Building pressure control test to examine if VOC contamination in indoor air is caused by an interior source or by a subslab source

When determining whether or not remediation of subslab contamination is warranted, it is often important to know if the presence of volatile organic compounds (VOCs) in indoor air is caused primarily by interior sources, or primarily by subslab contamination. With a Building Pressure Control test, the pressure differential across the building envelope and, thereby, also the pressure differential across the slab, can be controlled by a blower. By measuring the indoor air concentrations of VOCs under depressurization (upward pressure gradient over the slab) and under pressurization (downward pressure gradient over the slab), it can be determined if the subslab contamination contributes significantly to the VOC concentrations in indoor air. This technique has been applied at several sites in the Central Denmark Region, and the results show that a Building Pressure Control test is a quick and effective method to examine if VOC contamination in indoor air is caused primarily by interior sources or primarily by subslab sources. With numerous measurement points in the indoor air, at some sites this test method has identified the area where the subslab contamination is located. A pressure differential at ?5/+5 Pa across the building envelope was sufficient at all the test sites to control the pressure gradient across the slab to be uniquely upward/downward.