Benzene vs. Total VOC Readings: What Excavation Teams Need What project teams should know about benzene readings, perimeter air monitoring plans, and choosing the right instrument. Timely readings help teams understand changing air conditions beyond the site boundary. Why Benzene Levels Matter During Excavation Where benzene can come from Past fuel spills Leaking storage tanks Chemical releases Digging can disturb affected soil and let some of these substances enter the air. The amount can change as work moves across the site or reaches different soil layers. Why measure it Smell alone can’t show how much benzene is present, and some harmful substances have little or no odor. Suitable instruments are needed for useful readings. Boundary monitoring helps check whether air conditions are changing near homes, businesses, and other nearby properties. A clear monitoring plan shows which locations need attention. 2 How Real-Time Analysis Identifies Benzene Benzene is a VOC, one of many compounds that can enter the air as gases. Different instruments answer different questions. PID: broad VOC readings A photoionization detector measures a broad range of VOCs. A total VOC reading doesn’t show the exact amount of benzene, because the instrument may respond to several compounds at once. Results depend on the sensor and its calibration. Field GC: benzene-specific A field gas chromatograph separates compounds in an air sample and measures selected substances, so benzene can be identified instead of treating all VOCs as one group. Review instrument settings, calibration, and method limits before using results to guide decisions. 3 Plan Monitoring Around the Site Boundary A useful perimeter air monitoring plan begins with a clear map of the excavation area and the properties around it. Map the site Locate the digging, known or suspected contamination, and nearby places where people may be present. Choose points The best locations depend on site layout, compounds of concern, and the purpose of the assessment. Review each stage Locations may need to change as work moves closer to one side or exposes new soil. Record everything Log the location and time of readings so results can be compared later. Clear records explain why a reading was taken and what was happening on site. 4 Use Real-Time Data to Review Changing Conditions Frequent readings Can reveal changes a single sample might miss. Rise ≠ proof of cause A rise doesn’t prove excavation caused it; other site conditions may affect results. Unusual reading May call for a repeat measurement or a closer look at the affected area. Trends over time Show whether a change was brief or continued across measurements. Follow a consistent process. Compare readings with the work schedule, sample locations, and other available information before deciding what they mean, and avoid claims the data can’t support. 5 Choose Equipment That Matches the Monitoring Goal PID-based systems Provide real-time readings for total VOCs, useful for spotting changes in overall VOC conditions. They shouldn’t be presented as benzene-specific unless configured and validated to measure benzene directly. Field gas chromatograph When configured for compound-specific analysis, it may be more suitable for projects that need benzene measurements. What affects how useful results are: Equipment placement Calibration Sampling methods Regular data review Confirm system capabilities before monitoring begins. 6 Wrap-Up: Match the Method to the Question Results are most useful when documented Monitoring goal Instrument limits Sampling locations Site activities A qualified environmental professional can review findings alongside site history before recommending further action. Soil gas movement? Consider whether vapor intrusion screening and testing is also needed to assess pathways from the ground into buildings. Boundary air monitoring and vapor intrusion testing answer different questions, so one shouldn’t automatically replace the other. The right method for each concern gives a clearer picture of site conditions. 7 Thank You Contact us for more information: Website https://www.airlogicsllc.com/ Phone 908-803-1014 Email info@AirLogicsLLC.com Address 150 Cooper Road, Suite I-24, West Berlin, NJ 08091 The right data for the right question. 8