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BURNIE WASTE MANAGEMENT CENTRE
STAGE 1 LANDFILL LEACHATE TREATMENT WETLAND
DEVELOPMENT PROPOSAL & ENVIRONMENTAL MANAGEMENT PLAN
EXECUTIVE REPORT
NOVEMBER 2015
Perth12 Monger StreetPerthWA,Australia 6000t +61[0]8 9227 9355f +61[0]9 9227 5033
ABN : 39 092 638 410
Melbourne2/26-36 High StreetNorthcote VIC,Australia 3070t +61[0]3 9481 6288f +61[0]3 9481 6299
www.syrinx.net.au
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This Development Proposal and Environmental Management Plan was prepared by:
Syrinx Environmental Pty Ltd
Head Office:
12 Monger Street, Perth 6000, WA
Contact Person: Dr Kathy Meney
Company Director | Principal Scientist
Telephone: 08 9227 9355
Email: kmeney@syrinx.net.au
For:
Burnie City Council
Registered office
PO Box 973, Burnie 7320
Contact Person: Mr Rowan Sharman
Manager Engineering Services
Telephone: 03 6430 5752
Email: rsharman@burnie.net
Significant input regarding the landfill stability and potential associated risks was provided
by Tasman Geotechnics.
The DPEMP will be submitted to:
The Chairperson
Board of the Environment Protection Authority
GPO Box 1550, Hobart TAS 7001
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TABLE OF CONTENTS
1.0 PURPOSE OF REPORT 1
2.0 PROJECT OVERVIEW 1
2.1 KEY DRIVERS FOR THE DEVELOPMENT PROPOSAL 1
2.2 STAKEHOLDER CONSULTATION 2
2.3 EDUCATION & RESEARCH 2
2.4 SUMMARY OF BENEFITS 3
3.0 PROJECT PROPOSAL 4
4.0 EXISTING ENVIRONMENT 10
5.0 LEACHATE QUALITY & FLOWS 11
6.0 POTENTIAL IMPACTS AND THEIR MANAGEMENT 12
6.1 PATHWAYS AND RECEPTORS 12
6.2 POTENTIAL WATER QUALITY AND HYDROLOGY IMPACTS 14
6.3 POTENTIAL GEOTECHNICAL IMPACTS 15
6.4 PROPOSED DESIGN CRITERIA 17
6.5 PROPOSED MANAGEMENT RESPONSES 20
7.0 MONITORING & REVIEW 23
8.0 PROPOSED COMMITMENTS 24
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LIST OF TABLES
Table 1. Wetland components and design details. 19
Table 2. Proposed water quality protection levels for discharge to the Cooee Creek
unnamed tributary. 24
Table 3. Commitments table for the Burnie Treatment Wetlands proposal. 25
LIST OF FIGURES
Figure 1. Location of the Burnie Waste Management Centre and the Stage 1 Landfill. 3
Figure
2. General site layout showing location of major components & access points
for construction and maintenance. 5
Figure 3. Preliminary system design. 6
Figure 4. Typical section through surface flow wetland. 7
Figure
5. Long section showing proposed infiltration wet forest, stormwater swale for
treatment of low flows and modified creek discharge. 8
Figure
6. Cross section showing proposed infiltration wet forest, stormwater swale for
treatment of low flows and modified creek discharge. 9
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1.0 PURPOSE OF REPORT
This report is the Executive Summary Report of the Development Proposal and Environmental
Management Plan (DPEMP) for a leachate treatment and discharge system proposed to be
constructed by the Burnie City Council (BCC) at the Burnie Waste Management Centre
(BWMC). A Notice of Intent was submitted to the EPA in September 2015, and the activity was
assessed as a level 2 activity. A DPEMP is required to be prepared for this level of
assessment, and as such this document responds to the general guidelines required for these
documents and the specific guidelines prepared by the EPA for this particular project.
2.0 PROJECT OVERVIEW
This project is located at the Burnie Waste Management Centre (BWMC), Burnie, Tasmania,
and as shown in Figure 1.
Leachate treatment at the BWMC is a component of the federally funded Stormwater
Infrastructure Development Project (SIDP). The goal of this SIDP Project is to deliver a
stormwater improvement program across the Burnie city that will reduce discharge and
infiltration to TasWater’s waste water network in order to accommodate the forecast
wastewater flows from the new Lion cheese processing plant, a lead enterprise for the
expansion of the dairy industry on the north‐west coast of Tasmania and other similar
enterprises.
The SIDP carries environmental and efficiency benefits, and ultimately it is a critical
investment in infrastructure‐readiness to realise economic expansion opportunity for the
region.
2.1 KEY DRIVERS FOR THE DEVELOPMENT PROPOSAL
The principal issues surrounding the current leachate management system and which form the
basis of this current proposal, are as follows:
Capacity issues of the existing leachate management system – high rainfall conditions
have resulted in some overflow incidences to the unnamed tributary of Cooee Creek;
that on two (2) occasions in the last few years, Stage 2A leachate has almost
overflowed from the leachate pond into the adjacent creek/stormwater system.
Seepage issues ‐ more recently these risks to the Creek have been further
exacerbated by the seepage at the toe of the Stage 1 Landfill embankment. During the
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record August/September 2013 rainfall, leachate seeped through the northern earth
containment bund of the Stage 1 landfill.
Groundwater intrusion to the leachate collection system – groundwater accounts for
the majority (>80‐90%) of leachate flows. Given this combined flow is difficult to
separate it must all be treated as leachate. This significantly increases the overall
leachate volumes requiring treatment and management.
Capacity limitation of the existing sewer network, which currently results in raw sewage
and raw leachate overflows in events greater than the 1:10 year ARI directly into
Cooee Creek (TasWater pers. comm.).
The long‐term cost to maintain discharge to the sewer system via the Trade Waste
Agreement with TasWater. Currently these charges have been agreed at 489.6kL/day
charged at $1.07 per kL from July 2014 however; these costs will escalate in time.
The continuing disposal of leachate to sewer will limit TasWater’s ability to take
additional wastewater from industry including the Lion cheese factory, which will
constrain their ability to expand and will have flow‐on effects to the dairy and other
industries.
Increased charges for sewer disposal will flow on to the community via rates and have
a negative social impact.
2.2 STAKEHOLDER CONSULTATION
A consultation process has been undertaken with the local neighbouring community and
downstream water users, TasWater, and the EPA since April 2014. TasWater is supportive of
the project, including maintaining an emergency sewer connection (subject to review of
estimated flow and frequency data from BCC). The local community is generally supportive of
the proposed improvement works. Further consultation with the community is proposed prior to
the public notification period for the DPEMP and as part of the construction and operation of
the proposed system.
In addition to environmental gains, the project is expected to provide a range of social as well
as economic benefits to these key stakeholder groups.
2.3 EDUCATION & RESEARCH
The proposed wetland system is expected to greatly enhance the aesthetic and biodiversity
values of the landfill and enable better integration of the site with its surrounding environment.
The constructed wetland system will provide an opportunity for installation of boardwalks and
other interpretative signage, and for ongoing teaching and research opportunities with links to
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the UTAS Cradle Coast Campus, the TAFE and schools. This is expected to increase
community appreciation of the site and site usage, and it is anticipated that over the time
(especially after the wetland system achieves maturation) the site will be frequently utilised by
the local community.
Planting of the wetland will be undertaken with community involvement including local schools,
the TAFE, interested local community members and the NRM group.
2.4 SUMMARY OF BENEFITS
This proposal is expected to result in the following benefits:
Increase environmental flows to Cooee creek tributary.
Enhance stormwater management and the quality of stormwater discharges.
Reduce potential raw leachate overflows to the creek via the sewer network.
Improve community engagement with and understanding of the environment and the
use of constructed wetlands and natural processes in water quality treatment.
Figure 1. Location of the Burnie Waste Management Centre and the Stage 1 Landfill
Top of Stage 1 landfill looking east. Trees mark property boundary/buffer
Stage 1 leachate pump station looking north toward Cooee Creek tributary.
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3.0 PROJECT PROPOSAL
This project is the design and construction of a treatment wetland system and associated
hydraulic and civil infrastructure at the Burnie Waste Management Centre (BWMC) to manage the
Stage 1 Landfill leachate. It also includes decommissioning of the current (Stage 1) leachate
discharge system to TasWater’s sewage network, and replacement of this with site infiltration
(median flows) and point discharge (large flows) of highly treated leachate into an unnamed
tributary of Cooee Creek.
The existing Stage 1 leachate is highly diluted due to mixing with groundwater caused by a
compromised drainage system. The only contaminants that exceed the EPA Draft Water Quality
targets for Cooee Creek are ammonium nitrogen, total nitrogen and conductivity (dominated by
alkalinity). There are occasional exceedances of aluminium, chromium, copper, nickel and zinc.
The proposed leachate treatment system will ensure any water discharged to the creek will
comply with the ANZECC freshwater guidelines and the specific targets set for Cooee Creek.
The project essentially involves the use of constructed wetland technology to remove the low
level contaminants, the use of an extensive infiltration ‘wet forest’ area for indirect discharge of
treated water within the BWMC land, and the construction of an overflow discharge point to the
unnamed tributary of Cooee Creek, at the northern boundary of the site, adjacent private land.
Improvement works to the creek are also included.
The project also includes the refurbishment of the main Stage 1 leachate pumping station to
separate leachate from site stormwater flows and incorporate a new pump and connections to the
treatment wetland; construction of an emergency leachate overflow storage tank to enable gravity
conveyance and storage of peak leachate flows; and decommissioning of the existing TasWater
sewer discharge point and construction of a new gravity connection to the TasWater system
downgradient of the emergency storage tank, as a final contingency.
The general proposed layout is shown in Figure 2. A preliminary design general arrangement
drawing of the proposed system and supporting infrastructure is shown in Figure 3, and typical
sections shown in Figures 4-6.
Interim water quality targets have been proposed within this document using the Draft guidelines
for Cooee Creek along with the baseline data collected as part of this study. The Protected
Environmental Values (PEVs) for the unnamed tributary to Cooee Creek which passes through
private agricultural land and includes a piped section, are considered to be:
Protection of aquatic ecosystems - (ANZECC Water Quality Guidelines (2000)):
Recreational water use; and
Agricultural water use.
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Figure 2. General site layout showing location of major components & access points for construction and maintenance
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Figure 3. Preliminary system design
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Figure 4. Typical section through surface flow wetland
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Figure 5. Long section showing proposed infiltration wet forest, stormwater swale for treatment of low flows and modified creek discharge
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Figure 6. Cross section showing proposed infiltration wet forest, stormwater swale for treatment of low flows and modified creek discharge
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4.0 EXISTING ENVIRONMENT
The project site lies within a valley tract and within a rural area surrounded by predominantly
grazing and cropping farms. The site itself was established as a landfill site in 1987. Hence,
the existing environment has been heavily modified and the receiving environment (a tributary
to Cooee Creek) is degraded.
The studies and investigations undertaken for the site and wider region demonstrate that the
entire landfill operation is confined within a natural Tertiary basalt valley. The site acts as a
significant groundwater discharge zone with spring expressions along the valley slopes and
floor and discharge of all groundwater to the two creeks on‐site.
The Stage 1 subcatchment discharges to the northern ‘unnamed tributary’. The long term
hydrographs for the site and the groundwater contour levels (which are above the creek invert
level) support a “fill and spill’ groundwater model for the shallower sub‐regional flow systems;
i.e. rapid infiltration of rainfall recharge occurs to a maximum level (sustained through capillary
rise) at which point any subsequent infiltration is lost as discharge to the surrounding rivers
and streams.
A summary of the existing environment is as follows:
The site is within a groundwater discharge catchment, where all water flows to minor
creek systems formed predominantly by spring heads which discharge in turn to
downstream creeks – the available bore data indicates there is no vertical recharge of
the groundwater within the site, hence, there is unlikely to be a risk of leachate
entering and contaminating the groundwater aquifer. Infiltration of groundwater is
impeded by the weathered basalt ‘blanket’ that underlies the landfill.
The entire surface and shallow groundwater flows (including Stage 1 site water as well
as most of Stage 2 water) report to the unnamed tributary of Cooee Creek. This means
that this tributary is the immediate off‐site receiving environment and under current
conditions, receives all flows not managed within the leachate recovery and disposal
system.
Site water mixes hydrochemically – i.e. surface‐groundwater flows are connected at
spring discharge/artesian upwelling points, and eventually with the creek tributary.
Climate variability, under a scenario of reduced rainfall (and therefore, reduced
recharge) is likely to result in greater use of the groundwater resource, which may
impact on groundwater levels, groundwater dependent ecosystems and discharge to
rivers.
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The unnamed tributary (and sections of Cooee Creek) are considered to be degraded
and of low to moderate ecological value due to erosion, weed infestation, stagnation,
clearing of native vegetation and agricultural inputs. According to the Conservation of
Freshwater Ecosystem Values (CFEV) database (WIST, DPIWE), the creek above the
Stage 1 landfill site is identified as of moderate conservation management priority.
The two water quality monitoring events undertaken in Cooee Creek and its tributary in
April 2014 indicate the creek is slightly to moderately disturbed in terms of water
quality (condition 2 ecosystems) based on the ANZECC (2000). This classification has
been adopted by the EPA in the Draft Proposed Water Quality Objectives for Cooee
Creek.
No threatened ecological communities were identified within 500 m of the Proposed
Activities (i.e. within 500m of the BWMC). The stretch between the landfill site
boundary and Three Mile Rd is suitable habitat for the Burnie burrowing crayfish,
however no significant environmental receptors were located. Cooee Creek has
records of fauna protected under the EPBC Act (1999), and sightings of the giant
freshwater lobster, Burnie burrowing crayfish, swift parrot and Tasmanian devil are
recorded within 500 m of the site.
5.0 LEACHATE QUALITY & FLOWS
Of key importance and a point of distinction of this project compared to other landfill sites is
that the Stage 1 leachate strength is very weak, the composition is primarily dominated by
groundwater, and the key elevated pollutants of concern are similar to agricultural pollutants,
rather than more typical leachate parameters.
The relatively inert leachate chemistry is due to two processes:
The mixing of leachate with groundwater throughflow within the leachate collection
system (due to a compromised liner) causing significant dilution (leachate is ~90%
groundwater).
The mixing of groundwater with leachate within the leachate cell itself due to the
upwelling of groundwater. This has a flushing effect and has rapidly accelerated waste
degradation processes.
The only contaminants exceeding the EPA Draft Water Quality targets for Cooee Creek are
ammonium nitrogen and total nitrogen (median 7.9 mg/L for both parameters), (manganese
(median 2.4 mg/L) and conductivity (median 557 mg/L, dominated by alkalinity). There are
occasional exceedances of aluminium, chromium, copper, nickel and zinc.
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Despite this interaction and mixing, the leachate does not contaminate the groundwater
aquifers because the groundwater is under constant upward pressure and discharges to
surface creeks (ultimately the unnamed Cooee Creek tributary, which has the lowest invert
and in effect is the base of the valley within which the site is located). However, this mixing
results in a high volume albeit low strength leachate.
Leachate quality does not present any major obstacles for biological treatment approaches;
concentrations of metals & ammonia are below levels generally considered to be inhibitory and
or have bio-toxicity effects.
Based on the flow data for the period 2010 to May 2014, the current average and median
flows of the Stage 1 leachate are 357 kL/day and 306 kL/day, respectively. Around 70% of the
annual flows are below 400kL/day, 80% below 500 kL/day, and 90% at or below 600 kL/day.
Therefore, the leachate risk profile is narrow in terms of contaminants that exceed 95%
ANZECC freshwater protection targets, with ammonium nitrogen being the key pollutant of
concern. This is readily treated in biological systems.
6.0 POTENTIAL IMPACTS AND THEIR MANAGEMENT
There are two key considerations relevant to this proposal:
1. Potential environmental and human health issues associated with off‐site discharge of
treated leachate to an unnamed tributary of Cooee Creek.
2. Potential geotechnical issues associated with the location of the wetland on top of the
landfill cap.
6.1 PATHWAYS AND RECEPTORS
Groundwater
Groundwater quality monitoring has been undertaken across the site since 1991 as part of the
original site permit conditions and subsequently as part of the state (Mineral Resources
Tasmania, MRT) groundwater data collection program. Quarterly groundwater monitoring of
one upstream and two downstream bores is undertaken by the BCC. Historical data for the
downstream bores is contained in periodic MRT reports.
The existing long‐term dataset indicates that the groundwater aquifer is not contaminated by
leachate. The groundwater does carry an agricultural signature which is to be expected given
the recharge zone at the head of this minor creek catchment is within privately owned irrigated
cropping ground. Further, there is a springhead dam located on this private land above the the
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landfill site that has been filled with unapproved materials in the past, including tyres, which
may have contributed to elevated metals in groundwater.
In comparing the long term water quality data for groundwater bores with other regional bores
from the MRT program indicates there is no difference between the Burnie bores and other
regional rural bores in terms of quality with all contaminants measured all within groundwater
drinking level criteria (NEPM GIL criteria). Importantly, groundwater recharge zones are
located above the Stage 1 and Stage 2 landfill operations, with these and the majority of the
site within a groundwater discharge zone, hence all site runoff reports to Cooee Creek as
surface or subsurface discharge and the potential for groundwater contamination is remote.
Groundwater is not considered a receptor on site since the underlying hydrogeology confines
the aquifers with all superficial groundwater flows discharging directly to the creek.
Downstream groundwater users are also, by extension, not considered to be receptors since
there is no pathway. Groundwater springs that are collected in the groundwater drainage
system that was compromised during construction, does mix with leachate however is
collected within the leachate system and reports to the treatment system.
Stormwater
Stormwater quality is monitored quarterly by the BCC. Similar to groundwater, there are
upstream and downstream monitoring points.
Stormwater entering the landfill site contains elevated levels of nutrients (especially inorganic
nitrogen), most likely as a result of fertiliser use on the upstream farm properties.
Presence and seasonal variations in concentrations of some metals in stormwater (e.g. iron,
manganese, nickel) show similarity with the leachate, suggesting possible occasional
interaction/mixing between these streams (via leachate overtopping the leachate-stormwater
manhole separation weir). Hence, it is possible that during storm events stormwater gets
contaminated by leachate on site, and this can overflow to the creek.
A key project response to this risk includes the separation of the current stormwater discharge
infrastructure from the leachate collection and treatment system to avoid untreated leachate
discharge via the stormwater system.
Therefore, the project will have a positive environmental impact in terms of stormwater quality
and hence creek water quality by separating these two streams.
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Cooee Creek Tributary (Ecological & Human Receptors)
Baseline studies of the Cooee Creek and the unnamed tributary ecological values have been
undertaken for this project, including an ecological and water quality assessment of the creek
and stakeholder consultation and creek user surveys. Hydrological assessment and flood
studies have also been undertaken as part of this project and previously.
The unnamed creek is a minor part of the overall Cooee Creek catchment (<5% of the
catchment area), and constitutes less than 1.5% of the total Cooee Creek flows. Hydrological
assessment of the downstream culvert at Three Mile Road indicates that the creek and
culverts has sufficient capacity to convey up to the 100 year flood (ARI) event. Even in the
1000 year ARI event, flows are likely to be contained within the floodplain of the creek, rather
than flooding the road.
Therefore, even if leachate was to fully discharge to the unnamed creek (no risk factors have
been identified that would make this conceivable), the potential environmental impacts would
be localised and unlikely to be detectable at the Cooee Creek confluence (4kms downstream)
due to the significant dilution effects. The addition of treated leachate flows to the creek was
determined to have no negative hydrological impacts, but rather to have environmental flow
benefits.
6.2 POTENTIAL WATER QUALITY AND HYDROLOGY IMPACTS
Leachate Quality and Flows
An assessment of the flows and mass load of pollutants of the treated leachate likely to be
discharged to the creek indicates as follows:
>90% of summer‐autumn flows and >75% of winter‐spring flows will be infiltrated
within the landfill site along the northern boundary, with only flows in excess of the
infiltration capacity directly discharged to the creek. The infiltration capacity of the soils
ranges from 1*10^‐6 to 1*10^‐5 m/s, which is considered the ideal permeability for
natural attenuation of (treated) leachate.
Mass pollutant loads likely to be directly discharged to the unnamed tributary as a
result of this project have been modelled as low to insignificant. The mass of nitrogen
for example, which is the main pollutant of concern, is less than 10% of what is
currently discharged to the creek from point source Stage 2 stormwater flows.
The BCC has indicated that in designing a discharge system to the unnamed tributary
that works would include restoration and enhancement of this creek section, to
improve riparian vegetation, and control erosion and weed infestations.
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The NEST report (2014) also concluded that increasing environmental flows to the
creek would be a positive environmental impact. Cooee Creek tributary is degraded
and the diversion of groundwater discharge from the site to sewer has reduced
environmental flows to the creek. The proposed project will result in positive outcomes
for the creek, and ultimately improve the quality of water and aquatic habitat.
There are fifteen known water licence holders (21 water licence numbers and 65
abstraction points) along Cooee Creek and its tributary with this water used for
irrigation purposes (Water Information System of Tasmania, accessed November
2015). There are only two users along the unnamed tributary.
Water use is primarily during summer months for irrigation of vegetable crops. Given
that very little water will be directly discharged to the creek at this time of the year,
since most of the water will be highly attenuated within the infiltration zone and any
discharged via subsurface flows would be of higher quality than the current creek
water quality. The additional volumes would improve irrigation potential.
Hence, this project will not adversely affect creek users and in contrast the increased
environmental flows will increase the amount of water available for ecosystem health and
irrigation use.
6.3 POTENTIAL GEOTECHNICAL IMPACTS
Geotechnical Stability
A hydrogeotechnical investigation and geotechnical model has been undertaken as part of this
project.
The following potential hazards were addressed in this study:
Wetland leakage – potential to saturate the landfill cell and resultant impact on the
containment bund.
Wetland mass load – potential for landfill cap settlement and risk to overall stability as
a result of the added mass load on the cell.
Water table rise/flood – potential for the inflowing groundwater table to rise within the
waste cell and/or flood from an extreme rainfall event.
This quantitative risk assessment concluded that the proposed wetland system posed a low to
very low risk.
The key findings and implications are:
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Stage 1 landfill is set into the valley tract and as such the landfill is largely contained
within the natural topography.
The landfill is of relatively shallow depth (10 m) and has been closed for over 10 years
(ceased receiving waste in 2004 and was capped in 2005), and has already completed
primary consolidation. The landfill cap is currently experiencing less than 2mm/yr
settlement.
The estimated weight of the proposed wetland system is ~17kPa, which is a minor
load. Consolidation settlement of the landfill cap under the wetland mass load is
predicted to be 230 mm. Based on review of typical parameters, consolidation
settlement is likely to be completed within 2 years of placing a load. Long term
settlement as a result of biodegradation of the landfill is estimated at 2 mm/year. This
is within the adaptive design capability of the system.
The surface flow wetlands will be constructed with a LLDPE liner on top of the Stage 1
landfill cap, with only shallow operating water depths, such that the bund heights will
be limited to 1.2 to 1.5 m to accommodate liner, substrate, water and freeboard for
extreme storm events.
A slightly higher bund (0.1 m) will be incorporated to accommodate long‐term
settlement. The overall bund height will be less than 2 m to avoid the potential for
excessive settlement.
Leachate levels rise and fall within the landfill in response to rainfall and imply that
there is upward flow into the landfill. The flows are likely to originate at the springs, but
could also be in other areas where there has been excavations to borrow clay to create
floor of the landfill. The upward flow prevents leachate from leaking into the natural
aquifers. The landfill does have a standing leachate level within the cell, however there
is no evidence that this has an impact on the cell or containment bund.
The wetland will have minor leakage risk since it will be a LLDPE liner over existing
natural clay topsoil capping of very low permeability, and in part over a GCL liner with
very low permeability.
The proposed wetland may result in tensile strains in the capping clay (and in the
wetland structure itself) that are at the lower limit of the failure limits. This means that
the probability of either the wetland or the landfill cap being compromised is very low.
Based on Factor of Safety (FOS) analysis, the current landfill containment bund has a
very low probability of failure, including when modelled with saturated waste. The
presence of the wetland (modelled as a 17kPa pressure) has a small impact on the
calculated FOS.
Placing the wetlands at least 10m from the crest of containment bund will not impact
on the stability of the containment bund.
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The preferred wetlands location on the top eastern half of Stage 1A is at negligible risk
of being inundated from overland flows from catchments to the east or south of the site
or from flooding of the existing site stormwater infrastructure during an extreme 1000
Year ARI event (direct rainfall is contained within the available freeboard of the
wetland).
Therefore, construction of a wetland on top of the Stage 1 landfill cap at least 10m from the
landfill containment bund has a Low to Very Low risk profile for the hazards associated with
settlement of the landfill cap and the wetland, possible failure of the landfill containment bund,
and extreme rainfall events.
Overtopping of the wetland presents a moderate risk profile if the infrastructure at the wetland
is not adequately managed.
6.4 PROPOSED DESIGN CRITERIA
The following criteria apply to the design of the proposed wetland, which reflect the
environmental, hydrological and geotechnical constraints associated with the project setting.
Treatment of contaminants to the set Water Quality Targets for discharge to Cooee
Creek tributary, which are in line with the EPA Draft Water Quality Objectives for
Cooee Creek and ANZECC Water Quality Guidelines (2000) and incorporate findings
of the creek-specific water quality monitoring undertaken for this project.
A requirement to use plant species endemic to the area and local to Tasmania to
prevent weed issues, species appropriate to the hydrological regime and water quality,
species that will enhance the biodiversity values of the site and wider area.
Ability to appropriately treat (i.e. to the set water quality standards) up to the 90
percentile flows (note, 90 percentile flows calculated on present flow data as 600
m3/day).
Provision of back-up contingencies in case of power failure, maintenance outages and
storm events, including emergency storage tank.
Ability to detain and treat the leachate flows generated in >80-year storm events by
providing sufficient capacity within the wetland and pump system to deliver and contain
3600 m3 for 24-hours of flows (>80-year event).
Capacity to intercept and treat leachate seepages generated in extreme rainfall events
to prevent direct discharge of untreated leachate to the creek.
Provision of sufficient contingencies to enable recycling of leachate if treatment
standard is non-compliant with discharge standards, and/or for leachate volumes
beyond the pump capacity of the main system (i.e. extreme events).
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Sizing of the wetland freeboard and pipework infrastructure to contain the direct rainfall
volumes generated in a 1000 year ARI storm event to avoid overflows. Hydrological
modelling indicates the 1000 ARI event could be accommodated within the wetland
system with a freeboard of 182 mm, hence a minimum freeboard is set at 200 mm.
Height of wetland bunds to be no greater than 2 m to prevent potential excessive
settlement on the landfill cap.
For all wetland cells, allowance of a setback buffer of a minimum 10 m from the landfill
bund wall and central stormwater swale on top of the landfill cap, and 10 m from the
toe of the northern embankment, to ensure no compromise to landfill stability.
Design should accommodate settlement of the wetland over time in line with predicted
landfill settlement rates.
The preliminary design dimensions for each system component are shown in Table 1.
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BURNIE LEACHATE TREATMENT WETLAND DPEMP - EXECUTIVE REPORT
Table 1. Wetland components and design details
OFF LANDFILL CELL
CELL 1CELL 2 - MAIN
SURFACE FLOW WETLAND
CELL 3 - SUBSURFACE FLOW BIOFILTER
CELL 4 - POLISHING WETLAND
CELL 5
Pretreatment for metal removal Cell SF2A Cell 3 SSFA Cell 4
Infiltration wetland
Cell area (m2) 500 11,000 2,500 500 4,000
Total depth (substrate & water) (m) 0.9 0.6 - 0.8 0.6 0.8 0.1
Substrate typelocal limestone (10 - 50 mm dia) sandy clay scoria sandy clay
sandy clays / silty clays
Substrate depth (m) 0.3 0.3 0.6 0 - 0.3 -
e (void space as %) 0.0 0.0 0.45 0.0
Operating water depth (above substrate) (m) 0.6 0.3 -0.5 0.0 0.5 0 - 0.1
Operating volumetric capacity (kL) 300 3,300 675 250 400
Min freeboard height (to accommodate 1:1000 yr event) (m)
0.2 0.2 0.2 0.2 0.1
Freeboard capacity 100 2200 - 4400 500 100 400
Peak volumetric capacity (extreme event) (kL) 395 7,590 1,150 350 800
HLR (q) (M/yr) 1.07 - 0.54 0.05 - 0.02 0.22-0.1 1.1 - 0.5 0.1 - 0
Theoretical detention time (d) 1 - 0.5 11.21 - 7.6 2.61 - 1.22 0.9 - 0.4 4.4 - 0.9
WHOLE SYSTEM Area (m2) 18,500
Detention time (d) 11 - 20
ON LANDFILL STAGE 1 CELL
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BURNIE LEACHATE TREATMENT WETLAND DPEMP - EXECUTIVE REPORT
6.5 PROPOSED MANAGEMENT RESPONSES
Key management measures are summarised below:
MANAGEMENT MEASURES TO MINIMISE/ MANAGE RISKS ASSOCIATED WITH POTENTIAL WETLAND SYSTEM FAILURE OR IMPEDED PERFORMANCE
Design
Separation of the current stormwater discharge infrastructure and the leachate
collection and treatment system to avoid untreated leachate discharge via the
stormwater system.
Conservative sizing of the treatment system to treat the 90 percentile flows and, if
required, to enable leachate recirculation and further treatment prior to discharge.
In built storage capacity to accept and dampen variable flow volumes, including peak
storm event flows (the pump and storage capacity will accommodate >80-year event).
Multiple component system design with a sequential treatment train to ensure a
continuously high standard of treatment.
Discharge of average flow treated leachate via an on site infiltration Wet Forest to
reduce direct discharge to the creek and enable further attenuation of residual
nutrients through the soil profile.
Use of an open swale as the ultimate discharge pathway to the existing unnamed
tributary Cooee Creek for flows in excess of infiltration capacity.
Connection to sewer maintained in case of non-compliance, as final contingency.
Collection of extreme storm event leachate seepages that may occur along the
northern embankment within a phytoremediation swale.
Construction
Placement of the wetland system limited to at least 10m from the landfill crest.
Height of bunds limited to 2m.
Use of a LLDPE liner to reduce wetland seepage risks.
Construction of an emergency storage tank, recirculation system for non-compliant
water, and a connection to the TasWater sewer, as a final contingency measures.
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BURNIE LEACHATE TREATMENT WETLAND DPEMP - EXECUTIVE REPORT
The wetland designer will be retained during construction / contract management and
commissioning phases to ensure that all system components (e.g. liner, hydraulics,
planting, etc) and safeguard management elements are constructed as per design.
Commissioning and Operation
Performance monitoring will be conducted through the system to enable adaptive
response and to trigger emergency recirculation or disposal to sewer.
An appropriate annual maintenance budget will be included for the life of the wetland
to ensure that all required maintenance activities are done appropriately and with the
required frequency.
Operation and Maintenance Plans will be developed and will detail the required
maintenance activities and frequencies.
Appropriate equipment checks and maintenance regimes will be implemented.
Existing risk management plans will be updated to include responses to incidences
potentially connected with the treatment system. This will include incidence response
for any on site ponding and mosquito management.
Appropriate training of staff responsible for system maintenance will be undertaken,
including preparation of user-friendly management and maintenance plans.
MANAGEMENT MEASURES TO MINIMISE/ MANAGE RISKS ASSOCIATED WITH LANDFILL SETTLEMENT
Design
Appropriate freeboard capacity will be incorporated to accommodate the direct rainfall
volumes generated in a 1000 year rainfall event (182 mm) and to accommodate
leachate volumes generated in an 80-year event.
Bund heights will be limited to 2m to limit settlement effects.
Construction
Heavy machinery use will be avoided along the top of the northern containment bund
Accurate surveys of base levels will be undertaken, before wetland placement.
A minimum of four (4) survey markers will be installed and fortnightly monitoring of
settlement levels undertaken across the landfill pre-during and post construction for
several months.
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Operation
Annual monitoring of settlement levels across the landfill will be undertaken.
Annual assessment of the integrity of wetland cells and associated infrastructure
located on top of the landfill cap (bunds, liners, pipework, weirs etc), will be
undertaken.
Any repair work required due to settlement effects will be undertaken, to maintain
system integrity and performance.
MANAGEMENT MEASURES TO MINIMISE/ MANAGE RISKS ASSOCIATED WITH PROTECTION/ENHANCEMENT OF THE CREEK ECOSYSTEM
Design
The design will accommodate flow controls (rocks, swales) to dampen velocity,
encourage sediment drop out and reduce sediment transport to the creek.
Bioengineering measures (vegetated brushmatressing, rock stabilisation) will be
incorporated to stabilise embankments and facilitate re-establishment of native
species.
A meandering swale/cascade at the discharge point will be incorporated to slow flow
velocity prior to creek discharge (for stormwater average flows and peak treated
flows).
Construction
No clearing of native vegetation will be undertaken.
Sediment controls (traps, sediment curtains) will be installed during creek
enhancement works, and sediment reused within the landfill area.
Locally native species will be used in the treatment system to avoid invasive species
entering the creek and to enhance biodiversity.
Key species will be incorporated within the wetlands to enhance the habitat value and
water quality of the creek (e.g. shade species, nesting trees, protective understorey for
avoiding predators etc).
Enhancement of the northern boundary of the site will be undertaken by replacing
grassland and weeds with dense native vegetation (Wet Forest) to reduce the risk of
weeds to the creek, provide shading, assist in phytoremediation and
evapotranspiration.
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Restoration works will be undertaken in the immediate unnamed creek discharge area
to reduce weeds, enhance riparian vegetation, improve habitat and reduce erosion.
Operation
An ongoing weed management program within the wetland system and creek
discharge areas will be implemented.
MANAGEMENT MEASURES TO MINIMISE VISUAL IMPACTS AND ENHANCE VISUAL AMENITY AND COMMUNITY USE
No native vegetation clearing will be undertaken.
Each component of the wetland system will be appropriately landscaped in order to
visually integrate with each other and within the site.
Locally indigenous, shrubby vegetation and trees (Wet Forest) will be planted along
the northern boundary of the site within the infiltration area and swale.
BCC will provide controlled site access and interpretative walks/signage to enable
community use of the proposed system for education and research.
7.0 MONITORING & REVIEW
A commissioning and operational monitoring program has been proposed for the treatment
system which includes assessment of flows and quality at the inlet, throughout the system and
at the two treated leachate monitoring points. The two treated leachate monitoring points
include:
1. EFF 1 – at the end of the polishing wetland, prior to discharge on site into the
Infiltration Wet Forest.
2. EFF 2 – at the discharge point to the creek (new licensed discharge point).
EFF2 will be the compliance monitoring point to which the proposed water quality targets as
provided in Table 2 apply. Trigger values will be established for set parameters at EFF1 to
determine the requirement for recirculation of treated leachate. On-line (continuous
monitoring) parameters will include pH, conductivity and ammonia.
In addition to water quality, flow and mass load monitoring, geotechnical monitoring will be
undertaken to assess settlement rates pre, during and post construction, six monthly during
the first year, and annually thereafter. Permanent topographical survey markers will be
installed for this purpose.
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BURNIE LEACHATE TREATMENT WETLAND DPEMP - EXECUTIVE REPORT
In addition, wetland liner leakage will be monitored using the newly installed monitoring wells
on top of the Stage 1 landfill, and visual routine inspections of the phytoremediation swale
water levels after extreme rainfall events.
Table 2. Proposed water quality protection levels for discharge to the Cooee Creek unnamed tributary.
8.0 PROPOSED COMMITMENTS
The proposed commitments for this project are provided in Table 3.
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BURNIE LEACHATE TREATMENT WETLAND DPEMP - EXECUTIVE REPORT
Table 3. Commitments table for the Burnie Treatment Wetlands proposal
Design & Approvals
Construction Operation
1 Undertake works to separate the stormwater from the MH1 leachate chamber BCC
2 Limit the placement of the wetland system to at least 10 m from the landfill crest. BCC
3 Ensure appropriate freeboard to accommodate the 1000 year rainfall event (182 mm) BCC
4 Limit the height of bunds to <2 m to prevent excessive settlement BCC
5 Use a LLDPE liner to reduce wetland seepage risks BCC
6 Construction of an emergency storage tank and recirculation system and operate for non-compliant water BCC
7 Construct a new connection to sewer maintained in case of non-compliance, as final contingency. BCC / TASWATER
8 Retain wetland designer during construction / contract management phases to ensure quality control of all system components (e.g. liner, hydraulics, planting, etc) and safeguard management elements are constructed as per design. BCC
9 Ensure interception and treatment of extreme storm event leachate seepages that may occur along the northern embankment, within a phytoremediation swale. BCC
10 Establish a new compliance monitoring point at the creek discharge point and monitor flows (continuous, on-line) and pollutants as shown in Table 31, when discharge events occur. BCC
11 Establish a performance monitoring point at the polishing wetland outlet and install on-line flow and monitoring sufficient to determine recirculation requirements (as shown in Table 33). BCC
12 Undertake sampling in accordance with the proposed monitoring schedule shown in Table 33. BCC
13 Set aside an appropriate maintenance budget to be include in OPEX for the life of the wetland, to ensure that all required maintenance activities are done appropriately and with the required frequency. BCC
14 Develop Operation and Maintenance Plans which detail the required maintenance activities and frequencies and ensure their appropriate implementation. BCC
NO. COMMITMENTTIMING PHASE
RESPONSIBILITY
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Table 3 (cont.). Commitments table for the Burnie Treatment Wetlands proposal
Design & Approvals
Construction Operation
15 Ensure Construction Mangement Plans contain practices for managing environmental risks and safety risks during construction works. BCC
16 Ensure Construction Management Plans comply with specifications and policies and sign off accordingly. BCC
17 Update existing risk management plans to include responses to incidences potentially connected with the treatment system. This will include incidence response for any on site ponding and mosquito management. BCC
18 Install 4 survey markers and undertake forthnightly monitoring of settlement levels across the landfill pre-during and post construction for several months. BCC
19 No clearing of native vegetation. BCC
20 Use of sediment controls (traps, sediment curtains) during creek enhancement works, and reuse of sediment within landfill area. BCC
21 Use of locally native species in the treatment system to avoid invasive species entering the creek and to enhance biodiversity. BCC
22 Undertake restoration works in the immediate unnamed creek discharge area to reduce weeds, enhance riparian vegetation, improve habitat and reduce erosion. BCC
23 Undertake an annual condition assessment of the unnamed tributary to Three Mile Rd. BCC
24 Implement an ongoing weed management program within the wetland system and creek discharge areas. BCC
25 Provide controlled site access and interpretative walks/signage to enable community use of the proposed system for education and research. BCC
26 Undertake annual monitoring of settlement levels across the landfill. BCC
27 Undertake appropriate training of staff responsible for system monitoring & maintenance, including preparation of user-friendly management and maintenance plans. BCC
NO. COMMITMENTTIMING PHASE
RESPONSIBILITY