demand (BOD) loading, (4) eutrophication, and (5) release of pesticides, 

 heavy metals, and other toxins. Of these impacts the most insidious is 

 eutrophication. 



Central sewage treatment facilities have the potential for protection 

 of coastal waters if properly designed and operated. If not, they may only 

 accomplish a transfer of major pollution from dispersed sources to a 

 concentrated point source in coastal waters. Most existing sewage systems 

 are in the process of being upgraded to meet the minimum requirements for 

 the protection of coastal ecosystems. 



A proper septic tank system releases effluent into the drainfield 

 with no harmful effects and with all the benefits of simplicity and 

 economy. In low-lying areas with naturally high water tables, however, 

 liquid waste from septic systems may saturate the soil, rise to flow over 

 the surface of the ground and into the coastal waters. This pollution 

 potential is exacerbated in floodprone areas, where high tides and storms 

 periodically supersaturate the soil. These conditions weigh heavily 

 against the use of septic tanks in lowlands and in favor of central 

 sewage systems. 



4.10.2 Siting Considerations 



In coastal regions, wetlands often have been the most easily available 

 area for the location of treatment facilities and the least expensive, even 

 when the problems and costs of filling and general site preparation are 

 considered. In addition, the collection mains (trunk mains) have often 

 been routed through wetlands, where inexpensive land is available and 

 wastewater can flow easily by gravity to the treatment plant. 



The use of wetlands as sites for sewage plants is now generally 

 considered environmentally unacceptable. This may also apply to sewage 

 pipelines. 



Shallow estuaries tend to have poor flushing characteristics so the 

 longer that discharged sewage effluent remains concentrated in a water 

 body, the more pronounced will be it.s effects. Therefore, it is often 

 infeasible to discharge sewage effluent into a local estuarine water body 

 even after treatment. The requirement to discharge in other than an 

 estuarine water body may have important consequences on selecting a sewage 

 plant site. 



An issue open to resolution is whether certain deep bays and sounds 

 should be classified as "oceans" and thus be acceptable receiving waters 

 for secondary effluent. Since secondary treatment does not remove all 

 bacteria and is of very uncertain value in terms of virus removal, 

 outfalls in bays and sounds could endanger fish and wildlife resources 

 and habitats. The decision will depend wholly on local conditions affect- 

 ing dispersal, dilution, and assimilation of pollutants [91]. Disposal 



135 



