PARENT SESSION
PS20 - Passive Samplers for POPs
Sunday, 17 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P193) EVALUATION OF PASSIVE - DIFFUSION SAMPLERS TO MEASURE DISSOLVED OXYGEN, GEOCHEMISTRY AND VOCs IN GROUND WATER.
Namuduri, Sumedha*,1, Chakraborti, Koushik1, Hileman, Gregg2, Byl, Tom1,2, 1 Dept of Civil & Environmental Engineering,Tennessee State University, Nashville, Tennessee, USA2 U. S. Geological Survey, 640 Grassmere Park, Suite 100, Nashville, Tennessee, USA
ABSTRACT- Bioremediation and natural attenuation are important remediation options at sites where the ground water is contaminated with fuels or solvents. The efficiency of the biodegradation process is dependant upon the amount of oxygen and other geochemical electron acceptors. Collecting these samples with a bailer or pump can disrupt the concentration in water and provide misleading information about the aquifer. Vroblesky (2001) reports that plastic bags can be used as passive diffusive samplers for volatile organic compounds (VOCs). The polyethylene bags are filled with ultra pure water and then placed in wells for several days to come to equilibrium with the VOCs. The bag can be removed from the well and harvested to get a VOC concentration for the ground water near the sampler. The same concept was tested in this experiment. Polyethylene bags and cellulose dialysis tubing were filled with ultra pure water and placed within a 2 liter container with known geochemistry or in a karst well at Ft. Campbell, Kentucky. Water in the polyethylene bags was lower in dissolved oxygen than the water collected with the bailers (0.0 and 0.5 mg/L respectively). The accuracy of the samplers was also tested in the lab, comparing the dissolved oxygen with a meter and the modified Winkler titration. Under lab conditions, the various methods were always within 0.2 mg/L (range 0.0 to 6.5 mg/L). These results indicate that the polyethylene bag has potential for accurately monitoring the dissolved oxygen in the aquifer. The polyethylene bags did not perform as well for other geochemical parameters such as nitrate, dissolved iron, and sulfate. The dialysis tubing was better with regard to these geochemical parameters. Further tests need to be conducted to determine the range of usefulness and the time it takes to come to equilibrium.
Key words: Diffusion Sampler, VOC