Vapor intrusion mitigation systems are used to mitigate the risk of indoor air contamination from soil and groundwater contaminants. There are several types of vapor intrusion mitigation systems, including:          1. Sub-slab depressurization (SSD) systems: This is the most common type of vapor intrusion mitigation system. It involves drilling holes into the foundation and installing a pipe system that draws contaminated air from beneath the building's foundation and expels it outside.                      2. Passive venting systems: These systems use passive ventilation to draw air from beneath the building and vent it outside. This system is generally used in cases where the contaminant levels are low.                                 3. Active venting systems: These systems use mechanical ventilation to draw air from beneath the building and vent it outside. This system is generally used in cases where the contaminant levels are high.                                4. Vapor barriers: This system involves the installation of a vapor barrier beneath the building to prevent the migration of contaminants into the building. This system is generally used in cases where the contaminant levels are low.                                       5. Chemical injection: This system involves the injection of chemicals into the soil to break down the contaminants and prevent their migration into the building.                                                     6. Soil vapor extraction: This system involves the installation of wells into the soil and the use of a vacuum to extract the contaminated air from the soil. The selection of a vapor intrusion mitigation system depends on the specific site conditions, the type and concentration of contaminants, and the desired level of protection. It is important to consult with a qualified professional to determine the most appropriate system for a particular site.