2.1  On-Site Waste Disposal Systems

     Most on-site waste disposal systems consist of a septic tank

followed by a subsurface soil absorption system.      Results vary

relative to the treatment efficiency of wastewater by septic tanks.

Lawrence (1973) reported Suspended Solid removals of 35 to 45%, and

BOD removals of 15% or less. However, Viraraghaven (1976) reported

Total Suspended Solids removal of 25% with BOD and COD removals on

the order of 50%.    Typical effluent concentrations from septic

tanks for Suspended Solids, BOD, COD, Total Nitrogen and Total

Phosphorous are 75 mg/l, 140 mg/l, 300 mg/l, 40 mg/l, and 15 mg/l

respectively (Canter and Knox, 1986).

     The quantities of indicator bacteria such as fecal coliform,

whose presence suggests that other enteric organisms are also

possibly present, are usually high in septic tank effluent with

pathogenic bacteria such as Pseudomonas aerucinosa commonly being

isolated. When infections have occurred, viruses are also found in

septic tank effluent in high concentrations (Canter and Knox,

1986).   Because of the limited wastewater treatment provided by

septic tanks, their effluent must be purified further prior to

release to either surface of groundwater.    The primary mechanism

for providing this treatment is through on-site soil absorption

     Soil Absorption Systems are essential components of septic

systems.   Soil Absorption Systems, which may be trenches, beds,

pits or mounds, hydraulically receive septic tank effluent and