Introduction


Nearly 20,000 to more than 40,000 pounds of active ingredient pesticides, including insecticides, herbicides, rodenticides, and fungicides, were reportedly used in Oregon during 2007 and 2008 to control a wide variety of insects, weeds, rodents, and fungi (Oregon Department of Agriculture, 2008, 2009). These compounds included approximately 550–570 different active ingredients. Most pesticides were reportedly used on agricultural crops, with other major use categories including urban and residential applications on home gardens, lawns, golf courses, and commercial landscaping, as well as site preparation following logging, and along roads and other rights-of-way. The movement of water is an important mechanism for the transport of pesticides from where they are applied to other components of the environment (Larson and others, 1997). Consequently, this kind of extensive pesticide use increases the potential for contamination of hydrologic systems, especially surface water.


Monitoring of pesticides by the U.S. Geological Survey (USGS) throughout the conterminous United States has found widespread occurrence of pesticides in streams and rivers, particularly in developed areas, but also in predominantly undeveloped drainage basins (Larson and others, 1997; Gilliom and others, 2006). Pesticide studies by the USGS and others in Oregon have focused primarily on the Willamette Valley and show that a large number of pesticide compounds occur in streams and are most pronounced during periods of high runoff during spring and fall (Anderson and others, 1996, 1997; Rinella and Janet, 1997; Wood, 2001; Field and others, 2003; Rupp and others, 2006). The fate of these chemicals is largely controlled by prevailing environmental conditions that govern water transport, particularly precipitation that leads to runoff following application, and the physical properties of the individual compound that influence its persistence or how it partitions between different environmental media, such as water and sediment (Mackay and others, 1997). Other factors related to pesticide transport that are not dealt with in this study include the chemical formulation and method of application. Additionally, most pesticide products contain adjuvants or ingredients that are considered to be inert, acting only to increase the effectiveness of the active ingredient. Even though some of these compounds may have health consequences (Gilliom and others, 2006), they were not included in this analysis and will not be addressed in this report. 


Many pesticide compounds and their degradation products are known to have adverse effects on human health and aquatic life. These compounds and products are of particular concern when they impact sources of drinking water, because many organic compounds are unaffected by conventional drinking-water treatment (Coupe and Blomquist, 2004; Stackelberg and others, 2004). Given sufficient understanding of pesticide occurrence patterns, drinking-water treatment can be augmented when necessary by advanced treatment, such as activated carbon to remove dissolved organic chemicals. Alternatively, management strategies can be targeted toward decreasing pesticide loading from specific land-use applications that have been determined to degrade the quality of public drinking water. This study provides a foundation for these kinds of source protection activities by characterizing the occurrence of pesticides and other organic compounds in the McKenzie River, a tributary to the Willamette River in the southern Willamette Valley that serves as the sole source of drinking water for the City of Eugene, Oregon. This assessment is complementary to, and not a substitute for, required monitoring of drinking-water quality by Federal, State, and local programs that focus on post‑treatment compliance monitoring.


Background


The Eugene Water and Electric Board (EWEB) is the municipal utility that provides water and electricity to the City of Eugene, Oregon, from the McKenzie River. The McKenzie River has a history of providing drinking water of excellent quality (Alsea Geospatial and others, 2000). To better understand the potential threats to the high quality of water in the McKenzie River, EWEB developed and approved a Drinking Water Source Protection Plan in 2000 (Blair, 2000). This plan was implemented in 2001, and a comprehensive monitoring plan was developed to identify contaminant sources that could adversely affect water quality in the McKenzie River. In 2002, EWEB entered into an agreement with the USGS to design and initiate the pesticide component of their monitoring plan. Beginning in spring 2002 and continuing through spring 2010, approximately twice yearly pesticide samples have been collected in a reconnaissance or exploratory mode, primarily under spring and autumn storm runoff conditions at a suite of sampling sites representing varying land uses in the lower McKenzie River basin. This report describes the results of this reconnaissance study and focuses on relating detected pesticide concentrations to seasonal and dominant land-use characteristics in the basin. 


Purpose and Scope


The purpose of this report is to identify land-use sources of pesticides in the McKenzie River basin to support source reduction efforts made by EWEB to protect drinking water quality. The approach includes the following objectives: (1) to describe the occurrence of pesticides in the McKenzie River at the EWEB drinking-water intake, as well as in selected small streams and stormwater conveyances that reflect specific categories of land use; (2) to identify the seasonal and climatological factors that are associated with those patterns; and (3) to characterize the relationship between observed pesticide patterns and land use. A particular emphasis is placed on determining if any tributaries or specific land use present a greater threat to drinking water quality in order to more effectively focus future monitoring activity as well as guide the development of management strategies to reduce pesticide runoff. Physical and chemical characteristics of compounds are evaluated to provide insight into compound persistence and likely modes of transport. Concentrations of detected compounds are compared to the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Levels (MCLs) or USGS Health-Based Screening Levels (HBSLs) to assess known or suspected threats to human health from drinking water. This report also assesses the potential threat of endocrine disruption from detected compounds. Results are synthesized with current findings from other studies to generate a conceptual model of pesticide transport in the basin, which essentially represents a set of hypotheses to be evaluated with future data collection. The report concludes with a description of a possible direction for further monitoring that can effectively verify and refine the conceptual model.


The analyses in this report include data from 16 different sampling events conducted during 2002–10, encompassing a total of 117 ambient samples collected from 28 tributary and mainstem sites. Although the study area for EWEB’s drinking water source protection plan includes the entire McKenzie River basin upstream of the treatment facility, data collection for this project focused on sites downstream of Blue River. Sampling sites were selected to represent specific land-use categories, including forestry, urban, and agricultural activities, as well as the mouths of major tributaries characterized by a mixture of upstream land use. Constituents included a suite of 175 compounds in filtered water, including 72 herbicides, 43 insecticides, 10 fungicides, and 36 of their degradation products, as well as 14 pharmaceutical compounds. The term “pesticide” is used generically in this report to refer to any of the herbicide, insecticide, fungicide, or metabolite compounds.


Description of Study Area


The McKenzie River is located in western Oregon and has a drainage basin of approximately 1,300 mi² that is bounded on the west by the southern Willamette Valley and on the east by the Cascade Range (fig. 1). The river originates at the crest of the Cascades and flows south and west for about 90 mi to the confluence with the Willamette River near Eugene and Springfield, Oregon. The headwaters are located in the High Cascades physiographic province, which largely comprises young and highly porous volcanic material and represents approximately 24 percent of the basin (Tague and Grant, 2004). Downstream of the confluence with Blue River, the McKenzie River flows into the Western Cascades physiographic province (about 58 percent of the basin), which is much less permeable than the High Cascades (Tague and Grant, 2004). This region is characterized by steeply dissecting streams and relatively narrow canyons (Risley and others, 2010). In the lower McKenzie River basin, the river drains Quaternary alluvium (about 18 percent of the basin) where the river widens, and agriculturally productive soils are found along the valley bottom (Sherrod and Smith, 2000). 


Hydrologic characteristics vary across these geologic provinces so that they represent distinct regions of potential contaminant sources in the McKenzie River basin. The upper McKenzie River is fed by many large springs discharging large quantities of groundwater fed by snowmelt, and consequently a large volume of steady, year-round baseflow is discharged from the High Cascades region at high altitudes. Streamflow farther downstream is dominated by runoff from local precipitation events. Daily streamflow for the McKenzie River at the outlet of Clear Lake (located outside the study area at river mile 92.4) shows little variability throughout the year, while flows for the McKenzie River above Hayden Bridge (site 5) reflect runoff from winter storms as well as snowmelt in late spring (fig. 2).


Climate in the McKenzie River basin is wet and cool during the winter, and dry and warm during the summer. Mean annual precipitation (1961-90) in the study area ranges from about 50 in. near the river mouth to 65 in. at high altitudes, about 90 percent of which occurs between October and May (fig. 3) (Western Regional Climate Center, 2010). Local topography generates considerable microclimatic variability within individual storms so that rainfall often falls inconsistently over the area.


Land use in the basin is predominantly forest (about 92 percent). Land ownership is a mixture of private, State, and Federal. Rural and urban residential and industrial neighborhoods are a comparatively small component of drainage basin area (about 4 percent), although these neighborhoods are of concern because they predominate in the lower basin and their associated runoff discharges to the river close to the EWEB intake. Similarly, agricultural activity is of concern because it primarily occurs in the lower basin close to the river and the EWEB intake, even though agricultural lands also represent a small proportion of the drainage basin area (about 2 percent). Pasture and hay for livestock constitute most agricultural production; other crops include filberts, Christmas trees, grass seed, and blueberries (Morgenstern, 2006).


Natural flow patterns in the McKenzie River are influenced to varying degrees by the presence of five dams in the upper basin (outside the study area), as well as another dam and two canal diversions in the middle basin that are operated primarily for hydropower production. Reservoirs in the upper basin include the Carmen Reservoir complex, a hydroelectric project whose outflow is re-regulated by the Trail Bridge Reservoir to mimic inflow patterns. These are run-of-the-river reservoirs with short residence times, and they do not have a significant effect on streamflow patterns. Two Army Corps of Engineers flood control reservoirs (Cougar and Blue River Reservoirs) are located farther downstream, and their combined effect is to decrease peak flows from snowmelt in the spring and augment low flows in summer and fall (Risley and others, 2010). In the middle McKenzie River basin, two canals divert water into small EWEB reservoirs for power generation (Blair, 2000; Risley and others, 2010). The first canal near the unincorporated community of Leaburg diverts part of the mainstem river at Leaburg Dam for 5 mi before it is returned to the river through a hydroelectric facility. Farther downstream, the second canal diverts water near the unincorporated community of Walterville for 4 mi, where it is again returned to the river for power generation. 


In the lower McKenzie River basin, the stream network incorporates the stormwater drainage system of the City of Springfield, which includes five stormwater outfalls that drain either exclusively or occasionally into the McKenzie River. Three of these (at 72nd, 69th, and 64th Streets) empty into Cedar Creek, a major tributary in the lower basin, and collectively represent most of the storm water from the eastern portion of Springfield. A fourth outfall (at 52nd Street) drains into Keizer Slough, which is a slow-moving side channel that discharges to the McKenzie River about 0.25 mi upstream of the EWEB intake upstream of Hayden Bridge. The fifth outfall (at 42nd Street) drains primarily into another series of sloughs and canals that empty into the Willamette River most of the year; during heavy rain, however, it overflows into Keizer Slough. 


First posted May 30, 2012