2017-07-11 Planning & Environment Committee Agenda

PLANNING & ENVIRONMENT COMMITTEE MEETING AGENDA   11 JULY 2017




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PLANNING & ENVIRONMENT COMMITTEE MEETING AGENDA                                                     11 JULY 2017

              If the POD objectives were derived from the Water Studies P/L, the derived objectives
              predates the ANZECC Guidelines (2001), the Environmental Protection (Water) Policy
              (2009), the Mary River Environmental Values and Water Quality Objectives (nominates site
              as ‘Lowland Freshwaters), the Urban Stormwater Quality Planning Guidelines (2010) and
              most notably, the work of Fletcher et al (2004).
              As such, it is arguable that the targets associated with the POD are not reflective of currently
              accepted data and are unrealistic, particularly as data suggests undeveloped catchments
              generate pollutant loads in excess of the targets during storm events.
              Further, an extract from Water by Design (2007) WSUD: Developing Design Objectives for
              Water Sensitive Developments in SEQ Version 2. highlights the appropriate way of reporting
              on the concentrations based targets (as per the POD) and also suggests a move to the
              current Load Based Reduction targets. The extract is as follows:
                    The present concentration-based approach to stormwater quality management, as well
                    as the current method of setting the target concentration values, introduces several
                    ambiguities and inconsistencies to the regional framework for urban stormwater
                    management. Setting concentration-based targets for stormwater discharges relies
                    upon some Statistical assessment of stormwater quality and quantity. A typical
                    approach is to set a target median (50"" percentile) concentration. However, stormwater
                    in SEQ is ephemeral with “zero” flow for a substantial proportion (often more than 50%)
                    of the time. The definition of the median is therefore ambiguous. This ambiguity is
                    commonly resolved by taking the median concentration during periods when flow is
                    non-zero. However, since demonstration of compliance of a proposed stormwater
                    management system relies on numerical modelling, the median concentration can be
                    highly sensitive to the adopted model parameters. Adjusting these parameters to
                    generate a long period of very low baseflow can make it easier to demonstrate
                    compliance with the target concentration, while the majority of pollutant load is
                    discharged during events.
                    At present, receiving water quality objectives, derived from ambient “dry weather”
                    pollutant concentrations measured in receiving waters, are commonly adopted as the
                    target concentrations for stormwater discharges. This approach fails to recognise the
                    substantial difference between the pollutant characteristics of urban diffuse sources
                    during dry and wet weather flows, as well as the impact of pollutant load on receiving
                    waters.  In addition, it is inconsistent with ANZECC (2000,        p.2-17) and the
                    Environmental Protection (Water) Amendment Policy No. 30, 2006 (No. 1) (p 13) which
                    notes that scheduled receiving water quality objectives do not apply to stormwater
                    discharges. ANZECC (2000, p.3.3-2) recommends that load based guidelines be
                    developed for nutrients (Total Nitrogen and Total Phosphorus), biodegradable organic
                    matter and suspended particulate matter (or Total Suspended Solids). This is in
                    recognition of the important impact of the total mass (or load) of these pollutants on
                    aquatic ecosystem health.

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