Septic Tank and Drainfields
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This article describes the level of residential septic wastewater treatment that is achieved in the septic tank and drainfield. We explain that in a conventional septic tank and soakbed or drainfield, only about 40% of effluent or sewage treatment occurs in the septic tank while we depend on the soakbed or drainfield for the remainder of treatment as well as effluent disposal.
Other types of onsite wastewater treatment systems such as aerobic systems can achieve much higher levels of treatment in the septic tank but also require additional equipment and maintenance.
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What are the Percentages of Total Wastewater Treatment Achieved by Each Major Septic System Component?
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.] Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted.
By "wastewater treatment" we refer to the removal of the contents of septic systems that would be considered pollutants to groundwater or pollutants to nearby wells, streams, lakes, or other bodies of water. The chief pollutants of concern in septic wastewater are biological organisms (fecal coliform bacteria), and chemical (nitrates and nitrites).
Sewage may contain a wide variety of other pollutants which we elaborate in detail at Residential Septic Tank Sludge and Scum - what pathogens and contaminants do they contain?.
We provide a brief description of different types of septic systems and thus septic treatment systems at Alternative Septic System Designs This article describes the typical wastewater treatment levels achieved by each approach. What follows are the most basic numbers for conventional septic tank and drainfield systems.
Septic tank treatment of wastewater
Typically a conventional septic tank and drainfield is used to treat raw sewage or "blackwater" discharged from a home into an on-site wastewater system. The septic tank itself accomplishes about 45% of the onsite wastewater treatment level to be achieved. [Ref: Jantrania/Gross].
This same treatment level in septic tanks is cited by Burks/Minnis. This achieves what Jantrania/Gross refer to as OTL-1 or the "first level" of wastewater treatment and alone this would be considered insufficient by any septic system expert.
Drainfield treatment of wastewater
The septic system drainfield, also commonly referred to as leach field or leaching bed, accomplishes the remaining 55% of the onsite wastewater treatment level to be achieved. [Op.Cit. & by simple calculation from septic tank treatment levels of 45%.]
This article series is a supplement to the introduction (SEPTIC SYSTEM BASICS) to our online book SEPTIC INSPECTION & TEST GUIDE
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Citations & References
In addition to any citations in the article above, a full list is available on request.
- New York State Department of Health, APPENDIX 75-A WASTEWATER TREATMENT STANDARDS - INDIVIDUAL HOUSEHOLD SYSTEMS , [PDF] New York State Department of Health, 3 February 2010, retrieved 3/1/2010, original source: https://www.health.ny.gov/regulations/nycrr/title_10/part_75/appendix_75-a.htm
- 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). 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 I recommend for professionals--DF.
- 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), 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.
- 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). 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 I recommend for professionals--DF.
- Onsite Wastewater Treatment Systems, Bennette D. Burks, Mary Margaret Minnis, Hogarth House 1994.
- Onsite Wastewater Disposal, R. J. Perkins; Quoting from Amazon: This practical book, co-published with the National Environmental Health Association, describes the step-by-step procedures needed to avoid common pitfalls in septic system technology. Valuable in matching the septic system to the site-specific conditions, this useful book will help you install a reliable system in both suitable and difficult environments. Septic tank installers, planners, state and local regulators, civil and sanitary engineers, consulting engineers, architects, homeowners, academics, and land developers will find this publication valuable.
- Onsite Wastewater Treatment Systems, Bennette D. Burks, Mary Margaret Minnis, Hogarth House 1994 - one of the best septic system books around, suffering a bit from small fonts and a weak index. (DF volunteers to serve as indexer if Burks/Minnis re-publish this very useful volume.) While it contains some material more technical than needed by homeowners, Burks/Minnis book on onsite wastewater treatment systems a very useful reference for both property owners and septic system designers. We refer to it often.
- Septic Tank/Soil-Absorption Systems: How to Operate & Maintain, 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
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.
- US HEW, MANUAL of SEPTIC TANK PRACTICE [PDF] 1975, U.S. Department of Health, Education and Welfare, Public Health Servicve, original source: https://nepis.epa.gov/
- Manual of Septic Tank Practice, US Public Health Service's 1957, reprinted in 1963, 1967, 1969 and in a 1975 edition given just above.
- SEPTIC TANK/SOIL-ABSORPTION SYSTEMS: HOW TO OPERATE & MAINTAIN [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.
- 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.
- In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
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Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The HOME REFERENCE BOOK - the Encyclopedia of Homes and to use illustrations from The ILLUSTRATED HOME .
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