Control of lead discharges to water

Similarly, in the case of industrial effluents control maybe based on limitation of the discharge of another toxic metal, say copper or zinc, with a reduction in lead discharge occurring as an added bonus. In this chapter it is necessary, therefore, to consider both control methods specifically designed to limit the discharge of lead, as well as those more general methods which also affect concentrations of lead in effluents. 

Before discussing the range of treatment methods available, it is necessary to examine the various standards that apply to lead in water. These set the requirement for control, if any, and subsequently provide a basis against which to monitor the effectiveness of that control. 

The formulation of water quality standards is an extremely sensitive area of pollution control. It is one in which there is a tendency for political decisions to hold almost as much weight as scientific judgements. The approach to standard setting varies from one country to another and this has led to innumerable problems, particularly when international co-operation is required. This is well illustrated by the years of argument and discussion which have arisen in an attempt to reach agreement over the European Economic Communities (EEC) Dangerous Substances Directive and the Directive on Quality of Water for Human Consumption. 

Some time will therefore be spent on examining water quality standards 

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The Los Angeles District which administers the area s Joint Water Pollution Control Plant which discharges to the sea, has set an effluent requirement for lead of 0.1 mg dm" [9]. They propose to raise tliis, however, to 0.4 mg dm", based on a 50 1 dilution at the ocean outfall not previously allowed for. 

The standards applied to lead in industrial effluent depend upon whether the effluent is discharged directly to a surface water or indirectly via a sewage treatment works (Table 6.2). The use of municipal treatment plants to treat industrial effluent is favoured in Britain and elsewhere. Treatment of the mixed and diluted wastes that result can prove highly effective (Section 6.4.2). Furthermore, it is administratively easier to maintain control of polluting discharges if they are routed via one control plant. 

Elevated levels of lead in water arise principally from industrial discharges, highway runoff and weathering processes in areas of natural lead mineralization. Once the lead has entered a water body its mobility and distribution will be closely controlled by its chemical forms. These will alter according to the nature of the particular water body. 

The physico-chemical forms in which lead is found in water will exert a powerful control on its dispersal from the point of discharge, as well as on its subsequent mobility and ultimate distribution in different receiving waters. The form of the lead prior to its discharge will also play a part in estabHshing the effectiveness of particular effluent control strategies (Chapter 6). Once in the receiving water the toxic effects of the lead to aquatic life will be intimately related to the chemical form(s). However, despite its importance, the chemistry of lead in... 

The system developed by the Anglian Water Authority illustrates a partial application of this flexible approach to control (Fig. 6.2) [7]. Water quality objectives are set for each section of river based on the lowest relevant water quality criterion, derived in this case from a survey of the scientific literature. Local emission standards ( consents to discharge ) are then set to ensure that concentrations remain within the water quality objectives, taking into account the needs of the whole river system. In order to do this, use is made of a mass balance equation. Dilution by the receiving water is based on the mean flow in the river over the lowest flow 7 day period in 1973, a moderately dry year. In this rather simplistic application, no attempt is made to allow for transformations, losses etc. of lead in the receiving water. 

Heavy metal-laden effluents arise from mine drainage water, surface drainage and mill process waters. The most common treatment method is to discharge the wastes to a tailings pond in which the pH is controlled within the range 9.5 to 10.5. A minimum retention of 5 days is recommended with a pond of 4 to 11 ha for each 1000 tonnes of solids discharged per day [20]. A well controlled tailings pond can achieve effluent lead concentrations of 0.1 mg dm . ... 

The Federal Water Pollution Control Act and the Clean Water Act (CWA) of 1972, with 1977 and 1987 Amendments, collectively addressed water pollution as it impacts both groundwater and surface water quality and discharge permits. Section 304(a)(1) of the CWA as amended in 1977 required EPA to publish criteria for water quality reflecting the best scientific knowledge of the effects of water pollutants on health and welfare. Section 307(a)(1) of the amended CWA lists 65 toxic water pollutants for which EPA must publish criteria documents. Under the act, the Natural Resources Defense Council sued EPA to produce the documents, and a number of water quality criteria documents have been published, including criteria for lead. 

At a large-scale spill, most likely as a result of a transportation accident, local authorities and fire department should be notified immediately. People in the area should be evacuated. Action, whenever possible, should be taken to stop the methanol discharge and to isolate the damaged container Ifom the rest. Rescuers should stay upwind and use water spray to knock down the vapor and disperse the liquid. Local health and pollution control agencies should be notified, and the potential of methanol drainage to surface or underground water that may lead to the contamination of drinking water should be evaluated and monitored if needed. 

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