Recycled Water Irrigation in Australia - Environmental Sustainability: Role of Green Technologies - page 44

poor crop growth and health, mobilisation of
salts and contaminants, rising water tables and
run-off (NRMMCEP and HCAHMC 2006 ). The
irrigation requirement is essentially the differ-
ence between the crop water requirements and
the rainfall but also must take into account the
seasonal changes in rainfall, homogeneity of
water infi ltration and the leaching requirement
(Christen et al. 2006 ). Whilst leaching is often
necessary to drive salts below the root zone, it is
important that it is not conducted at the expense
of a rising water table. A balance must be reached
between the total water requirements of the crop
and preserving the normal hydrologic function.
Regional and local groundwater levels should be
monitored so that any changes can be detected
and managed appropriately.
The pathogen content of reclaimed water is
often the limiting factor with regards to irrigation
method; for example, class A water can be
applied to crops which are eaten raw by any irri-
gation method, water consistent with class B can
only be used to irrigate these crops by furrow or
dripper irrigation and class C must be applied by
subsurface drippers. Furrow or fl ood irrigation
has the advantage of being relatively inexpensive
and low in manpower requirements, but unless it
is well designed and managed, infi ltration can
vary greatly throughout the irrigation space.
Because sprinklers commonly apply water
directly on foliage, their use on produce con-
sumed raw is limited to class A water. Even with
class A water, direct ion toxicities (with saline
reclaimed water) and an increased propensity to
develop fungal disease can be a concern where
foliar application of water occurs (Christen et al.
2006 ). The most effi cient system with the least
environmental and human risk is generally con-
sidered to be drip irrigation (Christen et al. 2006 ).

reclaimed water should be tailored to optimise
the economic returns to the grower whilst also
minimising the impact on the receiving environ-
ment. This can best be achieved by undertaking a
comprehensive risk assessment of the whole
scheme and designing an irrigation management
plan to minimise the risk of adverse outcomes.
The risk assessment should be based on the
potential health impacts and soil, site and waste-
water characteristics as follows:
• The soil properties examined should include
soil texture, topsoil depth, depth to drainage or
root impeding layers, infi ltration rates, soil-
water holding capacity and soil chemistry.
• Site characterisation must make assessment of
topography, slope, soil homogeneity, history
of waste storage or disposal on site, depth to
groundwater and seasonal or permanent water
tables, areas of drainage hazard and separation
distances from sensitive areas.
• Wastewater analysis should describe the
reclaimed water with reference to total solids,
suspended and volatile solids, total P, inor-
ganic P, total N, NH 4 + -N, K, SO 4 2− , BOD, pH,
electrical conductivity, SAR, Ca, Mg, organic
C, Na and Zn.
• Potential health impacts must be addressed
with the relevant state health authority.

5 Case Study: Northern

Adelaide Plains Irrigation
Scheme

The Northern Adelaide Plains Reclaimed Water
Scheme (or Virginia Pipeline Scheme), South
Australia, provides irrigation for over 20 differ-
ent types of crops within an area of approxi-
mately 200 km 2 (Laurenson et al. 2010 ). It was
the fi rst scheme of its type in Australia and
remains as one of the largest reclaimed water
schemes in the southern hemisphere. It supplies
approximately 180 GL of tertiary treated, class A
wastewater from the Bolivar Wastewater
Treatment Plant (WWTP) to horticultural grow-
ers on the Northern Adelaide Plains through
more than 100 km of pipelines (Laurenson et al.
2010 ). In 2008, the scheme encompassed 400

4.2 Best Practice Management

Best practice irrigation with reclaimed water can-
not be achieved by a one-solution-fi ts-all
approach because there are a multitude of vari-
ables which must be considered, and each enter-
prise is unique. Irrigation schemes using