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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 scum & sludge layers: this article explains the necessity of measuring the thickness of the floating scum layer in a septic tank and of measuring the thickness of the settled scum layer in a septic tank as well. We include descriptions of how to make septic sludge and scum measuring tools and how to use them.
Whether your system is a conventional septic tank and drain field, an above ground septic system, or even a holding tank, pumping and inspecting the septic tank is a critical septic tank maintenance and septic system maintenance chore. Septic tank pumping frequency guidance is provided in a table at our website (seelinks listed at the "More Reading" links at the bottom of this article .) When the septic tank is pumped, measurements of the scum layer and sludge layer tell you the condition of the system.
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Septic tank sludge & scum thickness measurements, made or at least roughly estimated by the septic pumping contractor at the time that a septic tank is pumped, provide key information that permits the home owner to know
1) whether or not the septic tank is being pumped often enough, and
2) whether or not there is evidence that the septic fields have been damaged by having not pumped the tank soon enough.
At SEPTIC TANK PUMPING SCHEDULE we discuss three septic tank pumping frequency mistakes that can be avoided by either using a septic tank cleaning table based on actual wastewater production (number of occupants etc) or by making objective measurements which we discuss in this article. First the mistakes:
Actually inspecting the septic system, diagnosing any problems or failures, and inspecting conditions inside the septic tank will tell us whether the tank is being pumped at the correct frequency.
The floating scum layer in a septic tank includes oil and grease which, if pushed into the leach field, will clog that component of the septic system.
Oil and grease are particularly harmful to the aerobic portion of septic effluent treatment in the soil absorption system.
Therefore we want to clean the septic tank if the scum layer has thickened to the point of risking pushing grease and oil out of the tank.
The septic tank needs to be pumped when the floating scum layer has accumulated to reach 3 inches of the bottom of the outlet baffle or tee.
Septic tank schematic courtesy of Carson Dunlop Associates.
See SEWAGE LEVELS in SEPTIC TANKS for details on normal and abnormal levels and what they mean.
The sludge layer on the bottom of a septic tank includes various solids which are not dissolved in the septic effluent and which are dense enough to fall to the bottom of the tank.
The septic tank bottom sludge is comprised of "settleable solids" and that portion of "suspended solids" which will, given enough time, also settle out. These accumulate at the bottom of the septic tank until they are removed by a septic tank cleanout procedure.
Normally a septic tank should be pumped when the bottom layer of sludge is within 18 inches of the tank outlet.
WHEN TO PUMP the SEPTIC TANK - How thick can the septic tank sludge and scum layer be before septic tank cleaning is needed?
Thickness of the Floating Scum Layer & Bottom Sludge Layer in the Septic Tank Tell When to Pump Out the Septic Tank
This discussion explains how to decide when to pump & clean the septic tank based on an actual inspection of the septic tank sludge & scum layer thicknesses. An alternative that you can use if your septic tank is difficult to access or you don't have the ability to make these measurements (or to ask your septic contractor to make them) is to use the septic tank pumping schedule at SEPTIC TANK PUMPING SCHEDULE. That schedule considers the septic tank size and level of usage.
The following example was provided to us by Effluent Services, Ltd., an experienced septic service company in New Zealand. In New Zealand septic tank sizes range from 2000-6000 liters (500 gallons to 1,500 gallons U.S.) with the average being 3100 liters (about 800 U.S. gallons and below the minimum septic tank size permitted in most U.S. jurisdictions).
This is very sound reasoned. Homeowners should use the scum and sludge layers found when their septic tanks are pumped as a way to determine whether or not the tank is being pumped often enough. In areas where most septic tanks are on the comparatively "small' side, a two year regular pumping schedule is reasonable for light-usage. In our experience, a 500-gallon septic tank in a home with a family of four is going to need very frequent pumping if the drainfield, leach beds, or soakaway system is to be protected.
US Department of Agriculture Guidance on What Scum or Sludge Levels Require Septic Tank Pumping
Similar rules of thumb offered by USDA on how much sludge or scum mean the septic tank needs cleaning include:
Don't wait too long before removing septic scum and sludge People who wait until their septic system stops working due to a clogged or over-filled (with sludge and scum) septic tank have waited too long. As the bottom sludge layer increases in thickness, and as the top septic scum layer increases as well, the remaining "net free area" or "effective septic tank volume" of effluent in the tank is reduced in volume.
When a septic tank is operating with a low volume of "net free area" of septic effluent, the system lacks adequate volume to provide adequate settlement time (EFFLUENT RETENTION TIME) - time needed for sludge to settle to the tank bottom and scum to coagulate at the tank top. In this circumstance, although drains in the building seem to be just fine, the septic tank effluent is remaining in a constant state of stirred-agitation. In turn, that means that the system is pushing floating debris into the leach field or other absorption system.
Simply put and quoting the USDA,
Watch out: Pushing grease, scum, and small solid debris out of the septic tank and into the leach field reduces the future life of that expensive component of a septic system. In fact if a septic tank has become blocked or even nearly-blocked by solids, the system has already had a history of pushing solids into the drainfield and even if the system appears to still be working properly, the future life of the drainfield has been substantially reduced.
At SEWAGE LEVELS in SEPTIC TANKS we explain how to interpret the meaning of high or low sewage levels in the septic tank as well as thick or thin scum or sludge levels.
Continue reading at HOW TO MEASURE SEPTIC SCUM LAYER or select a topic from the More Reading links shown below.
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