Determination of Nonmethane Organic Compounds (NMOC) in Landfill Gases
This method is applicable to the sampling and measurement of nonmethane organic compounds (NMOC) reported as carbon in landfill gases (LFG). A probe that is perforated at one end is driven or augered to a depth of 0.9m (3 feet) below the bottom of the landfill cover. A sample is extracted into an evacuated cylinder. The NMOC content is determined by injecting a portion of the gas into a GC to separate the NMOC from carbon monoxide, carbon dioxide, and methane. The NMOC are oxidized to carbon dioxide, reduced to methane and measured by FID.
The sampling system consists of a probe, rotameter with flow control valve, and a stainless steel sample tank (cylinder/canister). The sample tank is cleaned and checked prior to use, is stainless steel, and is evacuated to 10mm Hg absolute pressure or less.
Method 3C is first used to determine the percent of nitrogen (N2) in the sample tank. The presence of N2 indicates that either filtration of ambient air into the LFG sample or selection of an inappropriate sampling site because anaerobic decomposition has not started. The sample is acceptable only if the N2 concentration is less than 20%. Method 3C can also be used to perform an air infiltration test for oxygen (O2). O2 should be less than 5%.
After the N2 check, nonmethane organic material (NMOC), Ctm, is measured in triplicate from the sample tank and the average value reported as in Method 25.
If the samples are to be used to demonstrate compliance, the method requires an audit sample to be analyzed along with the field samples. The audit sample results must be within 20% of the accepted true value in order for the results to be considered valid.
(EPA 40CFR Part 60 Appendix A)