Laserfiche WebLink
cnev,00 <br /> I_118 to 1/4 inch Tubing <br /> Ground Surface <br /> jSurface Seal <br /> Probe Rod < <br /> 4 <br /> n <br /> 1 <br /> (hive PoiM Holder&Vapor Sample Point 1 <br /> 4 Retractable or Disposable Drive Point <br /> Groundwater r <br /> 4 <br /> r <br /> Figure 3. Direct-push soil vapor sampling probe (Post Run Tubing System, PRT; <br /> Geoprobe"). <br /> A surface seal of hydrated granular bentonite is not needed with the PRT system. There <br /> is no sand pack or hydrated bentonite seal needed in the borehole. However, there is <br /> potential for cross-contamination resulting from contaminants being pushed downward <br /> by the drilling rods. Avoid lateral movement of the drive rods during the push and <br /> sampling processes. <br /> C. Sub-slab vapor sampling probes <br /> Sub-slab vapor sampling probes allow for collection of soil vapor data from directly <br /> beneath the slab of a structure. Note that sub-slab sampling probes are not recommended <br /> when groundwater is present directly below the slab, as drilling through the slab could <br /> allow groundwater to enter the building. Also, it is important to determine prior to <br /> drilling if the slab has a vapor barrier; if so, be aware that the vapor barrier will need to <br /> be repaired afterward. Drilling through tension slabs is not recommended. Tension slabs <br /> contain embedded steel cables that have been pulled taught after the concrete has cured. <br /> The tension in the cables strengthens the slab and helps prevent cracking. The slab can <br /> be damaged if a cable is cut during drilling. Petroleum hydrocarbons are amenable to <br /> aerobic biodegradation. Therefore, a conservative approach supports obtaining soil vapor <br /> samples at the center of the slab and away from utility conduits, where oxygen <br /> concentrations in soil are likely smallest. At least two probes should be emplaced, with <br /> one located in the center of the slab, unless the foundation is larger than 5000 W, in <br /> ETC Soil Vapor Sampling Technical Toolkit i 1 <br /> Version 1.4, September 7,2005 <br />