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purge volume. (1) Assess the vertical distribution of contaminants in the vapor phase within the unsaturated zone; 1. Clean,dry tubing should be used at all times. If any moisture,water,or an (2) Identify migration pathways at depth along which contaminants may have unknown material is present in the probe prior to insertion,decontaminate or migrated from sources;and replace the tubing. (3) Serve as discrete monitoring points to evaluate the efficiency of a cleanup action. 2. The bottom-end of the tubing should be attached to an appropriate vapor probe tip. The probe tip design should allow for optimum air flow and prevent Vertical profiling depends on DQOs and the CSM. Vertical profiling may may air flow restriction. Ensure the connection between the tubing and the vapor not be appropriate at any given site. Describe the rationale for vertical profiling in probe tip is air-tight to prevent leakage. the workplan for regulatory review prior to commencement of field work. Vertical profiling is appropriate for any of the following locations: 3. Metal tubes should not be used for collection of hydrogen sulfide samples. Nylaflowo,polyetheretherketone(PEEK),and Teflon®are recommended for • Sites identified with subsurface structures such as USTs,sumps,clarifiers, use in the soil vapor sampling train. Use of low-density polyethylene(L-D PE) waste or chemical management units is discouraged due to decreased performance relative to other tubing types in • Sites with subsurface sources such as oil fields,artificial fill,or buried both introduction of background analytes and sample recovery. Reduced animal waste recovery of naphthalene was reported when using Nylaflows tubing with • Sites with heterogeneous lithology small sample sizes(see Appendix B). • Sites with contaminated groundwater • Areas with significantly elevated VOC concentrations detected during previous sampling Soil Vapor Well Installation • Areas where elevated field instrument readings are encountered from soil matrix cuttings,cores or samples Vapor well installation procedures are described below. The probe tip,probe and • In the annular space of groundwater monitoring wells during construction probe connectors should all have the same diameter to provide a good seal where and assessment of the vertical extent of soil gas contamination is between the formation and the sampling assembly. Seal all holes and spaces necessary. with bentonite slurry to prevent ambient air intrusion. All available information such as geologic logs and field instrument readings from Installation Methods and Design: Soil vapor wells may be installed using a soil cuttings or cores should be used to select appropriate depths to collect soil variety of drilling methods,such as direct push methods, hollow stem auger,or gas samples:`Probes should be installed at depths with elevated vapor readings other techniques,as appropriate. Certain types of drilling methods,such as air and/or slightly above fine-grained soils. If vertical characterization to rotary and rotosonic,are not recommended because they can adversely affect groundwater is required,the deepest soil gas sample should be collected near soil gas data during and after drilling. However,for deeper soil gas wells or for the top of the capillary fringe. Soil gas probes should not be installed within or drilling in denser/coarser formations,alternate drilling methods(e.g.,air rotary below the capillary fringe. Where deeper soil gas sampling is necessary and no and rotosonic methods)may be employed with longer equilibration times prior to lithologic change or technical basis is observed,then default sampling depths of sampling. The mud rotary drilling method is not acceptable for soil gas probe 10 to 15 foot intervals may be selected for multi-depth sampling,until either emplacement under any circumstances. When additional sampling is not groundwater is encountered or VOCs are not detected. Nested vapor wells may anticipated,properly remove or decommission vapor wells with concurrence from be installed in the annular space of groundwater monitoring wells to serve as a the regulatory agency and in accordance with State and local requirements. dual-purpose well if both vapor and groundwater monitoring are required. A. Place the probe tip midway in the sand pack,as shown on Sampling Tubing Figure 1. The sand pack should be a minimum of one(1)foot thick. Install the sand pack to minimize disruption of airflow to the sampling tip. Small diameter(1/8 to 1/4 inch)sampling tubes made of material,which will not react or interact with site contaminants should be used. Use small-diameter B. Emplace at least one(1)foot of dry granular bentonite on top of each sand continuous tubing attached from the vapor probe to the ground surface to minimize pack,as shown on Figure 1. Following the dry bentonite,grout the borehole to the surface with hydrated bentonite. The purpose of the dry granular 3/3/2010 -19- 3/3/2010 -20-