RFI - Attachment F - Engineering Report

Loading Rates.
The highest loading rates for all sized particles were encountered in the commercial area.
High suspended solids loading rates were also observed in the base sub catchment. This
suggests that at source treatment is best applied in commercial areas and at the base of a
catchment as finer size particles often contain high concentrations of nutrients and heavy
metals.

High loading rates for nitrogen and phosphorous were encounter in the commercial area.
These high loading rates were present in large and small size particles. The high loading
rates for nitrogen in fine particles from the commercial area is attributed to mechanical
breakdown by traffic movement. It is suggested that street sweeping be performed in the
commercial area to prevent the break down of larger particles.

High loading rates were also encountered a base of the hill for nitrogen a phosphorous.
However the highest rates for phosphorous were in the larger particles.

3rd Party Modelling Comparison
Comparing the loading rates form 3rd part modelling by Hughes Truman engineering
consultants, it is estimated that the Enviropod is removing 65% TSS, 40% total
phosphorous, 21% total nitrogen and nearly 100% gross pollutants.

Not considered in the Hughes Truman’s export rates is the bed load. It was observed that
176 kg/ha of the exported load was bed load. This is a considerable mass not to be
considered. This has great implications when determining maintenance frequency of
treatment devices

Conclusion
Land use and topography greatly affect the loads and composition of the contaminates in
stormwater. Climatic conditions also have an effect on the loads and composition of
contaminates. Wind and rainfall have the ability to move and break down contaminants
making them more difficult to capture.




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