TRANSFORMING LEACHATE MANAGEMENT AT THE KIMBRIKI RESOURCE RECOVERY CENTRE, SYDNEY, AUSTRALIA

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1 TRANSFORMING LEACHATE MANAGEMENT AT THE KIMBRIKI RESOURCE RECOVERY CENTRE, SYDNEY, AUSTRALIA S. DEVER*, B. LAU*, AND A. ROBERTS** * Kimbriki Environmental Enterprises Pty Ltd & University of New South Wales, Sydney, Australia * Kimbriki Environmental Enterprises Pty Ltd, Sydney, Australia ** GHD Pty Ltd, Sydney, Australia SUMMARY: Landfilling operations commenced at the Kimbriki Resource Recovery Centre (KRRC) in 1974 and are expected to continue until around Management of landfill leachate at the site has been very challenging due to the local climate and insufficient available land on site for the disposal of leachate. In 2012 a review of leachate management was undertaken, which concluded that the existing management measures were no longer best practice and not in accord with current regulations and practices. Since 2013 Kimbriki Environmental Enterprises has been working on transforming leachate management at the KRRC to achieve current best practice. This paper describes the approach, process and measures undertaken by Kimbriki Environmental Enterprises Pty to achieve such. 1. INTRODUCTION The Kimbriki Resource Recovery Centre (KRRC) is located in northern Sydney, Australia. The KRRC is a government owned facility that incorporates a range of resource recovery activities as well as a landfilling operation. The facility is operated by Kimbriki Environmental Enterprises Pty Ltd (KEE) on behalf of two local authorities (Northern Beaches Council and Mosman Council). In 2016 the KRRC received approximately 330,000 tonnes of waste, of which 270,000 tonnes was recycled and 60,000 tonnes was landfilled. Landfilling operations commenced at the KRRC site in 1974 and since that time approximately 3.4 million tonnes of waste has been landfilled at the site. The landfilling operation is a valley type landfill that initially commenced at the bottom of the valley and has generally worked its way up the valley. Landfilling is expected to continue at the site until around In 1997, operation and development of the KRRC was re-approved, shortly after new regulatory guidelines (for landfill waste disposal sites) were issued by the state environment protection authority. From that time on and up until recently leachate management at the KRRC involved: diversion of upgradient stormwater around the landfill; compaction and covering of the landfilled waste; containment of leachate by the underlying, low permeability, sandstone rock; interception and collection of leachate at the bottom of the valley (southern end of the site) via a large compacted clay cut off wall and drainage system (behind the cut off wall); and disposal of leachate on site via re-injection back into the landfilled waste and controlled irrigation on site (via water tanker). Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2-6 October 2017 S. Margherita di Pula, Cagliari, Italy / 2017 by CISA Publisher, Italy

2 Management of leachate at the site has proven to be very challenging for many reasons, but particularly due to the local wet climate: the average annual rainfall at the site is approximately 1,300mm whilst monthly rainfall can exceed 500mm. In 2012 a detailed review of leachate management was undertaken (see GHD, 2012), which encompassed a detailed assessment of existing leachate management measures and the risks leachate presents at the site. The review also included a review of leachate generation and a review of options for improving leachate management at the site. The recommendations arising from the review included implementation of a range of measures to reduce the quantity of leachate generated at the site, including lining all new landfill cells (to prevent groundwater infiltration), and development of a lined leachate storage dam, a leachate treatment plant and pipeline to the local municipal sewerage system. The paper describes the approach and process of transforming leachate management at the Kimbriki Resource Recovery Centre, including the challenges and lessons learned along the way. 2. DESCRIPTION OF THE KIMBRIKI RESOURCE RECOVERY CENTRE The KRRC is a local government owned facility (owned by the Northern Beaches Council and Mosman Council) that incorporates a range of resource recovery activities as well as a landfilling operation. In 2016 the KRRC received approximately 330,000 tonnes of waste, of which 270,000 tonnes was recycled and 60,000 tonnes was landfilled. Landfilling operations commenced at the KRRC in 1974 and since that time approximately 3.4 million tonnes of waste has been landfilled at the site. The landfilling operation is a valley type landfill that initially commenced at the bottom of the valley and has generally worked its way up the valley. Landfilling is expected to continue at the site until around The layout and features of the facility are shown in Figure HISTORICAL LEACHATE MANAGEMENT PRACTICES In 1997, continued operation and development of the KRRC was re-approved by the local planning authority and shortly after new regulatory guidelines for landfill waste disposal sites were issued by the state environment protection authority. From that time on, up until recently, leachate management at the KRRC involved: diversion of upgradient stormwater around the landfill via drains around the perimeter of the landfill; compaction and covering of the landfilled waste (to minimize rainfall infiltration and consequent leachate generation); containment of leachate by the underlying, low permeability, sandstone rock, which typically has a permeability around 10-9 m/sec, with more pervious areas (associated with joints) having a permeability of 10-3 to 10-4 m/sec; interception and storage of leachate at the bottom of the valley (southern end of the site) via a large compacted clay cut off wall and leachate drainage system (behind the cut off wall); and storage of excess leachate in an earth dam; disposal of leachate on site via re-injection back into the landfilled waste and controlled irrigation on site (via water tanker).

3 Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2-6 October 2017 Figure 1: Existing Kimbriki Resource Recovery Centre Management of leachate at the site has proven to be very challenging for many reasons, but particularly due to the local wet climate: the average annual rainfall is approximately 1,300mm whilst the annual (pan) evaporation is 1,420mm. Monthly rainfall can exceed 500mm. Other challenges (in relation to leachate management) at the site include: A very large upgradient stormwater catchment (~80ha) that results in a large quantity of stormwater runoff entering the site perimeter stormwater drainage system immediately adjacent to the landfilled waste; The large area of the landfill where an engineered landfill lining system was not installed. Leachate containment relies on the low permeability of the underlying sandstone rock to prevent groundwater infiltration and to contain leachate; No secure leachate storage dam. The old soil / earth dam leaked and did not meet regulatory requirements for a leachate storage dam; Storing leachate in the unlined landfill. The storage of leachate in the landfill increases the head (pressure) on the underlying sandstone rock and consequently increases the potential for leakage of leachate from the landfill; Re-injection of leachate into the landfilled waste does not dispose of enough leachate

4 there is insufficient waste being landfilled (approximately 50,000 tonnes per year) to absorb the quantity of leachate generated; There is insufficient available land on site to dispose of leachate via irrigation. In addition the local climate is not suited to disposal of leachate by irrigation, particularly during winter months when evaporation is low and significant rainfall (>300mm in a month) does occur. 4. APPROACH TO IMPROVING LEACHATE MANAGEMENT AT THE SITE In 2012 a review of leachate generation and management was undertaken, which concluded that the existing management measures were no longer best practice and not sustainable in the longer term, particularly during extended wet periods (GHD, 2012). GHD recommended a range of measures to improve leachate management at the Site, including Installation of a perimeter groundwater interception system to reduce groundwater infiltration into the landfilled waste; Reduction in the size of the active landfilling/tipping face to reduce leachate generation; Installation of a leachate barrier system in the overflow dam and storage of leachate in this dam rather than in the landfill to reduce the potential for leakage of leachate from the landfill; Installation of a low permeability landfill barrier system (liner) in all new landfill areas that extend beyond the existing landfill footprint to minimise leachate migration into the underlying groundwater; Construction of a leachate treatment plant at the Site to treat leachate prior to disposal either on or off site; Disposal of treated leachate on-site via controlled irrigation during dry weather; and Installation of a pipeline to the Sydney Water sewer system to allow reliable disposal of treated leachate from the Site during both wet and dry conditions. Implementation of the recommendations has occurred progressively since 2013 and has encompassed the following: Design and construction of a leachate storage dam (12.8ML) that incorporates a low permeability geomembrane lining system; Development of a calibrated leachate generation model to allow leachate generation at the site to be assessed during a range of weather conditions; Detailed characterisation of leachate being collected at the site, to identify the level of contaminants in the leachate and to determine treatment requirements; Design and construction of a composite lined landfill cell, which incorporates a geosynthetic clay liner and geomembrane lining system, as well as a basal leachate drainage system; Design of an SBR type leachate treatment plant, which involved a preliminary assessment of treatment options, a leachate treatability study that involved laboratory bench scale testing for a period of 4 months, and then design of the SBR type leachate treatment plant. Design of a pumping station and pipeline to convey leachate (500kL/d) from the KRRC site to the local municipal sewerage system, located approximately 1.0 km to the north west of the site. The following sections provide a description of these works.

5 Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2-6 October UPGRADING THE EXISTING LEACHATE DAM To allow the quantity of leachate collected at the site to be determined it was necessary to construct a secure (lined) dam on site, large enough to store leachate for an extended period of time to all re-injection of leachate (back into the landfilled waste) to be stopped, which would allow the volume of leachate generated (and collected) at the site to be measured. Upgrading the existing leachate overflow dam involved: Investigation and evaluation of the existing leachate overflow dam; Design of the dam upgrading works; Re-constructing the dam wall; Installation of a groundwater drainage system (under the lining system); Installation of a low permeability composite lining system comprising (top to bottom): - 2.0mm high density polyethylene geomembrane layer; - 450mm thick layer of compacted, crushed sandstone (permeability k < 10-8m/s); New polyethylene pipe work to facilitate pumping of leachate to / from the dam, including a flow meter to measure the quantity of leachate pumped to the dam; 3 x surface aerators (self-aspirating propeller type) to maintain the leachate in an aerobic state (in the 5m deep dam) and thus minimise odour emissions. The completed dam is shown in Figure 2. The dam provides 12.8ML storage at normal maximum operating level and 14.9ML at maximum water level. The upgrading process commenced in the second half of 2013 and was completed in late 2014, at a total cost of approximately $AUD 0.70 million. Figure 2: Upgraded leachate dam 6. CHARACTERISING LEACHATE GENERATION AT THE SITE 6.1 General To provide a sound basis for upgrading leachate management infrastructure at the KRRC KEE undertook steps to determine the quantity of leachate generated at the site as well as the characteristics of the leachate generated, as described in the following sections.

6 6.2 Quantity of leachate To determine the quantity of leachate generated at the site KEE developed a computer based site leachate generation, storage and disposal model, which was calibrated using actual site data collected over a period of approximately 12 months. The model: Uses local climatic data from the local (Terrey Hills) Bureau of Meteorology (BOM) weather station and other nearby BOM Sites; Uses site specific data on the existing landfill cover layers, based on test pitting and laboratory testing; Uses the HELP model (version 3.95D developed by Dr. Klaus Berger at the University of Hamburg, 2013) to assess infiltration through the various landfill cover layers and into the landfilled waste; Makes an allowance for groundwater infiltration (based on the site calibration process); and Models leachate generation, storage and disposal. The site leachate generation, storage and disposal model was used to assess leachate generation, storage, and disposal at the site during the following scenarios Existing landfilling operation during a 25 year Average Recurrence Interval (ARI) wet rainfall year (1998) and a 2 year ARI (median) rainfall year (2010); For the final stage of landfilling when leachate generation will likely be at its greatest, as the landfill footprint is at its greatest and the quantity of intermediate cover is at its greatest; and For the final landform when the landfilled waste is fully capped and consequently leachate generation reduced. The results of the leachate modelling indicated the following: The quantity of leachate collected at the site varies significantly, from 100 to 800 kl/day, depending on climatic conditions; Leachate collection at the site can vary from 80,000 to 125,000 kl/year; Leachate collection during the final stage of landfilling may vary from 100,000 to 150,000 kl/year; Leachate collection after closure and capping of the landfill will reduce significantly and may vary from 15,000 to 25,000 kl/year; The recently upgraded leachate dam, which has capacity to store up to 14.9 ML, has sufficient capacity to manage leachate collected during the 25 year ARI wet rainfall year (1998) as well as a median rainfall year (2010); and The disposal of treated leachate to sewer may vary up to approximately 450 kl/day. Details of the modelling are provided in the Report on Leachate Generation at the Kimbriki Resource Recovery Centre (KEE, 2015). 6.3 Quality of Leachate To determine the quality of the leachate being generated at the site the leachate was sampled and tested over an extended period The results of the testing are summarised in Table 1, which shows the leachate contains a low level of degradable organics, and elevated levels of ammonia-nitrogen and salt, and is fairly typical of leachate from a landfill receiving non-putrescible solid waste.

7 Table 1: Summary of Leachate Quality Parameter Range Average Value ph Total dissolved solids (mg/l) 1,900 5,200 2,700 Suspended solids (mg/l) Total alkalinity (as CaCO 3 ) (mg/l) 1,600 4,000 2,500 Total Kjeldahl Nitrogen (mg/l) Ammonia (as N) (mg/l) Nitrate (as N) (mg/l) Total phosphorous (mg/l) Chemical oxygen demand 530 2,200 1,060 Biochemical oxygen demand (5 day) 10 1, Calcium (mg/l) Magnesium (mg/l) Sodium (mg/l) Potassium (mg/l) UPGRADING LEACHATE CONTAINMENT AND DRAINAGE 7.1 Design To improve leachate containment and to prevent the ingress of groundwater into the landfilled waste a new landfill cell (Cell 3B) was developed at the KRRC that incorporated a composite lining system and groundwater drainage system (below the liner), in accordance with the new (2016) guidelines issued by the state environmental regulatory authority (New South Wales Environment Protection Authority). Key features of the new landfill cell are outlined below: 150,000m 3 of rock excavation up to 25m deep see Figure 3; Steep landfill cell walls: 4V:1H up to 12m high - see Figure 3 and 5; Groundwater drainage system (under landfill cell lining system) to divert groundwater flow around the landfill cell; Composite basal lining system (~7,000m 2 ) and leachate drainage layer comprising (from top to bottom): - Geotextile separation layer (non-woven); - 300mm of drainage aggregate (60mm basalt railway ballast); - 3 layers of geotextile protection layer (>1,500g/m 2 ); - 2.0mm high density polyethylene geomembrane layer; - Geosynthetic clay liner (GCL); - 300mm of compact, crushed, sandstone; Sidewall lining system comprising (see Figure 4 and 5): - Geotextile drainage geocomposite (against the excavated rock face); - Geogrid geocomposite; - Linear low density polyethylene geomembrane layer (textured on one side against geogrid); - Geotextile protection layer (non-woven) (1,200g/m 2 ); and - Geotextile (woven) slip layer.

8 Figure 3: Typical cross section of landfill cell Figure 4: Side wall lining and anchoring system

9 Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2-6 October 2017 Figure 5: Steep landfill cell walls 7.2 Construction Construction of the new landfill cell commenced in May 2015 and the first loads of waste were placed in the cell in July 2016 see Figure 6. The works were tendered as two separate projects (bulk earthworks and landfill cell lining / leachate drainage works) to allow construction (of the bulk earthworks) to be undertaken whilst regulatory approval was obtained for the landfill cell lining and leachate drainage works. The bulk earthworks involved 150,000m3 of rock excavation, which was undertaken using conventional earth moving equipment i.e. dozer (with ripper), excavators (with hammers and bucket), and all terrain dump trucks. The landfill cell lining works were undertaken by a specialist lining contractor in accordance with a comprehensive technical specification and Construction Quality Assurance (CQA) program, to ensure the quality of the materials as well as the installation. Installation of the steep side wall lining system presented some challenges in relation to anchoring (see Figure 4 and 5), as well as accessing and joining the installed geosynthetic layers (see Figure 5). The total capital cost of the landfill cell was $AUD 5.3 million.

10 Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2-6 October 2017 Figure 6: Completed lined landfill cell (3B) (July 2016) 7.3 Lessons Learned Lessons learned from the design and construction process included: Do not skimp on the geotechnical investigations, to avoid encountering unexpected ground conditions, which can lead to significant design changes, construction delays and increased construction costs; Use known quality geosynthetics, to avoid delays in replacing materials that do not satisfy the specification. There are a lot of cheap, low quality geosynthetics on the market that are best avoided; Good planning (and program monitoring) is essential to ensure the project progresses quickly and smoothly; A good, capable, experienced contractor is worth their weight in gold (and time); A good working relationship with your contractor(s) is essential to ensure the project progresses quickly and smoothly; Engage experienced CQA engineers who are realistic and practical, and able to make decisions, quickly to avoid delaying the construction works; 8. PROPOSED LEACHATE TREATMENT PLANT AND PIPELINE TO SEWER GHD (2012) recommended the development of a leachate treatment plant and pipeline to sewer to provide a reliable and effective way of disposing of leachate during both dry and wet weather conditions. The layout of the proposed leachate treatment plant and pipeline to sewer is shown in

11 Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2-6 October 2017 Figure 7. Figure 7: Layout of leachate treatment and disposal system Development of the leachate treatment plant and pipeline commenced in early 2016 and involved the following: Evaluating the feasibility, permissibility and options for conveying leachate from the site to the local sewerage system; Evaluating options for treating leachate (for disposal to sewer); Concept design and costing of a leachate treatment plant and pipeline to sewer, to provide a basis for obtaining the various approvals required; Undertaking a leachate treatability to confirm the suitability of the selected treatment process and to provide data for the detailed engineering design of the leachate treatment plant; Obtaining planning and regulatory approval to construct and operate the leachate treatment plant and pipeline to sewer. This involved obtaining approvals from the local council, the local water (sewer) authority, the local road authority, and the environment protection authority;

12 Detailed engineering design of the pipeline to sewer, including the sewer connection works; Future activities, scheduled to be completed by mid-2018, include detailed engineering design, construction and commissioning of the leachate treatment plant and construction and commissioning of the pipeline to sewer. Operation of the completed system is anticipated to commence in the latter half of Key features of the proposed leachate treatment plant and pipeline to sewer are outlined below: Sewer discharge pumping station and pipeline to sewer (see Figure 7): - Pump duty: 6 140m head; - Onsite pipeline: 850m of DN125 polyethylene pipe, located above ground; - Offsite pipeline (Portion 1): 400m of DN100 stainless steel pipe (used because of bushfire hazard), located above ground; - Offsite pipeline (Portion 2): 400m of DN125 polyethylene pipe installed 5 to 10m below ground using Horizontal Directional Drilling (HDD) techniques. The HDD bore rises 80m from the northern end of the KRRC site to the sewer in the nearby residential area of Terrey Hills. Leachate treatment plant (see Figure 8): - Sequencing batch reactor (SBR). Two (2) reactors running in parallel; - Sized to remove (oxidize) up to 150 kg/day NH 4 +/N, based on a nominal design load (on the SBR) of 300 kl/day leachate at an ammonia concentration of 500 mg/l NH 4 +/N. - A BOD removal rate of up to 125kg/day and a hydraulic capacity ranging from 0 to 425 kl/day; - Incorporates a fine bubble diffused aeration system, ph control system, dissolved oxygen control system, phosphoric acid dosing system and antifoam dosing system; - SBR effluent quality: NH 4 +/N < 5mg/L BOD 5 < 20 mg/l Suspended solids < 100mg/L ph: Fully automated with remote monitoring and control; Estimated total capital cost: $AUD 3.2 million Estimated operating cost: $AUD 150,000/year (to treat and dispose of 125,000kL/year) The leachate treatment plant and pipeline to sewer will be operated and maintained by a specialist wastewater treatment contractor.

13 Figure 8: Concept layout of leachate treatment plant 9. CONCLUSIONS Landfilling operations commenced at the KRRC site in 1974 and are expected to continue until around Management of landfill leachate at the site has been very challenging due to the local climate and insufficient available land on site for the disposal of leachate. In 2012 a review of leachate management was undertaken, which concluded that the existing management measures were no longer best practice and not in accord with current regulations and practices. Since 2013 Kimbriki Environmental Enterprises has invested significantly (>$AUD 9 million) to transform leachate management at the KRRC, and achieve current best practice. When complete the KRRC will incorporate a large leachate storage dam (12.8ML) that incorporates a low permeability geomembrane lining system, composite lined landfill cells to contain leachate as well as prevent groundwater infiltration, and an SBR type leachate treatment plant and a pipeline to the local sewerage system, which will provide a reliable and effective means of disposing of landfill leachate during both dry and wet weather conditions. REFERENCES AND BIBLIOGRAPHY GHD, Leachate Management Action Plan.

14 GHD, Area 3B Landfill Cell Design Report. Kimbriki Environmental Enterprises Pty Ltd, Environmental Management Plan. Kimbriki Resource Recovery Centre, Kimbriki Environmental Enterprises Pty Ltd, Kimbriki Resource Recovery Centre, Report on Leachate Generation. Wastewater Futures Pty Ltd, Technical Memorandum, SBR Process Design for Leachate Treatment Plant. Wastewater Futures Pty Ltd, Kimbriki Resource Recovery Centre, Proposed Leachate Treatment Plant, Concept Design Drawings. Wastewater Futures Pty Ltd, Kimbriki Resource Recovery Centre, Leachate Treatability Study, October 2016.