ONLINE MONITORING OF AROMATIC-HYDROCARBONS USING A NEAR-ULTRAVIOLET FIBER OPTIC ABSORPTION SENSOR

A prototype ultraviolet absorption sensor was used to continuously mon itor the composition of vapor extractant from soil remediation wells a t the Lawrence Livermore Dynamic Underground Stripping Site over a per iod of five weeks. The sensor measured absorption in the spectral regi on of 230.0-300.0 nm, allowing direct detection of benzene and its der ivatives (including toluene, xylenes, and ethylbenzene). The spectra o f these compounds contain considerable fine structure, and deconvoluti on of the mixture spectra allowed a quantitative determination of the concentration of benzene to be made. Relative levels of total aromatic hydrocarbons were also determined. The trends measured by the on-line sensor were in agreement with standard off-line laboratory analyses a nd were obtained continuously in realtime. Continuous monitoring allow ed transient events as well as mid- to long-term trends in the extract ion process to be measured.