Chemical Contamination : Substances are periodically added to cooling 

 water as it passes through the plant to reduce scaling, corrosion, and 

 the growth of fouling organisms. The antifouling chemicals are often 

 extremely toxic to aquatic organisms in the receiving waters. Typical 

 chemical concentrations of the cooling waters of refineries and gas 

 processing plants are [7]: 



Chemical Concentration Maintained 



Sulfuric Acid Variable* 



Chromate 30.0 ppm (5-20)* 



Zinc 3.0 ppm (1-4)* 



Chlorine 0.1 - 0.2 ppm 



* to maintain a pH of approximately 7.0 



Concentrations of these substances can be lowered by treatment, e.g. 

 chrome reduction and precipitation using ferrous sulfate in a reducing 

 pit. The residuals produced from this process, like other hazardous 

 wastes, are disposed of in a landfill site. However, chemicals should be 

 used sparingly in treating the cooling water and should be replaced where 

 possible by mechanical or thermal systems of cleaning. 



In refineries, oil and oil products can leak into the cooling water 

 system and contaminate the cooling water. Cooling water, although 

 considered to be "not oily", actually comes in contact with oil due to 

 leaks in heat exchangers. When the leaks are severe, oil concentrations 

 may be so high that the cooling water stream must be treated for oil 

 removal prior to discharge. 



4.16 MOSQUITO CONTROL - SUBPROJECT 16 



The demand for mosquito control is much greater in areas of oil 

 and gas induced development rather than from OCS-related facilities. 

 General control methods, such as pesticide application, have a high 

 potential for disturbance of marsh habitats. When carefully planned, 

 effective control can be achieved through water management. 



4.16.1 Summary 



Pest control refers particularly to the control of mosquitoes, the 

 most widespread and most noticed of the nuisance species along the coast. 

 With respect to OCS primary development, mosquito control efforts are 

 limited usually to temporary spraying during severe infestations at the 

 time of construction. Control of biting flies, rodents and other pests 

 is usually in response to localized eruptions. Mosquito control is 

 primarily a function of the secondary development that can accompany OCS 

 facilities. Industrial and housing development in coastal shorelands brings 



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