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Toxins Prompted Relocation Of TCSOS Programs

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Sonora, CA — Over the last several years, numerous Tuolumne County Superintendent of Schools Office services were operated out of a building at 13885 Mono Way, but they left after a letter was received from the state about toxins being prevalent.

The issue was brought to light in an investigative report by KCRA 3 TV earlier this week.

The Department of Toxic Substances Control notes that it sent a letter to the owner of the building last May to take immediate steps to clean up tetrachlorethylene contamination at the former Heritage Dry Cleaner site, of which, the source unit was being occupied by the Superintendent of Schools Office since around 2014.

Superintendent Zack Abernathy noted to Clarke Broadcasting that the spaces were used by staff and students in the Adult Education Programs, TLC Middle School, Independent Study, and Aware programs. Upon receiving the letter, the students were moved and all of the programs were relocated to offsite locations. Other businesses utilizing spaces nearby have also taken steps to limit impacts.

You can read the full report from the state’s DTSC below:


13855 Mono Way, Sonora, California, 95370

The Department of Toxic Substances Control (DTSC) is providing oversight for the investigation and cleanup of tetrachlorethylene (PCE) contamination at the former Heritage Dry Cleaners and the surrounding areas (Site) located at 13855 Mono Way, Sonora, California, 95370. Indoor air samples taken May 2 through May 4, 2023, indicate a release of dry-cleaning solvents occurred at the Site.

The source of the contamination is believed to have come from the former Heritage Dry Cleaners (Source Unit) where PCE was detected at levels significantly above acceptable screening levels for indoor air at the former cleaners and adjacent units in the building.

DTSC issued a Proposition 65 Notice on May 12, 2023, to notify local officials of the risk of chemical exposure at the Site. DTSC issued an Order to the building owner on May 23, 2023, to take immediate steps to protect the public and environment from PCE exposure, and to conduct further investigation for cleaning up the Site. Details on the ongoing investigation, Proposition 65 Notice, and frequently asked questions (FAQs) related to indoor air contamination and PCE health impacts are shared below.

What are the Historical/Current Uses at the Site?

Heritage Dry Cleaners operated out of the Source Unit from the early 1980’s until 2014. The Source Unit is now occupied by the Tuolumne County Superintendent of Schools (TCSOS) office. The building the Source Unit is located in is comprised of five units: the TCSOS Office, TCSOS learning space, Sonora Cyclery bike shop, a dance/music studio, and a former salon.

What are the Historical/Current Investigations at the Site?

In 2011, the United States Environmental Protection Agency (US EPA) conducted a Preliminary Assessment which concluded the Source Unit was eligible for further federal assessment. In 2015, US EPA conducted a re-assessment and concluded the Source Unit was still eligible for further federal assessment. In October 2020, US EPA conducted another re-assessment and concluded the Source Unit was not eligible for further federal assessment at the time.
In October 2020, DTSC became the lead agency overseeing the Source Unit and began working towards collecting samples onsite. In August 2021, DTSC contracted AECOM to conduct a Site history review and to draft a Site Investigation Workplan to begin gathering the necessary equipment and personnel to begin environmental sampling. The final Site Investigation Workplan was approved in April 2023. In May 2023, DTSC’s contractor sampled all five units in the building.

Why did DTSC Issue the Proposition 65 Notice?

The Safe Drinking Water and Toxic Enforcement Act of 1986 (commonly referred to as Proposition 65) requires designated government employees to disclose warnings to local government/health officials about “illegal discharge of hazardous waste that may cause substantial injury”. Upon receiving the initial sampling results for the Site, DTSC immediately calculated human health risks to the Site occupants using the more health protective residential risk-based screening levels to account for school-age children at the Site. The results of the human health risk calculation indicated that long-term exposure to elevated concentrations of PCE in indoor air were “likely to cause an adverse physical condition of a substantial nature to one or more person”. Once this determination was made, the law required DTSC to issue the Proposition 65 notice within 72 hours.

What is PCE and How Does it Get into Indoor Air?

Tetrachloroethylene (Perchloroethylene or PCE) is a liquid solvent that was widely used in drycleaning until 2007 and fully eliminated in dry-cleaning in 2023. If released into the environment, PCE solvents can soak into the ground and seep into groundwater. In gaseous form, PCE vapors can migrate up through the soil and into the buildings above via small openings, such as cracks in foundations and aged plumbing lines, in a process called vapor intrusion.

What are the PCE Concentrations and Safety Measures at the Site?

Indoor air samples collected by DTSC’s contractor on May 2 through May 4, 2023, to determine a potential release of dry-cleaning solvents at the Site, contained PCE at levels significantly above the acceptable screening level. Additional sampling is expected to take place at the Source Unit and adjacent units as well as the nearby buildings (13895 and 13887 Mono Way Sonora, California 95370) on the Site.

What are the Potential Health Effects from Exposure to PCE?

Potential human health effects resulting from PCE exposure varies and is dependent on many factors including how much PCE one is exposed to, the frequency and overall duration of exposure, the exposure pathway (Inhalation, Ingestion, Dermal Absorption), and a person’s diet, lifestyle, and genetic makeup.

Risk to Children – It is not known whether children are more susceptible than adults to the health impacts of PCE exposure. Animal studies indicate PCE may have adverse health effects on pregnancy and unborn children, however studies in people, including children, are not clear.

Cancer Risk –The State of California considers PCE to be a likely carcinogen. Long-term and consistent exposure to PCE may lead to a higher risk of cancer. The potential cancer risk DTSC calculated for the Source Unit using the May 2023 sampling results means that 4 out of 1,000 people have a chance of developing cancer if consistently exposed to the highest level of PCE DTSC detected in indoor air for 24 hours a day for an average of 20 years over a lifetime.

Non-Cancer Risk – PCE at high levels, and/or under prolonged exposure to lower concentrations over a lifetime, may affect the central nervous system (causing neurobehavioral effects on learning and retention, mood, and vision), damage the liver, kidneys, and reproductive system and may be harmful to unborn children. The non-cancer hazard index (HI) of 40 calculated for the Site using the May 2023 sampling results is significantly above the acceptable HI of 1.0. This indicates that harmful health effects other than cancer are possible, but not certain.

What Measures Will DTSC Take to Protect Me?

On May 12, 2023, DTSC issued the Proposition 65 notice. Upon receiving the notice, TCSOS
promptly evacuated its faculty, staff, and students from the Source Unit and attached Learning Space
unit and has moved all programming offsite.

We are requiring the property owner to implement immediate vapor mitigation strategies at the
Source Unit and adjacent units, which may include:
• Increasing ventilation via doors and windows;
• Sealing gaps in the foundation and utility conduits;
• Adjusting the heating/ventilation (HVAC) system to prevent vapor accumulation in the buildings;
• Using activated carbon air purifiers;
• Installing ventilation systems under buildings to prevent vapor-intrusion.

We will continue to oversee these measures and will provide updates as the immediate and long-term actions are implemented.

What Happens Next in the Investigation?

DTSC met with the property owner and their consultant to discuss the Site remediation strategy on June 5, 2023. Our Order requires the property owner to do the following:

• Provide DTSC with a Vapor Mitigation Workplan to address vapor intrusion for the Source Unit
and other units in the building.
• Provide an Indoor Air Evaluation Workplan to conduct indoor air sampling at other buildings on
Site. We will order additional sampling as needed.
• Prepare a Remedial Investigation/Feasibility Study Workplan that assess Site conditions,
evaluates alternative remedies, and selects a remedy for Site cleanup.