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

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

2. Overview • Gas Chromatograph calibration • Syringe Technique • VOC exposure limit • Site Assessment • Potential sites • Soil Gas Surveys • Field Analysis

3. Gas Chromatograph • Output • chromatogram • converted to peak areas and peak times • Convert peak area to mass using injection of known mass (standard) • peak area is proportional to mass injected • mass injected can be converted to concentration given _________ _________ • Alternately use peak area (PA) as surrogate for mass injection volume (If a calibrated mass isn’t required)

4. vapor pressure at 25 °C MW density Octane 1.88 kPa 114.23 g 0.71 g/mL Acetone 24 kPa 58.08 g 0.79 g/mL Toluene 3.8 kPa 92.14 g 0.87 g/mL Gas Chromatograph Calibration • We can use the headspace sample from source vials to calibrate the GC. • We will use the ideal gas law and the vapor pressure of the VOCs. gas liquid

5. gas liquid octane Example Calibration: Octane Calculate moles, mass, and equivalent liquid volume of 100 µL headspace sample at 25 °C. Table moles mass volume

6. VOC Contaminated Site Map • Report gas concentrations in mg/m3. • Example: Given a peak area of 1 x 104 from an injection volume of 100 µL, calculate the concentration in mg/m3. Assume the peak area from the source vial injections was 2 x 108. sample PA mass injected for calibration sample volume calibration PA

7. Syringe Technique • The Problem: • VOC vapors sorb to glass barrel, Teflon plunger, and stainless steel needle • The Solution: • Remove GC needle. • Purge syringe 10 times with room air to remove any residual VOCs. • Put on sample needle. (continued)

8. Syringe Technique: solution • Insert into sample bottle (with syringe at zero volume). • Fill syringe fully with gas and purge syringe contents back into the source bottle (repeat 3 times). • Fill syringe and adjust to 100 µL. • Close syringe valve and remove syringe from sample vial and remove sample needle. • Put on GC needle. • Instruct GC to measure sample. • Insert needle in injection port, open syringe valve, inject sample, hit enter button all as quickly as possible. • Remove syringe from the GC injection port. Equilibrate with headspace Eliminate needle carryover

9. Octane Exposure Limits • OSHA PEL (Permissible exposure level) • 500 ppm TWA (approximately ____ mg/m3) • LC50 • CAS# 111-65-9: Inhalation, rat: LC50 =118 g/m3/4H. 500 (1 m3 of air is approximately 1 kg) concentration in octane source vial

10. 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

11. 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

12. 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

13. 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

14. 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.

15. 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

16. 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

17. 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.

18. 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.

19. 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

20. 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