On Tuesday, California’s Department of Toxic Substances Control (DTSC) held a public meeting for the McKinley site RAW, which aims to prevent “potential future risk to human [and] environment of the site,” particularly during the first phase of the school’s campus master plan. In October 2023, DTSC determined that a RAW was required to move forward with construction on a new two-story building with eight classrooms and a renovated front office, after results of soil and soil vapor samples showed detections of arsenic above regulatory guidelines in the soil, as well as detections of “volatile organic compounds” in the soil vapor.
The compound was noted to be mainly tetrachloroethylene (PCE), a chemical typically used in dry cleaning. The source of PCE within the McKinley site soil vapors is potentially from adjacent dry cleaners such as TJ Cleaners at 2441 Santa Monica Blvd. Officials from DTSC stated they have been in contact with TJ Cleaners to investigate contamination of its property, adding that they have requested historical records from the City of Santa Monica for two other unnamed dry cleaning locations that “might give more information” on the potential PCE source.
Though a RAW is required for McKinley, DTSC officials added that there is “no immediate risk” associated with contamination found in soil or soil vapor. For example, levels of arsenic found in soil was taken from samples anywhere from 2-8 feet beneath pavement, with the pavement acting as an exposure-preventing barrier. DTSC also stated that there is no indication of vapor intrusion in existing school buildings, saying they are “safe for occupancy.”
Removal action plans for both arsenic-containing soil and PCE-containing soil vapor were evaluated and compared based on “effectiveness, implementability and cost.”
For the soil, the best course of action was determined to be capping the surface of the site and planned classroom structure with pavement, eliminating the potential to come into contact with the elevated concentrations of arsenic. Exposed soil in landscaped areas would also be replaced to a minimum depth of four feet with clean landscaping materials like mulch and top-soil. This method was deemed “the most implementable option” due to planned construction including the installation of pavement.
“Containment through surface capping would not lessen toxicity or volume of the soils containing elevated concentrations of arsenic, but would limit mobility and potential migration of contaminants,” the RAW dated May 10 stated.
Estimated costs for this action include $100,000 during initial construction: $75,000 for dust and air monitoring during initial grading and earthwork, $15,000 for soil sampling as needed, and $10,000 for remedial action completion reporting. After the first year post-completion, annual inspection and reporting costs will be $5,000, along with $5,000 per year for allowance for cap maintenance and repair. Every five years, a $5,000 cost will be assessed for a five-year review, inspection and reporting.
The PCE-containing soil vapors will be mitigated via installation of a soil Vapor Intrusion Mitigation and Migration Engineering Controls System beneath the new classroom building. A generally-accepted alternative for similar site conditions, this method consists of “installing a barrier membrane system and a passive vapor collection system beneath the building slab.” The system, the RAW states, mitigates potential vapor intrusion risk in indoor occupied spaces, as well as reducing vapor intrusion risk in common building entry points like cracks, openings and penetrations in the building foundation floor slab.
Installation costs associated with this system are approximately $250,000 during construction; $150,000 towards materials and installation, $50,000 for quality assurance and quality control inspection, and $50,000 for initial commissioning and testing. Quarterly indoor air and sub-slab vapor sampling and monitoring will cost $25,000 per quarter during the first year, with another $25,000 for five annual monitoring. Biennial sampling and monitoring for years seven and beyond, or until vapor concentrations beneath the site are remediated to acceptable levels, will also cost $25,000. Annual allowance for repairs and maintenance are $10,000 for the first five years, then $10,000 biennially afterwards.
Though there was no attendance for the in-person portion of the meeting at the McKinley auditorium, there were several questions asked within the Zoom meeting component, including questions on the RAW implementation schedule and frequency of outdoor air monitoring. RAW implementation is anticipated to occur during July and August from 8am to 6pm on weekdays and 9am to 5pm on Saturdays. Air monitoring on outdoor air will be tested every half hour, while temporary fencing will be placed around the worksite for dust management.
Public comment period on the drafted RAW will continue through June 18, with comments to be directed to DTSC Project Manager Lina Hijazi by email, or by phone at (714) 484-5334.
