Environmental Enlightenment #191
By Ami Adini - Re-issued June 25, 2016

This is a SHORT, LIGHT and SIMPLE newsletter. Its purpose is to rekindle in the initiated terminology they have once learned, and enlighten the uninitiated on terms they may have heard but never known the meaning of.

Septic Tanks

In the study of potentials for contamination of soil and groundwater, we pay attention to septic tank systems.

Septic means putrefaction. A thing that causes putrefaction is septic.
(The word derives from Greek septikos which means putrefaction.)

Putrefaction is the decomposition of organic matter.
(The word derives from Latin putrere to be rotten + facere to make.)

A septic tank is a tank where solid matter within continuously flowing sewage is putrefied by bacteria.
Here is an illustration of a septic tank system. The two main parts are the tank and drain field.

(Illustration courtesy of the United States Environmental Protection Agency)

And here’s a cross-sectional view of a typical septic tank:

(Illustration courtesy of the Maryland Department of the Environment)

Inside the tank, wastewater separates into layers. Bacteria begin to digest the solids that have settled to the bottom of the tank and break them up into liquids and gases. The liquids rise to the outflow pipe and enter the drainfield

The next schematic shows the drainfield:

(Illustration courtesy of the United States Environmental Protection Agency)

Through the perforated pipes, the liquids percolate into the soil. The soil absorbs and filters the liquids, and microbes break down the leftover waste into innocuous material. Solids that are not digested by bacteria accumulate in the tank and must be removed periodically.

Sometimes, a seepage pit (dry well) serves instead of a drain field.

(Illustration courtesy of the United States Environmental Protection Agency)

Septic systems were the order of the day years ago, before the widespread installation of public-owned sewage mains. To this day, septic systems are widely used in areas where public-owned sewage systems have not arrived.

Where septic tanks are or were in use, chemicals dumped into toilet bowls and wash sinks would ultimately reach the soils and could percolate to groundwater.

(Illustration courtesy of the United States Environmental Protection Agency)

Septic tanks mostly receive domestic wastewater, which contains hazardous chemicals found in household products.

Some of the toxic chemicals found in household products are

  • acetone (cleaners, nail polish remover),
  • benzene (spot remover, solvent in paints and varnishes, weed killer),
  • 2-butoxyethanol (glass and oven cleaners),
  • ethanol (adhesive, detergent, disinfectant, tub and tile cleaner),
  • limonene (solvent, cleaner and degreaser),
  • methylene chloride (paint stripper, auto parts cleaner),
  • naphthalene (moth balls, gasoline additives),
  • pesticides (lawn care), and
  • perchloroethylene (adhesive, carpet spotter, metal cleaner, degreaser).


Residual amounts of these products were regularly dumped in sewers under the “down the drain” philosophy prevalent before environmental regulations were in effect.

According to the EPA’s On-Site Wastewater Treatment System (septic tank) Manual dated February 2002, toxic chemicals most prevalent in domestic wastewater are 1,4‑dichlorobenzene, toluene, xylenes, 1,1‑dicholoethane, 1,1,1‑trichloroethane, and acetone. The EPA indicated that these chemicals are found in household solvents and cleaners. 

In December 2002, the California Wastewater Training and Research Center at California State University, Chico, published Survey of Septage, Treatment, Handling and Disposal Practices in California, which stated that small amounts of polluting substances normal to household activity are present in domestic septage.

In March 2003, the EPA published Voluntary National Guidelines for Management of Onsite and Clustered (Decentralized) Wastewater Treatment Systems. They stated that such systems are used in 25% of U.S. homes and 33% of new development, are often not properly maintained, and are seldom subject to homeowner accountability standards.

In investigations of environmentally related risks in real estate transactions, we at times sniff evidence for historic or current septic tank systems. We then indicate a potential risk for contamination of subsurface soils and groundwater.


Materials for this newsletter were borrowed from the following sources:

You can find past issues of our "Environmental Enlightenment" at amiadini.com Wealth of information about environmental site assessments in the real estate transactions and issues concerning assessment and cleanup of contamination in the subsurface soil and groundwater.

Call me if you have any questions. There are no obligations.

Ami Adini Environmental Services, Inc.
Environmental Consultants & General Engineering Contractors
California Lic. #1009513 A B HAZ ASB
818-824-8102; mail@amiadini.com

Ami Adini is a veteran environmental practitioner with over 40 years of experience. He carries a Bachelor of Science degree (B.Sc.) in Mechanical Engineering including academic credits in Nuclear and Chemical Engineering and postgraduate education in these fields. His career includes design and construction of nuclear plant facilities, chemical processing plants and hazardous wastewater treatment systems. He is a former California Registered Environmental Assessor Levels I & II in the 1988-2012 registry that certified environmental professionals in the assessment and remediation of environmentally impacted land, and a Registered Environmental Professional (REP) since 1989 with the National Registry of Environmental Professionals (NREP). He is a California Business & Professions Code Qualifying Responsible Managing Officer (RMO) in the General Engineering Contractor classification with Hazardous Substance Removal and Asbestos certifications, and president of AMI ADINI ENVIRONMENTAL SERVICES, INC. (AAES), a general engineering contractor and consulting firm specializing in environmental site assessments, rehabilitation of contaminated sites and removal of environmental risks from real-estate transactions. (Contact Ami for a complete resume.) AAES provides practical solutions to environmental concerns using the highest standards of ethics and integrity while providing its clients with maximum return on their investments.