The International Information Center for Geotechnical Engineers

Landfill Gas Monitoring Systems - Landfill Gas Monitoring Regulations

 

4. Introduction of Landfill Gas Monitoring Regulations

 The United States’ first attempt at regulation of air pollution was passed in 1955, called the Air Pollution Control Act. It was passed more on the basis of freeing up funds for federal government research of air pollution. However it was not until 1970 that the federal government passed the clean air act that included Emissions Guidelines (EG) for regulation of existing landfills and New Source Performance Guidelines (NSPS) for new landfills. The federal government published minimum requirements but provided the states authority to implement stronger regulations. The EG apply to any landfill that was constructed before 1991 and has accepted waste since 1987. In the following sections, the minimum federal standards will be outlined. These standards should be used in determining necessity of using monitoring methods highlighted above. Sections referring to the control devices is literature not further discussed in this paper, but important in the design of safe landfills, a main purpose of the report.

 

4.1 Characteristics of Landfills Requiring Monitoring

 A landfill is required to be regulated based on the Non-Methane Organic Compund (NMOC) emission rate. It is very difficult to quantify the Landfill Gas (LFG), so for regulation standards, NMOC output levels are representative of LFG outputs. If a landfill has an NMOC emission rate of 50 Mg/year or more, the landfill operator is required to install a gas collection and control device system to regulate hazardous emissions.

If the landfill has a NMOC less than 50 Mg/year, the landfill owner must provide a yearly report of NMOC levels until the landfill is either no longer accepting waste, or levels rise above 50 Mg/year in which case a collection system must be installed as discussed above. The EPA requires periodical monitoring of NMOC emissions as they will fluctuate over time. (EPA, 1999)

 

 4.2 Required Technology

 Gas collection technologies are required by the EPA in active areas of the landfill. Active areas are those where the waste is producing gasses and are exposed to the environment. This is defined as locations in the landfill where either no more waste is being deposited in the cell, or where the first refuses are 5 years or older. The latter of these, called active areas, must be controlled even though waste is still being added to the area. Closed areas must have gas collection systems if the oldest waste is 2 years or older.

Federal regulations allow for a variety of gas collection technologies to be used. Because of the wide variety of site specific characteristics, many alternative systems may be utilized; however the most common collection systems are active and passive systems. Landfills are required to submit a Collection and Control System Design Plan prepared by a professional engineer that will be submitted to a regulatory agency for authorization to move forward with plans. For an active system, the plan must be designed to satisfy the following:

  1. Handle the maximum expected gas flow rate over the expected lifespan of collection system equipment,
  2. Collect gas from each area or cell in which solid waste has been placed for 5 years if the cell is active and 2 years if it is closed or at final grade,
  3. Collect gas at a sufficient extraction rate (A sufficient extraction rate is a rate adequate to maintain a negative pressure at all wellheads in the collection system without causing air infiltration.), and
  4. Minimize off-site migration of subsurface gas.

Passive systems must satisfy 1), 2), and 4) as well as have liners at the boundaries of the gas collection area. Both active and passive systems must direct the collected gas to a control device. (EPA, 1999)

 

 4.3 Gas Collection System Requirements

 For a landfill gas collection to be working most effectively, the system must be operating at a sufficient gas removal rate. The EPA provides some broad guidelines for this sufficiency. Each wellhead in the collection system must be sustained in order to direct the gas into the collection system rather than letting it escape. However, if the rate of gas extraction is too high, air from outside of the system will leak in, spiking the densities of some gasses. An insufficient collection rate may lead to LFG leaking out of the system and into the environment around. If the methane level at the ground surface of the landfill is greater than 500 parts per million, the collection rate is deemed inadequate.

Collection system parameters must also be periodically monitored, including pressure, nitrogen concentration, oxygen concentration, temperature, surface methane concentration. If these results are outside of an acceptable value, the collection system will need to be modified or upgraded, depending on the situation. Whatever design variances to the system parameters must presented to the State agency with justification, which will either to be approved or disapproved.

LFG is routed through the collection system to a control device. This control device, which is selected for the particular system must be running at all times besides start and stop times, and when it is malfunctioning. As long as all times when the collection system is inoperable for less than 5 days, it is allowable. If the period of malfunctioning is longer than 5 days, the collection system must be sealed and the valves closed to contain the dangerous gasses from leaking into the atmosphere. (EPA, 1999)

 

4.4 Gas Control Device Requirements

 The EPA’s suggestion for a best designed technology (BDT) for controlling the emissions is a device capable of reducing NMOC emissions by 98 weight-percent or reducing emissions to 20 parts per million by volume dry (ppmvd) as hexane. Devices deemed acceptable include open flares and enclosed combustion devices.

For flares, measurement of reduction percentage or gas concentration of the outlet is not feasible, so it is difficult to numerically evaluate emission performance. Instead, flares are approved or denied based on how they meet specifications provided by the EPA that are assumed to have 98% control. Therefore, a performance test is not required. Enclosed combustion devices are much more feasible to complete performance tests on. These performance tests must be in accordance with EPA methods.

The control device is required to be operating at all times outside of start and stop sequences, as well as malfunctions. Like the collection system, there is a 1 hour grace period for how long it is acceptable to be out of commission. If the control device is out of commission for longer than 1 hour, the collection system must be shut down and all atmospheric valves must be closed. (EPA, 1999)

 

4.5 Compliance Schedule

 Figure 17 provides a sample compliance schedule based on a promulgation of a landfill on March 12, 1996.

  Figure 15

Figure 17. Compliance Schedule (EPA, 1999)

 

4.6 Gas Collection and Control Device Removal Guidelines

 Gas collection and control systems can be capped or removed when all of the conditions listed below are satisfied (EPA, 1999):

  1. The landfill is closed,
  2. The landfill owner or operator notifies the implementing agency by submitting a Landfill Closure Report,
  3. The gas collection and control system has been operating continuously for at least 15 years, and
  4. The landfill NMOC emission rate has been calculated to be less than 50 Mg/yr on three successive test dates. The test dates should be no closer than 90 days apart and no farther than 180 days apart

  

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