Attachment 4 - Stormwater Managment Plan

SQIDEP Evaluation                                                    SPEL Basin, Sippy Downs


   3. Evaluation of Enduring Performance
The Independent Reviewers have endeavoured to consider the long term enduring
performance of the SPEL Basin.

The device includes an ion exchange element. The cation exchange capacity of the media
has been confirmed to have a long life-time at typical hydraulic loading rates and this
indicates the device would not need to have its media replaced to maintain chemical water
quality outcomes within the life expectancy of the media.

However the media may be subject to blocking and reduced hydraulic conductivity from
occlusion by sediment. The SPEL Basin system includes a littler basket and filter cartridge.
Both of these can be easily maintained, without replacement, and will add significantly to the
life expectancy and functionality of the device as they prefilter sediment.

A sensitivity analysis of the device was undertaken by modelling its performance in MUSIC
with a 40% reduced high flow bypass rate. Assuming the hydraulic conductivity and
consequently the high flow bypass was reduced by 40% (indicative of partially clogged filter
media) the performance of the device would reduce by 2-3%, i.e. marginally.

It was agreed with SPEL to include a requirement in their Technical Design Guideline that if
the media was observed to not fully drain down to its lowest level within 2 hours that the
media be investigated and if required replaced. This would ensure that hydraulic
conductivity was maintained at reasonable levels and the TFR would be maintained in turn
ensuring that the claimed treatment train effectiveness would be achieved in the longer term.

It is noted that it is not possible nor required of the Evaluators to determine the life of the
device or the media and we are confident that under similar conditions to the test site that
the device will have a reasonable life expectancy. It is recommended that SPEL continues
to monitor at least the hydraulic performance of the SPEL Basin to confirm its long term
performance and range of media life-expectancy under both light and heavy pollutant
loading rates.




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