Event Title

Arsenic Partitioning in Sediments Downgradient from an Abandoned Mine, San Diego

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Description

Black Mountain is home to a former arsenic (As) mine that closed in the early 1920s with no known remediation or documentation. This study tests if the As is bound to the organic carbon, is associated with fine grain sediments, and if As concentrations change downstream of the mine. Total As was measured using the XRF. Sediment organic carbon (% OC) was estimated using LOI technique and sediment grain was measured with the LPS. As concentrations ranged from 2320.5 mg/ Kg to 15.4 mg / Kg and the concentrations decreased with distance from the mine. Average % OC and total As per site had a weak negative relationship. Percent fines (% Silts + % Clays) had no significant relationship with total As. These results suggest that As is predominantly not adsorbed to the Organic Carbon. As concentrations are not related to grain size and therefore not related to the exchangeable fraction as smaller grain sizes have greater surface area compared to larger grain sizes. Based on sequential extraction experiments, the As is bound in the crystalline matrix (Wright et al, in prep.). This study suggests that the As at Black Mountain will not be easily mobilized during storm events and therefore will not be easily released into the environment.

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Arsenic Partitioning in Sediments Downgradient from an Abandoned Mine, San Diego

Black Mountain is home to a former arsenic (As) mine that closed in the early 1920s with no known remediation or documentation. This study tests if the As is bound to the organic carbon, is associated with fine grain sediments, and if As concentrations change downstream of the mine. Total As was measured using the XRF. Sediment organic carbon (% OC) was estimated using LOI technique and sediment grain was measured with the LPS. As concentrations ranged from 2320.5 mg/ Kg to 15.4 mg / Kg and the concentrations decreased with distance from the mine. Average % OC and total As per site had a weak negative relationship. Percent fines (% Silts + % Clays) had no significant relationship with total As. These results suggest that As is predominantly not adsorbed to the Organic Carbon. As concentrations are not related to grain size and therefore not related to the exchangeable fraction as smaller grain sizes have greater surface area compared to larger grain sizes. Based on sequential extraction experiments, the As is bound in the crystalline matrix (Wright et al, in prep.). This study suggests that the As at Black Mountain will not be easily mobilized during storm events and therefore will not be easily released into the environment.