Sewerage System

Various options were considered for providing for the treatment of sewerage at the airfield. These ranged from having separate septic systems through to a single centralised system. Of course the major problem with a centralised system was how to pay the cost of installation. The system was designed with a design population of 100 people. In the plan below it can be seen that parts of the system have the capacity to handle well over 200 people, this was done to allow for future growth.

As can be seen from the soil test results below, the absorbsion by the soil is very low and so the system was designed to be a transpiration type of system.

The management committee of the day decided to impose a "Contribution Charge" on all all of the Air Chalet and Commercial Hangar Lease holders to pay for a centralised system. Other users of the airfield got a "Free Ride" on the backs of the lease holders, a pattern that occurred over the years since.

In the initiial installation, the system was a pure septic system with final polishing of the water through a gravel/sand filter before being pumped into a extensive burried pipe system that "leaked" water into the soil for further bacterial action by the soil microbes and finally the water was removed by evaporation.

Subsequently the system was modified by the installation of a air pump that bubbled air through the final tank, changing this part of the system from anaerobic (meaning without air) to an aeroabic system. This is a fundamental change. Further the burried pipe system was scrapped and replaced by a "Vetiver" grass system.

Photo Above: Sewerage Treatment area (Jan 2006)

Photo below: an overall view of the area (August 2010)

Photo Below: Shows the vetiver grass bunded area. Vetiver grass is (Vetiveria zizanioides) used for the treatment of sewerage because it is fast growing and has the ability to take up the heavy metals, it is a "super absorber" - it has a very high capacity to absorb nutrients, particularly nitrogen and phrosphorus that is found in waste water.. The Vetiver grass wetland has been constructed in rows that follow the contour of the land. The area inbetween the rows is regularly mowed to control weeds and the grass regularly gets the top trimmed and the cut grass is taken to the local dump so that there is not a build-up of heavy metal contamination on the site.

For a number of years the association has been chasing a leak that allows a lot of rainwater into the sewerage system, in the photo (Sept 2010) below, member Peter Freeman digs a drain around what is believed to be the offender,- the lids on 2 sewerage septic (80 person) tanks located in front of AC-31 in the air chalet precinct. This the lowest area in the precinct and in heavy rain quite an amount of water flows across that region and into the surrounding spoon drain.

Later that month (25th Sept 2010) the airfield was subjected to a period of heavy rain and Peter's drains were put to the test. With the benefit of hindsight it may have been better if these had been installed slightly raised compared to the surrounding ground.

In September 2012 year, the area of vetiver grass was expanded to about double the existing area.The photo below shows Kev Wernew with his equipmentforming the rows in the new area.

Also during the later part of the 2012 year, the entrance to the sewerage area was made "All Weather". A pipe crossing was installed and "elphant ears" built on both ends of the ppipe to protect the ends.



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