Preliminary assessment of shallow groundwater chemistry near Goodell Creek, North Cascades National Park, Washington

Goodell Creek is located within North Cascades National Park and is high-quality habitat for Chinook salmon, which are listed as threatened under the Endangered Species Act. The creation of a levee near the mouth of the creek where it enters the Skagit River has cut off the historical flood plain from the active channel. There is an effort to remove the levee along the left bank of the creek to restore this connection and preserve this high-quality habitat; however, construction debris and blasting waste from the past have been used as fill during the creation of the levee in the 1980s, and there is concern that contaminated groundwater could reach the creek if the levee is breached. As a result, the U.S. Geological Survey, in cooperation with the National Park Service, assessed near-channel shallow-groundwater chemistry to determine how levee remediation should proceed. Groundwater was sampled in late summer in 2017. Deep groundwater at that time of year limited water-quality sampling. Six samples were collected in September 2017 and analyzed for nutrients, dissolved metals, and a suite of semi-volatile organic compounds. Laboratory data were almost always reported as below the method detection limits with the exception of data from a single shallow-groundwater well. Elevated concentrations of metals detected in water samples from this well were possibly caused by the buried metal in the vicinity of the sampling location. One sample collected close to the active channel of Goodell Creek showed no signs of contamination.