Post-development monitoring will be implemented by the developer of each subdivision area after the completion of the relevant civil and landscaping works. It will continue for a period of three years until handover of POS areas to the CoS. A monitoring summary report will be submitted to the CoS at the end of the three year monitoring period.
10.2.1 Condition
The overall condition of the site once developed will be monitored on a bi-annual basis until
handover of POS to CoS. The monitoring program should include a visual assessment to monitor the overall condition of the subdivision area, with the aim to ascertain that the maintenance activities are achieving the overall management objectives for the site. The parameters that will be monitored include:
• Nutrients and water quality
• Gross pollutants
• Terrestrial weeds
• Irrigation
• Vegetation density
• Condition of paths, walkways and other infrastructure.
Where applicable, the management and maintenance objectives will be detailed within future UWMPs along with details of the corresponding monitoring program.
10.2.2 Water quality
Water quality will be monitored to determine the effectiveness of the WSUD approach at managing nutrients, and to guide the future management actions that have the potential to influence water quality beneath, and leaving the site.
Groundwater quality will be used as an analytical tool to determine the success of the overall
development (i.e. as compared to pre-development monitoring). Monitoring bores should be located upstream and downstream of a representative POS area and, if relevant to the subdivision area, at the same location as the pre-development monitoring bores. Groundwater quality will be measured quarterly.
Surface water quality will be monitored to provide an indication of the overall performance of the WSUD measures and the overall development. Water quality within Saint Leonards Creek (see Figure 9) will be measured monthly over winter (when flowing), which typically occurs from June to
October. This monitoring is not required to be conducted for subdivisions located beyond the Saint Leonards Creek foreshore area.
Monitoring of water quality discharging from the subsoil network (if present) is also proposed. Water quality will be sampled at one discharge location within each future subdivision. Subsoil water quality will be measured monthly over winter (when flowing), which typically occurs from June to October.
A summary of the post-development monitoring program is shown in Table 11.
Table 11: Post-development monitoring program summary
Monitoring type Locations Frequency Parameters
Groundwater
Upstream and downstream of a representative POS area and pre-development bore locations (if relevant).
Quarterly (typically Jan, April, July, Oct) until handover
• In situ pH, EC, DO, temperature pH and Redox.
• Sample NH3, NOX, TKN, TN, TP, and reactive
phosphorous as P.
• Faecal coliforms and Escherichia coli.
• Inorganics and metals (included in standard laboratory drinking water suites).
• Hydrocarbons Subsoil drain discharge One discharge location (if
present) within subdivision.
Monthly over winter (typically from June to October) until handover
Surface water Within Saint Leonards
Creek. As above, and TSS
10.2.2.1 Trigger criteria
Interim water quality targets have been derived from average background levels measured during monitoring prior to development, provided in Section 3.4.4 and in Appendix E. Trigger values have also been established in consideration of the NWQMS (ANZECC and ARMCANZ 2000), the Swan- Canning WQIP (SRT 2009) guideline trigger values and the WQIP for Saint Leonards Creek (SRT 2011).
The trigger criteria proposed are shown in Table 12. These values may be subject to change in the event that additional site specific pre-development monitoring is undertaken.
Table 12: Water quality trigger values
Analyte Units Groundwater and subsoil discharge Surface water
pH ph units 3.7 – 8.0 6.5 – 8.0
EC mS/cm 0.12 – 1.32 0.12 – 0.3
TN mg/L 6.85 1
NH3 mg/L 0.08 0.08
NOX mg/L 4.34 0.15
TKN mg/L 2.58 NA
TP mg/L 1.05 0.1
Reactive phosphorous mg/L 0.8 0.04
TSS mg/L NA NA
Faecal coliforms colony forming unit /100 mL 23 23
Escherichia coli colony forming unit /100 mL 23 23
10.2.2.2 Contingency action plan
In the event that trigger conditions are reached during monitoring a number of contingency
measures may be employed. The first action that will be undertaken if trigger criteria are exceeded is to repeat the monitoring to remove the potential for sampling error. If trigger values are exceeded for two or more consecutive monitoring events, the following should be undertaken:
• Notification to Water Corporation if any WHPZs are affected.
• Compare upstream and downstream concentrations to identify whether the subdivision area is contributing to increased levels.
• Compare all concentrations (i.e. from groundwater, subsoil discharge and surface water quality) to identify the general area which may be contributing to increased levels.
• Implement appropriate contingency action(s) in consultation with CoS:
o Identify and remove source if possible.
o Review implementation of management and maintenance practices.
o Remove sediments from side entry pits, inlet pits etc.
o Scarify surface between plants within treatment measures and remove accumulated sediment (e.g. top 2 to 5 cm) if signs of sediment accumulation and/or clogging are evident.
o Manual scraping of moss if signs of excessive growth are evident within vegetated treatment measures, as moss can bind the surface and contribute to clogging.
o Investigate and undertake appropriate maintenance if poor plant health or meagre
coverage (e.g. poor species selection, shading, too dry, too wet, smothered by litter, weeds etc.) are evident within treatment measures.
o Manual removal of excess plant material within treatment areas to maintain plant densities.
• Resample water quality following implementation of agreed action(s) and repeat the sample comparison/analysis process d escribed above. If the downstream concentrations are found to be generally consistent with the upstream concentrations it may be necessary to revise trigger values in consultation with the CoS, Water Corporation and DWER.