Further information re Request to Change Approval MCU 132003.221132.8

    Table 2 Mean Annual Pollutant Loads               -
                                                           Base Case and Developed Mitigated Site (Modelling
                                      Period 1/1/1998   -

                                                            1/1/2002)   -
                                                                            Entire 65 ha site

                                                                                         30.5 ha Developed
                                                    65 ha Base Case Site
                             Parameter                                                 Mitigated Site + 34.5 ha
                                                        (Forested Site)
                                                                                          Forested Buffer
                            Flow (MUYr)                       426                                431
                             TSS (kg/yr)                     36,500                             32,300
                                 TP (kg/yr)                   37.0                               41.8
                              TN (kg/yr)                      422                                490




The pollutant exports from the entire site are seen to decrease for suspended solids, but increase for
total nutrients.        This also       assumes   that the    large external buffers to the site do not improve
stormwater quality in passage through them.

                                                                                                                     1
When these results are considered in the context of typical stormwater management targets                                that
are   applied to most developments, the requisite standards are met, as shown in Table 2.

    Table 3 Mean Annual Pollutant Load Reductions -Developed Mitigated Site Only (Modelling
                                                Period 1/1/1998 -1/1/2002)

                                                  Pollutant Load Reduction              Normal Development

                             Parameter          30.5 ha Developed Mitigated Site                Target
                                                    compared to Developed
                                                       Unmitigated site
                            Flow (MUyr)                      24.9%                                NA
                             TSS (kg/yr)                      80.7%                              80%
                              TP (kg/yr)                      68.9%                              60%
                              TN (kg/yr)                      52.4%                              45%




The     incorporation       of the detention       basin    upstream of Dodonaea Close will              serve    to detain
stormwater emanating from           approximate 2.8 ha forested catchment on the opposite site of
                                          an

Beckmans Road. The detention basin is likely to primarily serve a hydraulic control function by
attenuating peak flows through a culvert under the road. The requirement for flow attenuation at this
point relates to the integration of the site stormwater management systems with that of the adjoining
development.

If you have any questions regarding the above advice, please contact Damion Cavanagh on 02 6687
0466.

Yours Faithfully
BMT WBM Pty Ltd




      l,,~~~

Damion Cavanagh
Associate




I
    SPP Healthy Waters       -

                                 comparison of developed unmitigated versus development mitigated. It should be
noted that the assessment considers only the developed pOliions of the site and excludes undeveloped pOl1ions
i.e. the very large extemal buffer area outside of the defined development extent.




(:’815573.c.dcc F 815573 o 13.doc                                                                A part of BMT in Energy and Environment