Attachment 4 - Stormwater Managment Plan

SQIDEP Evaluation                                                     SPEL Basin, Sippy Downs


Dissolved Inorganic Nitrogen
This claim is for TSS, TP and TN. It does not include subspeciation of nitrogen. However
the Independent Evaluators have assessed the influent concentrations to determine if there
were unusually high organic nitrogen loads which might skew the claim and not be
consistent with a site that is reasonably representative.

We found that dissolved nitrogen is the dominant (> 50% by mass) form of nitrogen on this
site. The testing and analysis finds that the device performance is statistically significant in
relation to TN removal and this indicates the device is removing both particulate and some
forms of dissolved nitrogen.

Pollutant removal and statistical analysis
The statistical analysis and methodology for determining significance was reviewed. It was
found that the steps taken follow standard procedures for evaluating stormwater data.
Typically stormwater concentration data is not normally distributed, as denoted from a
Shapiro-Wilk normality test. Log10 transformation does result in normality of the data. Paired
Student T-test can be used on the transformed dataset to test significance between data
sets.

Afflux Consulting undertook its own Paired Student T-test and found the same result as
those reported by the Stormwater Research Group (see Appendix B).

Reported Concentrations Analysis
While the performance of the device is based on changes between influent and effluent
concentrations as reported and elsewhere the influent concentrations are examined (see
above) for representativeness of the recommended installation type, it is considered
worthwhile to examine the influent concentrations with respect to antecedent conditions to
gain an understanding of how the catchment is behaving.

Pollutant concentrations in runoff are influenced by a range of conditions that include the
type, intensity and timing of catchment activity, and can be influenced by specific events that
add to loadings, and detailed analysis is beyond a simple correlation with antecedent dry
weather (ADW)conditions.

In general, it is expected that

   •   prolonged ADW will lead to increased pollutant concentrations; and
   •   some pollutants (e.g. Total Suspended Solids) will exhibit a more definitive
       correlation with ADW.
Influent concentrations are listed in Table 2 for three ranges of ADW. Given the nature of
the catchment (e.g. road) it is not expected that TP or TN pollutant will be significant and it
is not possible to draw any definitive conclusions from these results, however they show (on
average) higher results for TSS for longer ADW periods and gives some level of comfort that
the catchment is behaving in terms of currently accepted build and wash off conceptual
models.




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