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

OverviewOverview

Gas Chromatograph calibration Syringe Technique VOC exposure limit Site Assessment

Potential sites Soil Gas Surveys Field Analysis

Gas Chromatograph calibration Syringe Technique VOC exposure limit Site Assessment

Potential sites Soil Gas Surveys Field Analysis

Gas Chromatograph

injection volumeinjection volume

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

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.

liquidliquid

gasgasOctaneOctane

AcetoneAcetone

TolueneToluene

vapor pressureat 25 °C

vapor pressureat 25 °C

1.88 kPa1.88 kPa

24 kPa24 kPa

3.8 kPa3.8 kPa

MWMW

114.23 g114.23 g

58.08 g58.08 g

92.14 g92.14 g

densitydensity

0.71 g/mL0.71 g/mL

0.79 g/mL0.79 g/mL

0.87 g/mL0.87 g/mL

Example Calibration: Octane

n

PVRT

n PVRT

K298

KmolkPaL

8.31

L10 x 100 kPa 1.88n

6-

K298 Kmol

kPaL8.31

L10 x 100 kPa 1.88n

6-

nmol 75.9 =mol 10 x 9.57n 9 nmol 75.9 =mol 10 x 9.57n 9

Calculate moles, mass, and equivalent liquid volume of 100 µL headspace sampleCalculate moles, mass, and equivalent liquid volume of 100 µL headspace sample

g 8.67g 10 x 8.67mol

114.23gmol 10 x 75.9 69 g 8.67g 10 x 8.67

mol114.23g

mol 10 x 75.9 69

nL 12.2 = L 10 x .221g 0.71L 10

g 10 x 8.67 93

6

nL 12.2 = L 10 x .221g 0.71L 10

g 10 x 8.67 93

6

liquidoctane

gas

KmolkPaL

8.31R

Kmol

kPaL8.31R

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.

38

4

mg/m 4.3g/L 4.3PA10 x 2g 8.67

L 100PA 1x10

sample PAsample PA

calibration PAcalibration PAsample volumesample volume

mass injected for calibrationmass injected for calibration

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)

Syringe Technique: solutionSyringe 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.

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

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.

336-

6

g/m 86.5m

L 1000L 10 x 100g 10 x 8.67

concentration in octane source vialconcentration in octane source vial

500(1 m3 of air is approximately 1 kg)

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

Hazardous Waste Site Surveys

loading zones hydraulically operated lifts accidental spills

storage tanks vegetative distress

herbicide application hazardous materials

stained soil

fill materialused to hide evidence of spillmay contain hazardous substances

water and sewer linesprovide pathways for migration of subsurface contaminants

Soil Gas Survey

Effective screening technique for mapping the extent of VOCs

Indicates location of contaminant sources

Advantagesrapidlow costminimal disturbance to siteno waste generatedadaptable to site conditions

Advantagesrapidlow costminimal disturbance to siteno waste generatedadaptable to site conditions

Disadvantagesdetection limits may be too highsome compounds may not be detectedfield results are semi-quantitative

Disadvantagesdetection limits may be too highsome compounds may not be detectedfield results are semi-quantitative

Sampling Matrix

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

Soil Gas SamplingSoil 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.

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.

Field Analysis Field Analysis

Less accurate and less sensitive than laboratory analysis!

Immediate results Examples

Portable Gas chromatograph Photoionization Air Monitor Flame Ionization Detector Test kits

Less accurate and less sensitive than laboratory analysis!

Immediate results Examples

Portable Gas chromatograph Photoionization Air Monitor Flame Ionization Detector Test kits

Analysis Matrix

http://www.perkin-elmer.com/photo/pvac.html#VOyager

Portable Gas ChromatographPortable 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.

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. MDLMDL

Photoionization Air MonitorPhotoionization 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.

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.

Flame Ionization DetectorFlame 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.

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.

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

http://www.cha-llp.com/tankmgt.htm

Underground Storage TanksUnderground 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.

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.