Increasingly, water authorities are recognising the benefits
of properly managed effluent irrigation. At the same time, treatment and
discharge (load-based licensing) costs are steadily rising, driven by
the need to mitigate the effects of effluent discharge on surface water
and groundwater, together with ever-tightening water quality standards.
This trend has encouraged a move towards land-based treatment of wastewater.
In a well-designed system, the overall impacts on groundwater quality
are generally small, but the potential remains for by-products of effluent
irrigation to compromise groundwater quality.
Assessment of the diverse impacts of effluent irrigation on underlying
groundwater resources demands a broader approach than that employed
in conventional contaminant hydrogeology practice. C. M. Jewell &
Associates Pty Ltd (CMJA) has a considerable depth of expertise in investigations
of land effluent irrigation sites. Our wide range of innovative investigative
tools include electromagnetic, aeromagnetic and DC groundwater geophysics,
aerial-photogrammetric analysis, soil/sub-soil surveys, drilling investigations
and specialised water sampling methods. Analysis of field data is planned
at a level appropriate to the project goals, but may include estimation
of infiltration rates, calculation of groundwater velocities, contaminant
mass balances, geographic analysis (using digital GIS technology), groundwater
modelling or contaminant transport modelling.
Each project is tailored to the requirements of the client, and takes
into account the need to provide supporting information to regulatory
authorities or project management.
CMJA's hydrogeologists offer an impressive range of project experience
in the field. Completed projects cover a number of industries such as
feedlots, sewage discharges, milk-processing facilities, dewatering
re-injection and landfill leachate discharge. Several of the more interesting
examples are given below.
Impact of expanded effluent irrigation, Gooloogong, NSW
Moxey Farms' proposals to expand dairy effluent irrigation were
assessed in relation to their potential to impact on underlying
groundwater. An alluvial sequence hosting a multi-layer aquifer
system was somewhat vulnerable to groundwater quality alteration
following the irrigation of dairy effluent over areas of pasture
and land used for fodder production. Investigative work comprised
extensive electromagnetic surveys to identify higher permeability
sand lenses, DC resistivity soundings to enhance depth resolution,
backhoe test pit examination, soil permeability testing, drilling
of boreholes into the unconfined aquifers and delineation of pre-irrigation
groundwater quality. Using the results of these investigations,
CMJA identified pasture areas with greater sensitivity and developed
a program to monitor shallow groundwater quality.
Wastewater storage and irrigation scheme, Bannockburn, Victoria
CMJA was asked to assess the likely impact on groundwater of a
proposal to store and irrigate sewage wastewater on land. A geological
and electromagnetic survey of the site indicated that once excess
fluid passed through residual soils and subsoils, groundwater
would move laterally in alluvial sands towards a local creek.
It was recommended that the storage basin be relocated, and shallow
groundwater quality monitored.
Potential effluent re-use sites, Dubbo, NSW
In the Dubbo area, much of the effluent produced by the sewage
plants is disposed of via effluent irrigation. Expected future
increases in the amount of effluent generated by the sewage plants
prompted Dubbo City Council to identify additional sites suitable
for effluent irrigation. CMJA was commissioned to review hydrogeological
conditions of the proposed sites, and to make a preliminary assessment
of the potential impact of effluent irrigation on groundwater
resources at each site.
Small-scale on-site effluent disposal systems, City of Blue
CMJA has conducted numerous site suitability assessments for on-site
effluent disposal systems within the Blue Mountains. Such a process
involves assessing the regional and local topography and hydrogeology,
and also identifying key soil characteristics of the site, including
geology, soil profile and permeability, as well as soil pH and
electrical conductivity. Assessments of this type help prevent
risks to public health, prevent adverse impacts on the water quality
of local watercourses and groundwater systems, and prevent the
degradation of soils and native vegetation. Such studies ensure
that the proposed effluent disposal system is functional and environmentally
sound in the long term.
How CMJA can help you
We have the expert capability to deal with the complexity of issues
and factors related to effluent irrigation assessments. Whether the
project's requirement is to unravel complicated hydrogeological settings,
to demonstrate nutrient cycling and geochemical processes, or to make
reliable predictions of water quality impacts, CMJA hydrogeologists
can meet that requirement.
The company also offers a full service consultancy in this field, from
water sampling to expert testimony.