Assessing Water Quality Downstream from the Former New Idria Mercury Mine
Abstract
We investigated water quality downstream from the former New Idria Mercury Mine in the California Coast Ranges during the 2019 El Niño winter season. This mine, which was the second largest mercury producer in North America, was designated a Superfund Site in 2011 with initial remediation completed in 2015. Preliminary cleanup efforts included redirecting acid mine drainage (AMD) and reducing erosion, but >40 acres of mining waste remain exposed along the channel of San Carlos Creek, which receives AMD and runoff from the site. Creek water upstream from the mine contained ~100 pM total mercury (HgT), similar to concentrations reported in the late 1990s. Downstream from the mine, HgT was as high as 10,000 pM, and then dropped to values below 500 pM over a ~5 km transect. This trend suggests particle bound mercury is settling out with iron that precipitates when AMD (pH ~3.5) mixes with San Carlos Creek (pH ~9). These HgT concentrations are lower than previously reported values (~15,000 to 3,500 pM), which may be attributed to remediation efforts, dilution from rain (~11.5 cm prior to our sampling event), and/or abundant vegetation in the channel enhancing particle capture. Organic bioaccumulative monomethylmercury (MeHg) concentrations along the same transect ranged from ~3 to 1 pM. While both HgT and MeHg were lower than in former studies, our results indicate that mining waste along the channel continues to impact San Carlos Creek. HgT concentrations were <20 pM in the vicinity of the Mendota Wildlife Area and Fresno Slough, approximately 100 km downstream from the mine. If mercury from the New Idria Mine reached this area, it has been buried or transported further downstream. In the future, we will assess seasonal trends in water and sediment quality and evaluate the importance of groundwater-surface water interaction on mercury speciation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B51I2360H
- Keywords:
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- 3339 Ocean/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 0409 Bioavailability: chemical speciation and complexation;
- BIOGEOSCIENCES;
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0461 Metals;
- BIOGEOSCIENCES