ENV-644: USE OF NEW MODELS TO SUPPORT VAPOUR INTRUSION MITIGATION DESIGN

Soil vapour intrusion of subsurface volatile organic compounds (VOCs) into indoor air of buildings is a significant potential concern at existing sites where chemical releases occur, or at new buildings at Brownfield sites with residual chemical impacts. While soil vapour intrusion mitigation systems are increasingly being implemented, there are limited published data on mitigation performance for VOCs particularly for industrial or commercial buildings or high density residential buildings with below ground parking garages. Data gaps include the effectiveness of passive and active venting systems and reduction in vapour intrusion that can be achieved relative to unmitigated buildings. Because of lack of knowledge and standardization, design practices and post-mitigation monitoring requirements vary widely and are, in some cases, over-conservative. To address these gaps, a comprehensive empirical review of data on the performance of active and passive venting systems and a study using the Modified Johnson and Ettinger Model was completed. The empirical data indicate performance of passive venting systems are variable in terms of venting air flow rates and pressures. The results of modelling for passive venting indicate a wide range of predicted reduction factors, defined as the vapour attenuation factor for a baseline unmitigated building divided by the attenuation factor for the mitigated case. Because of the potential for depressurized buildings and/or reverse vent stack effect, for passive venting systems a continuous leak free barrier that reduces the potential for soil gas diffusion and advection is essential. The performance of active venting systems can be more readily controlled and quantified based on design principles as supported by the results of modelling, which indicated higher reduction factors than for passive venting systems. For both passive and active venting systems, improved efficiency in venting can be achieved through aerated subfloors. A monitoring framework that is robust but efficient and sustainable is presented that incorporates the concept of a concentration exceedance factor and the type of mitigation system

A Negative Feedback Loop Regulates Integrin Inactivation and Promotes Neutrophil Recruitment to Inflammatory Sites

International audienc

Field-based evaluation of processes and models for soil vapour intrusion into buildings

This thesis presents the results of research on the validation of models used to evaluate the intrusion of subsurface volatile organic compounds (VOCs) into buildings, often referred to as the "soil vapour transport to indoor air pathway". Evaluation of this exposure pathway is important in the context of risk-based corrective action for contaminated sites. The study scope addresses both the fate and transport of VOCs in the unsaturated zone, and intrusion of VOCs through the subsurface building envelope (i.e., foundation). The primary approach adopted to investigate and validate models was to obtain extensive field monitoring data on VOC vapour transport and intrusion, obtained at a former petro-chemical plant site ("Chatterton" site). The Chatterton site, located near Vancouver, B.C., Canada, is contaminated with benzene, toluene and xylenes (BTX). To facilitate measurement of BTX intrusion, a small building (greenhouse) with controlled properties was constructed. A number of experiments were conducted to evaluate vadose zone processes and vapour intrusion for different greenhouse depressurization conditions. When the greenhouse was not subject to sustained fan-induced depressurization, there was significant aerobic biodegradation of BTX vapours between approximately 0.4 m and 0.8 m depth below the greenhouse, and subslab BTX vapour concentrations were low. When the greenhouse was depressurized to -10 pascals (Pa), the subslab BTX vapour concentrations were elevated, and significant vapour intrusion was measured using both tracer and flux chamber techniques, which was inferred to be a result of an upward BTX vapour flux that exceeded biodegradation capacity based on oxygen availability. A comprehensive analysis of case studies providing information on soil vapour intrusion was completed. This analysis, together with the Chatterton site results, were evaluated for key trends and factors affecting soil vapour intrusion. The vapour attenuation factors estimated based on field case studies were compared to those predicted using several screening level models, including the Johnson and Ettinger Model, a widely used model for this exposure pathway. The validation of screening models using field data is complicated in that model predictions can vary greatly depending on the model and input parameters used. Further, soil vapour fate and transport and intrusion into buildings is a complex process affected by numerous factors (soil properties, house conditions, and environmental factors); therefore, vapour intrusion will vary significantly depending on site specific conditions. The results of the model comparisons to field data indicated that screening level models, typically used for this exposure pathway, were found to generally yield conservative results (i.e., overpredict vapour intrusion); however, there were a few important exceptions. A multi-dimensional numerical model for vapour transport, which incorporated diffusion, biodegradation, sorption and soil gas advection, was also developed. Good comparisons between model predicted and measured vapour attenuation were obtained based on conditions observed at the Chatterton site.Applied Science, Faculty ofCivil Engineering, Department ofGraduat

The analysis and interpretation of the cone pressuremeter in cohesive soils

The cone pressuremeter is a promising new in situ testing device which combines the well known capabilities of a piezocone with a full displacement pressuremeter (FDPM). The focus of this thesis is to present results from FDPM tests performed as part of a cone pressuremeter sounding at three cohesive soil sites in the Vancouver area. The insertion of a cone pressuremeter results in a substantial amount of disturbance and the generation of excess pore pressures. As a result of the changing stress conditions, the length of the relaxation time or time delay between insertion and testing has a significant effect on the lift-off pressure and shape of the FDPM curve. Results indicate that increased relaxation periods lead to lower lift-off pressures. The strain rate used during a test is also significant with lower rates resulting in higher limit pressures and undrained shear strengths. Comparisons were made between the FDPM, self-boring pressuremeter (SBPM) and dilatometer lift-off and expansion pressures. FDPM test results are also influenced by the design and performance of the pressuremeter. Important equipment related considerations discussed are compliance, strain arm design and pressuremeter L/D ratio. The results of FDPM tests were used to estimate the undrained shear strength, shear modulus, stress history and in situ horizontal stress of cohesive soils and when possible compared to SBPM, field vane and dilatometer results. The use of cavity expansion theory for the analysis of the FDPM test is made difficult by the unknown stress conditions created by disturbance. Nevertheless, reasonable estimates of the undrained shear strength were made using cavity expansion methods with the FDPM undrained shear strength generally greater than the field vane and similar to those obtained from the SBPM test. Cavity contraction theory was also used to estimate the undrained shear strength with the results generally being less than the field vane undrained shear strength. Good comparisons were obtained between the FDPM and SBPM unload-reload shear moduli. Both the unload-reload shear moduli and the rigidity index were shown to attenuate with increasing shear strain. Two new methods using the rigidity index and normalized pressuremeter limit pressure were proposed to estimate stress history. Both techniques appear to be promising. Attempts to use the FDPM to estimate the in situ horizontal stress were unsuccessful when compared to the results of other available tests.Applied Science, Faculty ofCivil Engineering, Department ofGraduat