Many agencies have imposed limits on emissions of toxic air contaminants from new or modified sources. Typically the excess cancer risk from a new or modified source that is not controlled using Toxics Best Available Control Technology (T-BACT) must not exceed one in one million. Even with T-BACT installed, the excess cancer risk is limited to ten in one million. Restrictions on the allowable chronic or acute hazard associated with emissions from new sources may also apply.
A permit application submitted to a regulatory agency must include a demonstration that the requirements of NSR for air toxics will be met. In some cases, this can take the form of a screening assessment in which emissions are compared to thresholds. If the threshold is exceeded, a refined risk assessment will be required.
Verdant personnel prepared a risk assessment demonstrating that a pump and treat system for remediating contaminated groundwater would not pose a significant risk to the surrounding population. The project involved (1) estimating emissions from the treatment process, (2) performing air dispersion modeling, and (3) preparing a human health risk assessment. Verdant personnel presented the results of the risk assessment at a series of public meetings held by the SCAQMD.