Water quality in the Puget Sound basin, Washington and British Columbia, 1996-98

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

THIS REPORT summarizes major findings about water quality in the Puget Sound Basin that emerged from an assessment conducted between 1996 and 1998 by the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program. Water quality is discussed in terms of local and regional issues and compared to conditions found in all 36 NAWQA study areas, called Study Units, assessed to date. Findings are also explained in the context of selected national benchmarks, such as those for drinking-water quality and the protection of aquatic organisms. The NAWQA Program was not intended to assess the quality of the Nation’s drinking water, such as by monitoring water from household taps. Rather, the assessments focus on the quality of the resource itself, thereby complementing many ongoing Federal, State, and local drinking-water monitoring programs. The comparisons made in this report to drinking-water standards and guidelines are only in the context of the available untreated resource. Finally, this report includes information about the status of aquatic communities and the condition of in-stream habitats as elements of a complete water-quality assessment.

Many topics covered in this report reflect the concerns of officials in State and Federal agencies, water-resource managers, and members of stakeholder groups who provided advice and input during the Puget Sound River Basin assessment. Basin residents who wish to know more about water quality in the areas where they live will find this report informative as well.

THE NAWQA PROGRAM seeks to improve scientific and public understanding of water quality in the Nation’s major river basins and ground-water systems. Better understanding facilitates effective resource management, accurate identification of water-quality priorities, and successful development of strategies that protect and restore water quality. Guided by a nationally consistent study design and shaped by ongoing communication with local, State, and Federal agencies, NAWQA assessments support the investigation of local issues and trends while providing a firm foundation for understanding water quality at regional and national scales. The ability to integrate local and national scales of data collection and analysis is a unique feature of the USGS NAWQA Program.

The Puget Sound Basin is one of 51 water-quality assessments initiated since 1991, when the U.S. Congress appropriated funds for the USGS to begin the NAWQA Program. As indicated on the map, 36 assessments have been completed, and 15 more assessments will conclude in 2001. Collectively, these assessments cover about one-half of the land area of the United States and include water resources that are available to more than 60 percent of the U.S. population.

IV National Water-Quality Assessment Program

SUMMARY OF MAJOR FINDINGS

Stream and River Highlights

Streams and rivers in the Puget Sound Basin met most Federal and State water-quality guidelines. In general, large rivers were more likely to meet guidelines than were small streams. Concentrations of fecal bacteria frequently exceeded U.S. Environmental Protection Agency (USEPA) recreational criteria and State standards protecting beneficial uses of surface water, and insecticide concentrations were occasionally higher than guidelines recommended to protect aquatic life. A total of 74 manmade organic chemicals were detected in streams and rivers, with different mixtures of chemicals linked to agricultural and urban settings. Though most chemical concentrations appeared to be low, guidelines for drinking water and aquatic life that

The Puget Sound Basin is a 13,700-square-mile area of mountains and coastal lowlands in western Washington State and portions of British Columbia. About 4 million people live in the basin, mainly in metropolitan areas of Seattle, Tacoma, Everett, Bellingham, and Olympia. Headwaters of major rivers provide much of the drinking water for these metropolitan areas. Ground water is the primary source of drinking water in rural areas and, increasingly, for new suburbs.

are needed to make a full assessment do not exist for more than half the compounds detected.

Summary of Major Findings Concentrations of nitrate and phosphorus in the Nooksack and Green Rivers did not change between 1980 and 1997. During the same period, concentrations of nitrate in the Skokomish River and in Big Soos and Newaukum Creeks increased slightly (p. 12).

Ground-Water Highlights

Reliance on ground water as a source of drinking water is increasing with urban and suburban development. With some exceptions, ground water is of high quality. However, as indicated by elevated concentrations of nitrate and the presence of pesticides and other organic compounds, shallow ground water in both urban and agricultural settings is vulnerable to contamination. Monitoring wells in urban residential areas generally contained low-concentration mixtures of chemicals associated with transportation and household activities. Shallow ground water, at depths tapped for domestic supply in agricultural areas, contained fertilizer residues (nitrate) at concentrations that commonly exceeded the drinking-water standard. Other agricultural chemicals were also frequently detected, though mostly at concentrations below current Federal and State drinking-water guidelines.

Water Quality in the Puget Sound Basin

INTRODUCTION TO THE PUGET SOUND BASIN

The Puget Sound Basin encompasses the 13,700-square-mile area that drains to Puget Sound and adjacent marine waters. Included are all or part of 13 counties in western Washington, as well as the headwaters of the Skagit River and part of the Nooksack River in British Columbia, Canada. Streams and rivers drain three physiographic provinces—the Olympic Mountains in the west, the Cascade Range in the east, and the Puget Lowlands in the center of the basin (fig. 1).

Land Use Affects Water Quality and Stream Habitat

Nearly 4 million people, or about 70 percent of Washington State’s population, live in the Puget Sound Basin. Urban growth is rapid; by 2020, the population is expected to increase by 1.1 million people, with most growth in urban and suburban areas. Urban and agricultural land uses, which cover about 9 and 6 percent of the basin, respectively (fig. 2), are concentrated in the lowlands. Forest dominates land use and cover in the basin and is concentrated in the foothills and mountains (see map, p. 1).

Figure 2. Land use and cover in the basin is predominantly forest.

The quality of water and aquatic biota has been affected by a range of forestry, agricultural, and urban development practices. The chemical quality of surface water in the foothills and mountains is

Introduction to the Puget Sound Basin generally suitable for most uses. However, the physical hydrology, water temperature, and biologic integrity of streams have been influenced to varying degrees by logging (Black and Silkey, 1998). The quality of ground water in the upper watersheds probably differs little from natural conditions.

Because of development, many streams in the Puget Lowlands have undergone changes in structure and function with a trend toward simplification of stream channels and loss of habitat (Black and Silkey, 1998). Sources of contaminants to lowland streams and lower reaches of large rivers are largely nonpoint because most major point sources discharge directly to Puget Sound. Compared with that in small streams in the Puget Lowlands, the quality of water in the lower reaches of large rivers is better because much of the flow is derived from the forested headwaters.

More than half of the agricultural acreage in the basin is located in Whatcom, Skagit, and Snohomish Counties. Agricultural land use consists of about 60 percent cropland and 40 percent pasture. Livestock produce a large amount of manure that is applied as fertilizer to cropland, sometimes in excess amounts, resulting in runoff of nitrogen and phosphorus to surface water and leaching of nitrate to ground water. Runoff from agricultural areas also carries sediment, pesticides, and bacteria to streams (Staubitz and others, 1997). Pesticides and fumigant-related compounds are present, usually at low concentrations, in shallow ground water in agricultural areas.

Heavy industry is generally located on the shores of the urban bays and along the lower reaches of their influent tributaries, such as Commencement Bay and the Puyallup River in Tacoma and

Water Quality in the Puget Sound Basin Elliott Bay and the Duwamish Waterway in Seattle. Highdensity commercial and residential development occurs primarily within and adjacent to the major cities. Development in recent years has continued around the periphery of these urban areas but has trended toward lower density. This trend has resulted in increasing urban sprawl in the central Puget Sound Basin (fig. 3).

Urban land-use activities have had a significant impact on the quality of streams in the Puget Sound Basin (Staubitz and others, 1997). Water-quality concerns related to urban development include providing adequate sewage treatment and disposal, transport of contaminants to streams by storm runoff, and preservation of stream corridors.

Figure 3. Recent urban development in the Puget Sound Basin has been around the periphery of established urban areas.

Water Availability Is a Major Issue

Although surface water provides most of the drinking water for the major urban centers (fig. 4), ground water is used in rural areas, and reliance on ground water as a source of drinking water is increasing with urban and suburban development (Staubitz and others, 1997).

Water availability has been and will continue to be a major, longterm issue in the Puget Sound Basin. It is now widely recognized that ground-water withdrawals can deplete streamflows (Morgan and Jones, 1999), and one of the increasing demands for surface water is the need to maintain instream flows for fish and other aquatic biota.

Figure 4. Excluding water used for hydroelectric power, 41 percent of water was used for domestic supply in 1995. Ground water accounted for 47 percent of all withdrawals.

Hydrologic Conditions Probably Affected Study Results

Surface water was sampled during 1996 and 1997 when rainfall and streamflows generally were above the 30-year average (fig. 5). Because of increased runoff during periods of rainfall, larger amounts of sediment, nutrients, pesticides, bacteria, and other contaminants may have been transported from the land surface into streams and rivers than during drier years. High flows due to runoff from paved surfaces can also alter stream habitat.

Figure 5. Streams and rivers were sampled during 1996 and 1997 when streamflows generally were above the 30-year average.

Introduction to the Puget Sound Basin

Some Ground Water Is Susceptible to Contamination

Shallow ground water (less than 100 feet deep) in the Puget Lowlands is more susceptible to contamination in areas where the overlying sediments are coarse grained than where they are fine grained (see p. 16 and map, p. 20). This is because rainfall, or applied irrigation water, seep relatively easily through coarse-grained sediments and can transport contaminants to ground water.

Study Design Focuses on Land Use

Chemical and biological samples were collected from a mix of rivers and streams in forested, urban, and agricultural areas to assess overall quality as well as the effects of specific land-use practices. At some sites, water samples were collected monthly and during storms to assess the effects of storm runoff on contaminant washoff. Other sites were sampled only once, usually during normal flows.

Shallow ground water was sampled from aquifers in coarse-grained glacial deposits considered to be the most at risk to contamination. Water from these aquifers was sampled to assess general water quality and specifically to assess the quality of water in agricultural and residential areas. Monitoring wells and domestic wells were sampled. Data from a previous sampling of public-supply wells (Ryker and Williamson, 1996) are used to help evaluate the quality of drinking water and the quality of deep ground water. (See table 3, page 21 for details on study design.)

Pesticides in Surface Water Were Indicative of Upstream Land Uses, and More Pesticides Were Detected in Streams Than in Rivers

Twenty-nine pesticides were detected in Fishtrap Creek, which drains an agricultural area in the Nooksack River Basin (see map, p. 20), compared with 21 in Thornton Creek, an urban stream. In Fishtrap Creek, the more frequent detections of the herbicides atrazine and metolachlor, used more in agricultural areas, and less frequent detections of the herbicides dichlobenil and prometon (fig. 6), used more in urban areas, are consistent with the predominant land use in the

Figure 6. Pesticides detected in small streams (A) and large rivers (B) were indicative of land use, but detection frequencies in large rivers were lower because of dilution by flows from forested headwaters.

Water Quality in the Puget Sound Basin drainage basin. Urbanuse pesticides in Fishtrap Creek are probably transported from urban areas in the upper and lower parts of the basin.

The two large rivers sampled for pesticides, the Nooksack and Duwamish (see map, p. 20), integrate land-use effects. The herbicides prometon, simazine, and tebuthiuron, which are used in urban settings, were detected frequently in the Duwamish River (fig. 6). This is indicative of the urban land use surrounding and immediately upstream from the sampling site. Metolachlor, an agricultural herbicide, was detected more often in the Duwamish River than in the Nooksack River, which was sampled in an agricultural setting. Metolachlor in the Duwamish River was likely transported from agricultural areas upstream from the mostly urbanized lower part of the basin, where samples were collected.

Pesticides transported to the Nooksack and Duwamish Rivers are diluted by the volume of highquality water from forested headwaters, resulting in lower detection frequencies compared with Fishtrap and Thornton Creeks (fig. 6). In addition to lower detection frequencies, fewer pesticides were detected in the large rivers.

Diazinon was the most frequently detected insecticide in both small streams and large rivers (fig. 6). It is used heavily in urban areas of the Puget Sound Basin, and its frequent detection, sometimes at concentrations exceeding the chronic guideline for the protection of aquatic life (table 1), prompted a more focused study of pesticides in urban streams in Seattle and surrounding King County (see page 7).

The insecticides chlorpyrifos, diazinon, and lindane were sometimes detected at concentrations above chronic guidelines for the protection of aquatic life (table 1). Concentrations of diazinon exceeded its guideline in 9 percent of all samples, and in Thornton Creek, concentrations exceeded the guideline in 20 percent of samples. It is estimated that about half the 83,000 pounds of diazinon applied annually in the Puget Sound Basin are applied in King County (Tetra Tech Incorporated, 1988). Diazinon is the insecticide purchased most frequently by King County residents (fig. 7).

Figure 7. A comparison of pesticides detected in urban streams with retail sales data suggests that homeowner and nonresidential applications both are sources of pesticides in streams. Sales were reported in units, which represent a bag, bottle, or other package containing the pesticide.

Because of the prevalence of diazinon and other pesticides in Thornton Creek, the USGS collaborated with the Washington State Department of Ecology and the King County Hazardous Waste Management Program to study pesticides in streams in 10 urban and suburban watersheds in King County (see map, p. 20). Samples were collected during April and May 1998 when retail sales of pesticides are highest (Voss and others, 1999), and they were collected during storms when runoff can transport pesticides to streams.

Because USGS and Washington State Department of Ecology laboratories both participated in the study, additional pesticides not included in the NAWQA study were analyzed. To help determine sources of pesticides detected, King County provided sales data for pesticides sold in 10 large home and garden stores during 1997.

Twenty-three of 98 pesticides analyzed for were detected in the urban streams. Homeowner use as a source of pesticides in streams is indicated for compounds like the herbicide 2,4-D and the insecticide diazinon, which were detected in all streams and were sold frequently in the home and garden stores (fig. 7). Some pesticides sold in stores were not detected in streams, indicating that other factors, like the rate at which a compound breaks down, affect the relation between usage and detection.

Almost half of the pesticides detected in the streams had no retail sales, indicating that they are usually not applied by homeowners. In urban areas, pesticides are also applied in commercial areas, along road rightsof-way, and in parks and recreational areas.

Insecticides in Thornton Creek Were Also Detected in Urban Streams Throughout the Nation

Throughout the Nation, the insecticides diazinon, carbaryl, chlorpyrifos, and malathion were detected much more frequently in streams draining urban basins than in streams draining agricultural basins (U.S. Geological Survey, 1999b). Except for carbaryl, these pesticides also were detected more frequently in Thornton Creek, an urban stream, than in Fishtrap Creek, an agricultural stream (fig. 6).

Detection of these pesticides is related to usage. For example, diazinon and chlorpyrifos, which nationally rank 1 and 4 among insecticides used for homes and gardens, rank 1 and 2 in unit sales of insecticides sold by home improvement stores in urban and suburban areas of King County (fig. 7).

Insecticides in streams are a concern because even at relatively low concentrations they can exceed guidelines for the protection of aquatic life (table 1).

Historically Used Pesticides and PCBs Are Still Detected in Streambed Sediments and Fish Tissue

Streambed sediment and whole fish (sculpin, a bottom fish) tissue were analyzed at sites throughout the basin (see map, p. 20) in 1995 for organochlorine pesticides and PCBs. These compounds have been shown to have negative impacts on the health of aquatic organisms as well as the organisms that consume them. More organochlorine compounds were detected in both streambed sediments and fish tissue at sites surrounded by agricultural and urban land uses than at sites in undeveloped, forest, or mixedland-use areas (fig. 8).

Figure 8. Organochlorine compounds, including the insecticide DDT and PCBs, in streambed sediments and fish tissue were primarily detected in urban and agricultural streams.

Water Quality in the Puget Sound Basin The relation between land use and the probability of detecting organochlorine compounds in fish (sculpin) tissue were statistically significant. This relation suggests that urban and agricultural land uses both contribute to the probability that a fish is contaminated with organochlorine pesticides. The probability of detecting total PCBs in fish was significantly related to urban land use only (Black and others, 2000). These relations also suggest that there is a land-use threshold below which the probability of finding organochlorine compounds in fish tissue is unlikely (fig. 9).

Figure 9. The probability of detecting specific organochlorine compounds in one or more fish (sculpin) at a site increased with the percentage of urban and agricultural land in the drainage basin. Dieldrin, cis-Chlordane, and p,p’-DDT relations are based on the percentage of agriculture plus urban land upstream from the sampling site. The total PCBs relation is based on the percent of urban land upstream from the sampling site.

Organochlorine pesticides were detected in streambed sediment at 3 of 19 sites (fig. 10). At Thornton Creek, an urban stream, levels of DDE (a breakdown product of DDT) and DDT exceeded the Canadian Council of Ministers of the Environment’s (Canadian Council of Ministers of the Environment, 1995) probable effects level (PEL). Compounds exceeding the PEL are likely to result in adverse effects on aquatic organisms. It is important to note that levels of DDT in Thornton Creek sediment were higher than either one of its breakdown products, DDD and DDE. This may indicate that land disturbances in the basin have reintroduced buried soils contaminated with DDT.

Organochlorine compounds were also detected in the tissue of whole bottom fish (sculpin) collected at 8 of 18 study sites (fig. 11).

Figure 10. Concentrations of organochlorine compounds in streambed sediment in the Puget Sound Basin sometimes exceeded Canadian probable effects levels (PELs). Compounds above the PELs may have negative impacts on aquatic organisms.

Major Findings The largest number and highest concentrations of these compounds were in the fish collected from urban sites. At some sites, total PCBs and DDT concentrations were equal to or above the New York State Department of Environmental Conservation (NYSDEC) criteria for the protection of fish-eating wildlife (Newell and others, 1987).

Generally, the concentrations of organochlorine compounds in sediment and fish tissue were in the middle 50 percent nationally (see Appendix). Occasionally, concentrations of DDE, total chlordane, and total DDT were in the upper 25 percent of those reported nationally.

Characteristics and historical uses of organochlorine compounds detected in Puget Sound Basin fish tissue and streambed sediment

Organochlorine compounds are synthetic organic compounds containing chlorine. As generally used, the term refers to compounds containing mostly or exclusively carbon, hydrogen, and chlorine. Examples include organochlorine insecticides, polychlorinated biphenyls, and some solvents containing chlorine.

Chlordane (Octachloro-4,7-methanotetrahydroindane) is an organochlorine insecticide no longer registered for use in the United States. Technical chlordane is a mixture in which the primary components are

Water Quality in the Puget Sound Basin cis- and trans-chlordane, cis- and trans-nonachlor, and heptachlor.

Figure 11. Concentrations of organochlorine compounds in fish (sculpin) tissue from streams in the Puget Sound Basin sometimes exceeded New York State Department of Environmental Conservation (NYSDEC) criteria. Concentrations above criteria may have a detrimental effect on fish-eating organisms.

DDT (Dichloro-diphenyl-trichloroethane) is an organochlorine insecticide no longer registered for use in the United States.

Dieldrin is an organochlorine insecticide no longer registered for use in the United States. It is also a breakdown product of the insecticide aldrin.

Heptachlor epoxide is a breakdown product of the organochlorine insecticide heptachlor. It was used in the United States until the 1970s. Hexachlorobenzene (HCB) is a fungicide used as a seed and soil treatment. It was discontinued from use in the United States in the 1980s.

Polychlorinated biphenyls (PCBs) are a mixture of chlorinated derivatives of biphenyl, marketed under the trade name Aroclor with a number designating the chlorine content (such as Aroclor 1260). PCBs were used in transformers and capacitors for insulating purposes and in gas pipeline systems as a lubricant. Further sale for new use was banned by law in 1979.

Streams and Rivers in Developed Areas Were Enriched with Nutrients Relative to Those in Undeveloped Areas

The highest average concentrations of total nitrogen were in small streams draining agricultural areas. The concentrations were nearly twice those in streams draining urban areas and over 40 times the average concentrations in streams draining undeveloped land (table 2). Drainage basins in agricultural areas also yielded the most nitrogen per square mile (fig. 12). Concentrations and yields of total nitrogen in Puget Sound Basin streams and rivers correlate with usage and atmospheric deposition of nitrogen in drainage basins (Inkpen and Embrey, 1998). Fertilizers used in both agricultural and urban areas, manure associated with dairy farms, and atmospheric deposition are sources of nitrogen in Puget Sound Basin rivers (Embrey and Inkpen, 1998).

Figure 12. Basins in agricultural areas yielded the most nitrogen per square mile. The forested area upstream from the Nooksack River at North Cedarville yielded the most phosphorus. In basins with mixed land use, the dominant land use is indicated. The Green River above Twin Camp Creek and North Fork Skokomish River fall into the stream category because their drainage basins are relatively small.

Average concentrations of total phosphorus exceeding the USEPA desired goal of 0.1 mg/L to prevent excessive plant growth were detected in streams and rivers in all land-use areas except undeveloped land (table 2). Unlike total nitrogen, concentrations of total phosphorus in streams and rivers in the Puget Sound Basin do not correlate with usage and atmospheric deposition of phosphorus in drainage basins (Inkpen and Embrey, 1998). This is because phosphorus attaches to soil particles and usually remains close to application areas unless it is transported to rivers by soil erosion.

Because of the importance of erosion in transporting phosphorus to streams, yields of total phosphorus correlate with yields of suspended sediment. The highest yields of both suspended sediment and total phosphorus were in the Nooksack River at North Cedarville, which drains a forested area.

Erosion of unstable streambanks and landslides transport sediment and phosphorus to headwater streams in the Nooksack River Basin. Most of the unstable streambanks are associated with road construction and logging (U.S. Forest Service, 1995).

Major Findings Concentrations of nitrate, one of the major forms of nitrogen in water, and of total phosphorus have not changed much over the period 1980 to 1997 in several Puget Sound Basin rivers and streams (fig. 13). In three streams, nitrate concentrations have increased by a small amount, 0.014 mg/L per year or less. Only in

Figure 13. In three of six rivers and streams monitored by the Washington State Department of Ecology and King County, nutrient concentrations have remained stable from 1980 to 1997. In three others, concentrations of nitrate have gradually increased with time.

Newaukum Creek did concentrations of both nitrogen and phosphorus increase over time. Although data were not collected to determine the cause, trends often reflect land-use changes. For example, urban development might be a factor related to increasing nitrate concentrations in Big Soos Creek and in Newaukum Creek, which drains an agricultural basin with hobby farms and residential development.

Water Quality in the Puget Sound Basin

Runoff During Rainstorms Contributes Contaminants to Streams, Indicating Nonpoint Sources

Washoff of nutrients and pesticides during storms causes both seasonal and short-term temporal variations in concentrations. A typical seasonal pattern for Puget Sound Basin streams and rivers is illustrated by lower concentrations of nitrogen and phosphorus in Newaukum Creek from July through October when rainfall amounts are lowest (fig. 14).

Figure 14. Nutrient concentrations in Newaukum Creek were highest during the rainy winter and spring periods. Concentrations were lowest during late summer-early fall when rainfall amounts are lowest.

Figure 15. Peak concentrations of diazinon in Thornton Creek often occurred during spring rainstorms, which can produce an inch or more of rain in a day.

Commonly used pesticides, such as diazinon, often had higher concentrations during rainstorms when they were washed off from areas of application (fig. 15). Even when daily rainfall amounts were small, less than 0.05 inch, diazinon concentrations increased in Thornton Creek.

Bacteria Indicate the Presence of Fecal Contamination in Many Puget Lowland Streams

A study of 31 small lowland streams showed fecal coliform, E. coli, and enterococci bacteria to be present in every stream sampled during base flow. The presence of E. coli and enterococci bacteria is evidence that fecal contamination has occurred. During base flow, fecal contamination in urban streams could result from leaky sewer systems, failing septic systems, and direct fecal inputs from pets and wildlife, including waterfowl. In agricultural and rural streams, fecal contamination is likely to be mostly from animals, including farm animals (dairy and beef cattle, and horses). Other sources could be wildlife, with perhaps some input from onsite septic systems.

Figure 16. Concentrations of E. coli and enterococci bacteria exceeded U.S. Environmental Protection Agency recreational criteria, and fecal coliform bacteria exceeded Washington State standards in many lowland streams. Concentrations of bacteria in single samples were compared with criteria and standards. USEPA criteria for moderate full-body contact recreation apply to a single sample (U.S. Environmental Protection Agency, 1986). Washington State standards for fecal coliform bacteria apply to the geometric mean of concentrations in samples collected during a period of no more than 30 days (State of Washington, 1992). Because no minimum number of samples is specified, the standard is routinely applied to concentrations in single samples (Hallock and others, 1996).

Concentrations of all three fecal-indicator bacteria frequently exceeded standards and criteria (fig. 16); 81 percent of all sites had concentrations of fecal coliforms exceeding Washington State standards, and 48 percent of all sites had levels of E. coli exceeding USEPA’s recommended concentration for moderate water-contact recreation. Because concentrations of E. coli and enterococci are related to cases of gastrointestinal illness in swimmers (U.S. Environmental Protection Agency, 1986), there could be some risk of illness to children and adults playing and swimming in these accessible streams.

The types of fecal bacteria and their concentrations in streams were similar among urban, agricultural, and rural areas (fig. 16). However, concentrations of E. coli in the urban and agricultural streams were all well above those in the upper Green River in the forested headwaters of the basin.

Stream Habitat and Health Are Degraded in Agricultural and Urban Streams

During the late summer and early fall, between 1995 and 1998, the USGS and the Washington State Department of Ecology evaluated instream and riparian (streamside) habitat conditions at 45 sites. These evaluations indicated that habitat conditions at streams draining urban

Major Findings and agricultural basins were significantly different from those at streams draining basins with forest and undeveloped land (fig. 17). Compared with either urban or agricultural sites, forest and undeveloped stream sites had a much higher percentage of cobble substrate, ideal for a diverse population of aquatic organisms, and a lower percentage of sand, detrimental to salmon spawning. In addition, forest and undeveloped sites had a much higher variability in water flow velocities than either urban or agricultural sites. More variability in flow velocities increases habitat diversity and wildlife diversity. Midday water temperatures were also much lower in the forested streams. The higher temperatures observed in the agricultural and urban streams are not ideal for native salmon and other aquatic organisms.

Figure 17. Values of selected habitat variables indicate that habitat conditions are degraded in agricultural and urban streams compared with streams in forest and undeveloped land. For each habitat variable, except temperature, multiple measurements were taken within a 330- to 660-foot-long stream reach at each study site.

As part of the USGS and Washington State Department of Ecology habitat data collection, aquatic invertebrates (insects and worms) were also collected from multiple riffle habitats at all 45 sites. A number of invertebrate community measures were examined to evaluate the status and quality of the aquatic invertebrate community. For each invertebrate community measure, values were lower, significantly so in some cases, at the urban and agricultural sites (fig. 18).

Figure 18. As indicated by the average values of six different invertebrate community indicators of stream ecosystem conditions, conditions were better at sites in forest and undeveloped land than at sites in urban and agricultural areas. Lower values suggest a more degraded stream site. Taxa are different types of invertebrates.

Water Quality in the Puget Sound Basin Urban development and agriculture can reduce habitat quality, alter typical stream flows, and increase chemical contaminants and temperatures, all of which are reflected in invertebrate community measures. A reduction in the total number of different invertebrates, stoneflies, mayflies, intolerant invertebrates, and percentage of predatory invertebrates indicates stream ecosystem degradation. For example, the total number of different invertebrates was much higher at the forest and undeveloped sites. A greater number of different invertebrates indicates a less degraded stream system capable of supporting more numerous desirable species such as salmon.

A summation of many invertebrate community measures is also shown in figure 18. This measure is known as a Benthic Index of Biological Integrity (BIBI) and is an overall indication of the biological integrity or health of a particular stream site (Black and MacCoy, 2000). As seen in figure 18, urban and agricultural systems have lower biological integrity scores than the forest and undeveloped sites.

A total of 46 different aquatic invertebrate taxa were identified at 45 sites throughout the Puget Sound Basin. Of the 46, only 4 taxa prefer watersheds with low forest/undeveloped land cover, whereas 19 taxa prefer watersheds with high forest/undeveloped land cover (fig. 19). These results indicate that streams in watersheds dominated by urban and agricultural land are optimally suited for only a few of the different taxa and many of these taxa are indicators of degraded stream ecosystems. Watersheds dominated by forest and undeveloped land are preferred by a much larger number of different invertebrate taxa, many of which are indicators of healthy stream systems.

In the Puget Sound Basin, aquatic invertebrates collected at the 11 fixed monitoring sites were compared with those collected at 140 NAWQA sites nationwide.

(Tom Cuffney, U.S. Geological Survey, written commun., 2000) was developed by averaging 11 invertebrate metrics that summarized changes in richness, tolerance, food preference, and dominance associated with water-quality degradation. Invertebrate status scores in the basin ranged from low (less degraded) for streams in forest and undeveloped areas to high (more degraded) for other streams. As indicated by the invertebrate status scores, some Puget Sound Basin streams are highly degraded. This is the result of poor habitat conditions and possibly water chemistry. As shown in figure 17, high midday water temperatures and percent sand were observed in urban and agricultural streams, both of which have negative effects on aquatic organisms. In addition, numerous pesticides, some at concentrations above guidelines set to protect aquatic life, were detected at these sites (see Appendix).

Figure 19. More different aquatic invertebrate types (taxa) prefer streams that have watersheds with greater than 75 percent forest/undeveloped land cover. Each bar represents the preferred range of forest/undeveloped land cover for the specified number of invertebrate taxa out of the 46 taxa identified in the Puget Sound Basin. An animal is healthiest when it is in its preferred range. This figure indicates that more different invertebrate taxa prefer sites in forested/undeveloped watersheds, but not that more invertebrate taxa or total numbers of invertebrates were found at these sites. The method used to determine preferred land-cover percentages was based on the work of Line and others (1994).

Ground-Water Quality is Generally Good

Prior to conducting field studies, an analysis of existing data was conducted to determine which Puget Sound Basin aquifers are most at risk to contamination. Unconfined aquifers that are overlain by coarse-grained glacial deposits (see map, p. 20) were found to be the most susceptible to contamination (see sidebar). Aquifers in coarse-grained glacial deposits in the Puget Sound Basin are collectively referred to as the Fraser aquifer. Three studies were conducted in the unconfined part of the Fraser aquifer (Inkpen and others, 2000). A study-unit survey was conducted by randomly selecting 30 domestic wells without regard to land use to evaluate the overall quality of shallow ground water. Ground-water-quality studies were also conducted in residential areas in Pierce and Thurston Counties

Predicting Ground-Water Susceptibility and Vulnerability

A statistical model (Tesoriero and Voss, 1997; Erwin and Tesoriero, 1997) was created to predict which areas are (1) most likely to become contaminated if sources of contaminants are present (susceptibility) and (2) at the greatest risk of contamination, based on current land-use practices (vulnerability). Well depth, surficial geology, and land use were the factors that significantly correlated with elevated nitrate concentrations and were used in the models. Shallow ground water in areas with coarse-grained glacial deposits at the surface were the most susceptible to contamination. These areas become increasingly vulnerable to nitrate contamination as the amount of agricultural and urban land use increases. Vulnerable areas include the intensive agricultural areas in the northern part of the Study Unit as well as urban areas extending north and south of Seattle.

Water Quality in the Puget Sound Basin and in an agricultural area in Whatcom County (see map, p. 20) to examine the influence of these important land-use categories on shallow ground water. Shallow ground water in all parts of the Fraser aquifer sampled is used for domestic supplies.

The study-unit survey results indicate that ground water is of generally good quality, as only one well did not meet a drinking-water standard (for nitrate). Nitrate was detected in most wells, but the concentrations were low, having a median concentration of 1.0 mg/L (fig. 20). Pesticides were detected in 20 percent of study-unit survey wells (fig. 21) but were present at low concentrations (less than 0.2 μg/L) (micrograms per liter) and were well below drinking-water standards or guidelines. Based on data from a previous study (Ryker and Williamson, 1996), pesticides were not detected in wells more than 120 feet deep (Bortleson and Ebbert, 2000). Volatile organic compounds were detected frequently (80 percent of wells sampled) but were present at low concentrations (less than 1 μg/L).

Figure 20. Median nitrate concentrations in shallow ground water sampled for the studyunit survey (varied land use) were low. Higher nitrate concentrations were more common in both the residential land-use and agricultural land-use studies.

Radon concentrations exceeded the proposed drinking-water standard of 300 picocuries per liter (U.S. Environmental Protection Agency, 1999a) in about 50 percent of the domestic and monitoring wells sampled for radon (table 3, p. 21). Radon is a naturally occurring product from the decay of uranium. The median concentration of radon in ground water in the Puget Sound Basin was 320 picocuries per liter. Elevated radon concentrations are by no means unique to the Puget Sound Basin. In fact, radon concentrations in ground water collected for NAWQA studies throughout the Nation exceeded the proposed standard more often and had a higher median value (420 picocuries per liter) than in the Puget Sound Basin (Wentz and others, 1999).

Figure 21. A pesticide was detected in less than 15 percent of shallow ground-water samples beneath residential areas, and the most frequently detected compounds were each detected in less than 10 percent of these samples.

Nitrate Concentrations in Shallow Ground Water Beneath Residential Areas Were Elevated, but Concentrations of Other Compounds Were Low

Although nitrate concentrations in shallow ground water beneath the residential areas in Pierce and Thurston Counties were elevated compared with those in ground water sampled by the study-unit survey (fig. 20), only one sample exceeded the drinking-water standard. Stable isotope measurements of nitrogen in nitrate suggest that septic-system effluent is a significant source of nitrate in unsewered areas. Additional nitrate sources are indicated by the similar concentrations of nitrate in sewered and unsewered areas (Inkpen and others, 2000). Some nitrate in ground water in unsewered areas and most nitrate in sewered areas is likely from the application of fertilizers to lawns and gardens.

Figure 22. Volatile organic compounds were frequently detected at low concentrations in shallow ground water beneath residential areas.

In spite of the vulnerability of the unconfined Fraser aquifer, only a few pesticides were detected (fig. 21) and these were at low concentrations (less than 0.2 microgram per liter) beneath residential areas developed since 1970. These results suggest that pesticides currently used in residential areas may pose little risk to ground water. However, it should be noted that several commonly used pesticides (glyphosate, for example) were not analyzed.

Although volatile organic compounds (VOCs) were detected in over 90 percent of shallow ground-water samples in residential areas, concentrations were low (fig. 22). Most detections were less than 0.05 μg/L,

Major Findings and none was above drinking-water standards or guidelines. Solvents, chlorinated by-products, and fuelrelated compounds were the most commonly detected VOCs.

High Nitrate Concentrations and Fumigant-Related Compounds Were Detected in Shallow Ground Water Beneath an Agricultural Area

Nitrate concentrations in more than half of the shallow ground water sampled for the agricultural land-use study exceeded the drinking-water standard. Major sources of nitrate are animal manure from poultry and dairy operations and fertilizers applied to crops. High concentrations of nitrate have persisted for many years in wells sampled in this aquifer (Hii and others, 1999), suggesting that land applications of manure and inorganic fertilizers are contributing nitrate to this aquifer at a sufficient rate to sustain these levels (fig. 23).

Figure 23. Nitrate concentrations in shallow ground water often exceeded the drinking-water standard (10 milligrams per liter), with high concentrations persisting for many years. Nitrate concentrations in deeper ground water, while elevated, generally met the drinking-water standard. Both the shallow and deeper ground water are used for domestic supplies.

Water Quality in the Puget Sound Basin Nitrate concentrations in ground water in the agricultural land-use study area commonly exceeded 10 mg/L, a concentration that can promote excessive plant growth in streams where this ground water discharges. A detailed analysis of water-quality changes along ground-water flow paths was conducted in this area (flow-path study area, p. 20). High nitrate concentrations persisted throughout much of the shallow aquifer. It was not until ground water reached the riparian zone of Fishtrap Creek that nitrate concentrations decreased to low levels (fig. 24). A decrease in nitrate concentrations in ground water concurrent with an increase in nitrogen gas (N2) concentrations in this zone is evidence that nitrate is being converted to N2 by denitrification (Tesoriero and others, 2000).

Figure 24. Nitrate concentrations in ground water remain high until water seeps through stream sediments that favor microbial denitrification. This process can effectively transform nitrate to nitrogen gas before the water discharges to the stream.

The most commonly detected volatile organic compounds in the agricultural land-use study area were associated with the application of fumigants to soils prior to planting. One or more fumigant-related compounds (1,2-dichloropropane, 1,2,2- trichloropropane, and 1,2,3-trichloropropane) were detected in over half of the samples. Each of these compounds is present in varying amounts in historically and/or presently used fumigants. Concentrations of 1,2- dichloropropane in water from two wells were above the drinking-water standard for this compound (fig. 25).

The amount of 1,2-dichloropropane and 1,2,3-trichloropropane in fumigant formulations has dropped substantially over the past few decades (Zebarth and others, 1998), while the amount of 1,2,2-trichloropropane has decreased only slightly. The relative amounts of these chloropropanes in ground water were compared with those present in fumigant formulations to determine the origin of these compounds in ground water (Tesoriero and others,

Figure 25. Fumigant-related compounds were detected frequently in shallow ground water in the agricultural landuse study area. Concentrations of 1,2-dichloropropane exceeded the drinking-water standard in two samples.

Figure 26. Based on the relative amounts of chloropropanes in samples, higher concentrations of 1,2- dichloropropane are likely derived from older fumigant formulations.

MTBE Was Rarely Detected in Ground Water in the Puget Sound Basin

in press). Results indicate that high concentrations of 1,2-dichloropropane in ground water are largely due to older formulations (fig. 26).

STUDY UNIT DESIGN

The Puget Sound Basin study was designed to address local and national goals of providing widely

GROUND-WATER CHEMISTRY

comparable water-quality data focused on stream chemistry, stream ecology, and ground-water chemistry.

Of the 12 major and numerous minor tributaries to the Puget Sound, sampling was concentrated in four representative drainage basins: the Nooksack and Green River Basins with varied land uses, the Thornton Creek Basin in a totally urban environment, and the Skokomish River Basin, which is mostly forested.

STREAM CHEMISTRY

Some sampling was done outside these areas for special studies, such as the study of pesticides in urban streams.

Wells sampled for the survey of ground-water quality in the Study Unit were distributed throughout the Puget Lowlands. Agricultural effects on ground-water quality and changes in quality along flow paths were evaluated using wells located in the lower Nooksack River Basin. Wells sampled in residential areas surrounding Olympia and Tacoma were used for determining urban land-use effects on shallow ground-water quality.

Stream ecology, bed sediment, and aquatic biota sampling was done at all the fixed stream-chemistry sites, and one or more of these types of samples were

Water Quality in the Puget Sound Basin

STREAM ECOLOGY

collected at 14 other sites. Two-thirds of the sites were within the Puget Lowlands, while the remainder were in other ecoregions (Black and Silkey, 1998). Most data were collected 1996–98.

GLOSSARY

Water Quality in the Puget Sound Basin Glossary

REFERENCES

Water Quality in the Puget Sound Basin References

APPENDIX—WATER-QUALITY DATA FROM THE PUGET SOUND BASIN IN A NATIONAL CONTEXT

Water Quality in the Puget Sound Basin Water-Quality Data in a National Context Water Quality in the Puget Sound Basin Water-Quality Data in a National Context Water Quality in the Puget Sound Basin Water-Quality Data in a National Context

National Water-Quality Assessment (NAWQA) Program Puget Sound Basin

U.S. Geological Survey Circular 1216

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