Steps taken by the City of Barrie, Ontario to protect water resources from landfill leachate have the side-benefit of providing the city with time to further improve waste diversion and control long-term waste management costs. This will be achieved in part by redesigning the landfill and improving both its ability to contain landfill leachate and gas, while at the same time increasing waste density.
This project points to some of the trends in landfill management today, which use available technology and methods to solve current and future waste management issues.
Barrie’s municipal solid waste landfill began operations in the 1960s in what is marked on the diagram as Cell 1. As the landfill developed, there was an increased need to minimize the discharge of leachate, which typically contains salts, metals and volatile organic compounds. The city installed environmental controls to deal with this, including a groundwater collection gallery (consisting of a drain running along the east side of the landfill) and an array of three groundwater extraction (purge wells) along the south side.
A number of years ago, the city recognized that the long-term cost and operational implications of the control systems would be increasingly expensive and difficult to maintain. There were also concerns that, despite the environmental controls, as the landfill developed, leachate might migrate off the property resulting in non-compliance with environmental standards. A third factor was the growing burden that the collected leachate posed on the municipal sewage treatment system, which received the discharge from the environmental control systems.
These concerns, plus a desire to deal with the long term implications of the site and its controls, called for a more comprehensive solution. That solution — reclamation and re-engineering of the landfill — was developed and included in an updated “development and operations” report approved by the provincial environment ministry in 2006.
The solution now being implemented is expected to help solve another issue as well.
Like many other municipalities, Barrie is running out of landfill space, and the capacity of the site was anticipated to be reached in 2017. The city also recognized the benefit in extending the period before a lengthy and costly process of applying for a new landfill would be needed. As a result of the reclamation (mining) processes described below, a positive side-benefit will be to increase site life by up to seven years.
The solution, developed by Golder Associates, involves the progressive construction of a new landfill liner that isolates the landfill from the underlying ground. This is followed by processing the existing landfill waste to remove excess sand cover soil, and transferring the remainder into the newly-lined landfill space (with a higher degree of compaction). This process will be repeated in the entire western part of the landfill.
The first step was to prepare part of the existing space — Cell 3A in the diagram — so that it could better protect groundwater from leachate infiltration, as part of a construction program carried out by Golder Associates Innovative Applications (GAIA) in 2007. This involved building a 240,000 cubic metre engineered “cell” to capture the leachate. The “cell” consists of a state-of-the-art single composite liner and leachate collection system. The liner consists of geosynthetic clay (GCL) liner (two geotextile layers with clay between them) manufactured in Barrie overlain by a high-density polyethylene (HDPE) liner and a protective sand layer. The HDPE sheets are double-welded to leave a gap between the welds (used for leak testing).
Above the membrane layer is a drainage system involving 200 mm diameter perforated pipe to collect leachate, overlain by a 500 mm layer of five-centimetre (two-inch) diameter crushed stone. The crushed stone consists of granite rather than the usual limestone, which is expected to better withstand the dissolving effects of leachate. Above the granite layer is a protective geosynthetic filter fabric, another layer of sand, topped by a second filter fabric (to filter the leachate/waste prior to entering the collection system). At the lowest point in the landfill cell is a deep manhole connected to the City’s sanitary sewer system, and ultimately the municipal wastewater treatment plant.
New waste-processing methods
The next stage of the process takes advantage of further developments in waste management technology, and involves waste reclamation (mining) or, in effect, “recycling” of the existing waste to reduce its bulk. In many cases waste has partly decomposed and is more amenable to changing its shape into a less bulky form.
In a pilot mining project completed in late 2007 and early 2008 under harsh winter conditions, a six-foot diameter 21-foot long rotating drum (trommel) screen was used to screen the in-place waste to determine production rates as well as to assess slope stability issues.
In the full-scale project, two seven-foot diameter 33-foot long trommel screens will be fed by a bulldozer and a large excavator fitted with a hydraulic “thumb.” The resultant larger-diameter “overs” discharged from the screen will be placed in the lined landfill cell. Recyclable materials such as wire and other metal (as well as rubber tires) will be separated prior to screening and sent to a licensed recycling facility. Bulky items from the excavated waste, as well as those from the incoming fresh waste, will be processed with a low-speed grinder; this will transform items such as furniture, mattresses, tree stumps and construction demolition waste into smaller pieces to reduce voids and improve compaction.
The “fines” that pass through the screen consist mostly of sand that had previously been used as daily cover, and fine decayed organic material. These fines will be re-used as daily cover for the “overs” and incoming fresh waste, thus optimizing the use of the reclaimed landfill space. Recent changes to provincial regulations will require that many medium-sized landfills collect landfi ll gas (LFG), a byproduct of the anaerobic decay of waste. At the Barrie landfill, this gas is passively vented into the atmosphere; however, the redesigned landfill will make it easier and more efficient to install a LFG collection system connected to a flare, or possibly even an electrical generator. This will result in a reduction in the greenhouse gas generation potential of the LFG — another benefit to the environment.
A landfill in the Ottawa area that Golder designed received provincial approval to use shredded rubber from waste tires in place of some of the crushed stone drainage layer in the leachate collection system. This approach will be considered in the re-design of the Barrie landfill and, if it is a viable option, would help reduce the need to find a solution for tires previously disposed of at the landfill.
Sandy Coulter, B. Sc., is Manager of Environmental Operations for the City of Barrie, Ontario. Contact Sandy at firstname.lastname@example.orgPaul Dewaele, MSc, P. Eng., is a Senior Environmental Engineer in the Barrie, Ontario office of Golder Associates Ltd. Contact Paul at email@example.com
“As a result of the reclamation(mining) processes, a positive side-benefit will be to increase site life by up to seven years.”
“The Fines Will Be Re-Used As Daily Cover For The ‘Overs’ And Incoming Fresh Waste, Thus Optimizing Use Of The Reclaimed Landfill Space.”