DEVELOPMENT PROPOSAL & ENVIRONMENTAL MANAGEMENT … City Council, Leachate... · Burnie Leachate...

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

Burnie Leachate System DPEMP – Executive Report November 2015 i

BURNIE LEACHATE TREATMENT WETLAND DPEMP - EXECUTIVE REPORT

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: [email protected]

For:

Burnie City Council

Registered office

PO Box 973, Burnie 7320

Contact Person: Mr Rowan Sharman

Manager Engineering Services

Telephone: 03 6430 5752

Email: [email protected]

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

mailto:[email protected]�

Burnie Leachate System DPEMP – Executive Report November 2015 ii


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

Burnie Leachate System DPEMP – Executive Report November 2015 iii


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

Burnie Leachate System DPEMP Executive Report November 2015 1


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



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



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.



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.



Figure 2. General site layout showing location of major components & access points for construction and maintenance



Figure 3. Preliminary system design



Figure 4. Typical section through surface flow wetland



Figure 5. Long section showing proposed infiltration wet forest, stormwater swale for treatment of low flows and modified creek discharge



Figure 6. Cross section showing proposed infiltration wet forest, stormwater swale for treatment of low flows and modified creek discharge



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.



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.



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



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.



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.



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:



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.



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).



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.



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

Burnie Leachate System DPEMP November 2015 20

<INSERT DOCUMENT TITLE> <insert part heading if necessary>


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.




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.




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.




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.




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.




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




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

Date post:	15-Oct-2020
Category:	Documents
Upload:	others
View:	6 times
Download:	0 times

DEVELOPMENT PROPOSAL & ENVIRONMENTAL MANAGEMENT … City Council, Leachate... · Burnie Leachate...

Documents