Post by techworks on Aug 3, 2018 9:59:31 GMT 12
NZS1547:2012, Section 5.5.3.5 states:
“The effluent distribution system shall be designed to accept the discharge from the wastewater treatment unit and to convey it securely and evenly to the land application area. The effluent shall be uniformly distributed over the design area to help achieve effective aerobic/anaerobic decomposition within the soil”
The above requirement in NZS1547 effectively excludes the use of uncontrolled gravity trickle loading of conventional soakage systems other than in exceptional circumstances as this method will not achieve uniform distribution over the design area.
GD06 Section E1.5.2.1 confirms this by stating:
“Uncontrolled trickle flow by gravity was historically the conventional loading method and should now only be used where there is no alternative. The disadvantage of gravity trickle loading is that wastewater may not be distributed across the entire application area and in well-drained soils, can result in creeping3 failure”
I have discussed this with Bay of Plenty Regional Council staff and they agree with the above interpretation and have advised that the only time uncontrolled gravity trickle loading should be used in the BOP region is on remote sites where no other option is available.
However, I've also talked with a number of local drainlayers, and it is clear that that there are many septic tank systems still being installed in the BOP region that have been designed and installed utilising uncontrolled trickle loading as the means of effluent distribution with conventional soakage trenches.
I am a firm believer in the KISS principle for OSET designs, so although putting a pump on a septic tank system will significantly improve the distribution of effluent over the design area, it breaks the KISS principle as a pumps add another level of complexity and require a separate trade to install and maintain.
What are other designers thoughts on this? When is uncontrolled gravity trickle loading acceptable with a septic tank system and which Regional Councils and Building Consent Authorities are accepting this loading method?
“The effluent distribution system shall be designed to accept the discharge from the wastewater treatment unit and to convey it securely and evenly to the land application area. The effluent shall be uniformly distributed over the design area to help achieve effective aerobic/anaerobic decomposition within the soil”
The above requirement in NZS1547 effectively excludes the use of uncontrolled gravity trickle loading of conventional soakage systems other than in exceptional circumstances as this method will not achieve uniform distribution over the design area.
GD06 Section E1.5.2.1 confirms this by stating:
“Uncontrolled trickle flow by gravity was historically the conventional loading method and should now only be used where there is no alternative. The disadvantage of gravity trickle loading is that wastewater may not be distributed across the entire application area and in well-drained soils, can result in creeping3 failure”
I have discussed this with Bay of Plenty Regional Council staff and they agree with the above interpretation and have advised that the only time uncontrolled gravity trickle loading should be used in the BOP region is on remote sites where no other option is available.
However, I've also talked with a number of local drainlayers, and it is clear that that there are many septic tank systems still being installed in the BOP region that have been designed and installed utilising uncontrolled trickle loading as the means of effluent distribution with conventional soakage trenches.
I am a firm believer in the KISS principle for OSET designs, so although putting a pump on a septic tank system will significantly improve the distribution of effluent over the design area, it breaks the KISS principle as a pumps add another level of complexity and require a separate trade to install and maintain.
What are other designers thoughts on this? When is uncontrolled gravity trickle loading acceptable with a septic tank system and which Regional Councils and Building Consent Authorities are accepting this loading method?
