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Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Vapor Intrusion Management in China: Lessons Learned from the United States Jie Ma,*,† Lin Jiang,*,‡ and Matthew A. Lahvis*,§ †
State Key Laboratory of Heavy Oil Processing, Beijing Key Lab of Oil & Gas Pollution Control, China University of Petroleum-Beijing, Beijing 102249, China ‡ National Engineering Research Centre of Urban Environmental Pollution Control, Beijing Key Laboratory for Risk Modeling and Remediation of Contaminated Sites, Beijing Municipal Research Institute of Environmental Protection, Beijing 100037, China § Shell Global Solutions (US) Inc., Shell Technology Center, Houston, Texas 77082, United States Table 1. Government Guidelines Related to VI Risk Assessment in China year
guideline title
2014 2014 2014 2014
technical guideline for environmental site investigation technical guideline for risk assessment of contaminated sites technical guideline for environmental site monitoring guidance of environmental site investigation and remediation for industrial sites technical specification for soil environmental quality assessment (second draft for comment) risk control standard for soil contamination risk screening values for soil contamination of development land (draft for comment) technical guideline for volatile organic chemicals (VOCs) sampling in contaminated sites (draft for comment) technical guideline for soil gas sampling (in preparation)
2016 2016 2017 2018
implementation of separate guidelines greatly facilitates site closure and redevelopment by minimizing the number of unnecessary investigations and response actions especially at petroleum VI sites. • The United States Environmental Protection Agency (USEPA) recommends conceptual site models (CSMs) be developed at VI sites using a multiple-line-of evidence approach involving source (soil or groundwater), pathway (vadose zone), and receptor (building) characterization. The CSM is based on site-specific measurements of VOC concentrations in groundwater, soil, soil-gas, subslab air, indoor air, and outdoor air. The CSM can include an evaluation of the site-specific data using mathematical models.3 Preferential pathways (e.g., sewers, floor, and land drains) that facilitate vapor migration from source areas to indoor air can also be an important factor in the CSM development.1 Methods for sampling and characterizing preferential pathways are still being developed and standardized nevertheless. • VI risk assessments based on indoor air and subslab vapor samples can be complicated by background sources of VOCs in both indoor (e.g., building materials and consumer products) and outdoor air. Indoor air and subslab vapor concentrations can also be highly variable, both over time and space. The variability has been linked to several factors affecting air flow into and out of buildings, including fluctuations in barometric pressure, ambient air
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ontaminated land management is a significant issue in China where >100 000 factories are estimated to have been closed since 2001 and over 2 million hectares of highly contaminated brownfield lands have been left untreated. In developed countries such as the U.S., land contaminated with volatile organic compounds (VOCs) is commonly assessed for vapor intrusion (VI). VI is a risk pathway in which humans are potentially exposed to VOC vapors migrating from subsurface sources in soil and groundwater to indoor air in overlying building foundations. The U.S. has gained vast practical knowledge and experience in evaluating and managing VI since the pathway became routinely regulated around 25 years ago.1 The intent of this viewpoint article is to highlight some key lessons learned by the U.S. on VI which would be of particular benefit to China, where environmental guidelines are being rapidly developed to address brownfield redevelopment (Table 1). • Over the past few years, the U.S. regulatory community has recognized the need to separate VI guidelines for chlorinated and petroleum VOCs.2,3 Separate guidelines are needed because petroleum VOCs are susceptible to aerobic biodegradation which limits their potential for VI relative to chlorinated VOCs. Different approaches are required for VI screening, site investigation, modeling, and vapor mitigation.2 Experience has shown that the © XXXX American Chemical Society
Received: February 15, 2018
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DOI: 10.1021/acs.est.8b00907 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environmental Science & Technology
In summary, VI is expected to be a critical exposure pathway in China given the country’s focus on brownfield redevelopment and aspiration to return of large tracts of contaminated land to productive use. It is our hope that China capitalizes on many of the lessons learned from the U.S. to develop sustainable, robust, and risk-based VI guidelines, which can be emulated by other countries undergoing similar environmental and socio-economic transformations.
windspeed and direction, indoor/outdoor air temperature gradients, heating, venting, and air conditioning (HVAC) and other occupant activities.4 The variability underscores the need to measure pressure differentials to identify the direction of air flow across building foundations and opportune times for indoor vapor sampling. The variability in VOC concentrations in indoor air also raises concern over the representativeness of discrete indoor air samples for short-term risk assessment. Short-term risk assessments can generally be improved if discrete indoor air and subslab vapor sampling is targeted to quantify maximum exposures (e.g., winter months and highest concentration locations) or avoided altogether through the implementation of engineering or institutional controls. Rapid diagnostic tests, such as building pressure cycling, are also promising technologies that have recently been developed to aid short-term VI risk assessment. • In China, current risk assessment is often based on soil concentration data. Soil sampling is not, however, recommended for VI risk assessment because of the potential for volatile losses of VOCs during soil sampling, significant spatial variability of VOC concentrations in soils, and uncertainties in soil partitioning and in general overestimate vapor concentration in the partitioning calculations.3 China is therefore urged to develop guidelines for soil−gas sampling and associated soil−gas screening criteria. • Mathematical transport modeling is expected to be of critical importance in China given the need for predictive exposure assessments associated with brownfield redevelopment and planned or hypothetical building construction. It should be emphasized that the Johnson and Ettinger (J&E) model typically used for predictive risk assessment and now seeing application in China cannot precisely simulate the complexities of the actual VI exposure pathway. Restricting VI modeling to screening applications with parameter values and scenarios bounded by uncertainty analyses is recommended.3 The J&E model is not preferred for petroleum VI risk assessment because it neglects biodegradation and significantly overestimates risks. Better options include distance-based screening or models which incorporate oxygen-limited biodegradation.2 • The transfer value of U.S. learnings is somewhat muted by regional differences in building types: predominantly single-family homes in the U.S. and high-rise buildings in China. In particular, the wealth of knowledge gained from numerous empirical studies undertaken to document vapor attenuation across building foundations (and the associated empirical attenuation factor data) in the U.S. may have little value in China given these studies were conducted largely at single-family homes. Other factors, such as the operation of elevators and HVAC systems, further contribute to country-specific differences in vapor migration around and inside buildings and potential VI occurrence. The effects of elevators and HVAC systems on VI are not well documented and need for further studies. High-rise buildings may be more amenable than single-family homes to VI mitigation using positive pressure HVAC systems and ventilated basement parking garages.5 Implementation of such systems may eliminate the need for long-term liability management provided ventilation requirements can be met.
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AUTHOR INFORMATION
Corresponding Authors
*(J.M.) E-mail:
[email protected]. *(L.J.) E-mail:
[email protected]. *(M.A.L.) E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by Beijing NOVA program (xx2018062), National Natural Science Foundation of China (21407180), Science Foundation of China University of Petroleum-Beijing (2462018BJC003) and Ministry of Environmental Protection of China(201509034).We thank Emma (Luo) Hong for her internal review.
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REFERENCES
(1) McHugh, T.; Loll, P.; Eklund, B., Recent advances in vapor intrusion site investigations. J. Environ. Manage. 2017.20478310.1016/ j.jenvman.2017.02.015 (2) USEPA. Technical Guide For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites (EPA 510-R-15−001); U.S. Environmental Protection Agency: Washington, DC, 2015. (3) USEPA. OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air (OSWER Publication 9200.2−154); U.S. Environmental Protection Agency: Washington, DC, 2015. (4) McAlary, T. A.; Provoost, J.; Dawson, H. E., Vapor Intrusion. In Dealing with Contaminated Sites: From Theory towards Practical Application; Swartjes, F. A., Ed.; Springer, 2011; pp 409−453. (5) USEPA. Brownfields Technology Primer: Vapor Intrusion Considerations for Redevelopment (EPA 542-R-08−001); U.S. Environmental Protection Agency: Washington, DC, 2008.
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DOI: 10.1021/acs.est.8b00907 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
