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Section No. 8 <br /> Revision No. 1 <br /> Date:_January. 1997 <br /> Page 2 of 13 <br /> best where contaminant concentrations are expected to be high and the <br /> vadose zone is highly permeable to vapor. <br /> 2. Collection of soil gas using a sorbed contaminants active approach: <br /> involves the forced movement of bulk soil atmosphere from the sampling <br /> horizon through a probe to a collection device designed to extract and <br /> trap sample stream contaminants by adsorption; <br /> well suited to sites where soil is highly permeable to vapor and where <br /> contaminant concentrations may be lower than required for successful <br /> whole-air surveys; and <br /> contaminant trapping is accomplished by use of an adsorbent collection <br /> medium such as charcoal. <br /> 3. Collection of soil gas using a whole-air passive approach: <br /> involves the entry of bulk atmosphere or soil atmosphere components <br /> from a near-surface sampling horizon to a collection or containment <br /> device through a flux chamber or similar apparatus; and <br /> - useful to some very specific applications such as monitoring soil <br /> contaminant emissions from soil or water to assess the health hazard <br /> risk to the general public. <br /> 4. Collection of soil gas using a sorbed contaminants passive approach: <br /> - involves the passive movement of contaminants in soil to a sorbent <br /> collection device over time; <br /> - samplers are placed into shallow holes, backfilled and left in place for <br /> two to ten days; and <br /> - charcoal is generally used as the adsorbent. <br /> 5. Collection of soil samples for subsequent headspace atmosphere or extraction <br /> sampling: <br /> - examines contaminants that are present in a headspace atmosphere <br /> above a contained soil sample; and <br /> - can be a relatively poor method for determining many of the more volatile <br /> contaminants, so is therefore limited in value. <br /> 6. Collection of soil pore liquid headspace gas: <br /> - uses a suction lysimeter or other device to sample soil pore liquid; <br /> - soil vapor that collects in the soil pore liquid sampling device is extracted <br /> and analyzed; and <br /> - limited by the expense and complexity of installing the sampling devices. <br /> Methods 1, 2 and 4 are explained in detail in this document as they are the methods <br /> most commonly used by FDGTI for conducting soil gas surveys. Method 5 is commonly <br /> used for monitoring soil headspace in collected samples during drilling. The procedure <br /> for method 5 is presented in SOP No. 7. <br /> Soil gas samples can be obtained using the following methods of penetration: <br /> shallow driven points (less than 3 ft.) using a slam bar and % in. probe; can drive 30 or <br /> more points per day; good for contamination above about 30 ft. depth; must pre-drill <br /> through sealed surfaces such as concrete; <br /> hydraulically driven points using 3/ in. tube; slow method (10 to 15 points per day); good <br /> for deep contamination or complex geology; can cause filter cake that blocks soil vapor <br /> readings; and <br />