Stage 1 Irrigation Area_90 Beach Rd Noosa North Shore 12.06.2020 · MCU19/0117

EFFLUENT IRRIGATION MANAGEMENT PLAN - STAGE 1 } »
NOOSA NORTH SHORE ECO-TOURISM PORTAL q Cardno

 

3.

PROPOSED TREATED EFFLUENT IRRIGATION

It is proposed to reuse treated sewage effluent from the STP for landscape irrigation.
The location of the proposed irrigation area is indicated on Figure 1. The STP will
provide tertiary treatment with removal of microorganisms, suspended solids and
nutrients including nitrogen and phosphorous. Final effluent released from the STP will
be of a high quality with treatment to a Class A+ standard. Treated effluent use will be
carried out in accordance with the requirements of the National Water Quality
Management Strategy Guidelines for Sewerage Systems Use of Reclaimed Water.

The irrigation area will be vegetated with turf or pasture grass. Irrigation of the area will
be by sub-surface drip irrigation system. A diversion bank is proposed along the
western margin of the irrigation area to direct external runoff away from the irrigation
area towards the existing dam on the property to the north.

3.1 Irrigation Areas Design

MEDLI modelling was used to determine an acceptable combination of irrigation area
and wet weather storage size for effluent quantities generated from the STP. Various
combinations of irrigation scheduling, irrigation area, plant type and wet weather
storage volumes were trialled to determine a suitable combination that would result in
minimal overflows from the wet weather storage, acceptably low N and P levels in the
deep drainage, and no build up of phosphates or salinity in the soil or groundwater.

The expected effluent irrigation rate for the south site has been calculated as 47.1
kLiday (420EP x 112 L/EP/day), or 17.2 ML/year. These figures were adopted for the
purposes of MEDLI modelling. The EP figure of 420 is based on an average occupancy
rate of between 80% and 90% and is reduced from the EP of 482 at full occupancy of
the south site. The per capita wastewater generation rate is reduced from 140L/EP/day
to 112L/EP/day to account for the quantity that will be recycled for toilet flushing. The
application rate for treated effluent to irrigation areas was calculated as approximately
5 ML/ha/year requiring a disposal area of 3.8 hectares. The required wet weather
storage capacity was determined to be 3ML providing 60 days storage.

For Stage 1 the predicted EP of 112 will require a disposal area of 1 hectare, which will
be constructed as part of the Stage 1 operational works. The wet weather storage
required is approximately 940kL, however, it is proposed to construct the storage
lagoon for the full development during Stage 1. The storage lagoon will be a minimum
of 4.6ML capacity. The requirements for the size of irrigation areas will be confirmed at
each stage of development after monitoring of the receiving environment to
demonstrate that no environmental impacts arising from operation of the STP and
effluent irrigation system has occurred.

3.2 Irrigation Scheduling

Irrigation will be restricted to a maximum of 4 mm per day. The moisture content of the
irrigation area will be determined prior to irrigation taking place. It is proposed that
moisture-sensing probes will be installed throughout the irrigation area. Readings from
these will indicate the degree of saturation of the soil and whether irrigation can take
place. Should ponding occur, irrigation will cease until such time as the soil moisture
content has sufficiently reduced to eliminate further ponding.

 

Petrac Leisure NNS-S Pty Ltd Version 2 17 July 2006
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