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KIRTLAND AIR FORCE BASE ALBUQUERQUE, NEW MEXICO ...

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APPENDIX B<br />

The rate of migration through the soil pores depends on a variety of factors including the volatility and<br />

water solubility of the compounds of interest, concentration gradients, soil porosity, soil type, and soil<br />

moisture content. The rate of migration is greatest and thus the use of soil gas screening is most<br />

applicable to compounds of high vapor pressure and low water solubility. The best sites for soil gas<br />

surveys are those with porous soils (sands or gravels) that facilitate migration of the soil gas.<br />

Soil gas screening is a rapid method for characterizing horizontal extent of volatile organic<br />

contamination at a site. Soil gas surveys are generally performed prior to the drilling of soil borings and<br />

the installation of monitoring wells. The results of the soil gas survey are used to locate both monitoring<br />

wells and soil borings inside and outside of contaminated areas. By using soil gas surveys to determine<br />

locations, the number of monitoring wells and soil borings installed may be optimized. A reduction in<br />

the number of monitoring wells and soil borings reduces the number of samples collected for laboratory<br />

analysis. Many of the soil gas screening methods currently being used provide immediate chemical<br />

analysis results in the field. These results allow the survey to be directed by incoming data and provide<br />

information to direct the collection of subsequent soil gas samples.<br />

The following guidelines describe procedures for performing soil gas investigations using active soil gas<br />

sampling methods.<br />

In general, a soil gas survey consists of the following steps: (1) Applicability Determination: This<br />

determines if the method is applicable and cost effective for the given site. (2) Sampling and Analysis:<br />

This includes planning: to determine the sampling locations; sampling when a probe is driven into the<br />

ground and the soil gas is brought to the surface for collection; and analysis when a sample is analyzed<br />

using a field or laboratory instrument. (3) Data Interpretation. The data collected are analyzed to provide<br />

an indication of contaminants and contaminant patterns present. Recommendations concerning<br />

contaminant extent and the need for additional investigations are made based on the results.<br />

Determination of Applicability of the Method:<br />

Prior to performing a soil gas survey, it is determined if the method will be effective for the site and for<br />

the contaminants of concern. The following are the necessary conditions and prerequisites for an<br />

effective soil gas survey:<br />

VOCs are suspected to be present in the soil or groundwater.<br />

Soil is not saturated from a recent rain event or significant snow melt.<br />

Water table is at least 2 ft below the surface.<br />

The following are site characteristics that are advantageous, but not absolutely necessary, for an effective<br />

soil gas survey:<br />

The presence of high permeability soils. High clay or organic carbon content in the soil<br />

impedes migration and thus the detection of low concentrations of contaminants.<br />

Groundwater at less than 30 ft, if groundwater contamination is to be tracked. Groundwater<br />

depth is not important for establishing the extent of soil contamination.<br />

Temperatures above 0 degrees centigrade. Ambient temperatures below 0 degrees centigrade<br />

impede the ability of soil gas screening to detect low concentrations of contaminants.<br />

Kirtland AFB<br />

SOPs for Field Investigations B-101 April 2004

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