Analysis of Baseline and Perimeter Air Monitoring Data from the Calaveras Dam Replacement Project (CDRP), Fremont, California

This paper presents the results of 810 pre-project baseline samples collected over four years (2010-2011), and 7,210 offsite (ambient) and 14,314 perimeter samples collected over 7 years (2012-2018) during the CDRP project. The principal asbestos particles were chrysotile from serpentinite, and glaucophane-winchite amphibole from blueschist. The baseline data showed that asbestos concentrations measured at each station are not representative of a regional average background, rather, they reflect contributions from several variables such as: location on or near NOA-containing units, wind direction, intensity of localized soil disturbance, and time of year. The data shows that baseline sampling prior to a project cannot be used as a measure of “background” during the project. The analysis of amphibole composition in air and rock/soil samples was applied to differentiate local source impacts from the primary CDRP asbestos emissions. Of particular value was the application of the calcic-amphibole to total amphibole ratio (Ca index) measured during ABS sampling and comparison with the ratios measured in the samples. This analysis delineated three primary amphibole sources: 1) alluvium in the Sunol Valley with a high Ca index, 2) imported road surfacing material with a moderate Ca index, and 3) blueschist with a low Ca index. When the data was sorted by wind direction, the analysis showed that the contribution of CDRP-generated asbestos to monitoring stations was significant near the point of disturbance only, and did not significantly impact offsite stations that were located at or near sensitive receptors. The asbestos measured at the offsite stations were correlated with local geologic units. The analysis verified that the CDRP emissions were well below the project-specific risk-based thresholds established for the CDRP project, documenting that the offsite receptors were not exposed to an adverse risk by CDRP activities.