4.10.6 Septic Tanks 



If the necessary water and soil requirements can be met in the coastal 

 zone, and if septic systems are properly maintained and operated within 

 their physical capacities, they should be adequate for their purposes and 

 central sewage systems will not be needed. 



There are three major ecological issues relating to septic tanks in 

 coastal areas: (1) wastes leached into coastal waters when septic tanks 

 are located too close to the shore; (2) tidally induced high water tables 

 that provide direct and rapid flushing of drain fields into coastal waters; 

 and (3) inadequate drain field components or soil absorption characteristics 

 that cause tanks to overflow, particularly during rainstorms, and 

 pollute coastal waters. The solution to these problems lies in proper 

 location of septic tanks in relation to water. 



Health officials aggressively promote central sewage systems as the 

 inevitable and proper alternative to septic tanks. From an ecological 

 viewpoint, however, septic tanks may be quite acceptable if properly 

 built and operated. However, poorly designed septic tank systems leach 

 chemical contaminants to groundwater and thence to surface waters. 



A septic system is a microcosm of a land sewage treatment system. 

 Wastewater from one or several homes flows into a concrete septic tank, 

 where the solids settle to the bottom to be decomposed by bacteria into 

 organic matter (Figure 35). Nutrients are released during this partial 

 solids digestion and flow into drainage areas through subsurface tiles 

 to percolate through ground for removal. The nutrients are often taken 

 up locally by trees and shrubs, or are adsorbed to soil particle surfaces. 

 The drainage field functions to provide final purification within the 

 soil. If the distance between the septic system and surface waters is 

 insufficient, the liquid waste leaching through the soil is inadequately 

 treated. Consequently, it reaches the water basin in contaminated 

 condition, injecting a variety of substances, the most troublesome of 

 which are nutrients, particularly nitrogen compounds. Periodically the 

 resulting sludge in the bottom of the tank must be removed and disposed of. 



How well a septic tank sewage disposal system works depends largely 

 on such factors as soil permeability, groundwater level, stratigraphy, 

 the distribution of soil types, and slope [103]. Because shoreline soils 

 typically have poor percolation and drainage characteristics and shallow 

 water tables, often less than 5 feet [104], soils in shoreline areas 

 typically impose severe septic tank limitations. 



Nitrate is particularly troublesome, as it is extremely soluble and 

 mobile in groundwater. There is no national standard for the amount of 

 nitrate (or phosphate) allowed in coastal waters. But one may presume 

 a concentration higher than 0.2-0.5 ppm to be potentially adverse. The 

 storage and biological recycling of nitrate is a complex matter and the 

 selection of a fixed numerical value is elusive. 



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