A septic system cannot be considered ready for use until it has been tested. This learning task outlines the various tests involved in a Type 1 system.

Testing the Septic Tank

The Sewerage System Standard Practice Manual (SPM), states that tanks should be leakwatertight tested to meet the standard in Table II-34, which, simply put, says “Test all tanks using water, to verify a rate of leakage less than 0.1% of volume per day. Test the tank, penetrations, and the lid seal. Alternately use vacuum testing.”

Water Test

The tank, penetrations, and the lid seal should be subjected to a water test. To do this, plug inlet and outlet pipes. Fill the tank to 5 cm above the top of the tank lid (observe in the riser) with clean water (avoid overfilling to reduce risk of lifting the lid off the tank).

For concrete tanks, fill the tank and let it pre-soak for 24 hours before testing.

To measure leakage, measure water level in a riser, in which a loss of water will be more noticeable than in the tank due to the smaller size of the riser. The following information is provided to translate a drop in water level in a riser to a loss in volume.

Avoid the water freezing during and after testing. For testing plastic or fiberglass tanks, follow manufacturer recommendations. Some manufacturers recommend backfilling around the tank before or during filling the tank with water.

When performing hydrostatic testing in cold climates, consider that:

• Water is its densest at about 4°C (just above freezing), so water put into a tank at 10 to 20°C (typical of groundwater) and left in the tank overnight at freezing temperatures will drop the level in the tank a substantial amount (about 0.2% or 11 litres in a 5600 L tank). A “loss” of 11 litres (0.2%) in the risers will look like a leak.

Vacuum Test

As an alternative to water testing, a vacuum test may be used. The 2003 National Precast Concrete Association (US) standard states: “The recommended (vacuum test) procedure is to introduce a vacuum of 4 inches of mercury. Hold this pressure for 5 minutes. During this initial 5 minutes, there is an allowable pressure equalization loss of up to one half inch of mercury. If the pressure drops, it should be brought back to 4 inches and held for a further five minutes with no pressure drop.”

Testing the Dispersal System

The piping in a gravity distribution system piping, whether it is of the trickling or dosing type, will not be capable of holding any type of pressure test. Anything resembling a test for the parts of such a system downstream of the outlet of the tank effluent chamber would be done through the installation process, such as ensuring the laterals and distribution headers are level and correctly connected, etc.

Testing of a dosing siphon can be accomplished by filling the dosing chamber with water and observing the level as the siphon trips, ensuring that the appropriate amount of liquid is discharged to the field. Any adjustments as to the height of the bell can then be made if needed. The dose volume should be at least 67% of the field’s volume.

For systems that pump effluent from a septic tank, such as in dosing through gravity or pressure distribution, Section II-6.4 of the SPM specifies:

• A filtered (screened) vault with the inlet at the centre of the clear zone
• A maximum pumping rate of 190 L/min (50 USGPM).
• A maximum drawdown of 10% of the tank working volume.
• An alarm reserve volume of at least 50% of the daily design flow (DDF), measured to the tank lid base (without backup into building).

The points listed above should have been part of the design at the time of installation, however these can be part of the testing process as well. The pump and alarm are controlled by sensors or float switches. These should be manipulated to test the operation of the pump and alarm to properly react to the “pump off,” “pump on,” and “alarm” settings.

If the pump is part of a pressure distribution system, a “squirt” test is required to ascertain that the pump is delivering enough pressure and volume to operate the system as designed. This is done prior to the field piping being backfilled, so it could be considered as part of the installation process as well. The pump chamber is filled with water, and the pump is turned on. Minimum 3.2 mm [latex]\left(\frac{1}{8}''\right)[/latex] diameter holes (orifices) are drilled into the top of the small diameter lateral pipes, and these will be covered with orifice shields before being backfilled. Water must squirt to a minimum height of 60 cm (24 inches) for orifices that are 4.8 mm [latex]\left(\frac{3}{16}''\right)[/latex] or larger, and at least 1.5 m (60 inches) for orifices smaller than 4.8 mm [latex]\left(\frac{3}{16}''\right)[/latex] diameter. All squirt columns must be within 15% height of each other along the network, and within 10% along any lateral. Valves placed on the distribution mains and laterals can be adjusted to accomplish the above if needed.

Other dispersal systems will have required tests particular to them. These are covered in the SPM and their descriptions will not be undertaken in this learning guide.