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nwkace.army.mil/Geology/htrw.html

http://www.nwk.usace.army.mil/Geology/htrw.html. Overview. Site Assessment Potential sites Soil Gas Surveys Field Analysis. Site Assessment. Contaminated soil, a global problem Difficult to assess subsurface contamination can’t see it 3-d problem

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nwkace.army.mil/Geology/htrw.html

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  1. http://www.nwk.usace.army.mil/Geology/htrw.html

  2. Overview • Site Assessment • Potential sites • Soil Gas Surveys • Field Analysis

  3. Site Assessment • Contaminated soil, a global problem • Difficult to assess subsurface contamination • can’t see it • 3-d problem • even with lots of monitoring wells can miss important subsurface features. • Expensive to decontaminate sites • competing national priorities • highest priority needs to be prevention

  4. Hazardous Waste Site Surveys • fill material • used to hide evidence of spill • may contain hazardous substances • water and sewer lines • provide pathways for migration of subsurface contaminants • loading zones • hydraulically operated lifts • accidental spills • storage tanks • vegetative distress • herbicide application • hazardous materials • stained soil

  5. Sampling Matrix Soil Gas Survey • Effective screening technique for mapping the extent of VOCs • Indicates location of contaminant sources Soil Gas Survey Advantages rapid low cost minimal disturbance to site no waste generated adaptable to site conditions Disadvantages detection limits may be too high some compounds may not be detected field results are semi-quantitative

  6. Soil Gas Survey: Methods • Place hollow, small diameter probe in soil • Apply vacuum to probe • Extract soil pore gas • Take a sample of soil pore gas using: • syringe - on-site gas chromatograph analysis • Tedlar bag - on-site or off-site analysis • unaffected by most compounds • impermeable to gas exchange • stainless steel adsorption tube - quantitative laboratory analysis

  7. Soil Gas Sampling • Static sampling can be done two ways: • An in-situ adsorbent (usually an activated charcoal rod) is buried in the soil for a period of days to weeks. The adsorbent is retrieved and analyzed at a laboratory for VOCs. • Samples are collected from containers placed in the surface soil and analyzed using portable analytical instruments. • Concentrations in soil gas are affected by dissolution, adsorption, and partitioning. • Partitioning refers to the ratio of component found in a saturated vapor above an aqueous solution to the amount in the solution. • Contaminants can also be adsorbed onto inorganic soil components • or "dissolved" in organic soil components.

  8. Field Analysis • Less accurate and less sensitive than laboratory analysis! • Immediate results • Examples • Portable Gas chromatograph • Photoionization Air Monitor • Flame Ionization Detector • Test kits Analysis Matrix

  9. Portable Gas Chromatograph • Portable GC contains • a built-in 3-column configuration with isothermal oven which provides optimized fast GC analysis for up to 40 volatile organic compounds (VOC). • a miniaturized PID/ECD dual detection system which allows monitoring at 1-10 PPB levels of a wide range of aromatic, chloroalkene, and chloroalkane solvents. http://www.perkin-elmer.com/photo/pvac.html#VOyager

  10. Photoionization Air Monitor • The 2020 hand-held Total VOC air analyzer weighs just 1.75 lb. (0.79 kg). • Sample is drawn via the internal pump • Results are displayed on the built-in LCD. • The operating concentration range is 0.5 - 2000 PPM.

  11. Flame Ionization Detector • The Micro FID weighs 8.1 lb. (3.7 kg.), • the smallest and lightest datalogging Flame Ionization Detector (FID) available. • The concentration range is 0.1 - 50,000 PPM with a response time of less than 3 seconds.

  12. Potential Sites • Underground fuel storage tanks • home owner beware! • gasoline stations • Waste management facilities • Chemical storage facilities • Liquid waste lagoons • Injection wells • Chemical transfer facilities

  13. Underground Storage Tanks • Leaking underground storage tanks are a significant source of soil and water contamination in the United States. • New regulations went into effect in 1998 • Many facilities removed underground tanks and replaced them with double walled tanks or above ground tanks for petroleum product and chemical storage. http://www.cha-llp.com/tankmgt.htm

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