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HaloSnif

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Tech ID: 103
Project Overview
HaloSnif was designed to monitor carbon tetrachloride vapor in the vadose zone at the Hanford Site. However, it can measure any volatile chlorinated compound in air, gas, or water. HaloSnif was evaluated at Hanford as a real-time monitoring system for measuring carbon tetrachloride concentrations in soil gas extracted at the vapor extraction site. Targeted toward environmental cleanup, HaloSnif was developed as a monitoring system to provide real-time concentration data for volatile chlorinated hydrocarbons. One specific application demonstrated interfacing HaloSnif to a cone penetrometer rig to give profiles of carbon tetrachloride concentrations as a function of depth. A second application at Hanford included using HaloSnif as a real-time monitor for carbon tetrachloride concentrations in soil gas extracted and subsequently cleaned up. HaloSnif has also been used to monitor real-time concentrations of trichloroethylene, tetrachloroethylene, and carbon tetrachloride in water samples. With this most recent development, HaloSnif may be useful for process or facility monitoring at DOE or industrial sites.

Technology Description
 During monitoring operation, HaloSnif operates at sub-ambient pressure (40 torr). It continuously draws an air sample through a critical orifice into the plasma excitation chamber where it is mixed with helium and excited with a radio-frequency signal. The plasma chamber is coupled via a fused silica optical fiber to the signal processor unit. The optical emission of the plasma is filtered with a narrow band pass filter designed to monitor the 837.6 nm emission line from the excited chlorine atom. The intensity of the chlorine emission is directly proportional to the concentration of chlorine containing species in the sample gas. The detection sensitivity for carbon tetrachloride is 5 ppmv. The response of the system is linear from the detection limit to 10,000 ppmv. The detection limit for other chlorine containing compounds can be estimated by determining the ratio of chlorine in the compound of interest to that of carbon tetrachloride. Data acquisition is achieved using the LabView[TM] data acquisition software package installed on a Macintosh computer system. The data acquisition system is interfaced to the electro-optical signal processing module via a 1 to 10 volt analog output. Real-time concentrations of total chlorinated compounds are displayed on the monitor for observation by on-site personnel. All data is stored in computer memory for post-run processing and analysis.

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