vessels using the Qatalum Port.
Discharge of Scrubber Effluent 6.5.16 The bleed from the Power Plant cooling towers and used seawater from Aluminum Plant cooling systems will be used in the seawater scrubbers at the Reduction Plant, thus the only seawater discharge from the Project will be the final effluent from the scrubbers (estimated at a maximum of 16,000 m3/hr).
The discharge will be released into the existing QASCO channel at the point indicated in Figure 3.4. Previous surveys37 have identified that there are no sensitive marine habitats, flora of fauna within 500 m of the discharge point. The main potential impact associated with the seawater discharge is the temperature increase relative to that of intake water.
Engineering studies have determined that for the hottest months (June to October), where increases in sea temperature are will have the most significant impact on the marine environment, the Qatalum discharge will have a ?T of less than 4 ºC at the point it enters the QASCO channel. Table 6.5 below shows the average monthly seawater intake temperatures compared to the calculated temperature of the discharge at the point it enters the QASCO channel, and the resultant ?T. These are also shown graphically in Figure 6.14 and Figure 6.15.
Table 6.5 – Seawater and Discharge Temperatures Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Seawater Temp. (ºC) 21.0 21.0 24.0 26.3 30.
0 33.0 34.3 36.0 35.0 33.0 28.1 24.0 Discharge Temp.
(ºC) 28.5 28.7 31.3 33.1 35.
7 36.6 37.8 38.9 38.4 36.
7 33.6 32.2 Delta T (ºC) 7.5 7.7 7.
3 6.8 5.7 3.6 3.5 2.9 3.4 3.
7 5.5 8.2 Figure 6.14 – Seawater Intake & Discharge Temperature (at Entry to QASCO Channel) Figure 6.15 – Delta T of Seawater Discharge at Point of Entry to QASCO Channel 6.5.17 Table 6.5 shows that the highest ?T is 8.
2 ºC at the point of entry to the QASCO channel, which has been calculated to occur in December. In order to determine whether this “worst case” scenario would still enable compliance with the SCENR standard, Qatalum commissioned D’Appolonia to undertake analysis of the thermal dispersion of the combined Qatalum and QASCO cooling waters. The full report for this Study is presented in Appendix L and summarized below. Within the EIA study D’Appolonia carried out an analysis on the thermal dispersion of the planned wastewater discharged by the expanded QASCO facility using CORMIX-GI v4.3GT.
The modelling was carried out assuming a worst case (6.6 ºC ?T) temperature for the combined Qatalum / QASCO discharge. The results of the analysis showed that, for the combined Qatalum / QASCO discharge, the 3 ºC ?T criteria would be met within 50 m from the outfall and that at 100 m from the outfall the ?T would be in the region of 2.2 to 2.3 ºC.
On the basis of the above, and the lack of sensitive receptors within 500 m of the channel discharge point, the significance of the impact of heat loading to the marine environment, and subsequently flora and fauna, is assessed as negligible to minor. Other issues / impacts associated with the discharge are pH, COD and biocide concentrations. The acidic scrubber effluent will be neutralized and the pH carefully controlled (as described in Section 3.12) and monitored. Under typical operating conditions, the discharge will have pH of >6 at the point at which it enters the sea, which is in line with the Qatari standards. Further neutralization will occur rapidly through natural dispersion once the discharge enters the sea. A conservative estimate, on the basis of the thermal modelling results, is that an increase, to approximately pH 6.8, will occur within 100 m of the outfall.
On the basis of this, the localized extent of the potential impact and the limited sensitivity of the immediate receiving environment, impacts on water quality and marine ecology are assessed as negligible. The final stage of the scrubber effluent neutralization process requires the use of the existing discharge in the QASCO channel. In the abnormal event that the QASCO discharge stops, or is reduced, (e.g. during plant shutdown / maintenance) there is the potential for acidic (~pH 4) water to enter the sea at the discharge point.
This scenario was identified in the Environmental Risk Assessment and is addressed in Section 6.10 and in more detail in Appendix J. Elevated COD levels result in reduced levels of dissolved oxygen (DO), which is a fundamental requirement for the maintenance of balanced indigenous populations of fish, shellfish, and other aquatic biota. COD will be reduced by the installation of an aeration system (air injection nozzles) along the bottom of the QASCO channel, downstream of the point at which the Qatalum discharge enters the QASCO channel. The objective of this will be to meet the required SCENR dissolved oxygen (DO) level of 2 mg/l.
As noted above, previous surveys37 have identified that there are no sensitive marine habitats, flora of fauna within 500 m of the discharge point. On this basis the impact associated with elevated COD levels / reduced DO levels is anticipated to be of negligible significance. Biocide treatment will be undertaken periodically through chlorination; any residual chlorine will be destroyed by the sulphite formed through the seawater scrubbing process. Thus, the Qatari standard for residual chlorine in seawater discharges should never be exceeded and the impact on the marine environment will be negligible.
In addition, the entry of the Qatalum discharge to the QASCO channel should have a beneficial impact in that the sulphites present will also neutralize any residual chlorine in the QASCO discharge. Vessels Using the Qatalum Port 6.5.18 Ships using the Mesaieed Ports will be under the control of the MIC Harbor Master. The main source of potential impacts to the marine environment directly associated with shipping are discharge of ballast water and leaks / spills from refueling; however, discharge of ballast water within the port area is prohibited and there will not be any refueling facilities at the Qatalum Port Area. In addition, the area around the Port will have been recently dredged and, as such, will be further devoid of sensitive marine habit and species. On the basis of this, the potential impact to the marine environment is considered to be negligible.
Potential impacts arising as a result of emergency events / large scale accidents have been addressed in the environmental risk assessment Section of this Chapter (Section 6.10).