The purpose of the RAW, which constitutes the project subject to approval by DTSC, is to mitigate potential risk to human health and the environment from tetrachloroethylene (PCE, aka Dry Cleaning Fluid) in the soil, soil vapor and groundwater at the Site where a dry-cleaning facility formerly operated. The proposed remedy for the site consists of removing the floor slab within the former dry cleaning unit and installing a sub-slab depressurization (SSD) system (System). The System will prevent subsurface PCE vapors from entering the indoor air by pulling (vacuum) the vapors, which are then passed through carbon containers to remove the PCE, and the treated air is then tested before being released to the ambient air. A vapor barrier will also be installed over the top of the depressurization system and below the new slab. Installation of the vapor barrier also allows the SSD to be switched to a passive system after the highly contaminated vapors have been removed.
The proposed SSD/Vapor Barrier preferred alternative has been demonstrated to sufficiently reduce concentrations of PCE in indoor air, and to be protective of human health for commercial uses of the property. Eventually, PCE concentrations may be reduced to levels that would allow for unrestricted use of the property. Until such time as those levels are attained, a land use covenant (LUC) will be attached to the deed for the property to limit residential and other sensitive uses of the site. Current and anticipated future land use for the Site is commercial. Additionally, the groundwater will be restricted from use by a LUC.
DTSC is overseeing cleanup at the Site under a Voluntary Cleanup Agreement (VCA) signed by the project proponent and DTSC on January 9, 2017, and is proposing to approve the project pursuant to Chapter 6.8, Division 20, section 25355.5(a)(1)(C) of the Health and Safety Code (H&SC).
The proposed cleanup for the site consists of the following:
1. Removal of the floor slab within the former dry cleaning unit.
2. Next the sub-slab depressurization system will be installed. The SSD consists of a permeable gravel layer that has slotted pipes running through it. The slotted pipes are connected together and then connected to an industrial fan or blower. The purpose of the fan is to pull the PCE vapors from the permeable gravel layer and vent them through a carbon filter prior to venting to the top of the building.
3. After installation of the permeable layer and SSD system, a vapor barrier and new floor slab will be installed. The vapor barrier is a plastic like material that seals the floor and prevents PCE vapors from entering through the floor of the building.
4. After installation of the SSD/Vapor Barrier system, the indoor air will be sampled and analyzed to verify that the system is adequately preventing PCE vapors from entering the unit, and demonstrate that the unit is safe for occupancy.
A land use covenant will also be attached to the deed for the property to limit future sensitive uses of the site.