Office of
United States	Ground Water and
Environmental Protection Agency	Drinking Water
What is a large-capacity septic	LCSSs are an on-site method for partially treating and disposing of sanitary wastewater. Only
system (LCSS)?	those septic systems having the capacity to serve 20 or more persons-per-day are included
within the scope of the underground injection control (UIC) regulations. Many conventional
LCSSs consist of a gravity fed, underground septic tank or tanks, an effluent distribution
system and a soil absorption system. LCSSs may also include grease traps, several small
septic tanks, a septic tank draining into a well, connections to one large soil absorption system
or a set of multiple absorption systems that can be used on a rotating basis.
Sanitary wastewater from a wide variety of establishments, including residential (multi-unit
housing) and non-residential (commercial, institutional, and recreational) facilities. The
characteristics of the sanitary wastewater from these establishments vary in terms of biological
loadings and flow (e.g., daily, seasonal). Generally, the fluid is characterized by high
biological oxygen demand and chemical oxygen demand, nitrate, trace metals and other
inorganics, limited trace organics, and biological pathogens.
Available sampling data indicate that LCSS effluent may contain arsenic, fecal coliform,
nitrate, total nitrogen species, and formaldehyde (in septic systems serving recreational
vehicles) at concentrations above primary drinking water standards or health advisory levels.
The concentrations of aluminum iron, manganese, and sodium may exceed secondary drinking
water standards.
What are the characteristics of the Typically, LCSSs are located in well-drained soils; however, some LCSSs have been located in
injection zone of a LCSS?	areas with karst or fractured bedrock.
Are there any contamination	Contamination incidents caused by LCSSs have occurred in Racine, MO; in Coconino County,
incidents associated with LCSSs? AZ; and in Richmond Heights, FL. In addition, 24 other instances have been identified where
LCSSs failed and ground water contamination may have resulted. While there are surely other
examples of LCSS failure across the United States beyond these known incidents, the
prevalence of contamination cases appears low relative to the prevalence of these systems.
LCSSs are vulnerable to spills because any materials spilled or dumped down sinks, toilets, or
floor drains connected to the sanitary waste system can enter the septic tank. Examples of the
materials that may enter LCSSs include household cleaning products and wastes (e.g., cleaning
solvents and spent solutions) that were spilled as well as chemicals dumped illicitly (e.g., waste
How many LCSSs exist in the
There are about 43,000 LCSSs documented in the United States. Based on an inventory model
United States?
developed by EPA, the estimated number of LCSSs is 353,400 nationwide. With a 95 percent

prediction interval, the estimated number of LCSSs ranges from 304,100 to 402,600.
Where are LCSSs located within
LCSSs have been constructed nationwide.
the United States?

How are LCSSs regulated in states
Regulation of LCSSs varies among states. State regulations vary from stringent siting.
with the largest number of this
construction, and operation requirements (e.g., MA, MN) to general construction permitting
type of well?
(e.g., NJ, IA)
Where can I obtain additional	For general information, contact the Safe Drinking Water Hotline, toll-free 800-426-4791. The
information on LCSSs?	Safe Drinking Water Hotline is open Monday through Friday, excluding federal holidays, from
9:00 a.m. to 5:30 p.m. Eastern Standard Time. For technical inquiries, contact Amber Moreen,
Underground Injection Control Program, Office of Ground Water and Drinking Water (mail
code 4606), EPA, 401 M Street, SW, Washington, D.C., 20460. Phone: 202-260-4891. E-mail:
morccn.a mbe r Vv cpa.gov. The complete Class V UIC Study (EPA/816-R-99-014, September
1999), which includes a volume addressing LCSSs (Volume 5), can be found at
What types of fluids are injected
into LCSSs?
Do injectate constituents exceed
drinking water standards at the
point of injection?
Are LCSSs vulnerable to spills or
illicit discharges?