On a yearly basis this would translate to about 38 lb N per septic system. However most ammonia converted to nitrate is leached. Properly functioning septic systems may degrade water quality because nitrate is formed in the treatment process. Septic systems by design are expected to add some nitrogen to ground water. It is expected that the ground water will accept and dilute a small amount of nitrogen.
Local ordinances control the site of septic systems relative to wells and by soil types.
Septic tanks and waterborne disease. The number of septic systems within a given region is by far the most important factor controlling their potential to pollute ground water. The first 10 or 100 septic systems in a given area may have little effect. Septic tank effluent may be the most significant source of pathogenic bacteria and viruses in the subsurface environment. Another source of microorganisms to the subsurface is municipal sludge.