San Rafael, CA – The rehabilitation of the aging, 50-year-old runway at Marin County’s Gnoss Field Airport will require an additional $1.1 million to complete because of the discovery of naturally occurring asbestos in serpentine rock underneath the old runway. The escalated scope and complexity of the project has increased the expected cost from $2.28 million to an anticipated $3.38 million.
The Gnoss Field runway rehabilitation project got underway in September 2017. On October 6, two weeks after construction began, a sample of ground-up runway subbase material revealed 3.6 percent naturally occurring asbestos, which is above regulatory levels of 0.25 percent. Additional testing by the County found asbestos containing materials ranging from 0.08 percent to 4.8 percent. Naturally occurring asbestos is in serpentine rock, which is not typically found in low-lying diked bayland regions, such as where Gnoss Field is located. Due to the geological setting, which is three miles north of Novato, testing for the presence of serpentine rock was not part of the project’s design process. The former runway asphalt was also analyzed for asbestos and was determined safe.
The Marin County Department of Public Works (DPW) immediately consulted with Monte Deignan & Associates, an environmental and industrial hygiene firm, to implement air monitoring, prepare a safety plan and conduct contractor and employee training. Construction work stopped until worker safety and monitoring measures could be implemented. Under the firm’s direction, construction restarted October 30 with the implementation of strict environmental and workforce safety precautions, including air quality monitoring, continual soil samples and mandatory protocols for safely handling asbestos.
Following the safety procedures, all subsequent monitoring and sampling results have been below regulatory action levels. With asbestos exposure risk at background levels and the asbestos material utilized as subbase material and covered for containment, it was determined on November 13 that the special precautions were no longer needed. The project contractor, Team Ghilotti, expects to complete the project by the end of the year, weather permitting. Ongoing project updates have been made available on the airport’s webpage.
The additional $1.1 million project cost accounts for the necessary additional materials to cover the naturally occurring asbestos and additional safety protocols. Furthermore, the extended duration of the project, which was originally expected to be finished by the end of October, required more workforce hours. The consulting cost of $100,000 was needed for the air monitoring, environmental consulting, geotechnical investigation, and construction management supervision.
While a Federal Aviation Administration (FAA) grant covered 90 percent of the original estimated budget, DPW expects it will take six months to resolve all of the costs associated with this changed condition. Then the reimbursement amount for a potential FAA supplemental grant will be determined. In the meantime, the additional $1.1 million will come from the County’s General Fund as a one-time loan. The loan will be repaid by the airport’s Special Aviation Fund, generated by Gnoss Field’s revenue stream, and expected to be financed over 10 years. DPW will report to the Board of Supervisors in six months to present the result of the potential secondary FAA grant as well as other financing options to repay the loan.
The 120-acre airport, on the eastern side of Highway 101 and Mount Burdell, normally handles about 85,500 flight operations per year and is a popular destination for both business and pleasure pilots. It is normally open 24 hours a day, but it closed in September for the renovation project.