SCG 31030 Stormwater Management Plan · OPW22/0319

5.2      CONSTRUCTION PHASE:

5.2.1    Silt and Sediment Erosion:

A potential for sediment mobilization/transportation exists during and beyond the construction of the proposed
development. This can elevate turbidity levels of stormwater runoff.

A RUSLE assessment of the site confirms proposed development is a Low Risk for soil loss (< 150 Tonnes).

Potential Causes

         •      Stormwater scour and erosion of excavated or stripped surfaces and stockpiled soils.

         •      Wind borne transportation of sediments.

         •      Disturbance/breakup of soil profile via vehicular traffic followed by stormwater scour and erosion.

         •      Transportation of sediments from site via excavation vehicles.

Mitigating Measures

         •      Construction of silt fences around the development site located to cut off all runoff.

         •      Provide 80-100mm crushed rock (no fines) hardstand under all vehicle paths expected during
                construction. Generally, this would be provided from the existing crossover and extended to a
                distance within the site that would accommodate the maximum delivery vehicle length expected.

         •      Provide rumble grates at exit points from the basement excavation ramp.

         •      Where possible maintain existing landscaping/grasses downslope from construction areas to act
                as buffer/silt trap.

         •      Install temporary downpipes from completed roof structures and ensure runoff passes through silt
                fences.

         •      Minimise concentrating surface flows.

         •      Place silt barriers around council stormwater pits that the site drains to.

         •      Cover soil stockpiles with hessian or similar.


5.3      COMPLETED DEVELOPMENT:

As the site area is less than the trigger value for stormwater quality, the site is exempt from the requirement for
stormwater treatment. Regardless the following measures will be implemented.

5.3.1    Sources of Contaminants:

Gross Pollutants

Gross pollutants include litter, grit and heavier sediments which can be mobilised from within or from neighbouring
sites.

Potential Causes

         •      Unsecured refuse areas.

         •      Unlandscaped areas prone to stormwater scour.

         •      Insufficient drainage for surface runoff from within the site.

         •      Wind Bourne transportation.


 SCG Consulting engineers                                  5                                  SCG Ref: 31030(SWM)


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5.2 CONSTRUCTION PHASE:
5.2.1 Silt and Sediment Erosion:

A potential for sediment mobilization/transportation exists during and beyond the construction of the proposed
development. This can elevate turbidity levels of stormwater runoff.

A RUSLE assessment of the site confirms proposed development is a Low Risk for soil loss (< 150 Tonnes).

Potential Causes

° Stormwater scour and erosion of excavated or stripped surfaces and stockpiled soils.

° Wind borne transportation of sediments.

° Disturbance/breakup of soil profile via vehicular traffic followed by stormwater scour and erosion.
° Transportation of sediments from site via excavation vehicles.

Mitigating Measures
° Construction of silt fences around the development site located to cut off all runoff.
° Provide 80-100mm crushed rock (no fines) hardstand under all vehicle paths expected during
construction. Generally, this would be provided from the existing crossover and extended to a
distance within the site that would accommodate the maximum delivery vehicle length expected.

° Provide rumble grates at exit points from the basement excavation ramp.

° Where possible maintain existing landscaping/grasses downslope from construction areas to act
as buffer/silt trap.

° Install temporary downpipes from completed roof structures and ensure runoff passes through silt
fences.

° Minimise concentrating surface flows.

° Place silt barriers around council stormwater pits that the site drains to.

° Cover soil stockpiles with hessian or similar.

5.3 COMPLETED DEVELOPMENT:

As the site area is less than the trigger value for stormwater quality, the site is exempt from the requirement for
stormwater treatment. Regardless the following measures will be implemented.

5.3.1 Sources of Contaminants:
Gross Pollutants

Gross pollutants include litter, grit and heavier sediments which can be mobilised from within or from neighbouring
sites.

Potential Causes

° Unsecured refuse areas.

° Unlandscaped areas prone to stormwater scour.

° Insufficient drainage for surface runoff from within the site.
° Wind Bourne transportation.

SCG Consulting engineers 5 SCG Ref: 31030(SWM)