Introduction
Groundwater is the South East region's main source of water.
It supports internationally significant ecosystems and recharges
Blue Lake.
The groundwater of the South East is in two aquifers: an upper
unconfined aquifer and a lower confined aquifer. Over most of
the South East these two aquifers yield high quality water that
is used extensively over the region. >> More
The unconfined aquifer underlies much of the South East region
and is the main water source, supplying water to most towns in
the region. Groundwater may come to the surface in some areas
on the plains, and be as deep as 60 m in the Tintinara area. More
detailed information on the depth of the watertable can be obtained
from The
Department of Water, Land and Biodiversity Conservation.
The water in the confined aquifer entered in Victoria. This water
is estimated to be more than 25,000 years old by the time it reaches
parts of South Australia. It is separated from the unconfined
aquifer by an impermeable layer. The confined aquifer is not present
under the whole of the South East and is thin or absent in some
parts such as Padthaway. The depth of the confined aquifer varies
from 35 m to 300 m. The confined aquifer is under pressure in
many places, which can cause water temperatures to be as high
as 30°C.
What are the concerns about the aquifers?
Salinity of the unconfined aquifer is one of the major factors
that limits water use in the South East. The salinity increases
significantly towards the north and west of the region. It varies
from 400 mg/L, which is suitable for drinking, in the lower South
East to 35,000 mg/L, or about the same as seawater, in the Tintinara
area.
Groundwater contamination of the unconfined aquifer is the result
of either point source contamination (e.g. spills from copper-chrome-arsenate
wood preservation industries) or diffuse source contamination.
Point source contamination of the aquifer is due to the historical
disposal of wastes into it by industries such as dairying, timber
mills, gasworks, cheese factories, abattoirs and septic disposal.
The Environment Protection Act now prohibits disposal of waste
into the aquifer.
Inappropriate pesticide use has resulted in groundwater contamination,
to the extent that organochlorine and triazine pesticides have
been detected in groundwater in parts of the region.
Diffuse source contamination of the unconfined aquifer is due
to agricultural activity and forestry. Diffuse nitrate pollution
has had the largest effect on the aquifer with increasing nitrate
levels being observed in groundwater south of Mount Gambier and
in the Coonawarra area. Pesticides have also been detected in
limited testing of groundwater in the lower South East. The problem
of diffuse source contamination is being addressed by better land
management practices.
The water quality of the confined aquifer is very good because
the aquifer is protected from contamination not only by its depth,
but also by the presence of the confining layer that separates
the two aquifers.
What is being done to improve the condition
of groundwater in the South East?
The EPA has a regional office in the South East. One of its roles
is to manage and regulate potential pollution of the aquifers.
Key EPA strategies for managing pollution include:
- groundwater monitoring programs as core licence conditions
for licensees who could pollute groundwater
- a risk assessment of groundwater contamination associated
with historical and current copper-chrome-arsenate timber treatment
plants
- a risk assessment of pollution threats to Blue Lake is currently
being made as a joint government and CSIRO research project.
This project is intended to link aquifer hydraulics with surface
water pollution threats to provide planning and management tools.
The risk assessment will provide the basis for future groundwater
monitoring in the Mount Gambier region
- presence on regional management boards, engaging the community
and industry and providing guidance
- development of a code of practice for regional stormwater
disposal
- development of a concept model of Blue Lake identifying information
gaps
- monitoring programs targeting key aquifer units and Blue Lake
- commissioning work to investigate long-term trends in nitrates.
There are close links between groundwater quantity, quality and
supply in the South East. To this end, The
Department of Water, Land and Biodiversity Conservation is
investigating the flow patterns around and into Blue Lake. This
work will feed into a risk assessment of the lake.
Groundwater monitoring in the South East
The EPA monitors groundwater across the South East for a wide
range of analytes. Many industrial sites, ranging from timber
mills to landfills, are required to monitor the groundwater in
the vicinity of their site to ensure that they are not affecting
the groundwater.
The EPA groundwater monitoring program in the South East is grouped
into programs centred on the main towns and areas of agricultural
activity including Keith, Millicent,
Coonawarra and Padthaway.
The area in between these groups (referred to as the Greater
Mt Gambier Program) is also monitored to ensure groundwater quality
throughout the South East region is covered. Go here
to see a summary of groundwater monitoring results for the South
East region.
The aquifer system that feeds Blue Lake in Mt Gambier (the Blue
Lake Capture Zone) is also separately monitored because of
its importance as a water supply.
Reports
Nutrient movement through SA soil
(674KB PDF)
Contamination
of Australian Groundwater Systems with Nitrate
Nitrate
contamination of the Blue Lake, Mt Gambier
Links
South East
Natural Resources Management Board
This page was last modified 05-09-2006
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