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2.7.9 Methane and Hydrogen Sulfide Sampling Programs: If the presence of methane and/or hydrogen sulfide is suspected, they should also be included in the analytical plan. After evaluating the initial soil gas data, the Agency may recommend that testing for methane or hydrogen sulfide cease. A Methane Sampling Program: Methane samples may be analyzed by a GC using modified EPA Method 80158, EPA Method TO-3, or ASTM 3416M (EPA 3C), or by an appropriate hand-held instrument (e.g., Land Tech Gas Analyzer GA-90, Gas Emissions Monitor GEM-500, GEM-2000). 1. Detection Limit: The DL for methane analysis should not exceed 500 parts per million by volume(ppmv). 2. Methane Sample Containers: In addition to the gas-tight sample containers previously specified in Section 2.6.1, TedlarTm bags may be used for collection of methane samples with a holding time of no more than 24 hours. 3. Methane Screening Level: When methane is detected at 1,000 ppmv or more, additional sampling and/or further investigation is recommended to identify the source(s). 4. At sites where methane is investigated and detected at a level of 5,000 ppmv or more, fixed and biogenic gas(02, CO2, and CH4) data should be obtained using a Thermal-Conductivity Detector(TCD) or a hand-held instrument. 5. To determine that the area is pressurized by migration of gases, pressure readings of each sampling tube system should be recorded in the field logs and reported along with the methane concentration. 6. Special GC Requirements: The GC method requires calibration curves for analytes such as methane since it is not a normal target analyte for such an analytical method. 7. Special Hand-Held Instruments Requirements: Hand-held instruments should be calibrated in accordance with the manufacture's instructions. When a hand-held instrument is used to analyze methane samples, the Agency recommends that at least 10 percent of all positive methane samples(e.g., more than 5,000 ppmv), rounded to the nearest whole number, be confirmed by another hand-held instrument(different unit or brand) or by a GC method. B. Hydrogen Sulfide Sampling Program: Hydrogen sulfide may be analyzed by a GC using the South Coast Air Quality Management District(SCAQMD) Method 307-91 or EPA Method 16, or by an 01/28/2003 _ 19-