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KIRTLAND AIR FORCE BASE ALBUQUERQUE, NEW MEXICO ...

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APPENDIX B<br />

SOP B3.2<br />

Methods for Using Portable Gas Chromatographs<br />

Purpose<br />

This guideline describes sampling and analytical methods currently accepted for performing soil gas<br />

surveys. Soil gas surveys are effective qualitative screening tools for characterizing volatile organic<br />

contamination at hazardous waste sites. A soil gas survey, when performed properly, can delineate<br />

groundwater contamination, define the areal extent of soil contamination, help pinpoint source areas,<br />

indicate possible migration pathways, and show overall ―clean‖ and ―dirty‖ areas of a particular site.<br />

Soil gas is useful for initial site characterization, groundwater contamination mapping, and source<br />

delineation for sites where volatile organic compounds may be present. Soil gas surveys cannot detect<br />

semivolatile organic or heavy metal contamination.<br />

Scope<br />

Two types of soil gas sampling methods are available—active soil gas sampling and passive soil gas<br />

sampling. Active soil gas sampling is the more common method. It consists of advancing a probe into<br />

the soil and extracting a gas sample under vacuum. The sample is then analyzed in the field or sent to an<br />

onsite laboratory for analysis. Passive soil gas sampling is the less common method. It consists of<br />

burying a passive soil gas sampler in the soil, leaving it for several days to months, retrieving it, and<br />

sending it for laboratory analysis. Passive sampling has several disadvantages relative to active<br />

sampling. The primary disadvantage is that two mobilizations are required—one to bury the samplers,<br />

and one to retrieve them. In addition, the results are not available from the laboratory for at least one and<br />

often several weeks. Thus the passive method does not conform well to the tight-scheduled nature of<br />

many environmental restoration assignments. Procedures for performing passive soil gas investigations<br />

are not included in this guideline.<br />

The accuracy of results from soil gas screening will depend on the limitations of the sampling methods<br />

and analytical instruments. These limitations are discussed in below. In general, the technique is not<br />

intended to accurately determine volatile organic compound concentrations in soil and groundwater.<br />

Rather, it is a qualitative screening tool used to provide a preliminary definition of the areal extent of<br />

contamination. These data are then used to determine the locations in which to place soil borings and<br />

groundwater monitoring wells. Subsequent analysis of soil and groundwater samples may, however,<br />

provide some means of correlating the soil gas results to the soil and groundwater results.<br />

Definitions<br />

Soil Gas—The gas that is present in the interstitial spaces between soil particles. Soil gas cannot be<br />

present in soil that is 100 percent saturated with water; therefore, soil gas is present only above the water<br />

table.<br />

Probe—A general term that denotes the device used to advance the hole and collect the soil gas sample.<br />

VOCs—As defined by EPA chemical analysis methods 8010, 8020, and 8240, a volatile organic is a<br />

compound with a boiling point of less than 125 degrees Celsius (°C). The compound should also have a<br />

vapor pressure greater than 1 mm of mercury at 25°C to be effectively detectable in soil gas. Solvents<br />

such as trichlorethylene and fuels such as gasoline are volatile organics. Pesticides are not considered<br />

volatile organics. The most common compounds included in soil gas surveys are dichloroethylene,<br />

trichloroethylene, tetrachloroethylene, trichloroethane), benzene, toluene, ethylbenzene and xylenes.<br />

Also commonly included are gasoline, diesel, and jet fuel.<br />

Kirtland AFB<br />

SOPs for Field Investigations B-99 April 2004

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