Representations

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 (50th 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.