[Effects of Source Depletion on Vapor Intrusion Risk Assessment]

Area of Science:

• Environmental Science
• Risk Assessment
• Geochemistry

Context:

• Regulatory site investigations often use the Johnson & Ettinger (J&E) model for vapor intrusion risk assessment.
• The J&E model's assumption of constant source concentration contradicts real-world conditions of source depletion.
• Accurate prediction of indoor air concentrations is crucial for evaluating potential health risks.

Purpose:

• To compare the predictive accuracy of the J&E model, the SD source depletion model, and the RBCA source depletion model.
• To evaluate how different models account for source depletion in vapor intrusion risk assessment.
• To determine the most suitable model for quantifying vapor intrusion risk under realistic site conditions.

Summary:

• The J&E model significantly overestimates indoor air concentrations and associated risks due to its constant source assumption.
• SD and RBCA source depletion models predict decreasing concentrations over time, reflecting real-world depletion.
• The SD model demonstrated better alignment with mass conservation principles and was deemed more suitable for realistic risk quantification than J&E and RBCA.

Impact:

• Identifies the limitations of the widely used J&E model in vapor intrusion assessments.
• Highlights the importance of incorporating source depletion dynamics for accurate risk evaluation.
• Provides a more realistic approach (SD model) for quantifying vapor intrusion risk, potentially leading to more effective site management strategies.