Event Title
ENV-643: SUB-SLAB DEPRESSURIZATION SYSTEM RETROFITS TO EXISTING BUILDINGS: TWO CASE STUDIES
Location
London
Event Website
http://www.csce2016.ca/
Description
Ontario Regulation 153/04 outlines the process wherein a property impacted by soil and/ or ground water contaminants is evaluated for risks to human and ecological health, and may be redeveloped for more sensitive land uses. Under the Regulation, once a property has been sufficiently characterized, a Record of Site Condition (RSC) may be filed, to document the condition of the property. Owners of contaminated lands may choose to remediate the property, to meet the Ontario Ministry of Environment and Climate Change (MOECC) generic soil and ground water Standards, or develop new site-specific Standards via the Risk Assessment (RA) process.
Many of the soil and ground water contaminants of concern (COC) frequently identified during the environmental site assessment process are volatile. If an RA is undertaken to address volatile COC, it must take into consideration the potential for vapour intrusion. The fundamental underlying principle for vapour transport is based on observations that small but persistent pressure differences established between the exterior and interior of buildings may cause infiltration of soil air through the substructure of buildings. When this occurs, the COC have the potential to cause an adverse effect on the health of building occupants, via the inhalation pathway. If the conclusions of the RA are that an adverse effect is likely, vapour mitigation will be proposed as a risk management measure (RMM) and mandated by the MOECC by describing them on a Certificate of Property Use (CPU) which is registered on the title of the land, thus obligating all current and/ or future property owners to comply.
In practice, vapour mitigation options are limited, particularly for sites with existing buildings and where redevelopment is not planned. In some cases, buildings are not fitted with HVAC systems suited to increased air exchange rates or maintenance of a constant positive pressure, which would serve to “push back” against upward vapour movement. Nor can an existing building be fitted with vapour barriers, or easily equipped with an extensive sub-grade vapour venting system. In many cases, a sub-slab depressurization (SSD) system, retrofitted to the building, is the best option. Such a system would consist of one of more vapour extraction points, connected to a blower with the capacity to generate a slight negative pressure within the porous sub-grade media. However, the success of such a system depends to a large extent upon the characteristics of the sub-grade fill material, in addition to the building configuration and features such as the presence of footings and foundation thickness and quality. As such, there are many risks associated with uncertainties when the building sub-slab environment is not fully understood and each project is unique, where existing buildings are concerned. Two case studies will be presented, describing the process of designing and constructing SSD systems within existing buildings, to mitigate vapour intrusion by chlorinated volatile organic compounds (VOCs).
Included in
ENV-643: SUB-SLAB DEPRESSURIZATION SYSTEM RETROFITS TO EXISTING BUILDINGS: TWO CASE STUDIES
London
Ontario Regulation 153/04 outlines the process wherein a property impacted by soil and/ or ground water contaminants is evaluated for risks to human and ecological health, and may be redeveloped for more sensitive land uses. Under the Regulation, once a property has been sufficiently characterized, a Record of Site Condition (RSC) may be filed, to document the condition of the property. Owners of contaminated lands may choose to remediate the property, to meet the Ontario Ministry of Environment and Climate Change (MOECC) generic soil and ground water Standards, or develop new site-specific Standards via the Risk Assessment (RA) process.
Many of the soil and ground water contaminants of concern (COC) frequently identified during the environmental site assessment process are volatile. If an RA is undertaken to address volatile COC, it must take into consideration the potential for vapour intrusion. The fundamental underlying principle for vapour transport is based on observations that small but persistent pressure differences established between the exterior and interior of buildings may cause infiltration of soil air through the substructure of buildings. When this occurs, the COC have the potential to cause an adverse effect on the health of building occupants, via the inhalation pathway. If the conclusions of the RA are that an adverse effect is likely, vapour mitigation will be proposed as a risk management measure (RMM) and mandated by the MOECC by describing them on a Certificate of Property Use (CPU) which is registered on the title of the land, thus obligating all current and/ or future property owners to comply.
In practice, vapour mitigation options are limited, particularly for sites with existing buildings and where redevelopment is not planned. In some cases, buildings are not fitted with HVAC systems suited to increased air exchange rates or maintenance of a constant positive pressure, which would serve to “push back” against upward vapour movement. Nor can an existing building be fitted with vapour barriers, or easily equipped with an extensive sub-grade vapour venting system. In many cases, a sub-slab depressurization (SSD) system, retrofitted to the building, is the best option. Such a system would consist of one of more vapour extraction points, connected to a blower with the capacity to generate a slight negative pressure within the porous sub-grade media. However, the success of such a system depends to a large extent upon the characteristics of the sub-grade fill material, in addition to the building configuration and features such as the presence of footings and foundation thickness and quality. As such, there are many risks associated with uncertainties when the building sub-slab environment is not fully understood and each project is unique, where existing buildings are concerned. Two case studies will be presented, describing the process of designing and constructing SSD systems within existing buildings, to mitigate vapour intrusion by chlorinated volatile organic compounds (VOCs).
https://ir.lib.uwo.ca/csce2016/London/Environmental/23
