Abstract
Subsurface VOC monitoring has been mainly based on manual sampling, transport, and analysis, which would require a sufficient amount of samples to ensure data accuracy and reliability, and additional costs to ensure sample quality. Therefore, a continuous on-site monitoring system is desirable for accurate measurement and subsequent risk assessment. In this study, benzene, toluene, ethylbenzene, and xylene (BTEX) were continuously monitored by the system based on a thermal desorber (TD) and gas chromatography (GC) in an oil-contaminated site that consisted of saturated and unsaturated zones. For the saturated zone, fully automated groundwater sampling and purging processes were performed, and the gasified samples were applied to the TD–GC system. For the unsaturated zone, the gaseous sample in the site was directly applied to the TD–GC system. After verifying the accuracy and precision of the monitoring system, the continuous monitoring system was successfully operated for more than a month in the field. The monitoring system used in this study is applicable to other sites for continuous monitoring, thus providing a scientific background for advanced risk assessment and policy development.
Highlights
Volatile organic compounds (VOCs) generally enter the soil and groundwater from external sources [1,2]
VOC monitoring has mainly been conducted during on-site sampling, which is followed by laboratory analysis [11,12]
The demand for fast and continuous VOC monitoring is increasing; more attention has been paid to portable VOC sensors
Summary
Volatile organic compounds (VOCs) generally enter the soil and groundwater from external sources [1,2]. Once introduced into the soil, gaseous VOCs are generated continuously and can enter humans via vapor intrusion, leading to chronic exposure through VOC inhalation [6]. VOC monitoring has mainly been conducted during on-site sampling, which is followed by laboratory analysis [11,12]. Such monitoring inevitably requires transfer time of the samples along with pretreatment (sometimes conducted), possibly altering the original sample quality. The demand for fast and continuous VOC monitoring is increasing; more attention has been paid to portable VOC sensors. As a representative portable VOC sensor, the photoionization detector (PID) has become commercially available; the combination of PID with gas chromatography (GC) has been recently investigated for monitoring VOCs in the water and air [13,14].
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