Controlling LFG Surface Emissions

Jeffrey G. Dobrowlski

Frequently known as a trend setter even in the wastes industry, Californians have been managing their landfill surface gas emissions for nearly a decade.

Similar to the EPA's New Source Performance Standards, California's Rule 1150.1 requires landfill owners and operators to monitor and reduce surface emissions at all sites operating as of April 1985.

This rule is enforced by the South Coast Air Quality Management District (AQMD), an agency of the California Air Resources Board.

California landfills must be monitored in several categories: ambient air and weather station monitoring; instantaneous and integrated surface sampling; landfill gas migration perimeter probe monitoring; and landfill gas collection system sampling.

Ambient Air Monitoring Ambient air monitoring provides a benchmark for background air quality. One or more ambient air monitoring/sampling stations must be located on the landfill or at its perimeter.

Considering southern California's meteorological patterns, the samplers' locations provide predominant offshore (drainage land breeze) and onshore (sea breeze) wind flow patterns. Local nightly wind drainage patterns also are sampled at canyon landfills with steep slopes.

Ambient air sampling must be conducted during calm weather with less than two miles per hour wind speeds and onshore breezes of less than 10 miles per hour.

Sampling cannot be conducted when it's raining, if average wind speeds are greater than 15 miles per hour for a 30 minute period or when wind gusts are greater than 25 miles per hour.

Wind speed and direction must be continuously recorded to characterize the micrometeorology and verify that ambient air sampling meets meteorological requirements.

Ambient air sampling equipment includes:

* 10-liter Tedlar (polyvinyl fluoride) bag with stainless steel capillary tubing inlet;

* DC operated pump;

* Associated tubing (usually Teflon);

* Bypass valve to control the sample flow rate;

* Rotameter for flow indication; and

* 24-hour timer with automatic shutoff.

The air samplers are placed at pre-determined locations. Ambient air samples are taken monthly over a 24-hour period; wind data is continuously recorded.

To prohibit photochemical reactions, ambient air bag samples are enclosed in light-sealed containers, usually cardboard boxes. Within 72 hours of collection, the Tedlar bag samples must be analyzed for total organic compounds (TOC) and toxic air contaminants.

Instantaneous Monitoring Instantaneous surface monitoring identifies and repairs areas of the landfill surface exceeding 500 parts per million (ppm) TOC, measured as methane. The entire landfill surface must be monitored each month, with individual repairs made within 24 hours to a week, depending on the monitoring plan.

Portable monitoring equipment is used for instantaneous surface monitoring. A portable flame ionization detector, such as a Gastech Flame Ionization Detector, is used to meet the following state regulatory demands:

Range: 0 - 1,000 ppm (v/v) linear scale or 0 -10,000 ppm (v/v) logarithmic scale.

Minimum detectable limit: 5 ppm (or lower).

Response time: 15 seconds (or shorter).

Flame out indicator: audible and visual.

Accuracy: + 4 percent (or better).

Precision: + 3 percent (or better).

Ambient temperature: 0 - 50 degrees Celsius.

To obtain the readings, the monitoring staff places the portable flame ionization detector probe or wand less than three inches above the landfill surface. The staff walks in an alternating pattern in 25-foot intervals, looking for surface cracks or odorous areas. If a hotspot exceeding the 500 ppm limit is detected, the staff flags it in the field and locates the area on a site map, noting date, time and concentration.

Heavy equipment operators repair hotspots by scarifying and adding clean fill, wetting down and recompacting the area. Once the repairs are completed, the hotspot areas are checked again.

If an area still exceeds 500 ppm after three repair attempts, the landfill owner must contact the AQMD and implement an approved mitigation plan. This may include additions to the landfill gas collection system such as horizontal or vertical gas wells.

If the AQMD determines that the 500 ppm limit is exceeded, they can issue a Notice To Comply. If the limit is exceeded by an overt act, a Notice of Violation can be issued.

More Surface Sampling Composite surface sampling, also called integrated surface sampling, is required each month. Here, the landfill surface is divided into monitoring/sampling grids, each approximately 50,000 square feet.

Sampling a portion of the landfill area is required each month; the sample size depends on the total landfill area. California's limit for TOC concentrations is 50 ppm, measured as methane.

The average wind speed (over a 10-minute period) must be five miles per hour or less, and instantaneous wind speeds must be less than 10 miles per hour. As with instantaneous surface sampling conditions, integrated surface sampling must be conducted in dry weather. (State regulations define dry conditions as no rain for the past 72 hours and a dry landfill surface.)

Integrated surface samplers include a stainless steel inlet probe, a pump and flow meter and a 10-liter Tedlar bag (see "Integrated Surface Sampler" diagram on page 43).

The integrated surface sampling procedure is identical to instantaneous sampling except that a composite sample is taken from each grid. A typical 50,000-square-foot grid must be sampled in 25 minutes. Wind velocity and direction are continuously monitored during sampling.

Landfill Perimeter And LFG A landfill perimeter probe sampling system determines if gas is migrating offsite. AQMD's system meets the requirements of the California Integrated Waste Management Board.

AQMD's system includes probes installed outside the refuse deposit area and parallel to the landfill's perimeter; probe locations not more than 1,000 linear feet apart; and at least one probe installed at a pre-approved depth at each location.

Probe sampling is required monthly. Methane concentration limits of 5 percent methane are set and enforced by the California Integrated Waste Management Board. The depth of each probe is determined by the refuse depth within 500 feet of the probe, as follows:

First depth: 10 feet below surface.

Second depth: 25 percent of refuse depth or 25 feet below surface, or whichever is deeper.

Third depth: 50 percent of refuse depth or 50 feet below surface, or whichever dimension is deeper.

Fourth depth: 75 percent of refuse depth or 75 feet below surface, or whichever is deeper.

One sample is required from each main landfill gas header line entering a gas treatment and/or disposal facility. This sampling is required monthly and is collected in a Tedlar bag over a 10-minute sampling period. Samples must be analyzed within 72 hours for TOC and toxic air contaminants. Again, all bag samples must be kept in light-sealed containers.

The South Coast Air Quality Management District requires that all data be reported within 45 days of each quarterly period.

All methane concentrations, TOCs, toxic air contaminants, weather and wind data, along with quality control data sheets are required in each quarterly report. In many cases, additional data, such as corrective actions, must also be reported.

Monitoring personnel must be permanently assigned to the project to consistently comply with the monitoring and sampling requirements.

Compliance with Rule 1150.1 is a costly procedure. Various types of monitoring, sampling and calibration equipment and materials are needed, as well as laboratory analytical services. Preparing quarterly reports is another costly task.

However, environmental benefits can be significant. The gas collection system's efficiency will increase when cracks and crevices are sealed off, allowing greater vacuum to be applied while minimizing air intrusion.

The surrounding community also is better served when the landfill complies with the regulations, including a dramatic reduction of foul odors. This good-faith effort not only exhibits a strong level of environmental responsibility, but perhaps more important, helps correct the common perception that landfills are not properly managed.