ISDS 



determining survival of enteric organisms in subsurface soil systems. Generally, optimum 

 survival conditions occur in moist soils with good moisture-holding capability at low 

 temperatures in more alkaline soils of pH above 5 that are devoid of normal flora 

 (Heufelder, 1988). 



Soil adsorption of viruses is govemed by a range of physical factors, but adsorption 

 does not immobilize these pathogens, which can be re-released after periods of rainfall to 

 migrate further through the soil. Kreissl (1980) postulated that "contact time" in the 

 unsaturated zone of the soil is the most important removal consideration for pathogens. He 

 stated that direct contact of pathogen-containing effluent with groundwater should be 

 considered synonymous with system failure, as such contact frequently results in long- 

 distance transpon of pathogens. 



Heufelder found no extant epidemiological evidence specifically linking ISDS practices 

 with disease outbreaks for adjacent recreational water usage, but pointed to much evidence 

 of outbreaks of gastroenteritis and hepatitis involving consumption of contaminated water 

 (e.g., Gerba et al. 1985). McGinness and DeWalle (1983) describe a case report in which 

 an outbreak of typhus occurred among all members of a family whose private well was 

 located over 400 meters from the ISDS of a neighbor infected with the disease. 



Movement of Nitrogen and Phosphorus from ISDS 



Factors affecting movement of nitrogen from ISDS include degree of soil adsorption, 

 uptake by plants, ammonia volatiUzation, and denitrification. These processes, are not 

 promoted by conventional ISDS design, and subsequent nitrate-N movement has been 

 widely documented. Because background nitrate levels in undeveloped areas are typically 

 under 100 parts per billion, nitrate inputs can induce eutrophication at levels far below 

 those sufficient to represent a public health concern. Nitrate levels in drinking water are 

 regulated by EPA, which has established a 10 mg/1 standard to safeguard infants from 

 methemoglobinemia. 



Nutrient loading due to migration of ISDS effluent has contributed to eutrophication in 

 Rhode Island coastal ponds and estuaries where nitrogen has been identified as the limiting 

 nutrient, as in most coastal waters (Redfield, 1934; Ryther and Dunstan, 1971). In these 

 areas, eutrophication may rcadUy be induced by the cumulative effects of fertilizer and 

 ISDS inputs in addition to those of domestic animals and natural sources, such as rainfall 

 and soil organic matter. Nixon (1982) found ISDS effluent to be a very significant source, 

 contributing an estimated 12 to 44 percent of the annual nitrogen load to the eight south 

 shore coastal ponds. 



A background document on nutrient movement from ISDS prepared by L. Joubert for 

 the ISDS Task Force Final Report (1987) summarized the results of recent scientific 

 findings. Key points are ouUined here: 



Preul (1966) found that nitrate can move finely with percolating effluent to 

 groundwater, posing a "serious threat" in coarse textured soils, with dilution alone acting to 

 reduce concentrations further from the source. Other authors have also concluded that 

 denitrification is extremely limited in many soil conditions, and that nitrates encountering an 

 impervious layer beneath the leachfield move in solution without significant further 

 alteration (Reneau, 1977; Walker et al., 1973). Nitrate can migrate significant distances. 

 Ellis and Childs (1973) documented migration distances of 330 feet. 



45 



