Borehole testing in landfills is a method used to assess and monitor the generation of gases within a landfill site. A “borehole” refers to a carefully constructed well or hole that is drilled into the ground, specifically for the purpose of monitoring gas flow from landfills. These gases are produced because of the decomposition of organic materials in the waste. As they can pose environmental and safety hazards, it’s crucial to regularly measure their concentration levels. The process involves several steps and aims to analyze a variety of gases, predominantly methane (CH4), carbon dioxide (CO2), oxygen (O2), and hydrogen sulfide (H2S), among potential others. Here is an overview of the process:
- Planning and Safety Considerations
- Site Assessment: Identifying potential locations for borehole placement to ensure a comprehensive analysis of landfill gas production across different areas of the site.
- Safety Measures: Establishing safety protocols due to the potential risks associated with drilling into landfills, such as explosive gas mixtures or the release of hazardous substances.
- Borehole Drilling and Installation
- Drilling: A borehole is drilled into the landfill using specialized equipment. The depth and distribution of boreholes will depend on the size of the landfill and the composition of the waste.
- Installation of Monitoring Wells: After drilling, a well is typically installed in the borehole. This well is often lined with a perforated pipe surrounded by gravel to allow gases to enter while keeping out debris. The top of the well is sealed to prevent air entry and escape of gases.
- Gas Extraction and Monitoring
- Gas Extraction: Using a pump or vacuum system, gas samples are extracted from the boreholes. This can be done at regular intervals or continuously, depending on the monitoring objectives.
- Gas Analysis Equipment: The extracted gases are analyzed using gas analysers or chromatographs, which can detect and quantify the concentrations of various gases. Portable analysers are often used for field measurements.
Gases Monitored
- Methane (CH4): The primary component of landfill gas, representing a potent greenhouse gas and an explosion hazard at certain concentrations.
- Carbon Dioxide (CO2): A significant byproduct of the decomposition process and another important greenhouse gas.
- Oxygen (O2) and Nitrogen (N2): Measured to understand the balance of gases within the landfill and the extent of aerobic vs. anaerobic decomposition.
- Hydrogen Sulfide (H2S): A toxic gas produced in landfills, particularly those with high sulfur content waste. It’s important to monitor for health and safety reasons.
- Volatile Organic Compounds (VOCs): Some tests may include the analysis of various VOCs, which can be health hazards and contribute to air pollution.
- Data Analysis and Reporting
The collected data is analysed to assess the gas production rates, composition changes over time, and potential risks associated with gas migration. This information is crucial for regulatory compliance, landfill management practices (such as gas collection and flaring systems), and evaluating the potential for energy recovery (in the case of methane).
- Maintenance and Continuous Monitoring
Routine maintenance of the boreholes and continuous monitoring are necessary to ensure the integrity of the testing process and the accuracy of the collected data. This may involve clearing blockages in the wells and calibrating or repairing equipment as needed.
Environmental Laws
Environmental laws in Australia regarding borehole testing at landfill sites involve various guidelines and policies that are implemented by state environmental protection agencies. These laws are designed to ensure that landfill operations, including borehole testing, are conducted in a manner that minimizes environmental impacts, protects human health, and ensures safe and sustainable waste management practices.
For example, the Environment Protection Authority (EPA) in Victoria has issued publications which include comprehensive guidance for managing all stages of a landfill. This includes criteria for siting, design, operation, and management of landfills to meet environmental objectives and required outcomes, with specific guidance on borehole testing as part of the landfill’s environmental monitoring program (ref: https://www.epa.vic.gov.au/for-business/find-a-topic/landfill-guidance/landfill-guidance-and-policy-documents). The Waste Management Policy (Siting, Design and Management of Landfills), emphasizes adherence to the Best Practice Environmental Management (BPEM) guidelines, where the practices for gas monitoring, including borehole testing, are outlined.
Included in the EPA Victoria’s Landfill Gas Fugitive Emissions Monitoring Guidelines document are the following details on gas monitoring instruments typically used. The applicable field instruments generally fall into two categories:
- Category 1 (for landfill gas monitoring bores)
Extractive landfill gas analysers that measure volumetric concentrations (% v/v) of methane, carbon dioxide, oxygen and, depending on the configuration selected, the trace gases carbon monoxide, hydrogen sulphide, ammonia and hydrogen in parts per million (ppm). These analysers must also measure bore relative pressure (mb or hPa) and gas flow (L/Hr). Gas flow is included as a parameter to be measured due to its importance in landfill gas risk assessment.
- Category 2 (for other monitoring locations)
Low-concentration methane detectors that measure methane in parts per million (ppm) are generally used for monitoring emissions of methane from: the surface of the landfill and penetrations through it; subsurface services; and buildings and structures.
It is essential the correct instrument is selected for the monitoring task, and the instrument is calibrated, operated and maintained in accordance with the manufacturer’s instructions. (ref: https://www.epa.vic.gov.au/about-epa/publications/1684 , page 4)
The EPA in New South Wales specifies, in their Solid Waste Landfill Guidelines document (pages 33-36), clear guidelines for landfill gas management and monitoring. The following excerpts are taken directly from that document. For the complete text with specific gas monitoring guidelines please download the EPA document from the link above.
- A surface gas monitoring program should be established to detect any emissions through the cover/capping material and fugitive emissions from any gas extraction system present. The threshold level for further investigation and corrective action is 500 parts per million (volume/volume) of methane at any point on the landfill surface for intermediate and finally capped areas.
- Landfill gas sub-surface monitoring: For most putrescible waste landfills and for large and/or high-risk non-putrescible waste landfills, the occupier should establish a sub-surface landfill gas monitoring program to demonstrate that landfill gas is not migrating off-site. The need for, and the extent of, this program should be guided by a landfill gas risk assessment for the site in each case. The threshold levels for further investigation and corrective action are detection of methane at concentrations above 1% (volume/volume) and carbon dioxide at concentrations of 1.5% (volume/volume) above established natural background levels.
- A landfill gas accumulation monitoring program should be implemented to demonstrate that gas is not accumulating at dangerous levels in enclosed spaces on or near the landfill. Landfill gas is primarily made up of methane and carbon dioxide and must not accumulate in buildings. Methane is explosive in the range of 5% to 15% (volume/volume), and landfill gas can be an asphyxiant in enclosed spaces. The threshold level for further investigation and corrective action is detection of methane at concentrations above 1% (volume/volume).
In South Australia, the EPA provides guidelines titled “Environmental management of landfill facilities – solid waste disposal”, which updates previous guidance. This document sets out the requirements for the environmental management of landfill facilities, including municipal solid waste and commercial and industrial waste landfills. It encompasses aspects such as the design and operation of landfills, with a focus on minimizing the environmental impact, which implicitly includes the practices around borehole gas monitoring and testing. The following table is referenced from this document and demonstrates their specified landfill gas threshold levels.
(ref: https://www.epa.sa.gov.au/files/4771343_guide_landfill.pdf , page 89)
These regulations and guidelines ensure that landfills are managed in a way that acknowledges the evolving nature of waste, emphasizing the significance of designing and operating landfill facilities, including the management of landfill gases through borehole testing to ensure that safety, environmental, and operational standards are met.
CAC GAS Solution.
CAC Gas provides calibration and specialty gas mixtures for landfill monitoring and gas measurement applications. Our gases are available in a variety of cylinder sizes from 1L to more than 7000L.
We supply EPA Protocol calibration gas mixtures, ISO 17025, ISO 17034 gas mixtures, and gas mixtures for stack gas, fugitive emissions, air quality or vehicle emissions, combustion efficiency, biogas, soil remediation and agriculture environmental applications as well as gas standards TO 14,15 and 17 for a variety of applications to measure VOC’s.
