Factors that Determine the Wastewater Treatment Effectiveness & Life of a Septic Drainfield or Soakbed

How well do drainfields treat septic effluent how long do septic drainfields last?

This article focuses on how the septic drainfield treats residential wastewater, lists factors which determine the effectiveness of a septic leach field in treating septic effluent, and explains life expectancy and basics of onsite wastewater treatment processes - an explanation of the basics.

What Factors Determine Drainfield Effectiveness in Treating Septic Wastewater or Effluent?

Wastewater treatment is "The process of removing pollutants and pathogens from wastewater, discharging the water to the environment where it is recycled, and disposing of the byproducts of the treatment process." [Onsite Wastewater Treatment Systems, Burks & Minnis, cited below.]

The treatment of wastewater achieved by soils in a properly working and properly designed drainfield (for example at proper flow rate, soil characteristics, total area and treatment time, and proper depth to achieve both aerobic and anaerobic processes) can achieve onsite treatment level 2 (OTL-2).

While texts commonly cite soil depth to limiting conditions (such as bedrock or impermeable clay) and soil percolation rate (water flow rate through the soil), I add these additional practical considerations that are also determining influences on the ability of a drainfield to treat wastewater to make the following list:

• Septic Drainfield size 
  
  in relation to total wastewater load - the total square feet of area available (and presuming that piping is properly installed parallel to slope lines etc.)
  
  See Septic Systems - Design, ... for a discussion of how to determine the necessary septic field size.
• Extraneous Drainfield Water Loads:
  
  Septic Drainfield exposure to additional water saturation from groundwater, surface, or building runoff
  
  See FLOODED SEPTIC SYSTEMS, REPAIR
• Drainfield Piping:
  
  Condition of drainfield piping: tipped D-boxes, broken connections, clogs forcing effluent into only a portion of the system
• Soil percolation rate or soil porosity,
  
   influenced by both starting soil conditions and age of the drainfield as it may become clogged by grease, solids, or salts which have escaped the septic tank.
  
  See Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs.
• Soil depth to limiting conditions
  
   such as bedrock, impermeable clay, etc, and soil depths which may limit the presence of aerobic bacteria (this is why cesspools probably do not treat effluent - only anaerobic bacteria are likely to be active at the soil depths equal to the typical bottom depth of a cesspool.)
• Drainfield loading rate:
  
  how often and in what quantities does wastewater arrive at the drainfield - how much time does it have to process effluent. This factor is in essence a re-statement of the percolation rate factor to add consideration of the level of usage of the system.
• Drainfield loading effluent management:
  
  [added by df]: how much solid waste of what size is carried into the soakbed or drainfield? A broken septic tank outlet baffle, missing septic tank tee, or failure to pump the septic tank often enough to give adequate EFFLUENT RETENTION TIME, as well as mis-applications of septic tank additives can all result in passage of solids into the septic soakbed or drainfield. The result is rapid soakbed clogging and reduced septic system life.
• Soil compaction:
  
  the extent to which drainfield soils have been compacted by vehicle or other traffic.
  
  See Causes of Septic System Drainfield Failure
• Plantings over septic fields: 
  
  the extent to which certain plants have been installed or permitted to grow over a drainfield can affect its ability to dispose of water by evaporation, or the extent of root clogging.
  
  See SEPTIC SYSTEMS, PLANTS OVER

...

Continue reading  at SEPTIC BACTERIA CONTAMINATION LEVEL or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• SEPTIC INSPECTION & TEST GUIDE
• SEPTIC SYSTEM BASICS)
• WASTEWATER TREATMENT BASICS
  • FIVE WASTEWATER TREATMENT TASKS
  • FIVE WASTESATER TREATMENT PROCESSES
  • PERCENTAGES of WASTEWATER TREATMENT ACHIEVED
  • SEPTIC TANK TREATMENT of WASTEWATER
  • DRAINFIELD TREATMENT of WASTEWATER
  • DRAINFIELD TREATMENT EFFECTIVENESS
  • SEPTIC BACTERIA CONTAMINATION LEVEL

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