Closed, Illegal, and Abandoned (CIA) Disposal Sites

Continuous Landfill Gas Monitoring for Structures Located Near Landfills and Disposal Sites (Part 3)

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Continuous Gas Monitoring System Components (Cont'd)

• Programmable Logic Control (PLC) Software
• Online Gas Detection System Equipment Manufacturers and Distributors
• System Installation

(Note: Information on operations and maintenance of systems is located further down on this page.)

Programmable Logic Control (PLC) Software. Laptop and desktop computers using a Windows Operating Environment and a phone modem or direct connection are the most common method for interfacing with and programming controllers and data loggers. Most controllers and loggers come with the PLC software needed to specify and program the loggers for data collection (which sensors, number of readings, interval of readings, etc.), and also program set point values and conditions for alarms, ventilation, etc. Figure 7 is a sample screen shot from a typical PLC program.

Figure 7. Programmable Logic Control (PLC) Graphical Programming Software Screen Shot

List of Online Gas Detection System Equipment Manufacturers and Distributors

System Installation. System installation should be performed by a qualified controls or industrial electrical contractor with experience in the installation of instrumentation and controls, automatic control, and direct digital control systems. The installation work scope generally requires that each system component be properly mounted, wired for power and signal, calibrated and tested, in accordance with manufacturer specifications and instructions and that the overall system be function checked and tested as a condition of accepting completed work. The gas sensors should be checked and calibrated using a 1.25 percent and 5 percent methane calibration gas. Wireless systems (operated on radio frequencies) can reduce the complexity and cost of installation, particularly where running cable below ground is difficult or not possible. Wireless equipment component costs are higher than conventional hardwired equipment, but the installation costs can often offset this difference in cost. Wireless sensors do require power for both the sensor output (4-20 mA) and radio transmitter. Wireless transmitters can transmit up to 1 mile line of sight.

Figure 8. Installation of a Wireless Continuous Gas Monitoring System

General notes for installation are as follows:

• Power source (120 V/60 Hz) required to operate data logger, controller, sensor and PC interface (on site); power consumption is nominal; battery backup required.
• Standard telephone connection (modular jack) required to data logger for remote data access and downloading.
• Sensor should not be placed in a corrosive environment or subject to irrigation waters, although designed for outdoor use.
• Sensors can be used in constructed “probe vaults” to simulate utility boxes.
• Wireless systems should be used if feasible to minimize installation costs.
  • Ensure receivers and transmitters are “line-of-site” without obstructions.
  • Locate antennas as high as possible in structures.
  • Purchase and use signal repeaters if signals are weak.
• For systems where "hard-wiring" is used:
  • Cable runs should consider subsurface utilities and landscaping (cost increases with burying cable in areas with pavement, landscape and utilities).
  • Conduit may be considered for cables in common areas or potentially subject to traffic or vandalism; 12 inch direct burial of cable is acceptable (per National Electric Code [NEC]).
  • Cable runs need to meet voltage drop requirements based on length of run and cable or wire size (generally 1000 feet or less for 12-gauge wire).
  • Sensor should be “clustered” if possible to minimize installation disturbance.

System Operations and Maintenance

The system operations should be thoroughly tested during initial startup operations, following the installation of the system components. A trial run of data collection should be performed to ensure that the data acquisition unit is properly programmed and that gas monitoring data is being recorded at specified times and intervals. Generally, continuous gas monitoring data should be taken every 15 minutes, 24 hours per day, 7 days per week, and 52 weeks per year. The data should be downloaded monthly and the system function checked weekly for the first two months of operation and monthly thereafter. Downloaded monthly data should be checked for erroneous or inconsistent readings. Calibration of the gas sensors should be performed quarterly (for the first year of operation).

• System should be calibrated once per quarter or if erroneous readings are detected during monthly download.
• System data should be downloaded monthly or as required based on memory size and data collection frequency (24-hr, 7-day, 365-day is typical).
• System requires a dedicated phone line and power supply (with separate circuit and breakers).
• Most systems come with back-up battery to maintain data; however, power restoration is critical.

For additional information, see the program responsibilities for the Board's Remediation, Closure, and Technical Services Branch.

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Last updated: April 18, 2008