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• What Determines the Effectiveness & Life of Septic Drainfields and Septic System Wastewater Treatment Levels for Residential Septic Waste Treatment
• What portion of septic wastewater is treated in the septic tank or drain field?

This chapter 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.

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.]

Technical review by industry experts has been performed and is ongoing - reviewers welcomed and are listed at "References." This document is a chapter of Inspecting, Testing, & Maintaining Residential Septic Systems an online book on septic systems.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

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

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
• 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.
• 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 Planting Over Septic System Components.

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WASTEWATER TREATMENT BASICS
  The Basics of Septic Waste Treatment
  Five Wastewater Treatment Tasks
  Five Wastewater Treatment Processes
  Percentages of Wastewater Treatment Achieved
  Septic tank treatment of wastewater
  Drainfield treatment of wastewater
  Drainfield Effectiveness
  Septic bacteria contamination levels

• Advanced Onsite Wastewater Systems Technologies, Anish R. Jantrania, Mark A. Gross, Taylor & Francis 2006. Wastewater treatment levels are given for various system designs including conventional septic systems [this text p. 9] This text can be purchased directly online by clicking on the Septic Systems category in our InspectAPedia Bookstore
• Onsite Wastewater Treatment Systems, Bennette D. Burks, Mary Margaret Minnis, Hogarth House 1994. This text can be purchased directly online by clicking on the Septic Systems category in our InspectAPedia Bookstore

SEPTIC SYSTEMS HOME
SEPTIC INFO ARTICLES
HOME BUYERS GUIDE to SEPTIC SYSTEMS
SEPTIC INSPECT & TEST
SEPTIC SYSTEMS ONLINE BOOK
SEPTIC SYSTEM SAFETY WARNINGS
SEPTIC SYSTEM DESIGN BASICS
SEPTIC DESIGN ALTERNATIVES
SEPTIC INSPECTIONS
SEPTIC SYSTEM DEFINITIONS
SEPTIC FAILURE LAWSUIT
SEPTIC REFERENCES
SEPTIC CONSULTANTS
SEPTIC AUTHORITIES
SEPTIC SYSTEM BOOKS REFS CODES

More Information on Building Diagnostic Inspections and Repairs

More Reading about septic system function and onsite wastewater treatment:
Biomats: Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
Buyers' Guide: Home Buyer's Detailed Guide to Septic Systems - Buying a Home With a Septic Tank
Components of a Septic System- the Basic Parts of a Conventional Septic Tank and Leachfield, a chapter in the Home Buyers Guide to Septic Systems
SEPTIC SYSTEM DESIGN ALTERNATIVES: Advanced Onsite Wastewater Disposal Designs for Septic Systems - design engineers, consultants, products, books for special problem situations, difficult soils, old system repairs. Aerobic septic systems, chemical, composting, incinerating & waterless toilets, Evaporation-Transpiration (ET) Septic Systems, septic media filters, greywater systems, holding tank septic systems, mound septics, raised bed septics, pressure dosing septic systems, sand bed filters, peat beds, constructed wetlands, septic disinfection systems.
Retention Time & Net Free Area and effective septic tank working volume are discussed at "retention time" in our septic tank pumping guide.
Safety Septic System, Septic Tank, & Cesspool Safety Warnings for Septic Inspectors, Septic Pumpers, and Homeowners.
Sketches of the Septic System Components Private Sewage Disposal Systems - Septic Drawing Library
What is a Septic System An Engineer's View - Types of treatment tanks, adsorption systems, pumps, and other special equipment are discussed in some further detail in this text
Reference sources for this web page:
Onsite Wastewater Treatment Systems, Bennette D. Burks, Mary Margaret Minnis, Hogarth House 1994 - one of the best books around, small font, weak index
Anish Jantrania, Ph.D., P.E., M.B.A., Consulting Engineer, Mechanicsville VA, 804-550-0389 new (2006) book, Advanced Onsite Wastewater Systems Technologies can be ordered from his publisher. Outstanding technical reference especially on alternative septic system design alternatives, written for designers and engineers.
Septic System Owner's Manual, Lloyd Kahn, Blair Allen, Julie Jones, Shelter Publications, 2000 $14.95 U.S. - easy to understand, well illustrated, one of the best practical references around on septic design basics including some advanced systems; a little short on safety and maintenance. Buy this book here

Septic Systems Online Book

Basic references on septic systems

• The Septic System Information Website home page for this topic
• Septic Systems Inspection, Testing, & Maintenance- online textbook. Detailed how to inspect, maintain, repair information
• The Home Buyer's Guide to Septic Systems
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• Home & Outdoor Living Water Requirements
• Septic Tank Capacity vs Usage in Daily Gallons of Wastewater Flow, calculating required septic tank size, calculating septic tank volume from size measurements
• How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
• Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
• Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.

Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include

• Pennsylvania State Wastewater Treatment Fact Sheet SW-161, Septic System Failure: Diagnosis and Treatment
• Pennsylvania State Wastewater Treatment Fact Sheet SW-162, The Soil Media and the Percolation Test
• Pennsylvania State Wastewater Treatment Fact Sheet SW-l64, Mound Systems for Wastewater Treatment
• Pennsylvania State Wastewater Treatment Fact Sheet SW-165, Septic Tank-Soil Absorption Systems
• Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)

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