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

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Orthoohosphate (mg/l as P) Free Active Chlorine (mg/l) Apr-03 Apr-03 Jul-03 Jul-03 Nov-03 Nov-03 Mar-04 Mar-04 Jul-04 Jul-04 Nov-04 Nov-04 Mar-05 Mar-05 Jul-05 Jul-05 Nov-05 Nov-05 Mar-06 Mar-06 Jul-06 Jul-06 Nov-06 Nov-06 Mar-07 Mar-07 Jul-07 Jul-07 Nov-07 Nov-07 Mar-08 Mar-08 Jul-08 Jul-08 Oct-08 Oct-08 Feb-09 Feb-09 Jun-09 Jun-09 Oct-09 Oct-09 Feb-10 Feb-10 Jun-10 Jun-10 Oct-10 Oct-10 Feb-11 Feb-11 Jun-11 Jun-11 Oct-11 Oct-11 Feb-12 Feb-12 State of Saldanha Bay & Langebaan Lagoon 2011 Activities & discharges 16 14 12 10 8 6 4 2 0 Figure 3.28. Monthly trends in the concentration of Orthophosphate in effluent from Langebaan WWTW, June 2009 - December 2011. Allowable limits as specified in terms of a General Authorisation under the National Water Act 1998 are represented by the red line. 14 12 10 8 6 4 2 0 Figure 3.29. Monthly trends in the concentration of Free Active Chlorine in effluent from Langebaan WWTW, June 2009 - December 2011. Allowable limits as specified in terms of a General Authorisation under the National Water Act 1998 are represented by the red line. 3.3.7.3 Summary In general the waste water treatment plans at Saldanha and Langebaan are having difficulties in keeping effluent levels and water quality parameters under the general limits specified under the National Water Act 36 of 1998. Of particular concern are the consistently high concentrations of Nitrates, in the form of Ammonia, being discharged at Saldanha. Ammonia has been shown to be toxic to plants and seagrasses at very low concentrations. Chlorine levels in the effluent from both WWTWs are high, exceeding the limits of a general authorisation at least half of the time. 46 ANCHOR e n v i r o n m en t a l
State of Saldanha Bay & Langebaan Lagoon 2011 Activities & discharges 3.3.8 Storm water Storm water runoff, which occurs when rain flows over impervious surfaces into waterways, is one of the major non-point sources of pollution in Saldanha Bay (CSIR 2002). Sealed surfaces such as driveways, streets and pavements prevent rainwater from soaking into the ground and the runoff typically flows directly into rivers, estuaries or coastal waters. Storm water running over these surfaces accumulates debris and chemical contaminants, which then enter water bodies untreated and may eventually lead to environmental degradation. Contaminants that are commonly introduced into coastal areas via storm water runoff include metals (Lead and Zinc in particular), fertilizers, hydrocarbons (oil and petrol from motor vehicles), debris (especially plastics), bacteria and pathogens and hazardous household wastes such as insecticides, pesticides and solvents (EPA, 2003). It is very difficult to characterise and treat storm water runoff prior to discharge, and this is due to the varying composition of the discharge as well as the large number of discharge points. The best way of dealing with contaminants in storm water runoff is to target the source of the problem by finding ways that prevent contaminants from entering storm water systems. This involves public education as well as effort from town planning and municipalities to implement storm water management programmes. The volume of storm water runoff entering waterways is directly related to the catchment characteristics and rainfall. The larger the urban footprint and the higher rainfall, the greater the runoff will be. At the beginning of a storm a “first flush effect” is observed, in which accumulated contaminants are washed from surfaces resulting in a peak in the concentrations of contaminants in the waterways (CSIR 2002). Several studies have shown degradation in aquatic environments in response to an increase in the volume of storm water runoff (Booth and Jackson 1997, Bay et al. 2003). Storm water runoff that could potentially impact the marine environment in Saldanha and Langebaan thus originates from industrial areas (490 ha), the Saldanha Bay residential area (475 ha), industrial sites surrounding the Port of Saldanha (281 ha), and Langebaan to Club Mykonos (827 ha) (Figure 3.30). All residential and industrial storm water outlets drain into the sea. There are approximately 15 outlets in the Saldanha Bay residential area. Historically, storm water from the Port of Saldanha and ore terminal was allowed to overflow into the Bay but now most of this is diverted to storm water evaporation ponds and any material settling in these ponds is trucked to a landfill site. The number of storm water outlets in Saldanha Bay industrial zone (along the western margin of Small Bay) is not known, nor is the number of drains between Langebaan and Club Mykonos (CSIR 2002). The CSIR (2002) estimated the monthly flow of storm water entering Saldanha Bay and Langebaan Lagoon using rainfall data and runoff coefficients for residential and industrial areas. In this report, these estimates have been updated by obtaining more recent area estimates of industrial and residential developments surrounding Saldanha Bay and Langebaan Lagoon using Google Earth and acquiring longer term rainfall data (Figure 3.30 and Table 3.6). Runoff coefficients used to calculate storm water runoff from rainfall data were 0.3 for residential areas and 0.45 for industrial areas (CSIR 2002). Note that runoff from the Port of Saldanha and ore terminal have been excluded from these calculations. 47 ANCHOR e n v i r o n m en t a l
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Afrolittorina knysnaensis (no/0.5 m
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