After leaving the plant, the heated water may adversely affect 

 the natural patterns of life and behavior of aquatic species. This is 

 often called "thermal pollution". How pervasive and damaging this pollu- 

 tion may be depends upon the characteristics of the discharge (e.g., 

 temperature, volume) and the size and flushing characteristics of the 

 public water basin that receives the effluent. 



Since organisms can be filled by impingement on the cooling water 

 intake screens, by passage through cooling water systems, or by heated 

 effluent, specific requirements are imposed on the volume of cooling 

 water, the temperature of the discharge, and the location and design of 

 the intake and discharge structures. 



Intake structures may impinge on ecologically vital areas (particu- 

 larly in estuaries) and cooling water may draw from or discharge into 

 them. Cooling water should not be withdrawn or discharged into vital areas. 

 Their locations should be known from biological surveys that precede site 

 selection for the plant. 



4.15.2 Intake Design and Operation 



Cooling water systems require close scrutiny, regardless of volume of 

 flow. On the one hand, those with a very low volume demand and need for 

 chemical antifouling treatment may be acceptable without major safeguards. 

 On the other hand, those with a high volume demand or extraordinary require- 

 ment for chemical treatment may be acceptable only with extensive safe- 

 guards such as closed-cycle cooling or mechanical cleaning. 



Power plants have such extraordinarily high demands for cooling 

 water — one million gallons per minute is not uncommon — that they must be 

 reduced by requiring closed-cycle systems, which recirculate cooling 

 waters, rather than open-cycle (or "once-through") systems, which 

 continuously withdraw and discharge large volumes of water. Open-cycle 

 systems may be acceptable for sites on the open ocean coast provided that 

 necessary precautions are taken. Normally, closed-cycle cooling should 

 be used for sites on confined estuarine water bodies such as tidal rivers, 

 bays, or lagoons. 



Entrainment, often the major shource of disturbance associated with 

 cooling water taken from surface waters, refers to withdrawal of 

 suspended aquatic life with the cooling water and their exposure to 

 heat, turbulence, abrasion, and shock within the heat exchanger. The 

 effects are especially direct and severe when plants are located in 

 estuarine spawning and nursery areas of finfish and shellfish because 

 their eggs, larvae, and juvenile stages are easily killed. Plankton face 

 the same hazards from passage through an OCS facility, such as a refinery, 

 as they would through a powerplant. 



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