The Basics of Onsite Septic Wastewater Treatment

An explanation of the basics of onsite residential wastewater treatment
What are the jobs of the septic tank and drainfield?
An explanation of the five basic processes in wastewater treatment: mechanical filtration, biological oxidation, disinfection, waster disposal, and byproduct or solid waste disposal
What portion of septic wastewater is treated in the septic tank or drain field?
Questions & Answers about residential onsite wastewater or septage or sewage treatment
References

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Wastewater treatment: this article explains the 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."

The Basics of Onsite Wastewater Treatment

Onsite Wastewater Treatment Systems - Burks & Minnis

This article is a supplement to the introduction (SEPTIC SYSTEM BASICS) to our online book SEPTIC INSPECTION & TEST GUIDE whose chapters are shown at the left of this page. Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical review by industry experts has been performed and is ongoing - reviewers welcomed and are listed at the end of each article.

Our photograph at page top shows a private septic system which demonstrated failure even before we began our septic loading and dye test. A too-small septic tank installed at the top of a steep hill emptied into a too-small gravel pit buried in less than 36" of soil which in turn sat upon solid rock at the top of this steep site.

Effluent could be seen running down the face of nearby rocks whenever the septic system was in use. In the upper portion of the photo (above at page top) you can see a overflow pipe protruding from the septic tank itself, and also hay which the owner or contractor had piled atop of this system in anticipation that we would not notice its unfortunate condition.

Of course by simply taking a few steps down the hillside and looking up, these regrettable conditions were quite visible. Effluent simply ran down the hillside and into a nearby stream.

The Basics of Wastewater Treatment in a Private Septic System

"Treatment" of wastewater (sewage that flows out of building toilets, sinks, showers) means making sure that the wastewater released to the environment is acceptably clean. In a most-conventional private home septic system, this is about what happens:

House Toilet to Septic Tank: Waste flows from building toilets (and sinks, showers, etc.) through building drains, usually by gravity, out to a septic tank, buried in the ground, often close (10 ft.) to the house. The job of the septic tank is to retain solid waste, oils, and grease in the tank, and to perform limited (perhaps 45%) treatment of the sewage by bacterial and other microbial action which digest organic waste and pathogens. Periodically the solid sludge from the tank bottom and floating scum from the tank top must be removed by a septic pumping contractor.
Septic Tank to Drainfield: Liquid from the septic tank (clarified effluent) flows out of the septic tank and into the drainfield - a network of perforated pipes buried in the ground, often in gravel-filled trenches, perhaps 12" to 24" below ground level. In the drainfield, also called leach field, seepage bed, or soil absorption system, the effluent seeps out of perforations in the pipes, through gravel in the trench, and into the soils below the trench system.

Suspended solids (tiny bits of floating sewage debris) which escaped the septic tank by flowing in the effluent, are filtered by the soils of the drainfield and captured there.
Drainfield to Nature: a biomat of bacteria and other microorganisms grows naturally in the soil below and around the drainfield. These microorganisms further digest or break down both the captured suspended solids filtered by the soil, and other pathogens and organics and nitrites and nitrates which are present in the septic effluent. As effluent passes through and is processed by this biomat, it is eventually released to local soils where it joins ground water already present in the area (disposal).

For difficult home sites where there is limited space, rocky ground, or wet soils, a variety of "advanced" wastewater treatment systems are available to successfully handle the process I've just described.

What follows this very very basic description of onsite wastewater treatment is simply the same scenario just described, but with the introduction of the terms which septic designers and other experts use to describe various alternative methods of treatment of wastewater.

All of these systems have the same objective: when septic effluent is finally released to the environment it must be as clean or cleaner than the natural groundwater which is already there, and must be clean enough so as not to be a health hazard or harmful to the environment.

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
  Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
  Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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  Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
  Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
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 SYSTEM INSPECT DIAGNOSE REPAIR 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 SYSTEM INSPECT DIAGNOSE REPAIR category in our InspectAPedia Bookstore

Also see these Septic System Inspection & Testing articles

Abandoned or New Septic System inspection & testing suggestions
Baffles, Septic Tank septic tank baffles defects and inspection suggestions
Buyer's Guide Home Buyer's Guide to Septic Systems Inspection & Testing - What to Do, Step by Step.
Cesspools Home Buyer's or Owner's Advice
Cesspool Age Estimates help evaluate cesspool condition and need for repair or replacement
Cesspool Safety Warnings include dangers of cave-in and fatality
Clearances & Distances from septic system components to other site features, property boundaries, waterways, etc.
Don't Pump Before Testing Septic Systems: warnings for home buyers about septic tank pumping
Drainfield Inspection Procedure Septic Leach Fields - how to inspect and diagnose septic drainfield failures
DRYWELL DESIGN & USES Home Buyer's or Owner's Advice
Dye Amounts, Water Volume: how much septic dye and how much water to use to perform a septic dye test
Dye Tests: how to perform a Septic Loading and Dye Test - the complete procedure for septic loading & dye testing, a septic function test
Failure Causes - Septic Systems Basic Septic Inspection Procedures: for septic tanks, septic drainfields, cesspools, drywells, distribution piping
Failure Causes - Septic Tanks - How to Inspect Septic Tanks and evaluate the septic tank condition, baffles, sludge levels, damage, evidence of septic failure, etc.
Failure Causes - Septic Drainfields: how to inspect septic leach fields & what causes septic field failure
SEPTIC FAILURE SPOTS - Where septic system trouble is likely to show up regardless of septic dye testing
Life Expectancy of Septic Systems and septic system components
Media Filter Septic Systems types of alternative septic systems using sand, peat, textile, foam cube or other filter media, single pass vs. recirculating media filters, how to identify them.
Pumps Septic pumps, sewage ejector pumps, grinder pumps, effluent pumps, sump pumps, & septic pumping stations compared; pump alarms. Advice.
Septic & Cesspool Safety - septic system, septic tank, & cesspool safety warnings for septic inspectors, septic pumpers, and homeowners.
Septic D-BOX Inspection provides for help in finding and inspecting the septic system drainfield distribution box
SEPTIC or SEWER CONNECTION? - how to determine if a building is connected to a septic tank or to a public sewer line
Septic Site Inspection Procedure - Simple Outside Visual Site Inspection Gives Key Information About Septic System Condition
Septic Sludge & Scum Levels in Septic Tanks - Measuring the Level of Accumulated Solids, Sludge and Floating Scum in Treatment Tanks
Septic Tank Inspection Procedure - How to Inspect Septic Tanks and evaluate the septic tank condition, baffles, sludge levels, damage, evidence of septic failure, etc.
Septic Tank Location - How to Find the Septic Tank, how deep will the cover be, how to document its location
Soil Percolation Tests Perc Tests or Deep Hole Test for Soil Absorption Rate Testing
SPOTTING SEPTIC BREAKOUTS - Spotting Dyed Septic Effluent Breakout Outside - Where Septic Dye is Likely to Show Up During a Septic Dye

Septic System References & Books

"International Private Sewage Disposal Code," 1995, BOCA-708-799-2300, ICBO-310-699-0541, SBCCI 205-591-1853, available from those code associations.
"Manual of Policy, Procedures, and Guidelines for Onsite Sewage Systems," Ontario Reg. 374/81, Part VII of the Environmental Protection Act (Canada), ISBN 0-7743-7303-2, Ministry of the Environment,135 St. Clair Ave. West, Toronto Ontario M4V 1P5 Canada $24. CDN.
Manual of Septic Tank Practice, US Public Health Service's 1959
The Home Buyer's Guide to Septic Systems
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
Septic Tank/Soil-Absorption Systems: How to Operate & Maintain [ copy on file as /septic/Septic_Operation_USDA.pdf ] - , Equipment Tips, U.S. Department of Agriculture, 8271 1302, 7100 Engineering, 2300 Recreation, September 1982, web search 08/28/2010, original source: http://www.fs.fed.us/t-d/pubs/pdfimage/82711302.pdf.
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
Septic Tank Pumping Guide: When, Why, How to pump the septic tank
Table of Required Septic & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc.
Ten Steps to Keeping a Septic System Working, suggestions from the U.S. EPA, edits and additions by DJF
What is a Septic System An Engineer's View & Septic System FAQ's
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.)

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Inspecting Septic Systems: Online Book, Inspection, Test, Diagnosis, Repair, & Maintenance: our Online Septic Book: Septic Testing, Loading & Dye Tests, Septic Tank Pumping, Clearances, details of onsite waste disposal system inspection, testing, repair procedures.

Advanced Onsite Wastewater Systems Technologies, Anish R. Jantrania, Mark A. Gross. Anish Jantrania, Ph.D., P.E., M.B.A., is a Consulting Engineer, in Mechanicsville VA, 804-550-0389 (2006), Advanced Onsite Wastewater Systems Technologies. Outstanding technical reference especially on alternative septic system design alternatives. Written for designers and engineers, this book is not at all easy going for homeowners but is a text we recommend for professionals--DF. I>
Builder's Guide to Wells and Septic Systems, Woodson, R. Dodge: $ 24.95; MCGRAW HILL B; TP; Quoting from Amazon's description: For the homebuilder, one mistake in estimating or installing wells and septic systems can cost thousands of dollars. This comprehensive guide filled with case studies can prevent that. Master plumber R. Dodge Woodson packs this reader-friendly guide with guidance and information, including details on new techniques and materials that can economize and expedite jobs and advice on how to avoid mistakes in both estimating and construction. Chapters cover virtually every aspect of wells and septic systems, including on-site evaluations; site limitations; bidding; soil studies, septic designs, and code-related issues; drilled and dug wells, gravel and pipe, chamber-type, and gravity septic systems; pump stations; common problems with well installation; and remedies for poor septic situations. Woodson also discusses ways to increase profits by avoiding cost overruns.
Country Plumbing: Living with a Septic System, Hartigan, Gerry: $ 9.95; ALAN C HOOD & TP; Quoting an Amazon reviewer's comment, with which we agree--DF:This book is informative as far as it goes and might be most useful for someone with an older system. But it was written in the early 1980s. A lot has changed since then. In particular, the book doesn't cover any of the newer systems that are used more and more nowadays in some parts of the country -- sand mounds, aeration systems, lagoons, etc.


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