Attachment 4 - Stormwater Managment Plan

SQIDEP Evaluation                                                    SPEL Basin, Sippy Downs


    4. Discussion
Our independent evaluation finds that:

    1) As shown in Table 1, The testing regime and results comply with SQIDEP protocol
       requirements.
    2) In addition, the catchment parameters, expected runoff concentrations, and rainfall
       mapping to event recording are within standard, or expected guidelines though it is
       noted this site is considered “clean” or lightly loaded relative to default EMC values
       adopted in MUSIC. Of itself, this implies that, based on diminishing returns, the
       performance claims are more difficult to achieve and therefore conservative however
       the device itself may demonstrate clogging more prematurely on more heavily loaded
       sites. In this sense the field test may not have stress tested the device as much as it
       will experience in the real world. None the less the claim is considered valid and
       generally representative.
    3) The field study appears to be a scientifically sound study and would be repeatable
       under similar conditions which it is noted are deemed representative.
    4) There will be some sites where media life is reduced due to higher sediment loads
       and we note this SQIDEP claim and this independent evaluation do not involve a
       claim against expected media life. This however is addressed in part by the need for
       the asset owner to observe draining times and if draining times fall below 2 hours to
       then investigate if the media is blocked and needs replacing.
    5) The cation exchange capacity of the media is reportedly very high and indicates the
       CEC is very unlikely to limit media life.
    6) We were unable to assess the longer term vegetative health of the system though
       during the investigation rigorous and healthy plant growth was evident.
    7) We did not find evidence of cherry picking of storm events.
    8) We found that the dominant forms nitrogen in this study were dissolved nitrogen
       indicating that filtration, absorption and adsorption are occurring.
Final Agreed Pollution Reduction Performance

The final agreed pollutant reduction performance can be seen in




Figure 6 and includes total suspended solids, total phosphorus, total nitrogen, and gross
pollutant claims.


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