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However, assessment and/or characterization of the deeper vadose zone may be required in the future to protect groundwater resources. 2.2.4 Sampling Tubes: Sampling tubes should be of a small diameter(1/8 to 1/4 inch)and made of material (e.g., nylon, polyethylene, copper or stainless steel)which will not react or interact with site contaminants. For example, metal tubes should not be used for collection of hydrogen sulfide samples. A Clean, dry tubing should be utilized at all times. If moisture,water, or an unknown material is present in the probe prior to insertion, the tubing should be decontaminated or replaced. B. After use at each location: 1. Non-reusable(e.g., nylon or polyethylene)sampling tubes should be discarded; or 2. Reusable sampling tubes should be properly decontaminated as specified in Section 2.2.7. C. A drawing of the proposed probe tip design and construction should be included in the project workplan. 2.2.5 Soil Gas Probe Emplacement Methods A Permanent or Semipermanent Soil Gas Probe Methods: Permanent or semFpermanent soil gas probes may be installed, using a variety of drilling methods. Please note that the mud rotary drilling method is not acceptable for soil gas probe emplacement. Other drilling methods such as air rotary and rotosonic can adversely affect soil gas data during and after drilling and will require extensive equilibration times. Therefore, they are not recommended. Other soil gas probe designs and construction (e.g., soil gas wells or nested wells)may be appropriate and should be discussed with Agency staff prior to emplacement. When additional sampling is not anticipated per consultation with the Agency, such probes may be properly removed or decommissioned after completion of the soil gas investigation. 1. The probe tip should be emplaced midway within a minimum of one (1)foot of sand pack. The sand pack should be appropriately sized (e.g., no smaller than the adjacent formation) and installed to minimize disruption of airflow to the sampling tip. See Figure 1 for more information. 2. At least one(1)foot of dry granular bentonite should be emplaced on top of each sand pack to preclude the infiltration 01/28/2003 -6-