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SEPTIC SYSTEM INSPECT DIAGNOSE REPAIR
SEPTIC CARE INSTRUCTIONS
SEPTIC D-BOX INSTALL REPAIR
SEPTIC DRAINFIELD FAILURE DIAGNOSIS
SEPTIC DYE TEST PROCEDURE
SEPTIC FAILURE SIGNS
SEPTIC INSPECTION & TEST GUIDE
SEPTIC LIFE EXPECTANCY
SEPTIC SUPPLIES & PARTS
SEPTIC SYSTEM DESIGN ALTERNATIVES
SEPTIC SYSTEM DESIGN BASICS
SEPTIC SYSTEMS, HOME BUYERS GUIDE to
SEPTIC SYSTEM SAFETY WARNINGS
SEPTIC TREATMENTS & CHEMICALS
SEWAGE BACKUP PREVENTION
SEWAGE EJECTOR / GRINDER PUMPS
SEWER GAS ODORS
SEWER LINE REPLACEMENT
SINKHOLES, WARNING SIGNS
SOAKAWAY BED FAILURE DIAGNOSIS
SULPHUR & SEWER GAS SMELL SOURCES
TOILETS, INSPECT, INSTALL, REPAIR
TRAPS on PLUMBING FIXTURES
TREATMENTS & CHEMICALS, SEPTIC
VIDEO GUIDES: Septic Videos
WATER CONSERVATION MEASURES
WATER SOFTENERS & CONDITIONERS
WATER SUPPLY & DRAIN PIPING
WATER, WELLS, WATER TANKS: TESTING GUIDE
WASHING MACHINES & SEPTIC SYSTEMS
WASTEWATER TREATMENT BASICS
WINTERIZE A BUILDING
Septic tank depth: to what depths are septic tanks or cesspools or seepage pits or drywells commonly buried?
Here we describe the depth at which septic tanks are installed and we explain the use of septic tank risers to make it easier to pump out, clean, or service deeply-buried septic tanks.
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 are listed at "References." Comments and suggestions for content are welcome.
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This septic tank depth article is part of our septic system article series that summarizes guidelines on the required septic tank size based on anticipated level of daily gallons of sewage wastewater flow.
The typical residential septic tank size required for a given average daily sewage wastewater flow in gallons is provided in a table of septic tank sizes. Also
This chapter also explains how to calculate septic tank volume based on septic tank inside dimensions measured in feet, and we discuss the sizing, installation, and functions of septic tank tees to prevent septic system clogging. Links to related septic system testing and design information are given.
Septic tanks can be installed pretty much at any depth in the soil. Even in freezing climates, the septic tank serving an occupied home or even an unoccupied one is unlikely to freeze, partly because of latent heat the bottom of the septic tank receives from the earth and partly because of the heat generated by the bacterial action going on in the septic tank. (DO NOT add antifreeze to a septic system.)
Factors Determining Septic Tank Depth
The principal factors that determine the actual depth at which a septic tank is likely to be buried (and thus how deep you may have to dig to find the septic tank) at a particular site include:
Deep septic tanks should have a service riser installed. Septic risers are large-diameter "wells" that are placed over a septic tank inlet baffle access port (and possibly outlet) to permit easy access for septic tank pumping, inspection, and baffle repair. If the septic tank happens to be buried more than just a few inches below ground surface, good practice includes installing a septic riser, a large diameter pipe that gives good access to the septic tank for inspection and cleaning.
Details are at SEPTIC TANK RISERS.
Continue reading at SEPTIC TANK LOCATING EQUIPMENT or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: septic tank depth must permit adequate drain line slope
(Feb 12, 2014) Anonymous said:
If my sewer discharge pipe is 6ft+ below the ground surface does the septic tank inlet not have to be slightly lower in order for the waste to flow into the tank. Can a person use an effluent pump to discharge the waste to the field or do you use the effluent pump before the septic tank.
Anon. I agree completely. A waste line drains by gravity and slopes between 1/8" and 1/4" per linear foot. If your drain line had to run 20 feet from house outlet to tank inlet, the tank inlet has to be at least (20 x .125) " lower
Question: fill over septic tank on a hill
(May 16, 2014) Anonymous said:
We have a septic tank which is on a sloped hill, and are wondering how much fill we need to put between it and a retaining wall to keep it from freezing in the winter. One side will be completely buried. Thanks for any advice!
Anon, in some locations even an above ground septic tank survives moderate freezing locations without insulation, as being in-use it's warmed by inflowing wastewater. But a tank that's not in use or is in very cold areas indeed may need protection.
The quantity of insulation needed to avoid freezing depends on how cold is the exposure - something you don't state. Take a look at the insulating values of earth found at
SOIL R-VALUES - for help in deciding how much fill you need.
A very general comment is to take a look at the frost line depth for your area.
Watch out: even very large amounts of insulation won't prevent freezing of an inactive plumbing system or component in very cold areas. Rather the insulation slows the time to freeze but it can also slow solar or geothermal gain that counteracts freezing.
Also see this discussion about whether or not to turn off water in a winterized building:
Thanks for your response to my question yesterday!
Use a solid closed cell foam board that does not absorb water.
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Design Manuals for Septic Systems