Closed, Illegal, and Abandoned (CIA) Disposal Sites

Continuous Landfill Gas Monitoring for Structures Located Near Landfills and Disposal Sites (Part 1)

Landfill gas migration from disposal sites into nearby structures is a potential threat to public health and safety. The purpose of the continuous landfill gas monitoring pages (Parts 1-3) is to provide useful information in applying continuous gas monitoring systems to structures on or near landfills and former disposal sites to meet regulatory requirements.

The table of contents below highlights information provided on the pages.

Table of Contents

• Typical Landfill Gas Migration Routes
• Regulatory Requirements for Continuous Landfill Gas Monitoring
• Continuous Landfill Gas Monitoring System Overview
• Continuous Monitoring System Components, Manufacturers, Specifications, and Costs
• Continuous Monitoring Systems Operations and Maintenance Requirements

Typical Landfill Gas Migration Routes

The diagram below shows how landfill gas, depending on site-specific conditions, can migrate from a former disposal site through surrounding soils, utility corridors, etc., into subsurface vaults and facility foundations creating potentially harmful situations if not monitored appropriately.

Figure 1. Typical Landfill Gas Migration Routes
Select Figure 1 to view a larger image.

The purpose of continuous landfill gas monitoring is to document any detected presence of landfill gas migration into nearby structures located on or near landfills, and to alert responsible parties and regulators to determine if the concentration of gas exceeds 1.25 percent or 10 percent of the lower explosive limit (LEL) for methane (5 percent). Continuous gas monitoring systems generally consist of standardized “off-the-shelf” equipment, which includes gas sensors, automatic controllers, and data acquisition systems and software that are typically compatible with most PC computers with Windows Operating Systems.

Regulatory Requirements

The excerpts below are from federal and State regulations which require the monitoring migrating gas from landfills and former disposal sites into nearby structures. Complete State legal citations can be found at 27 CCR, Chapter 3, Subchapter 4, Article 6.

• Federal Regulations (40 CFR Part 258.23) Explosive Gas Control (Adobe PDF, 188 KB)
• State Regulations (27 CCR, Chapter 3, Subchapter 4, Article 6)
• 27 CCR Gas Monitoring & Control Regulations
  • 20919.5 (a) (1) Explosive Gas Control
  • 20921 Gas Monitoring & Control During Closure & Postclosure
  • 20931 Structure Monitoring
  • 20934 Reporting
  • 20937 Control
  • 21190 Postclosure Land Use
• 27 CCR 20919.5 (a) (1) Explosive Gas Control “…owners…must ensure that: (1) the concentration of methane gas generated by a facility does not exceed 25 percent of the LEL for methane in facility structures…”
• 20921 (a) (1) requires that “…the concentration of methane gas must not exceed 1.25 percent by volume in air within on-site structures…”
• 20931 (a) “…monitoring network design shall include provisions for monitoring on site structures, including but not limited to buildings, subsurface vaults, utilities or other areas where potential gas buildup would be of concern…”
• 20931 (c) “…structures located on top the waste disposal area shall be monitored on a continuous basis.”
• 20934 (a) (1) “…monitoring reports shall include: (1) the concentrations of the methane….within each on-site structure…”
• 20937 (a) (3) “…the documentation of date, time, barometric pressure, atmospheric pressure, general weather conditions and probe pressures…”
• 20937 Control (d) “…when the results of monitoring in on site structures indicate levels in excess of those specified in Section 20923(a), the operator shall take appropriate action to mitigate the effects of landfill gas accumulation in on site structures, and public health and safety, shall include one or more of the following:…(4) Alarms, (5) Ignition source control (7) Ventilation…”
• 27 CCR 21190 (a) Proposed PCLUs shall be designed and maintained to: (3) prevent landfill gas explosions…”
• 27 CCR 21190 (e) “…construction of structural improvements on top of landfill areas…shall meet the following conditions:…(1) automatic methane gas sensors, designed to trigger an audible alarm when methane concentrations are detected, shall be installed in all buildings…”
• 27 CCR 21190 (e) (8) periodic methane gas monitoring shall be conducted inside all buildings…”

Continuous Landfill Gas Monitoring System Overview

A continuous monitoring system is designed to detect the presence and concentration of gas in monitored spaces within a structure and relay the data to a central controller which receives and stores the data in a data acquisition system at specified times and intervals (prescribed by the user). The controller can output a control signal in response to an input signal condition, which is based on programmed logic, and provide output signals which will enable audible alarms, enable ventilation systems, or telephone fire departments to alert them of a specified condition. The ability of the controller to perform these functions is called programmable logic control (PLC). PLC is commonly used to monitor and control processes for facility heating, ventilation, and air conditioning (HVAC) systems, water and sewage treatment plants, and petroleum and chemical processing plants.

Figure 2. Continuous Monitoring System Overview (Adobe PDF, 101 KB)

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Last updated: April 18, 2008