Description of Study Area and Sampling Sites

The McKenzie River generally is considered to be a high-quality source of drinking water. The Oregon Department of Environmental Quality’s (2008) Oregon Water Quality Index rates the river’s water quality as excellent throughout the year. However, the basin includes managed forest land, agriculture, urban (residential) development, and a number of areas where septic systems are present in near stream alluvial aquifers. Each year, approximately 5–10 percent of the forest land is sprayed with chemicals (Lane Council of Governments, written commun., 2009). Agricultural activities include hazelnut orchards, blueberries, Christmas trees, peppermint, row crops, livestock, and pasturelands (Southern Willamette Valley Local Advisory Committee, 2004), and chemical use associated with each of these land uses poses potential threats to the water quality in the river. During late September and early October 2007, passive samplers were deployed at three sites in the McKenzie River basin. The three sites include the inlet to EWEB’s drinking-water treatment plant and two upstream tributaries to the McKenzie River—Cedar Creek and Camp Creek (fig. 1).

The Cedar Creek and Camp Creek subbasins were selected for study because both include land-use activities that may be sources of organic contaminants to the McKenzie River. The Cedar Creek subbasin covers about 10 mi² and is approximately 60 percent forest (table 1). Less than 2 percent of the forest land in the Cedar Creek subbasin is sprayed with pesticides. Approximately 18 percent of the subbasin is used for agriculture and 15 percent is residential. The Camp Creek subbasin covers just over 26 mi² and also is approximately 60 percent forest and 18 percent agriculture. However, in contrast to the Cedar Creek subbasin, more than 10 percent of the forest land in the Camp Creek subbasin is sometimes sprayed with pesticides, and only about 2 percent of the subbasin is residential. Although there are widespread agricultural and residential uses of pesticides in both of these subbasins, the actual amounts of specific chemicals used are poorly documented.