A summary of the proposed groundwater management design criteria and how these are addressed within the site is provided in Table 9.
Table 9: Groundwater management compliance summary Criteria
number Criteria description Manner in which compliance will be achieved
GW1 Maintain or improve the quality of groundwater leaving the site.
Drought tolerant turf and vegetation species that require minimal nutrients will be used.
No ongoing fertiliser use is proposed within tree pits, bio-pockets, swales, BRAs or the living stream, as these will be vegetated with nutrient absorbing vegetation species.
Education of residents regarding fertiliser use and nutrient absorbing vegetation species within lots.
Application of herbicides to comply with DoH guidelines.
GW1 Maintain or improve the quality of groundwater leaving the site.
Street sweeping on a regular basis.
Treatment of stormwater runoff and groundwater intercepted by subsoil drains within WSUD measures such as tree pits, bio-pockets, swales and BRAs.
Treatment of groundwater prior to being conveyed by subsoil drains through the use of appropriate soil medium.
Any imported fill should be suitable for protecting the underlying groundwater source.
GW2
Finished floor levels of habitable buildings will have a minimum 500 mm clearance from the MGL or meet appropriate separation distances from the CGL where groundwater control is proposed (IPWEA 2016).
Imported fill may be required to ensure the required clearances to MGL or CGL are met.
GW3
Infiltration structures will have appropriate clearances from MGL or meet appropriate separation distances from the CGL where groundwater control is proposed (IPWEA 2016).
Imported fill may be required to ensure that the required clearances to MGL or CGL are met. If subsoil drains are installed beneath infiltration structures, the CGL can be taken as the invert of the subsoil drains.
GW4
Where utilised, subsoil drains will be set in accordance with relevant guidelines (DoW 2013c) and should have a free draining outlet.
Subsoil drain inverts will be set in accordance with relevant guidelines and have free draining outlets.
8 Public Drinking Water Source Protection Area Management
A summary has been provided to detail how the proposed SP responds to its listing as a P3* PDWSA and the location of four WHPZs within the site (see Section 3.4.1). Table 10 summarises the
management measures proposed for the site against recommended measures for protecting water quality within P3* PDWSA, as taken from WQPN 38: P3* area (DWER 2018).
Table 10: Managing water quality for P3* PDWSA
Recommended measures for LWMS Management measures Land use
Restricted to certain types of land uses.
The land uses proposed for the site (see Appendix A) are:
• Residential lots (including possible future lifestyle village)
• POS (including gas pipeline easements)
• Primary schools
• Road reserves.
These land uses are allowable under WQPN 25: Land use compatibility tables for PDWSA (DoW 2016). Neither are they recommended to be avoided under WQPN 38: P3* area (DWER 2018). Therefore, the land uses proposed respond appropriately to the P3* PDWSA listing.
Sewerage
Development must be connected to reticulated sewer.
The site will be connected to reticulated sewer (see Section 5.4).
Pre-development water quality monitoring program in place, including for pathogens, nutrients and other contaminants. Results should be presented in the LWMS.
A pre-development groundwater water quality monitoring program was completed to support the overarching DWMS (Emerge Associates 2018).
Nutrient concentrations can be compared to the relevant guideline values for lowland rivers in South Western Australia presented in the NWQMS (ANZECC and ARMCANZ 2000) and the HRAP target concentrations (SRT 2009). Average TN within BH3, ALB2, MW01 to MW04, and MW07, and average TP within MW04 and MW07 exceeded both the NWQMS and HRAP concentrations. TN within MW06 exceeded the long-term HRAP concentration but not the NWQMS concentration. TP within ALB2 exceeded the NWQMS concentration, but not the HRAP concentration. Nutrient concentrations are typical of agricultural land uses where livestock has been pastured and fertilisers utilised. These bores are shown in Figure 2 and Figure 3.
As agreed with DWER during assessment of the DWMS, an additional groundwater quality monitoring event was completed to measure pathogens.
The ADWG of “not detected in any 100 mL sample of drinking water” should be referenced (NHMRC and NRMMC 2017). Escherichia coli and faecal coliforms were detected within MB02 (which had the highest reading), MB04 and MB06.
This monitoring event confirms the presence of existing faecal matter within groundwater as a result of the current land uses across the site.
Surface water quality monitoring within existing drains was proposed to occur opportunistically (in response to rainfall) as part of the previous monitoring program. While the base of existing drains were noted to be damp during winter and periods of high groundwater, the water wasn’t of sufficient depth to sample. Historical surface water quality monitoring within Saint Leonards Creek (downstream of the site) has indicated that the creek has moderate
concentrations of TN and TP, but high concentrations of some metals (ANZECC and ARMCANZ 2000; SRT 2009, 2011).
Table 10: Managing water quality for P3* PDWSA (continued)
Recommended measures for LWMS Management measures Water quality monitoring program
and sampling and analysis plan during and post-construction, including for pathogens. Identify contingency action plans, triggers and timeframes.
Monitoring during subdivision works (see Section 10.1) will occur for the duration of civil and landscaping works until practical completion. To summarise:
• Monitoring will occur on a monthly basis unless more frequent sampling is required to satisfy other processes and approvals.
• Monitoring will include dewatering volumes, TSS, sediment and erosion control, construction activities, and impacts on Saint Leonards Creek.
Post-development monitoring (see Section 10.2) will be implemented by the developer of each subdivision area after completion of the relevant civil and landscaping works for a period of three years until handover of POS areas to the CoS. To summarise:
• Condition monitoring will occur on a bi-annual basis and include visual assessments of gross pollutants, sediments, weeds, vegetation density and other POS infrastructure.
• Groundwater quality on a quarterly basis, and surface water quality and subsoil drainage discharge quality on a monthly basis over winter (see Table 11). Interim water quality trigger values (see Table 12) have been derived from pre-development background levels.
• A contingency action plan is proposed if trigger values are reached (see Section 10.2.2.2).
Additional monitoring will be required if temporary sewerage pumping arrangements are proposed (see Section 10.3). Monitoring will begin from approval of subdivision application (i.e. pre-development), continue during construction and end when the network is connected to Water Corporation’s reticulated sewer network. To summarise:
• Groundwater quality on a quarterly basis (see Table 11). Water quality trigger values (see Table 12) will be updated with additional pre-development monitoring. Concentrations will be compared to trigger values, NWQMS (ANZECC and ARMCANZ 2000) and ADWG (NHMRC and NRMMC 2017).
• A contingency action plan is proposed if trigger values are reached (see Section 10.2.2.2).
If temporary sewerage pumping arrangements are essential, they should be located as far away as possible from bores. Automated telemetry of sewerage levels needs to be in place to prevent overflows.
A fully reticulated sewerage system is proposed for the site. The servicing approach outlined in Section 5.4 does not require the use of temporary sewerage pumping. However, given the fragmented land ownership of the site, temporary sewage pumping arrangements may be proposed by some
developers. A developer considering temporary sewerage pumping for their subdivision will need to enter a Tanking Performance Agreement with the Water Corporation (2020), as this is only approved as a last resort. If this occurs, pumping should be located beyond the WHPZs shown in Figure 5 and monitoring measures implemented to prevent sewerage overflows (DWER 2018). This is noted in Section 9.5.
If sewerage pump stations cannot be located outside PDWSAs, they are, at the very least, to avoid WHPZs.
The project engineers have developed a full concept plan that forms the basis of an agreement with the Water Corporation for servicing of the site (KCTT 2019).
No pump stations are proposed. See Section 5.4.
Sewerage pump stations should be sized for capacity and use of the development only (i.e. not to service a larger catchment area extending beyond the development).
Table 10: Managing water quality for P3* PDWSA (continued)
Recommended measures for LWMS Management measures POS
Design to reduce demand for local water supplies, fertilizer and
pesticides e.g. use local native species and minimise turf.
The conceptual landscape designs provided in Appendix I promote the retention of existing trees and the use of feature planting across the site. These concepts strategically locate turf within playing fields, in pockets near play equipment and over the gas pipeline easement.
Stormwater and groundwater management Use the Stormwater management
manual for Western Australian and Decision process for stormwater management in Western Australia.
This LWMS has referred to the Decision Process for Stormwater Management in Western Australia (DWER 2017) and Stormwater Management Manual for Western Australia (DoW 2007a).
Make a commitment to refer the UWMP to DWER prior to finalisation.
UWMPs should be approved by CoS with advice from DWER (see Table 13).
End of conveyance stormwater infrastructure and subsoil drains should not outlet within WHPZs.
There are a number of drainage areas located in POS that are situated within WHPZs (POS 1, 2, 5 and 10). These drainage locations have been driven by existing low points and the need to tie in to existing levels at site boundaries, therefore it is considered appropriate to locate drainage in these areas. See Appendix J.
An appropriate soil medium (either amended soil with PRI>10 or media that meets the biofiltration guidelines (Payne et al. 2015)) will be used to line the BRAs and remove nutrients from runoff during infiltration, as discussed in Section 6.2.5.
The indicative arterial subsoil drainage network is proposed to outlet into the living stream and POS 13. These outlets are not located within the WHPZs.
Treatment of discharges from subsoil networks can be achieved at the end of pipe (i.e. into a WSUD measure) or prior to water entering subsoils drains (i.e.
through media or high PRI soils), as discussed in Section 7.2.
Infiltration areas should be outside WHPZs where possible, but if unavoidable, biofiltration should be used.
Managing chemicals, fuels, fertilisers and litter Adequate contingency planning in
case of groundwater or surface water contamination, i.e. emergencies.
Construction management plans submitted to the CoS will include contingency planning regarding chemicals and fuels, e.g. spill response procedures.
Fertiliser application rates and irrigation requirements should be matched to local soils and plant requirements, to manage leaching and contaminant of local water sources.
The following proposed management measures will reduce irrigation and fertiliser requirements across the site:
• Retain remnant native trees and vegetation where possible. Minimise the amount of turf beyond playing fields and select species for planted areas that require no ongoing irrigation.
• No ongoing fertiliser use is proposed within tree pits, bio-pockets, swales, BRAs or the main channel of Saint Leonards Creek, as these will be vegetated with nutrient absorbing vegetation species.
• Drought tolerant turf and vegetation species that require minimal water and nutrients to be used.
• Improve soil with conditioner certified to Australian Standard AS4454.
• Design and install the irrigation system according to best water efficient practices.
• Mulch garden beds with a product certified to Australian Standard AS4454.
• Minimise use of fertiliser and utilise slow release fertilisers. The application of fertiliser on turf within active POS areas or playing fields should be conducted in accordance with best management practices (SRT 2014).
Table 10: Managing water quality for P3* PDWSA (continued)
Recommended measures for LWMS Management measures Only use clean fill that is suitable for
protecting drinking water quality, i.e.
does not introduce contaminants.
Clean fill should be used where fill is required to ensure groundwater level management requirements are achieved. This has been noted in Section 9.2.
Retain areas of existing native vegetation as much as possible.
Where possible, and appropriate from a landscape perspective (e.g. safety), existing trees within POS areas should be retained to provide amenity for future residents.
No underground fuel or chemical storage, i.e. no service stations.
The land uses proposed in the SP (see Appendix A) do not include any commercial areas (i.e. service stations).
Adequate erosion control. Overflow from stormwater management structures should occur via a broad and shallow weir structure or similar (i.e. a low point that can be designed to avoid erosion), and/or appropriate outlet structure (e.g. gully pit within a median swale). Similarly, erosion controls will need to be considered when designing the Saint Leonards Creek main channel during subdivision.
Use appropriate herbicides. The application of herbicides will be compliant with PSC 88: Use of Herbicides in Water Catchment Areas (DoH 2006).
Education and awareness Include PDWSA awareness-raising strategies targeted at community, land sales and purchases, and builders such as brochures
(www.dwer.wa.gov.au), signs and notices.
Educational material will be provided to lot purchasers to provide information on water efficiency and water quality protection measures that they can implement within lots. Specific water conservation and protection topics may include:
• Water use reduction
• Water efficient technologies
• Fertiliser use
• Planting species
• Living in a PDWSA.
Recycled water
The use of recycled water is generally not supported.
The use of recycled water is not proposed.
Infrastructure
Planning, constructed and maintained to protect drinking water source, particularly WHPZs.
Infrastructure corridors, construction and maintenance should be completed in accordance with WQPN 38: Infrastructure corridors near sensitive water resources (DoW 2007b).
Bores
Bores need to be appropriately located and constructed to prevent contamination of the public drinking water source.
Bores should be located and constructed in accordance with Minimum
construction requirements for water bores in Australia (National Uniform Drillers Licensing Committee 2012).
Bores should not be located in WHPZs.
Production bores will need to be located beyond the existing gas pipeline corridor and WHPZs, as noted in Section 9.7.
Bores no longer used should be properly decommissioned.
Once bores are no longer used, they will be decommissioned in accordance with Minimum construction requirements for water bores in Australia (National Uniform Drillers Licensing Committee 2012). For example, some of the existing production bores shown in Figure 5 may be decommissioned following subdivision works or prior to handover of POS to the CoS.
9 Future Subdivision and Urban Water Management Plans
The requirement to undertake preparation of more detailed water management plans to support subdivision is generally imposed as a condition of subdivision. The development of any future UWMP(s) should follow the guidance provided in UWMPs: Guidelines for Preparing Plans and for Complying with Subdivision Conditions (DoW 2008b).
While strategies have been provided within this LWMS to address planning for water management within the site, it is a logical progression that future subdivision designs and the supportive UWMP(s) will clarify details not provided within the LWMS. The main areas that will require further
clarification within future UWMP(s) include:
• Geotechnical investigations
• Imported fill specifications and requirements
• Modelling and configuration of Saint Leonards Creek
• Modelling and configuration of estate drainage structures
• Wastewater servicing
• Implementation of water conservation strategies
• Confirmation of irrigation source
• Non-structural water quality improvement measures
• Management and maintenance requirements
• Construction period management strategy.
These are further detailed in the following sections.