United States

Environmental Protection

Agency

Office of Water

Washington, D.C.

EPA 832-F-00-044

September 2000

Decentralized Systems

Technology Fact Sheet

Septic Tank Leaching Chamber

DESCRIPTION

A leaching chamber is a wastewater treatment system

consisting of trenches or beds, together with one or

more distribution pipes or open-bottomed plastic

chambers, installed in appropriate soils. These

chambers receive wastewater flow from a septic tank

or other treatment device and transmit it into soil for

final treatment and disposal. 

A typical septic tank system consists of a septic tank

and a below-ground absorption field (also called a

drainfield, leaching field, or nitrification field). Leaching

chambers are drainfields used to dispose of previously

treated effluent. The drainfield system typically consists

of leaching chambers installed in trenches and

connected to the septic tank via pipe. Effluent flows

out of the septic tank and is distributed into the soil

through the leaching chamber system. The soil below

the drainfield provides final treatment and disposal of

the septic tank effluent. After the effluent has passed

into the soil, most of it percolates downward and

outward, eventually entering the shallow groundwater.

A small portion of the effluent is used by plants through

their roots or evaporates from the soil. Figure 1 shows

a typical leaching chamber. 

Leaching chambers have two key functions: to dispose

of effluent from the septic tanks and to distribute this

effluent in a manner allowing adequate natural

wastewater treatment in the soil before the effluent

reaches the underlying groundwater aquifer. Although

the septic tank removes some pollutants from

wastewater, further treatment is required after the

effluent leaves the tank. Nitrogen compounds,

suspended solids, organic and inorganic materials,

and bacteria and viruses must be reduced before the

effluent is considered purified. These pollutants are

reduced or completely removed from the wastewater

by the soil into which the wastewater drains from the

leaching chambers.

Depending on the drainfield size requirements, one or

more chambers are typically connected to form an

underground drainfield network. The leaching

chambers are usually made of sturdy plastic and do not

require gravel fill. The sides of each chamber have

several openings to allow wastewater to seep into the

surrounding soil.

A typical leaching chamber consists of several highdensity polyethylene arch-shaped, injection-molded

chamber segments. A typical chamber has an average

inside width of 51 to 102 centimeters (20 to 40 inches)

and an overall length of 1.8 to 2.4 meters (6 to 8 feet).

The chamber segments are usually one-foot high, with

Source: Infiltrator Systems Inc., 2000.

FIGURE 1 LEACHING CHAMBER
wide slotted sidewalls, which are usually 20 degrees

toward the chamber center or away from the trench

sidewall. Each chamber segment is designed to

mechanically interlock with the downstream chamber

segment, forming a complete drainfield trench that

consists of an inlet plate with a splash plate below the

inlet on the trench bottom, and a solid-end plate at the

distal end of the chamber drainfield line.

Common Modifications

Typical leaching chambers are gravelless systems, with

drainfield chambers with no bottoms and plastic

chamber sidewalls, available in a variety of shapes and

sizes. Some gravelless drainfield systems use large

diameter corrugated plastic tubing covered with

permeable nylon filter fabric not surrounded by gravel

or rock. The area of fabric in contact with the soil

provides the surface for the septic tank effluent to

infiltrate the soil. The pipe is a minimum of 25.4 to

30.5 centimeters (10 to 12 inches) in diameter covered

with spun bonded nylon filter fabric to distribute water

around the pipe. The pipe is placed in a 30.5 to 61

centimeter (12 to 24 inches) wide trench. These

systems can be installed in areas with steep slopes with

small equipment and in hand dug trenches where

conventional gravel systems would not be possible. 

Use of these systems decreases overall drainfield costs

and may reduce the number of trees that must be

removed from the drainfield lot. However, fabricwrapped pipe cannot overcome unsuitable site

conditions and should not be installed where gravel

systems will not function properly or in fine sandy

organic rich, coastal plain soils with shallow

groundwater.

APPLICABILITY

Leaching chambers are widely used as drainfield

systems for septic tank effluent discharge. Many

leaching chambers have been installed in 50 states,

Canada, and overseas over the last 15 years.

Currently, a high percentage of new construction uses

lightweight plastic leaching chambers for new septic

tank systems in states such as Colorado.

Leaching chambers are an alternative to the

conventional septic tank drainfield, which consists of

several trenches with gravel beds and perforated

plastic pipes. Leaching chambers allow more of the

soil profile to be used since the septic tank effluent is

distributed to the ground below and the soil

surrounding the chamber. Therefore, leaching

chambers are more effective than traditional gravel

drainfields, especially when the drainfield must be

located on a steep slope. Leaching chambers are

suitable for lots with tight sizing constraints or where

water tables or bedrock limit the depth of the

drainfield. Some states offer up to 50 percent sizing

reduction allowance when using leaching chambers

instead of conventional septic tank gravel drainfields.

Because they can be installed without heavy

equipment, leaching chamber systems are easy to install

and repair. These high-capacity open-bottom

drainfield systems can provide greater storage and

more time for proper infiltration than conventional

gravel systems and, therefore, are also suitable for

stormwater management. 

Current Status

Septic tank system drainfields are usually classified as

two types: gravel or gravelless systems. In gravel

drainfield systems, the pipelines distributing septic tank

wastewater are placed over a layer of gravel. Four

inches of additional rock are then typically placed

around the pipe and two inches above the pipe.

Gravelless systems provide the same functions as

gravel drainfields while overcoming the potentially

damaging impacts of gravel such as compaction of

moist soil during installation and reduction of infiltration

by obstructing the soil. The leaching chambers create

a larger contact area for effluent to infiltrate into the

soil, providing efficient treatment.

Typically, leaching chambers consist of series of large,

two to four foot wide modular plastic arch segments

that snap together. These arch segments replace the

perforated drainpipes used in gravel drainfields. The

wide chambers are manifolded with conventional

plastic pipe such as high-density polyethylene (HDPE).
ADVANTAGES AND DISADVANTAGES

Limitations

Leaching chamber application is limited under certain

conditions. The main limitations for installation and

normal operation are small lot sizes, inappropriate soils,

and shallow water tables. Leaching chamber systems

can be used only in areas with soils that have

percolation rates of 0.2 to 2.4 minutes per millimeter (5

to 60 minutes per inch). Neglect of septic tank and

leaching chamber maintenance can lead to drainfield

failure and soil and groundwater contamination.

Reliability

Leaching chambers are reliable, do not have moving

parts, and need little maintenance to function properly.

They are usually made of plastic materials, with a useful

life of 20 years or more in contrast to the average

useful life of a drainfield of 15 years, with a maximum

of 20 to 25 years.

Some systems can be combined with other drainfield

systems such as mounds and pressure distribution

systems. Some can also be used for stormwater

applications. Leaching chambers do not require more

maintenance than conventional drainfield systems. 

Advantages

Key advantages of leaching chamber systems

compared to gravel drainfields include: 

• Easier and faster to install.

• Soil in the trenches is not as likely to be

compacted.

• Less expensive in areas where gravel must be

transported over a long distance, such as parts

of eastern North Carolina, the Rocky

Mountains, eastern Oregon, and Connecticut.

• Leaching chambers allow for lower intrusion of

soil and silt into the drainfield and thereby

extend the useful life of the drainfields.

• Some leaching chambers have greater storage

volumes than gravel trenches or beds.

• Inspection of the chambers is easier.

• Eliminates the need for gravel.

• Leaching chambers require a smaller footprint.

Some states allow up to a 50 percent

reduction in drainfield size compared to

conventional gravel drainfield systems. 

The lightweight chamber segments available on the

market stack together compactly for efficient transport.

Some chambers interlock with ribs without fasteners,

cutting installation time by more than 50 percent over

conventional gravel/pipe systems. Such systems can

be relocated if the site owner decides to build on the

drainfield site. Leaching chamber systems can be

installed below paved areas and areas of high traffic.

Disadvantages

A key disadvantage of leaching chambers compared to

gravel drainfields is that they can be expensive if a lowcost source of gravel is readily available. Also, tests to

assess the effectiveness of these drainfield systems have

yielded mixed results. Direct effluent infiltration is

advantageous in some soils yet detrimental in others.

While open chambers can break up tight, clay soils and

open up more airspace for biological treatment, they

are less effective than gravel drainfields in preventing

groundwater pollution. Because the open bottom

allows septic tank effluent to infiltrate the soil unfiltered,

high percolation rates (sandy soils) and groundwater

levels must be carefully considered before installing

such systems. 
DESIGN CRITERIA

The size of a leaching chamber system is based on the

wastewater flow and soil properties. For a three

bedroom home, the area needed for a leaching

chamber system could range from 18.6 sq. meters

(200 square feet) for a coarse-textured soil up to

185.8 sq. meters (2,000 square feet) for a finetextured soil. When the total drainfield area is

estimated, setbacks from the house and property lines

must be provided. These are usually state-regulated

and vary from state to state. Table 1 recommended

setback distances.

The key design parameter for leaching chambers is the

maximum long-term acceptance rate (LTAR), which

depends on the type of drainfield soils. Table 2

presents recommended LTARs for leaching chamber

sizing.

The design LTAR should be based on the most

hydraulically limiting naturally occurring soil horizon

within three feet of the ground surface or to a depth of

one foot below trench bottom, whichever is deeper.

To determine the total trench bottom area required, the

design daily wastewater flow should be divided by the

applicable LTAR. The minimum linear footage of the

leaching chamber system should be determined by

dividing the total trench bottom area by 1.2 meters (4

feet), when used in a conventional drainfield trench.

No reduction area is allowed for leaching chamber

systems installed in bed or fill systems. In addition to

the area needed for the leach field, space should be

reserved for possible expansion (for example, a 50

percent expansion area is required in New York State;

a 100 percent repair area is required in North

Carolina).

Leaching chamber systems in septic tank drainfields are

typically installed in three foot wide trenches, separated

by at least nine feet, edge to edge. Soil backfill is

placed along the chamber sidewall area to a minimum

compacted (walked-in) height of eight inches above the

trench bottom. Additional backfill is placed to a

minimum compacted height of 30.5 centimeters

(12 inches) above the chamber. The leaching chamber

trench bottom is usually at least 61 centimeters

(24 inches) below finished grade, and the inlet invert is

approximately 20.3 centimeters (8 inches) above the

trench bottom, and at least 43.2 centimeters

(17 inches) below the finished grade. Most health

codes limit the length of individual trenches to

18.3 meters (60 feet). A leaching chamber system

should have at least two trenches. Figure 2 shows a

schematic of a leaching chamber trench.

TABLE 1 SETBACK DISTANCES

FROM LEACHING CHAMBER

DISPOSAL AREAS

Item Minimum Distance, ft

Private Water Supply Well 100

Public Water Supply Well 300

Leak or Impoundment 50

Stream or Open Ditch 25

Property Lines 10

Water Line Under

Pressure

10

Sewer Interceptor Drain 25

Source: Schultheis, 1999.

TABLE 2 LEACHING CHAMBER LONG-TERM ACCEPTANCE RATE

Soil Type

Long-Term Acceptance Rate (gpd/ft./yr)

Natural Soil Saprolite

Sands 0.8 – 1.0 0.4 – 0.6

Coarse Loams 0.6 – 0.8 0.1 – 0.4

Fine Loams 0.3 – 0.6 -

Clays 0.1 – 0.4 -
Individual chamber trenches should be leveled in all

directions and follow the contour of the ground surface

elevation without any dams or other water stops.

Leaching systems installed on sloping sites may use

distribution devices or step-downs when necessary to

channel the level of the leaching chamber segments

from upper to lower elevations. The manufacturer’s

installation instructions should be followed and systems

should be installed by an authorized contractor.

PERFORMANCE

The performance of leaching chamber systems is

determined by the characteristics of the soil, available

slope, space, soil depth over the groundwater table,

and other site-specific factors. The overall performance

of leaching chambers is highly dependent on the

performance of the connected septic tanks. 

OPERATION AND MAINTENANCE

Septic tank/leaching chamber systems can operate

independently and require little day-to-day

maintenance. Proper maintenance of the septic tank

includes inspection to determine the rate of sludge and

scum accumulation in the tank every three to five years.

Under normal conditions, the septic tank should be

pumped every five to eight years.

Materials that do not readily decompose (grease and

cooking oil, coffee grounds, disposable diapers,

tampons, cigarette butts, condoms, plastics, etc.)

should not be flushed into septic tanks because they

may clog the tank inlet and/or outlet and cause the

leaching chambers to fail. Harmful chemicals, such as

pesticides, herbicides, gasoline, oil, paint and paint

thinners should not be discharged to sanitary drains

because they may harm soil microorganisms in the

drainfield which provide natural wastewater treatment.

Excessive use of chlorine-based cleaners can harm the

normal operation of leaching chambers because they

may cause soil dispersion and sealing, reducing soil

treatment capabilities.

COSTS

Leaching chamber costs depend on many factors,

including:

1. Soil type.

2. Cost of land.

3. Site topography.

4. Groundwater level.

These site and system specific factors must be

examined and incorporated when preparing a leaching

chamber cost estimate.

Construction Costs

Even with favorable soil conditions, a leaching chamber

system is more expensive then a conventional gravelpipe drainfield. The cost of a standardized, 2.13 meter

(seven foot) leaching chamber segment ranges from

$50 to $150. While drainage pipe is less expensive

per foot, a larger drainfield footprint is needed for

conventional gravel drainfields. The cost for a singlefamily septic tank leaching chamber drainfield typically

ranges between $2,000 and $5,000 in 1993 dollars.

If the site is inadequate for a new drainfield and the

field must be removed and replaced with a new one,

the cost of a new leaching chamber system may exceed

$10,000.

Source: Infiltrator Systems Inc., 2000.
Operation and Maintenance Costs

Operation and maintenance costs for these systems are

minimal. Key costs associated with the proper

functioning of the drainfield systems include septic tank

cleaning, which typically ranges between $500 to

$1,500 per cleaning.

REFERENCES

Other Related Fact Sheets

Septic System Tank

EPA 832-F-00-040

September 2000

Septage Treatment/Disposal 

EPA 832-F-99-068

September 1999

Septic Tank-Soil Absorption Systems 

EPA 832-F-99-075

September 1999

Other EPA Fact Sheets can be found at the following

web address:

http://www.epa.gov/owmitnet/mtbfact.htm

1. Anderson, J.L., R.E. Machmeier, and M.J.

Hansel. Long-term Acceptance Rates of

Soils for Wastewater. Proceedings of the

Third National Symposium on Individual and

Small Community Sewage Treatment Systems.

1981.

2. Crites R. and Tchobanoglous G. 1998. Small

and Decentralized Wastewater

Management Systems. McGrill-Hill, New

York.

3. Dix S. P. and V. Nelson. The Onsite

Revolution: New Technology, Better

Solutions. Water Engineering and

Management Journal, October 1998.

4. Infiltrator Systems, Inc. 2000.

http://www.infiltratorsystems.com/.

5. Keys, J. R., E. J. Tyler, and J. C. Converse.

1998. Predicting Life for Wastewater

Absorption Systems. Proceedings of the

Eighth National Symposium on Individual and

Small Community Sewage Treatment Systems.

6. May, R. March/April, 1991. Chamber

Leachfield Systems. Journal of Environmental

Health, 

7. North Carolina Department of Environment,

Health, and Natural Resources, Division of

Environmental Health. 1995. On-site

Wastewater Section. Innovative Wastewater

System Approval Guidelines.

8. North Carolina Rural Communities Assistance

Project, Inc. February 1994. Considering

the Alternatives: A Guide to Onsite

Wastewater Systems in North Carolina.

9. Ricklefs, S. Evaluating Innovative Systems:

A Field Study of Leaching Chamber Design.

In Proceedings of the 1992 Texas On-site

Wastewater Treatment and Research

Conference.

10. Schultheis, Robert A. and Gwen Hubbie. A

Homeowner’s Guide: Septic

Tank/Absorption Field Systems. University

of Missouri, WQ0401, 1999.

11. Tobias, S. 1990. Onsite and Alternative

Wastewater Treatment Systems,

Sacramento, California Rural Community

Assistance Corporation.

12. U.S. EPA. Design Manual: Onsite

Wastewater Treatment and Disposal

Systems, EPA/625/1-80-012. Cincinnati,

Ohio. Center for Environmental Research

Information, 1988.

13. U.S. EPA. 1992. Septic Systems and

Groundwater Protection: A Program

Manager’s Guide and Reference Book.

Washington, D.C.: Office of Water.
For more information contact:

Municipal Technology Branch

U.S. EPA

Mail Code 4204

1200 Pennsylvania Avenue, NW

Washington, D.C. 20460

ADDITIONAL INFORMATION

Alternative Septic System Test Center

Tony Millham, Project Manager

2 Spring Street

Marion, MA 02738

Bio Systems Ag Engineering

David Gustafson

1390 Eckles Avenue

St Paul, MN 55108

Extension Service

David A. Bryant, Director

Montana State University

Bozeman, MT 59717

Lockwood, Dietershagen Associates

Ken Lockwood

1 Earl M. Court

Clifton Park, NY 12065

The mention of trade names or commercial products

does not constitute endorsement or recommendation

for use by the U. S. Environmental Protection Agency

(EPA).