Decision Report
7. Location and siting 1 Siting context
7.5 Soil type
DWER’s GIS mapping software indicates that the premises are situated on colluvium, including valley-fill deposits, variably lateritized.
The application stated that the area is underlain by Guildford Formation pebbly silt with potential for some alluvial soft clay deposits associated with the Helena River.
Sampling of ten boreholes during the geotechnical investigations conducted in 2016 and 2017 indicated the soil profile outlined in
Table .
Works Approval: W6115/2018/1
IR-T04 Decision Report Template v2.0 (July 2017)
7 Table 8: Soil profile
Description of materials encountered Depth (m bgl) Thickness (m) Pump Station
TOPSOIL: grey-brown silty sand, fine to medium grained, with roots 0.00 to 0.10 3.70 to 6.00 FILL: orange-brown, dark brown, black and grey clay, sandy clay and
sand, with brick rubble, concrete rubble, timber pieces and tyres.
Clays are soft to hard.
3.80 to 6.00 7.50 to 9.70
CLAY: brown and grey, low to medium plasticity, firm to very stiff, with sand, trace gravel, with sand layers/lenses
13.50 Beyond maximum investigation depth Pressure Main Route
TOPSOIL: brown sand, fine to medium grained, with roots 0.00 to 0.05 3.00 Interbedded:
SAND: yellow and brown, fine to medium grained, trace fines, up to 1.8m thick; and
CLAY / SANDY CLAY: brown and grey, low to medium plasticity, firm to hard.
3.10 Beyond maximum
investigation depth
The soil profile being predominantly sands and clays is conducive to a medium permeability which can provide a pathway to groundwater.
Acid sulfate soils
DWER’s GIS mapping software indicates that parts of the premises are situated within a high to moderate ASS risk area. A soil and groundwater investigation was undertaken at the site, on behalf of the Applicant, to investigate the potential for ASS to impact on the surrounding environment during construction works. The investigation formed the basis for the
Management Plan developed for the construction program.
As part of the site investigation, four boreholes were drilled across the premises to depths ranging between 2.0 to 7.5m bgl. One of the boreholes was converted to a groundwater monitoring well. Groundwater was elevation in the well was measured at 2.35 mbgl.
A summary of the soil profile identified during the site investigation is detailed above in Section 7.5 - Soil type.
Applicant’s key findings
The A summary of the findings of the ASS investigation are as follows:
1. ASS was identified in fill/clayey soils within the construction zone, at levels exceeding DER ASS Guideline action criteria.
2. Based on the location of ASS and PASS, the primary activities that will require management during construction are: dewatering and excavation of soil and fill.
3. A Management Plan was developed to outline the strategies to manage the potential for ASS to impact the environment during construction. It is
understood a site specific CEMP will be developed to detail management measures specific to the construction technique chosen.
Works Approval: W6115/2018/1
IR-T04 Decision Report Template v2.0 (July 2017)
8 4. The Management Plan includes requirements for monitoring and treatment of
excavated soil with ag-lime and monitoring and treatment of dewatering effluent during construction. However, it is noted that, depending on the final construction method, soil disposal and re-use requirements may change and dewatering assumptions and volumes may also be updated in the CEMP.
5. Groundwater monitoring will be required during construction and for 6 months following post-construction; and
6. The surface water body (Broz Park Lake) to the east of site and the Helena River to the north of the site are considered to be at low risk of adverse impact due to construction works and will require limited monitoring during and post- construction.
The ASS investigation and Management Plan were undertaken in accordance with the DER ASS Guideline. Proposed management and treatment of ASS is described in Section 8.6 as part of the risk assessment.
Wind direction and strength
The wind roses in Figure 4 provide the annual wind direction and strength (km/h) for the periods 9am and 3pm between the years 1944 to 2016 (most recent data available). The Bureau of Meteorology (BoM) provides the 9am and 3pm wind speed and direction for the Perth station (station number 009021).
The region has a dominant annual wind direction consisting of easterly to north-easterly winds during morning and south westerly and westerly winds in the afternoon. Any air emissions from the premises will impact residential receptors to the east, south and south-west. It is important to note that these wind roses show historical wind speed and wind direction data for the Perth area and should not be used to predict future data.
Figure 4: Wind rose for Perth Metro at 9am and 3pm (1944-2016)
Works Approval: W6115/2018/1
IR-T04 Decision Report Template v2.0 (July 2017)
9 Rainfall and temperature
The closest Bureau of Meteorology (BoM) station with current weather data is located approximately 9.7 km from the Premises at Bickley.
The mean rainfall and maximum temperature for the Bickley BoM weather station is presented in Figure 3 below. Based on the historical averages for the region, the Premises are likely to exhibit warm to hot temperatures between November to April with a mean annual rainfall of 1092.4mm (1969-2018) with rainfall predominantly in May to September.
Figure 3: Mean temperature and rainfall - Bickley
Works Approval: W6115/2018/1
IR-T04 Decision Report Template v2.0 (July 2017)
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