The Department of Toxic Substances Control (DTSC) approved the Removal Action Workplan (RAW) for the Mission Bay South Block 14 School Project located at Mission Bay Drive at Owens Street, San Francisco, California (Project Site). The RAW remediation activities consist of installing engineered covers and caps over impacted
fill material at the Project Site and installing a Vapor Intrusion Mitigation System (VIMS) to mitigate volatile organic compounds (VOCs) and methane vapor intrusion into the buildings.
To address total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAHs), VOCs, and metals that exceed their respective residential screening levels, the following remediation activities will be implemented:
Engineering Cover: In areas of landscape, a minimum of 1 to 1.5 feet of impacted fill material would be removed, a water permeable “marker” fabric placed, and covered with a minimum of three feet of clean import fill. Following the removal of impacted material, clean import fill would cover the impacted fill material and reduce potential risks to human health and the environment.
Engineering Cap: Engineering caps would be constructed of concrete, asphalt, or other impermeable material. Engineering capped areas would generally be utilized for pathways (e.g., sidewalks), around buildings, and over multi-use spaces.
Vapor Intrusion Mitigation System: In order to address the indoor air inhalation pathway, the design, installation, and operation of a site-specific, active VIMS system would be installed as part of the redevelopment of the site. Installation of a VIMS at the site would mitigate the potential migration of methane and VOCs to indoor air in the proposed buildings from the subsurface. The VIMS would consist of a sub-slab venting system, an impermeable vapor barrier, a sub-slab gas detection system, and an active sub-slab mechanical extraction system.