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Note: This information is intended to clarify techniques that should be used during soil sampling of VOCs to minimize volatilization during soil sampling and collection.
Volatile Organic Compounds (VOCs) should be sampled quickly after soil classification or collection to minimize volatilization of contaminants. Two samples should be taken from each two-foot section of core or grab sample. One sample should be put into a laboratory issued 4-ounce jar with Teflon-lined lid or other IDEM approved sampling device, and chilled in a cooler filled with ice. The jar should be filled with soil to minimize or eliminate headspace in the jar. The remaining sample should be placed in a sealable bag and staged in an area where the sample can volatilize.
Depending on the temperature, the staged sample should be given time (generally within 1-15 minutes) to volatilize for field screening. The sample should be field-screened using a calibrated field instrument to determine if the matching sample in the cooler should be sent to the lab. Typically, a Photo Ionization Detector (PID) should be used for gasoline releases and a Flame Ionization Detector (FID) should be used for waste oil and high-end liquid hydrocarbon fuels such as diesel or kerosene. Please keep in mind that a FID will not work at temperatures below 40° F. (Do not send the field-screened portion of the sample to the lab. These samples will be biased low and will be considered invalid.)
Samples selected for laboratory analysis from each borehole should be taken from the interval exhibiting the highest field instrument response. If all field instrument responses are low a sample should be taken from the interval directly above the water table. This may include the "smear zone". In addition to the above minimum requirements, samples must be taken at all points where odors or soil discoloration indicate soil contamination.
The selected chilled samples that are already in the cooler should be sent to the lab at 4° C. All chains of custody must be signed and include the time and date of arrival, the temperature received, and all other pertinent information. All field procedures and field instrument readings must be documented in a permanent field record and included in the report. The specific times that the samples are containerized and field analyzed must be included in this field record. Any questions on sampling or methodology can be directed to IDEM's OLQ Chemistry section.
Soil cores should be classified according to IDEM's OLQ Geological Services non-rule policy document Drilling Procedures and Monitoring Well Construction Guidelines [PDF].