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SITE
HISTORY, OWNERSHIP AND USE
One-Mile Dam, or Railway Dam as it is also known,
is a freshwater lagoon on Lot 5027 Dinah Beach Road, Stuart Park.
The NT Government
property is owned under the 1979 “Special Purposes Lease
00454” by the Aboriginal Development Foundation Incorporated
and occupied by the One Mile Dam Community, Kumbutjil Association
Inc.
Approximately
150 people, reside at the property.
One-Mile Dam,
a 3250 square metre lagoon, is located downstream of a light industrial
area of Darwin. Neighbouring properties include major oil storages,
the Tank Farm, AMPOL, BP and Shell depots. During the past few
years’ land uses inthe vicinity have changed to residential
with new multi residential subdivisions at Stuart Park and Dinah
Beach. Relocation of the Tank Farm to East Arm and remediation
of the Shell depot are recent land rehabilitation initiatives
for the neighbourhood.
Ownership of land and drainage easements in the immediate
One-Mile Dam
stormwater catchment is as follows (Appendix 1 – Copies Certificate
of Title):
1) Lot 5027 plan 75/116; Aboriginal Development
Foundation Incorporated – Special Lease
2) Lot 5196 plan S 75/116 – Department
of Transport & Works – Administrative Parcel
“Drainage easement”
3) Lot 5193 plan S 75/116 – Department
of Transport & Works – Administrative Parcel
“Drainage easement”
4) Lot 5940 plan S 911035 – Crown,
– Administrative Parcel
5) Lot 4360 plan A000413 – Ampol
Petroleum Limited
SITE
MAP 1 One Mile Dam
- Environment
Report – One Mile Dam
ENVIRONMENTAL HEALTH
One-Mile Dam, thought to be fed by a subterranean spring, has
acted as a stormwater detention pond for the immediate industrial
area and parts of the wider Darwin CBD for many decades.
Despite this
history, anecdotal evidence suggests that the lagoon supports
an abundance of fish, turtles and various other aquatic flora
and fauna. In keeping with environmental change experienced in
waterbodies that act as sediment/debris traps elsewhere in Australia,
water quality at One-Mile Dam has deteriorated over time. This
deterioration is evidenced by blue-green algae blooms, accumulation
of litter and rubbish.
It is also
to be expected that trace elements, including heavy metal and
hydrocarbon, may build up over time from urban and industrial
stormwater run-off carrying with it contaminants from accidental
and inadvertent spills and discharges. Weed invasion and significant
bank erosion at One-Mile Dam impact terrestrial native flora.
Decaying flora and fauna lead to elevated pathogen levels.
Deterioration of Water Quality – Causes and Effects
• Eutrophication as a result of increased
amounts of dissolved and particulate
nutrients (phosphate, nitrogen, ammonia), organic matter and heavy
metals from
stormwater runoff, and erosion.
• Blue-green algae blooms, the direct result
of the eutrophication, lead to oxygen
depletion, increases in pH, release of toxins and toxic decomposition
by-products
(ie. Sulphides)
• Resuspension and/or remobilisation into
the water column of anoxic toxicants
previously locked up in sulphidic sediments (result of pH, salinity
changes,
bioturbation, rainfall)
THE ONE MILE DAM REMEDIATION PROJECT
Stormwater management requires a coordinated
partnership approach as run-off, particularly in rainfall intense
tropical regions, occurs on a catchment scale where land ownership
and property boundaries are of little relevance.
It is for this reason that the One-Mile Dam community, Kumbutjil
Association Inc, has enlisted the assistance of Greening Australia
NT, Yilli Reung Aboriginal Housing Corporation, Darwin Regional
CDEP Inc, Northern Territory Government and Darwin City Council
to initiate a program designed to improve the environmental health
of One-Mile Dam.
Measures
to be implemented include:
• a spot check assessment of One-Mile Dam’s
water quality and sediment quality followed by the development
of a formal water quality monitoring and environmental health
improvement program;
• rehabilitation of the Dam’s banks
through erosion controlling revegetation and weed management projects;
• the installation of litter curtains to
contain some run-off sediments, litter and rubbish.
The NT Government provided $ 10,000 funding in February 2005 through
the 2004/05 EnvironmeNT Grants.
WATER/SEDIMENT QUALITY ASSESSMENT
Sample collection and analysis
While anecdotal evidence suggests that various NT Government departments
have conducted some water quality monitoring at One-Mile Dam there
appears to be no formal ongoing monitoring regime for the site.
Analytical water quality data was not available for review.
For this reason,
and to facilitate the development of an ongoing monitoring and
rehabilitation program, an initial assessment was conducted at
2 easily accessible sites (Appendix 1 – Site Map 2):
-
Environment Report – One Mile Dam
1. Sampling site 1 was located within One Mile
Dam at the mouth of the stormwater drain to Lot 5196 which flows
towards Frances Bay; and 2. Sampling site 2 was
located midway on the lagoon, directly opposite the Community Office
Two water and two sediment samples were taken at each site for
trace element analysis by ICPMS and ICPOES. Northern Territory
Environmental Laboratories Pty Ltd (NTEL) conducted analyses for
trace elements. A second set of water samples,to determine pathogen
levels, were taken at the same sites for analysis by DBIRD’s
Water Microbiology Laboratory. (Appendix 2 - Analytical
results)
Trace element levels investigated are commonly associated with
the land use of the
area and include Aluminium (Al), Arsenic (As), Boron (B), Cadmium
(Cd), Copper (Cu), Mercury (Hg), Lead (Pb), Sulphur (S) and Tin
(Sn).
Pathogen analysis was restricted to water samples and consisted
of the indicators faecal coliform, Escherichio coli (E.coli) and
enterococci organisms, commonly used to assess a waters suitability
for recreational use.
RESULTS
Analytical results overall are consistent with those frequently
observed in urban stormwater drainage systems. While
heavy metals in One-Mile Dam waters are within water quality guideline
values for recreational pursuits except for Aluminium (Al), the
microbiological characteristics of One-Mile Dam indicate that
swimming and other recreational activities can not be recommended.
The implementation
of a more extensive monitoring program is highly recommended given
the substantial quality differences between the 2 sites sampled
during this very limited assessment. An efficient, cost effective
ongoing monitoring regime should be developed as a matter of priority
if One-Mile Dam is to be used for recreational activities.
Heavy Metals
Heavy metals do not degrade but are transferred or stored in bottom
sediments, which act as a sink. Various reactions both microbiological
and physio-chemical can transform and redistribute metals within
the sediments and to the water column. The presence of sulphides,
an acidic gas, may act to release heavy metals from bottom sediments.
Heavy metals in larger concentrations are toxic to many marine
species and can be bioaccumulated by fauna through the food chain.
It is therefore in the interest of the long-term environmental
health of One Mile Dam to minimise sediment deposition into the
lagoon.
Elevated levels of cadmium, lead and copper (in the water column
and sediments) can be prevented over time by appropriate management
initiatives such as the periodic removal of solids building up
around stormwater drainage points.
Pathogens
Microbiological characteristics of One-Mile Dam show that
the water was unsuitable for human interaction. Swimming
and other recreational pursuits should not occur while Escherichio
coli and enterococci organisms are at the level determined during
sampling.
While Faecal coliform bacteria are virtually present in all warm-blooded
animals, the high level of E. coli and enterococci organisms found
should give rise to an investigation of the local sewerage system
to ensure its integrity is intact.
Pathogen levels in excess of guideline recommendation may lead
to ear, eye, nose and throat infections, skin diseases and gastrointestinal
disorders. (Hart 1974,
McNeill 1985)
REHABILITATION OPTION
With the decommissioning of the tank farm and after completion of
land rehabilitation at the nearby fuel storage, hydrocarbon discharges
into One-Mile Dam should decrease significantly. Combinations of
several rehabilitation measures are available to improve the environmental
health of One-Mile Dam and halt further deterioration.
- Environment
Report – One Mile Dam
RECOMMENDATIONS
1. Examination of the local sewerage system should be undertaken
to ensure leakage and overflows into the Dam do not occur.
2. The biologically
activated carbon PICABOL, known to absorb a range of organic and
inorganic pollutants (blue-green algae toxins, hydrocarbons and
heavy metals), can be floated in the Dam to remove contaminants
from the water column over time. Floating geotextile bags filed
with PICABOL are capable to remove contaminants for up to 2 years
as water filters through the activated carbon.
3. Floating litter curtains should be installed at each of the
drainage out and inlets to contain litter and gross pollutants
for periodic removal and disposal to landfill.
4. The current fencing, installed by Yilli Rreung Aboriginal Housing
Corporation, should be retained and supplemented with No Swimming/No
Fishing signage until otherwise indicated by water quality monitoring
results.
5. A Weed management and revegetation program should be implemented
to halt erosion and improve visual amenity at the site.
6. A monthly Water Quality and 6-monthly sediment and biological
tissue monitoring program should be developed and implemented
at representative sites to monitor environmental health changes
(improvements and deteriorations) at One Mile Dam. The sampling
program should also include Hydrocarbon analysis given the area's
land use history
7. If future sediment monitoring indicates that heavy metals and/or
hydrocarbons are present in excess concentrations, application
of Phoslock™, a modified bentonite product which seals bottom
sediments preventing release of contaminants should be considered.
CSIRO
Land and Water and the Western Australian Water
and Rivers Commission developed Phoslock™, a modified
bentonite, in the mid 1990s. Extensive laboratory and field trials
have shown that it is effective in removing filterable reactive
phosphorous (FRP). Furthermore, the thin layer of PhoslockTM,
which settles on the bottom sediments of water bodies, has also
been demonstrated to be effective in prohibiting the release of
FRP from the sediments.
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by
ANGELIKA HESSE -
----------Environment
MANAGER --------- DARWIN
CITY COUNCIL
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Note:
Recommendations in this report are based on a very
preliminary environmental quality assessment. Further environmental
monitoring of One-Mile Dam may lead to a re-evaluation of conclusions
and recommendations made.
Except as otherwise stated in this report, Darwin City Council has
not undertaken further verification regarding the accuracy or completeness
of information sources that may be available for One Mile Dam.
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Cleaning
up the Dam
Rehabilitation
project underway (15th
May, 05)
Volunteers
welcome |
Download
pdf file (130kb)
Environmental
Rehabilitation
Report - by
ANGELIKA HESSE |
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