The frequency of pumping depends on several factors:
Capacity of the septic tank
Volume of wastewater (related to size of household) Amount of solids in wastewater (e.g. garbage disposals produce more solids)
Table I lists estimated pumping frequency according to septic tank capacity and household size. The frequencies were calculated to provide a minimum of 24 hours of wastewater retention assuming 50 percent digestion of the retained solids.
TABLE 1 Estimated septic tank pumping frequencies in years
(for year-round residences)
Tank Household size (number of people)
size 1 2 3 4 5 6 7 8 9 10
(gal)
—————Years between pumping————–
500* 5.8 2.6 1.5 1.0 0.7 0.4 0.3 0.2 0.1 –
750* 9.1 4.2 2. 6 1.8 1.3 1.0 0.7 0.6 0.4 0.3
900 11.0 5.2 3.3 2.3 1.7 1.3 1.0 0.8 0.7 0.5
1000 12.4 5.9 3.7 2.6 2.0 1.5 1.2 1.0 0.8 0.7
1250 15.6 7.5 4.8 3.4 2.6 2.0 1.7 1.4 1.2 1.0
1500 18.9 9.1 5.9 4.2 3.3 2.6 2.1 1.8 1.5 1.3
1750 22.1 10.7 6.9 5.0 3.9 3.1 2.6 2.2 1.9 1.6
2000 25.4 12.4 8.0 5.9 4.5 3.7 3.1 2.6 2.2 2.0
2250 28.6 14.0 9.1 6.7 5.2 4.2 3.5 3.0 2.6 2.3
2500 3E.9 15.6 10.2 7.5 5.9 4.8 4.0 3.5 3.0 2.6
Note: More frequent pumping is needed if a garbage disposal is used. Generally the indicated frequency will vary with the volume of solids (+20% for high volume, -20% for low volume).
As indicated in the footnote to Table 1, garbage disposers will increase the frequency of pumping. For example, if this same three bedroom house with six residents had a garbage disposal and was generally producing a higher volume of wastewater, the pumping frequency would be calculated as follows:
1.3 years – [(0.2) x 1.3 years] = 1.0 year
If you have just moved into a home, you may not know the size of the tank. In this case, you should have the tank pumped and inspected. The company pumping the tank will tell you its size, age, and condition.
Septic tanks will not fail immediately if they are not pumped. However, an un-maintained septic tank is no longer protecting the soil absorption field from solids. Continued neglect may result in system failure and even replacement of the soil absorption field. In some cases, site limitations may make replacement of the absorption field impossible. If system replacement is the only option, contact your local Sewage Enforcement Officer (SEO) or municipal sanitarian or health department since a permit for the new system will be required.
More explanation: In order for a tank to function properly, adequate liquid volume must be maintained to allow for sufficient “settling time” which permits solids to either settle out as sludge or join the floating-scum layer at the top of the tank. Baffles in the tank prevent the floating scum from leaving the tank, an event which would lead to rapid failure of the absorption system. When pumping is too infrequent, even if the tank is not totally clogged with solids, the reduced liquid volume in the tank cuts settlement time and forces small floating solids out to the absorption system, shortening its life.
Updated 03/01/03 Created 12/22/95 File: tankpump.htm
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More information on septic systems can be found at Mr. Friedman’s website http://www.inspect-ny.com/septbook.htm
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