Does Exposure to Naturally Occurring Asbestos (NOA) During Dam Construction Increase Mesothelioma Risk? DANIEL W. HERNANDEZ* Dragados USA, Inc., Flatiron West, Inc., Sukut Construction, Inc., Joint Venture (DFSJV), Calaveras Dam Replacement Project, 8022 Pinot Noir Court, San Jose, CA 95125
Key Terms: NOA, Amphiboles, Mesothelioma, Blueschist, Glaucophane, Particle Dimensions ABSTRACT The Calaveras Dam Replacement Project, a major construction project completed in 2019, involved hundreds of workers using heavy earth-moving equipment and mining operations, including blasting, drilling, rock crushing, and other operations designed to move millions of cubic yards of earth. Much of the material was composed of serpentinite, blueschist, and other rocks that contain chrysotile and a variety of amphibole minerals, including glaucophane, winchite, actinolite, tremolite, and other asbestos-related amphiboles. This article explores the unique characteristics of the blueschist that required extensive protective measures to be undertaken by the contractor to protect workers and surrounding sensitive receptors. This article will provide an overall summary of the dimensional characteristics of the airborne blueschist elongate mineral particles encountered during construction activities to compare and contrast current understanding of cleavage fragments versus asbestiform mineral fibers.
INTRODUCTION Located to the east of the San Francisco Bay Area, the Calaveras Dam Replacement Project is substantially underlain by exhumed Franciscan mélange composed of a variety of rocks. Rocks encountered during construction included serpentinite, which contains chrysotile, blueschist, greenstone, and other rocks that contain various amphiboles. At least 20 species of amphiboles, including actinolite and glaucophane (considered naturally occurring asbestos [NOA] minerals [NIOSH, 2011]), were discovered within the project boundary. In addition, winchite (associated with the well-known Libby Amphibole [U.S. EPA, 2014]) was also determined to be present.
*Corresponding author email: risicaredan@gmail.com
The construction of the dam required the disturbance of over 13 million yards of these materials involving operations that included mining, drilling, blasting, sorting, sizing, dozing, excavating, loading, transporting, dumping, and compaction. Operations complementing the construction of the replacement dam included slope shaping, rock breaking, and rock crushing. Early in the project, the contractor noted that countable fibers (fibers with a 3:1 or greater length:width aspect ratio, widths greater than 0.25 μm, and length greater than 5 μm) were substantially higher in personal breathing zone exposure samples collected during the disturbance of the blueschist, as compared to during the disturbance of other NOA-containing media (serpentinites). This was somewhat surprising, since the “blueschist rock” did not appear to be asbestiform, as in the classical definition of asbestos as “visually fibrous,” with individual fibers being separable by finger pressure (Figure 1). Since the dam required the mining and processing of approximately one million cubic yards of blueschist for the upstream rock shell, the contractor conducted a thorough industrial hygiene investigation of blueschist operations. Based on thousands of air samples collected, it was determined that glaucophane (compositionally similar to crocidolite) and winchite were the dominant amphiboles emitted when disturbing blueschist materials. The blueschist amphibole mineral belongs in the solid solution series of gluacophaneriebekite, which is currently recognized by the National Institute for Occupational Safety and Health (NIOSH) as a non-asbestiform habit of an asbestos mineral and is considered “asbestos” if cleavage fragments derived from this material meet the definition of fiber, as viewed microscopically (NIOSH, 2011). Considerable issues are associated with the disturbance of amphibole mineral rocks since the asbestiform crystalline habit is relatively rare in nature (Harper et al., 2008; Wylie, 2017), as compared to that of the coarsely crystalline non-asbestiform analog of the same mineral.. Disturbance of these non-asbestiform mineral analogs may result in the release of “cleaved” elongate mineral particles and/or
Environmental & Engineering Geoscience, Vol. XXVI, No. 1, February 2020, pp. 29–33
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