ISDS 



septic systems clearly presented a major potential source of groundwater pollution, and that 

 current design practices, including well separation distances, might be inadequate to protect 

 public health. 



Tomson et al. (1984) presented specific findings regarding trace level organics: a) many 

 tank effluents contain more than 100 trace level organics largely attributable to household 

 products; b) ten percent of trace level organic loadings by volume may be deteaed up to 

 200 feet from the leach field in sandy soils; c) Trace level organics may travel only a few 

 feet in heavy clay soils; d) five classes of trace level organics account for most of the 

 persistent organics. (According to McKay et al. (1985), these contaminants are likely to 

 persist indefinitely once they have entered groundwater.) 



In view of these findings, Tomson et al. (1984) recommended that trace level organics 

 be specifically considered in tank siting studies and permitting, that soil type be given strict 

 consideration in siting, and that a rapid lab soil screening technique (such as that currentiy 

 being developed at Rice University) be used to assess the potential for migration of 

 organics and pathogens from tanks and leachfields. 



Microbial Contamination Attributable to ISDS Effluent Leachate 



Improperly treated ISDS effluent can create significant health hazards if bacteria, viruses 

 and other pathogens, which may be present in effluent, contaminate groundwaters, 

 saturated surface soils, or other receiving waters. Research indicates that bacteria and 

 viruses are capable of travelling considerable distances, and that transport may be 

 particularly rapid in highly permeable soils. Heufelder (1988) prepared an extensive 

 review of many pertinent issues relating to entrainment of non-point source-related 

 pathogens in groundwater, transport of groundwater-entrained organisms to estuarine 

 areas, and survival of viruses in marine systems. A review of the scientific Uterature on 

 microbial contamination of soils and groundwater by ISDS was prepared for the ISDS 

 Task Force by J. F. Musseknan. Selected material from these reviews is briefly 

 simimarized here. 



The Task Force review indicates that the character of the unsaturated soil zone beneath 

 the ISDS is critical in determining transport and fate of bacterial and viral pathogens, 

 particularly where groundwater is near the base of the system. A review by Gerba (1985), 

 presented to the Task Force, identified eight factors as influencing die movement of viruses 

 and bacteria in soils: rainfall, pH, soil composition, flow rate, soluble organics content, 

 cations, adsorption characteristics of the viruses and bacteria, and degree of saturation. 



Viruses have been found to travel as many as 408 meters horizontally in groundwater 

 from sewage infiltration basins (Keswick and Gerba, 1980), while coliform bacteria have 

 been observed to be transported more than one kilometer in loamy sand aquifers, and 

 several kilometers in karstic aquifers. Soil saturation has been identified as a key factor in 

 transport of viruses by a number of authors. 



Heufelder (1988) cited a literature review by Hagedom (1984) which indicated recorded 

 entrainment of various enteric organisms for distances of 0.6 to 830 m (2 to 2723 ft) and 

 survival times of up to 27 weeks. Hagedom stated that soil type was the major factor 

 affecting the entrainment distance of enteric organisms. Gerba and Bitton (1984) in 

 Heufelder (1988) cite moisture content, moisture holding capacity, temperature, pH, 

 organic matter content, and competition/antagonism from soil flora as key factors in 



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