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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5027

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Introduction

Background

In Oregon, more than 11,000 pesticide products are registered for use to control brush, weeds, insects, fungi, rodents, nematodes, and other pests. This includes 771 active ingredients (Janet Fults, Oregon Department of Agriculture, written commun., 2008). Much of the pesticide use is on agricultural crops, home gardens, lawns, landscaping in urban and industrial areas, golf courses, forestland, and along rights-of-way such as roads, railways, and utility lines. During the past 15–20 years, studies conducted by the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program have documented widespread occurrence of pesticides and degradates in streams and ground water in the United States, especially in areas affected by human development. More than 90 percent of water samples from streams in agricultural, urban, or mixed-land-use settings contained 2 or more pesticide compounds, with 5 or more pesticide detections occurring in 70 percent of samples, and 10 or more compounds occurring in 20 percent of samples (Gilliom and others, 2006).

Previous studies conducted in Oregon indicate that a wide variety of pesticides and degradates are making their way into streams (Anderson and others, 1997; Rinella and Janet, 1998; Wentz and others, 1998; Wood, 2001; Grange, 2002; Sandahl and Jenkins, 2002) and ground water (Hinkle, 1997). Studies by Anderson and others (1997) and Rinella and Janet (1998) detected 36 and 50 pesticides, respectively, in Willamette Valley streams and discovered that the large diversity of crops grown in the northern Willamette Valley (for example, row crops, berries, nurseries, and vineyards) results in a wide variety of pesticides being applied and later detected in these streams. In the southern valley, however, the diversity of crops is small, consisting primarily of grass seed and other seed crops (Anderson and others, 1996), which reduced the types and variety of pesticides detected (Anderson and others, 1997).

The Clackamas River in northwestern Oregon originates on the western slope of the Cascade Mountains and enters the Willamette River south of Portland, downstream of the Tualatin River and Willamette Falls. The Clackamas River drains a diverse landscape of natural and developed areas, including forestland, agricultural areas, industrial land, rural residential areas, golf courses, and dense suburban developments (pl. 1). In 2000, the USGS began sampling for pesticides in the Clackamas River basin as part of a cooperative study with the Clackamas Watershed Management Group (CWMG). The first pesticide study included samplings during two storm events (May and October 2000). A total of 27 pesticides and degradates were detected in either the lower Clackamas River or in major lower-basin tributaries that discharge to the Clackamas River upstream of drinking-water intakes (Carpenter, 2004).

Pesticide concentrations during this first study were highest in Sieben and Rock Creeks—two relatively small streams on the northern side of the lower Clackamas River basin. These streams drain basins that are being urbanized from forested, agricultural, and rural residential land into suburban developments. The highest pesticide loads (or amounts) entering the Clackamas River were found in Deep Creek, a large tributary that drains the area southeast of Boring. Deep Creek and its tributaries drain large areas of nursery and greenhouse operations along with rural residential property and the city of Sandy and community of Boring (pl. 1).

The occurrence of pesticides in the Clackamas River and its tributaries is of concern to Federal, State, and local natural resource agencies and drinking water providers that use this valued resource. In addition to providing a source of drinking water for more than 300,000 residents, the Clackamas River is home to several species of anadromous salmon and steelhead, resident fish and other aquatic life, and some fish species are listed as threatened under the Endangered Species Act (National Marine Fisheries Service, 2006).

In 2001, the USGS NAWQA Program initiated a Source Water Quality Assessment (SWQA) study to characterize the water quality of major rivers and aquifers used as a source of water supply to community water systems in the United States. In 2002, the Clackamas River was selected to be one of nine community water systems to be sampled as part of the surface-water component of the SWQA study (Carter and others, 2007). This study built on the initial drinking-water pilot studies conducted by the USGS and USEPA, which examined the quality of pre- and post-treated (source and finished) drinking water from 12 water-supply reservoirs across the country (Blomquist and others, 2001; Coupe and Blomquist, 2004). These latter studies indicated that conventional water treatment did not completely remove pesticides and degradates during treatment, and although all concentrations were less than USEPA drinking-water standards, 9–30 pesticide compounds were detected in finished water from each of the 12 water-treatment plants (median number of pesticide compounds detected was 23).

These and other studies utilizing low-level (parts per billion, or lower) methods have detected pesticides and other contaminants in source and finished water, which raises concerns about the potential implications for human health and aquatic life in these rivers. Studies of the potential for cumulative effects from exposure to multiple pesticide compounds are needed to address such concerns because pesticides seldom occur in streams by themselves—they are nearly always found with other pesticides and degradates in multicompound mixtures (Gilliom and others, 2006).

Study Purpose and Report Scope

This report includes data from four USGS studies conducted between 2000 and 2005. The initial study included sampling of the mouths of the major lower-basin tributaries, plus a limited number of samples collected from the lower Clackamas River and of finished drinking water (Carpenter, 2004). Since then, three additional studies: the Source Water-Quality Assessment (SWQA) and Effects of Urbanization on Stream Ecosystems (EUSE) topical studies, and a USGS/Clackamas Watershed Management Group (CWMG) project in 2005 (repeat of 2000 study), have provided more information on the occurrence and distribution of pesticides in the lower Clackamas River basin. In all, about 119 pesticide samples were collected from 30 sites during the 6-year period (fig. 1; tables 1 and 2).

Two of the previously mentioned three additional studies were part of the USGS NAWQA Program. The SWQA drinking-water study examined the quality of source and finished water from the Clackamas River and eight other community water systems across the country (Carter and others, 2007). The EUSE study investigated the physical, chemical, and biological effects of urbanization on streams (Ian Waite, U.S. Geological Survey, written commun., 2007), with 3 sites in the Clackamas River basin included in the sampling along with 25 other streams. In 2005, a fourth pesticide study was conducted, another collaboration between the USGS and CWMG that included targeted sampling during one autumn and one spring storm. More details on each study are provided below.

Sampling of the Clackamas River for pesticides and other synthetic organic compounds as part of the SWQA study began in 2002. This two-phase study included sampling of source water (from a source water tap at the study water-treatment plant) in 2002–03 (Phase 1). During Phase 2 (2004–05), source and finished water samples from the same water-treatment plant were analyzed. During the SWQA and the USGS/CWMG repeat study in 2005, the treatment process at the water-treatment plant tested used direct filtration with multimedia rapid-sand filtration technology (anthracite coal, silica sand, and garnet sand). Coagulation chemicals and disinfectant (aluminum sulfate, aluminum chlorohydrate, and gaseous chlorine [Cl₂]) are injected near the beginning of the treatment process. A filter aid polymer is injected between sedimentation and filtration to enhance particle removal by the filter media. Occasionally, powdered activated carbon (PAC) was used at concentrations of between 2 and 5 mg/L as a final treatment step to reduce odors and improve taste, most often during summer months. Pesticide data collected during the SWQA are interpreted in this report, but the other data collected for the SWQA study, including information on other anthropogenic organic and wastewater-related compounds, are published in Carter and others (2007).

The 2003–04 EUSE study included three streams in the Clackamas River basin (all within the Deep Creek basin) that were sampled as part of a larger study in the Vancouver, Portland, Salem, and Eugene metropolitan areas (Ian Waite, U.S. Geological Survey, written commun., 2007). Three Clackamas River basin sites—North Fork Deep Creek, Tickle Creek, and upper Deep Creek—were sampled six times each for pesticides, nutrients, suspended sediment, and other water-quality constituents. Information on biological assemblages, including fish, benthic (bottom dwelling) invertebrates, and algae also were collected once from each stream during low-flow conditions in 2004. Contaminant data also were collected from semipermeable membrane devices (SPMDs), which were placed in the river to sequester pesticides and other organic compounds over a period of about 30 days. Data from this study are being used to characterize biological assemblages as they relate to urbanization and stream conditions, including pesticide occurrence during high- and low-flow conditions. Water sampling did not, however, target storm runoff during the EUSE study.

The most recent 2005 storm event sampling study, a repeat and expansion of the 2000 spring/autumn storm event study, included most of the initial sites plus additional sampling locations in the Sieben, Rock, and Deep Creek basins to further identify pesticide source areas. In 2005, Carli and Cow Creeks were added to the network of sampling sites to characterize storm-runoff conditions from these highly urbanized basins. These two streams drain the lower northwestern part the lower Clackamas River basin, where most of the commercial and industrial development is located. The most extensive storm event sampling occurred in September 2005, when 24 tributaries, the lower Clackamas River (source water), and finished water from the study drinking-water treatment plant were sampled for dissolved pesticides during a 1.5-inch rainfall event. During this storm, about a dozen sites in the Deep Creek basin were sampled, including multiple sites within the Noyer, North Fork Deep, and Tickle Creek basins, where much of the agricultural nursery land is concentrated.

This report summarizes data collected from the four USGS studies conducted between 2000 and 2005, and describes the spatial and temporal patterns in the occurrence of pesticides in the lower Clackamas River basin. This report also evaluates the potential for risks to aquatic life and human health by comparing pesticide concentrations to established benchmarks, when available, and concludes with potential directions for further study.

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