16-001014-02A (Ultimate SCMMP)

Filter Inspection and Replacement

Fine sediment and silt may accumulate within the filter media of the Bioretention Device over time. Removal of sediment
and silt trapped within the filter media is expected to be the most costly maintenance requirement for Bioretention Device.

It is recommended that a visual inspection of the infiltration properties be undertaken at least three times per year with
more frequent inspections no greater than three months apart between October and May. This is to determine whether
built-up fine sediment and silt has reached a point where the filter media has become clogged.

The infiltration properties of the filter media within the Bioretention Device needs to be checked after a period of
significant rainfall event, which is defined as a 24 hour period with rainfall greater than 200mm, or a shorter period with an
average rainfall intensity greater than 50mm/hr. This is an ideal period to assess the infiltration properties as water should
not pond for an extended period. Therefore inspections should occur 24 to 72 hours after an appropriate rainfall event.

In the event that isolated boggy patches occur within the Bioretention Device then the subsoil drainage pipes could be
blocked. If this is not the case and no other blockages have been observed then surface of the media is to be tilled (raked
and aerated) to a depth of 150mm. This will require temporarily removing and storing the surface vegetation prior to tilling
the surface. Should the infiltration properties be improved then the removed vegetation and coarse aggregate layer can
be replanted. Should tilling prove unsuccessful or if an infiltration check indicates filter media to be clogged, then the top
portion of the filter media is to be replaced as follows:

1)   Removal of surface vegetation and coarse aggregate layer and store for re-establishment;
2) Remove the top 150mm of filter media and dispose of in an approved manner;
3) Till the remaining filter media to a further depth of 300mm;
4) Place a new layer of appropriate filter media as per the specification (refer to Appendix B), free from organic matter,
   clay and silt; and
5) Replant the removed vegetation.
If blockages occur frequently, a filter media with a higher saturated hydraulic conductivity should be considered.
Reassessing the species and planting density of vegetation is also an option.
Unless changes to the filter media specification are made through a review of the SQID performance, the filter media to
be used for the Bioretention Device is to be a Sandy Loam as per the FAWB Guidelines for Filter Media in Biofiltration
Systems (Version 3.01, 2009).

Subsoil Drainage Inspection & Cleanout

The build-up of fine sediment and silt within the subsoil drainage pipes is unlikely as it will be trapped by the filter media.
However the subsoil drainage is to be checked annually for blockages that may be caused by foreign matter entering
through cleanout inspection openings or by small fauna. This can be done by either:
    Observing the condition of the subsoil drain through the cleanout and inspection openings located towards the
     downstream end of a subsoil drainage pipe.
    Observing the amount of sediment and silt flushed into the downstream field inlet when water is pumped into the
     upstream end of the subsoil drainage line (through a cleanout and inspection opening).
If a considerable amount of sediment and silt is observed or carried into the downstream inlet, then each subsoil drainage
line must be flushed out with high pressure water.
Water is to be pumped into each subsoil drainage pipe through the upstream cleanout inspection opening until all
sediment has been ejected from the pipe. To collect the water and ejected sediment within the downstream pit a
temporary barrier is to be placed over the downstream pipe opening (such as sand bags) and a pump used to draw the
water, sediment and silt out of the pit and irrigated onto areas of open space away from the basin. This will ensure the
sediment and silt does not enter the downstream waterway.
If frequent issues occur with the subsoil drainage system, CCTV checking could be undertaken to identify any damage
subsoil drainage.


16-001014-02A | SMCMP | PALM LAKE RESORTS                          COOROY RETIREMENT COMMUNITY, TRADING POST
                                                                                               ROAD, COOROY                  | 14