Dissatisfied with a state agency's assurances that hazardous chemical vapors from a former Stanford Research Park industrial site on California Avenue pose no risk to nearby residences, College Terrace neighbors plan to hire a consultant to monitor the indoor air-quality of their homes, they said.
The decision to move forward with their own consultant came after the state Department of Toxic Substances Control (DTSC) concluded that Stanford University's plan to mitigate the impact of toxins discovered on its property at 1601 California Ave. is sufficient and no additional testing at the site or adjacent properties is necessary.
Elevated contaminants in the soil were detected in one area the vicinity of a former plating solution sump and operational areas of a former manufacturing facility but the vapors from the chemical do not pose a threat to residents in nearby College Terrace, the agency concluded.
The university, which is building 180 homes for junior faculty on the property, plans to move a number of residences from the most contaminated "hot spots" to another location on the property as part of its mitigation plan. It also proposes to cap some of the contaminated areas with roads and add vapor barriers to new homes to prevent fumes from seeping in.
The site has been thoroughly evaluated; the extent of soil vapor is defined; the development plan protects human health; and an international expert on vapor intrusion concurs with Stanford's findings and approach to address the vapor problem, according to the agency.
The agency approved the Revised Supplemental Investigation and Risk Assessment Report on April 4, according to a letter supplied by Stanford.
For College Terrace residents who live just across California Avenue, concerns remain high that hazardous trichloroethylene (TCE) vapors found in the University Terrace construction site in November 2015 may still pose a risk to their neighborhood.
TCE is a solvent used mainly to remove grease from metal parts but also is an ingredient in adhesives, paint removers and other products. It breaks down slowly in soil and water and is known to cause some cancers, according to the U.S. Environmental Protection Agency (EPA).
But the university's consultant Haley & Aldrich, Inc., found the levels are below maximum levels allowable for residential sites, a finding that is in line with EPA guidelines, which are also accepted by the state DTSC, officials noted in their report.
College Terrace resident Fred Balin, who has been following the developments, said when TCE vapor becomes trapped in an enclosed space, it can concentrate and become a health hazard. The issue for College Terrace is that residents remain vulnerable because their homes do not have vapor barriers and other safeguards planned for the new construction, he said.
In January, a College Terrace Residents' Association subcommittee studying the site asked the DTSC to review Stanford's findings and require the university to remove the contaminated soil, conduct additional monitoring along their neighborhood's border, and take additional safety measures to prevent TCE from potentially migrating into the soil under their homes.
The subcommittee, which includes a research chemist, a NASA environmental scientist and a toxic-vapor-control expert, outlined nine major concerns and concluded that the consultant's report showed the TCE vapor has the ability to migrate through the soil. Subterranean water channels might transport the chemical vapors to their neighborhood, where it could enter their unprotected homes. The residents' position was supported by the Center for Public Environmental Oversight, a Mountain View-based watchdog group.
After reviewing Stanford's proposal, DTSC concluded that the university's plan for the development of University Terrace is adequately protective. In addition to moving some homes off of the contaminated area, and it will add compacted clean soil to a height of 15 feet, add 10-inch-thick concrete slabs that are resistant to cracking, and install vapor barriers and other measures to prevent vapor leakage. Homes will have a restrictions covenant that prevents digging up the foundation for future construction, DTSC noted.
DTSC also concluded that Stanford had remediated the site by removing the source of TCE when it removed the former plating solution sump in March 2015. Building demolition of 1601 California in March and April 2015 also included removal of all chemical-storage areas, piping, sewage and storm drain lines. The site did not reveal concentrations of TCE in the soil that would warrant deep excavation, the agency noted.
DTSC said that there was also no proof that the TCE soil vapor had migrated. It maintains that the soil vapor remains in defined areas.
The College Terrace subcommittee disagrees with this finding. Data it extrapolated from Haley & Aldrich's report shows the chemical vapor had migrated 300 feet and contaminated part of another site, at 1501 California Ave., which is also part of the development, said Ed Schmitt, research chemist and association subcommittee member who investigated the data.
DTSC wrote that TCE was not detected in soil vapor collected at nearby sampling at 1501 California at concentrations exceeding the DTSC screening level.
According to Lenny Siegel from the Center for Public Environmental Oversight, TCE was found in soil vapor at a depth of 25 feet at 1501 California, about 300 feet down-gradient from the former sump. DTSC had also previously attributed the presence of TCE vapor at 1501 California to the 1601 California sump release, he noted. Siegel said he supports installing venting technologies for the homes rather than barriers.
"Since TCE has moved 300 feet, either in aqueous or gaseous form, to the next property, I don't see how Stanford and DTSC can conclude that vapors cannot move 50 feet into homes," he wrote in response to DTSC's findings.
DTSC noted that TCE was detected in shallow groundwater beneath the 1601 California site, but the concentrations are limited in extent and below environmental screening levels for groundwater, and they would not contribute to vapor intrusion.
Out of nine groundwater samples taken by consultants, low TCE concentrations were found in two, at 45 and 13 micrograms per liter respectively, the agency wrote. Boring samples down to a depth of 68 feet did not show continuous migratory channels that would serve as potential pathways for the TCE-vapor contamination, DTSC wrote.
The spread of soil vapor also is not likely because the primarily fine-grained, clayey soil along California Avenue inhibits its migration, DTSC concluded.
"The sampling pattern and analysis demonstrate that TCE in soil vapor remains within the site. There are 15 soil-vapor sampling locations parallel to California Avenue and opposite the College Terrace community in which analytical results show that TCE either was not detected or detected below the DTSC residential screening level. These results lead to the conclusion that TCE-impacted soil vapor does not extend off site to S. California Ave.," DTSC wrote.
Siegel maintains there isn't enough data to justify assumptions about soil lithology or the direction and magnitude of TCE migration.
"Based on prevailing groundwater flows, I agree that vapor exposures in College Terrace are not likely, but I don't believe that enough groundwater or vapor sampling has been done to rule it out," he wrote.