One of the challenges when residing in the Philippines is the proper location and design of your septic tank, particularly for a lot having an area below 100sqm or worst lower than 50sqm.
As much as possible, must NOT be within the "building footprint" but outside with a distance of:
- 1.50m away from any building structure or
- 1.50m away from property line adjoining private property , and
- somewhere near your main road of access for "desludging purposes".
Desludging - cleaning and removal of your "septage" in your septic tank, where "septage" is a combination of thickened scum, sludge and liquid that needs to be removed.
Ever heard of "Malabanan Siphoning Services"?
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| image from malabanan lipa batangas |
Say you manage to find a location on your lot, the next problem is how you discharge those wastewater (effluent) coming from your septic tank (ST) if your location is not serviced with sewer pipelines.
CHAMBERS
- Digestive - 1st chamber which is 2/3 of your total septic tank capacity
- Leaching/Secondary chamber - 2nd chamber which is 1/3 of your total septic tank capacity
Before the usual practice is to have the 1st chamber (inlet) bottom sealed, while the secondary chamber (outlet) is open with layered gravel and sand to separate sludge and let water naturally seeps into the soil.
Layered gravel is not a treatment to your ST effluent but just a way to segregate the solid (sludge) from the liquid.
Some ordinances now requires not only two chambers but three chambers instead, with sealed bottom depending on location specially if near bodies of water or along coastal areas.
Rationale why its bottom needs to be sealed is to prevent neighboring properties or the property itself get contaminated from possible wastewater seepage to nearby deep wells or other source of water.
MINIMUM
Minimum number of chambers as per law is to have at least 2 chambers, but some LGU's may require more than 2 or more, so best to check with your local LGU.
- Minimum Width of INTERIOR of chambers = 0.90m
- Minimum Length of INTERIOR of 2 chambers = 1.50m and 0.90m respectively
- Minimum Depth of INTERIOR of liquid (effluent) = 0.60m to 1.80m
- Air space = 0.228m but on actual construction 0.30m
TYPICAL SECTION
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| septic tank section |
HOW TO PROPERLY DISCHARGE EFFLUENT
Since the country lacks sewage treatment plants, alternative way for individual home owners who don't have access to sewer lines is to provide "drain field".
An extension pipe drilled with holes at the bottom with gravel bed underneath and surroundings before covering with polyethylene sheet (or geo-textile fabric alternative).
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| image from averettseptic.com |
A short video regarding drain field to get the idea (from YT by TechniHUB )
Harsh reality, this is not applicable for limited lot spaces even in some subdivisions that provision for sewer lines were not considered or have no access at all.
Either you allot the ground floor level for your ST and have your second floor for your needed space or have your ST avail "siphoning" every 3 to 5 years.
HOW TO DESIGN YOUR SEPTIC TANK
1. Determine first the total gallons capacity to get the cubic meter capacity in liters and be able to derive your chamber sizes later.
Table B-2 Septic Tank Capacity
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| septic tank capacity table |
Example:
With a 3 bedroom residence of 20 DFU (drainage fixture unit) can serve a minimum of 1000 gallons, which when converted to liters = 3,785 liters.
Converting liters to cubic meter divide with 1000 liters = 3.785 cu.m (volume)
2. Check as per plan location of ST (septic tank) with the corresponding width and length of space, then check from Table B-1 for the minimum distance allowed to building structures and property line.
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| table B-1 |
Say you have 4 meters width and 6.58 meters length open space available, let's assume a width for our ST.
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| septic tank location |
Therefore:
4m - 1.5m (from your building) - 1.5m (from property line) = 1 meter as width space for your ST.
3. Assume any value of liquid depth from 0.60m to 1.80m, say 1.20m
4. Solve for ST LENGTH with V = l x w x h
3.785 cu.m = L x 1m x 1.2m
L = 3.785 cu.m / 1.2 m2
L = 3.15 m
Get 2/3 and 1/3 from computed Length for your Digestive and Leaching chambers
Digestive = 2.1m
Leaching = 1.05m
COMPUTED SEPTIC TANK DIMENSIONS
1m x 2.10m x 1.50m Digestive chamber
1m x 1.05m x 1.50m Leaching/Secondary chamber
1.50m derived from adding 1.20m liquid depth with 0.30m air space for bacteria, as per code air space of 0.228m to be exact but for construction purposes rounded to 0.30m.
In case you are required to have three chambers, simply duplicate the size of your secondary chamber.
