RFI - Attachment F - Engineering Report

      Fletcher et al. (2004) recommended the event mean concentrations (EMC) for
      a number of land uses in Australia, which are widely used in design (Table 1).
      It is found that contaminant concentrations for the case of Mitchell Community
      College carpark testing are much smaller than reported by Fletcher et al.
      (2004).

          Table 1. EMC for different land uses in Australia (Fletcher et al., 2004)
          compared with Mitchell Community College carpark testing (values in
            parentheses indicate Mitchell Community College carpark result)

          Contaminant            Range (mg/L)            Typical value (mg/L)

        Suspended solids            900-800                       270
                                  (10.30-98.20)                 (34.60)

          Total Nitrogen            1.00-5.00                     2.2
                                   (0.35-2.95)                   (1.00)

        Total Phosphorus            0.15-1.50                     0.50
                                   (0.07-0.90)                   (0.22)


In another study by Morison (2001) for St Martins Shopping Village carpark in
Western Sydney using a rainfall simulator (calibrated for a 1 in six month storm of 15
minutes duration) showed a first flush effect for 10 minutes with an approximate
EMC for a duration of 15 minutes of Suspended Solids (95 mg/L), Total Nitrogen
(1.85 mg/L) and Total Phosphorus (0.15 mg/L). The results from Morison (2001) and
Fletcher et al. (2004) when compared with Mitchell Community College carpark
testing exhibit a large difference, which perhaps are due to different land use
characteristics and traffic volume representing local conditions.

It should be highlighted that if the EMC in the influent is higher, the contaminant
removal efficiency by a stormwater quality improvement device should be higher.
Hence, it is highly likely that the efficiency ratio for StormFilter® observed for the
Mitchell Community College system would be much higher if the influent EMCs were
higher as reported in Australia.

In relation to the constituent species of the contaminants in the runoff from carparks
and roads in Australia, there is little measured data available except for Ammonia.
Data from Sydney and the Illawarra (based on urban runoff) have shown a mean
concentrations in the range of 0.02 and 0.54 mg/L and data from Hornsby showed a
mean Ammonia EMC in the range of 0.01 and 0.11 mg/L, and in the case of Grafton
it has been found to be in the range of 0.02 and 0.41 mg/L (Fletcher et al., 2004).
These Australian values of Ammonia do compare well with the EMC range of 0.05
mg/L and 0.72 mg/L (mean: 0.27 mg/L) from the Mitchell Community College carpark
testing.

Parker (2010) conducted a study using stormwater quality improvement systems
(bio-retention and wetlands) in Coomera, Gold Coast (south-east Queensland) to

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