Post-fire water quality is an emerging issue in an era of global change. In October 2017, an unprecedented set of fires devastated many forested and urban areas within Sonoma, Mendocino and Napa counties California, impacting the Russian River Watershed. Ash from the Pocket, Tubbs, Nuns, and Redwood Valley fire provides a significant source of fine particulate ash-leachate runoff flowing to the Russian River and contributing tributaries during storms, as well as infiltration into local groundwater basins that support baseflow to the Russian River during the dry season. The Sonoma County Water Agency (SCWA), in collaboration with the U.S. Geological Survey and Lawrence Berkeley National Laboratory, is evaluating whether these fires have changed surface water quality within the Russian River Watershed. SCWA operates a riverbank filtration (RBF) system which supplies drinking water to over 600,000 in Sonoma and Marin Counties. Major water quality changes that may result from burned areas of the watershed include increased loading of sediments, nutrients, and dissolved organic carbon (DOC) which are hypothesized to potentially impact filtration efficacy. RBF facilities rely on natural attenuation of contaminants by subsurface microbial populations within riverbed and aquifer sediments. Changing water quality dynamics, such as availability of labile DOC, could have consequences for these important microbial processes. Given the frequency and magnitude of projected future climatic disturbances affecting groundwater-surface water interactions and water quality across many locations in the Russian River watershed, our present work assesses three main goals: 1) determine how the recent fires have impacted the hydrological, and chemical conditions of Russian River water quality, 2) evaluate how post-fire storm events will impact the hydrological and chemical connectivity across the Watershed including the tributaries, main stem, hyporheic zone, and groundwater, 3) continue to evaluate potential effects of ash-based DOC on infiltration and filtration efficacy. Our work will present pre- and post-fire water quality results from the Sonoma County Water Quality Monitoring Program and will present a statistical analysis of storm-based discharge-concentration relationships across the watershed network.

Advanced simulation capabilities to explore pre-and-post fire water quality after the 2017 wine country fires

2019 Fall National Meeting

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