Key Takeaways & Executive Findings
- •• • BTEX contamination exhibited a localized 'point-source leakage' pattern, with detection rates of 24.3%–47.1% and coefficients of variation (2.32–3.90) confirming high spatial heterogeneity, necessitating high-resolution site investigation rather than grid sampling. • • Benzene, ethylbenzene, and m/p-xylene exceeded Class I screening values, with benzene posing the highest risk: carcinogenic risk up to 7.42×10⁻⁴ and non-carcinogenic hazard quotient up to 38.24, far above acceptable thresholds (typically 1×10⁻⁶ and 1, respectively). • • Vapor intrusion was the dominant exposure pathway, contributing over 87% of benzene's total risk, underscoring the need for vapor intrusion mitigation in redevelopment planning. • • MIP detection revealed that benzene and toluene migrated as a whole, while chlorobenzene exhibited delayed migration due to strong adsorption, indicating that co-contaminant transport models must account for compound-specific retardation.
Abstract
The relocation of numerous industrial enterprises in China has left behind soil contamination, particularly by volatile organic compounds such as BTEX, whose migration and health risks are of great concern. Coastal plains, characterized by high groundwater tables and interbedded sedimentary strata, exhibit contaminant distribution and migration patterns distinct from inland regions. This study investigated a decommissioned resin plant site in the Yangtze River Delta coastal plain, systematically analyzing the spatial distribution, migration, and health risks of soil BTEX. Seven BTEX compounds were detected with detection rates ranging from 24.3% to 47.1%. Maximum concentrations of benzene, ethylbenzene, and m/p-xylene exceeded China's Class I construction land screening values. The contaminant plume was predominantly located in the southern product warehouse area, while the potential source was traced to the upstream wastewater treatment unit, indicating a 'source-sink' spatial mismatch. Vertically, contaminants exhibited a 'shallow-layer volatilization, middle-layer enrichment, and deep-layer retardation' pattern, with significant enrichment in silty clay at 3–6 m depth and sharp concentration declines in mucky clay. Membrane Interface Probe (MIP) multi-parameter detection revealed that benzene and toluene migrated as a whole, whereas chlorobenzene lagged due to strong adsorption. Benzene posed the most significant health risk, with carcinogenic risk up to 7.42×10⁻⁴ and non-carcinogenic hazard quotient up to 38.24, both exceeding acceptable levels. Inhalation of indoor air contaminated by vapor intrusion from underlying soil contributed over 87% of benzene's total risk, dominating the exposure pathway. This study elucidates the unique migration and risk formation mechanisms under high water table and interbedded strata, providing a scientific basis for precise investigation, risk assessment, and remediation of similar contaminated sites.
1. Introduction
Industrial site contamination poses a significant challenge to urban redevelopment, particularly in coastal plains where high groundwater tables and interbedded sedimentary strata complicate contaminant fate. Traditional site assessment methods often assume homogeneous subsurface conditions, leading to inaccurate risk characterization and ineffective remediation strategies. The presence of volatile organic compounds like BTEX, with their high mobility and toxicity, demands a nuanced understanding of their spatial distribution and migration pathways under such hydrogeological settings.
This study addresses the critical gap by integrating high-resolution MIP probing with comprehensive health risk assessment at a decommissioned resin plant in the Yangtze River Delta coastal plain. The research systematically uncovers the 'source-sink' spatial mismatch and vertical stratification of BTEX contamination, driven by groundwater flow and lithological heterogeneity. By quantifying the dominant role of vapor intrusion in benzene risk, the findings provide actionable insights for targeted investigation and risk mitigation, offering a methodological framework applicable to similar coastal industrial sites.
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WANG Lei, XIE Li, SUN Rui, TAN Xuejun, ZHANG Xiang, JIANG Wenchen (2026). Source-Sink Spatial Mismatch Characteristics and Health Risks of Soil BTEX in a Decommissioned Industrial Site on a Coastal Plain. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202608027
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Frequently Asked Questions
What are the key hydrogeological factors controlling the vertical distribution of BTEX in coastal plain sites?
The vertical distribution is primarily controlled by the interbedded sedimentary strata. In this study, significant enrichment occurred in the silty clay layer at 3–6 m depth due to adsorption, while concentrations sharply decreased in the deeper mucky clay layer, which acts as a natural barrier. The high groundwater table also promotes lateral migration, leading to the observed 'source-sink' spatial mismatch.
How does the 'source-sink' spatial mismatch affect risk assessment and remediation strategies?
The mismatch indicates that high-concentration zones (sinks) may be located downstream from the actual source, complicating source identification. Risk assessments based solely on source areas may underestimate risks in sink areas. Remediation must address both source and plume, requiring a comprehensive understanding of groundwater flow and contaminant transport.
What is the significance of the MIP multi-parameter detection in this study?
MIP detection provided real-time, high-resolution data on contaminant distribution and migration. It revealed that benzene and toluene migrated as a whole, while chlorobenzene lagged due to strong adsorption. This information is crucial for predicting contaminant transport and designing effective remediation, as it highlights compound-specific behaviors that conventional sampling might miss.
Why is vapor intrusion the dominant exposure pathway, and what are the implications for site management?
Vapor intrusion contributed over 87% of benzene's total risk because benzene is volatile and can migrate from subsurface soil into indoor air through building foundations. This finding implies that risk mitigation should prioritize vapor intrusion controls, such as vapor barriers or sub-slab depressurization systems, especially for future residential or commercial use.
What are the limitations of this study in terms of extrapolating to other coastal plain sites?
The study is site-specific, and the findings may not be directly transferable to other coastal plains with different geological and hydrogeological conditions. However, the methodological approach—integrating MIP probing with risk assessment—can be adapted. Site-specific investigations are necessary to account for variations in stratigraphy, groundwater chemistry, and contaminant sources.
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