Assessing the impact of chloride deicer application in the Siskiyou Pass, southern Oregon

First posted September 30, 2022 For additional information, contact: Director, Oregon Water Science CenterU.S. Geological Survey2130 SW 5th AvenuePortland, 97201 Chloride deicers have been applied by the Department of Transportation (ODOT) to Interstate Route 5 (I–5) from Oregon-California border north mile marker 10 for several years in high-elevation area known as Siskiyou Pass. Magnesium chloride (MgCl2) and sodium (NaCl) are keep interstate highway safe drivers allow efficient transport goods people through adverse weather conditions, particularly snow ice. The U.S. Survey entered into a cooperative agreement with ODOT research effects Carter Wall Creek watersheds that drain vicinity Pass.The Stochastic Empirical Loading Dilution Model (SELDM) was used estimate combinations prestorm-streamflow, stormflow, highway-runoff, event mean constituent concentrations (EMCs), well stormwater-constituent loads at sites interest. study evaluated roadway application on downstream highway-runoff conditions (particularly EMCs), exceedance rates criterion maximum concentrations, concurrent runoff stormwater constituents site SELDM also evaluate efficiency hydrograph extension best management practices reduce peak concentrations. Several scenarios were developed sensitivity analyses model benefit collecting specific local sets data, such streamflow, precipitation, riverine water-quality samples, volumetric coefficient statistics.Results showed modeling Pass area, (1) inclusion streamflow data is important obtaining accurate EMCs, (2) precipitation load calculations, (3) EMC upstream stormflows most collect concentration statistics.