Oregon Water Quality Index Report for Middle Willamette Basin 

Water Years 1986-1995

For illustrative purposes, the Willamette Basin is separated into three parts: Upper Willamette, Middle Willamette, and Lower Willamette. The Upper Willamette includes the headwaters of the Coast and Middle Forks of the Willamette River, the McKenzie subbasin, and the mainstem Willamette River from the convergence of the forks to the point immediately upstream of the convergence with the Santiam River. The Middle Willamette extends to the Willamette River at Canby and includes the North and South Santiam, Yamhill, and Molalla-Pudding subbasins. The Lower Willamette extends to the mouth of the Willamette River and includes the Tualatin and Clackamas subbasins.

Water quality trends in the Middle Willamette Basin show mixed results. The Yamhill River showed significant improvement while the Pudding and Molalla Rivers showed a significant decrease in water quality. Comparing minimum seasonal Oregon Water Quality Index (OWQI) values (Table 1), water quality in the Middle Willamette basin ranges from excellent (North Santiam River site) to very poor (Salt Creek site). Water quality data were routinely collected by the DEQ Laboratory in 1986-1995. Special intensive studies were performed in the Yamhill subbasin in 1986-1992 and on the Pudding River in 1989-1992.

Water quality is commonly impacted by the introduction of organic matter to streams. The presence of organic matter increases biochemical oxygen demand, which means less dissolved oxygen is available for aquatic life. The introduction of untreated animal or human waste increases the possibility of bacterial contamination of water, increasing the risk of infection to swimmers. Eutrophication is the process of enrichment of water with nutrients, mainly nitrogen and phosphorous compounds, which results in excessive growth of algae and nuisance aquatic plants. It increases the amount of organic matter in the water and also increases pollution as this matter grows and then decays. Employing the process of photosynthesis for growth, algae and aquatic plants consume carbon dioxide (thus raising pH) and produce an overabundance of oxygen. At night the algae and plants respire, depleting available dissolved oxygen. This results in large variations in water quality conditions that can be harmful to other aquatic life. While natural sources of nutrients can influence eutrophication, the introduction of nutrients strengthens the process. Sources of nutrients include wastewater treatment facility discharge and faulty septic systems, runoff from animal husbandry, fertilizer application, urban sources, and erosion. High water temperatures compound the decline in water quality by causing more oxygen to leave the water and by increasing the rate of eutrophication. Removal of streamside vegetation, among other factors, influences high stream temperature and, via erosion, increases sedimentation of streams.

Table 1. Seasonal Average OWQI Results for the Middle Willamette Basin (WY 1986 -1995)

Summer: June - September; FWS ( Fall, Winter, & Spring): October - May
Scores - Very Poor: 0-59, Poor: 60-79, Fair: 80-84, Good: 85-89, Excellent: 90-100

South Santiam Subbasin

The South Santiam Subbasin drains lands primarily used for agriculture and logging operations. DEQ Laboratory routinely monitors water quality at the most downstream bridge in the subbasin, the South Santiam River at Highway 226 near Crabtree. Water quality at this site represents the cumulative affects of upstream nonpoint and point sources of pollution, including municipal sewage treatment plants (STPs), at Sweet Home and Lebanon. Water quality in the South Santiam River is impacted by high levels of fecal coliforms, total phosphates, and biochemical oxygen demand. This indicates the introduction of organic materials to the water. High levels of fecal coliform can be associated with the presence of untreated human or animal waste. These high concentrations occur primarily in the wet fall, winter, and spring seasons, indicating runoff from fields, ditches, and storm drains carrying organic material to streams and rivers in the subbasin. Frequent overflows from the Sweet Home STP during storm events may also contribute to these conditions. Water quality in the South Santiam River and subbasin is generally good in the fall, winter, and spring (Table 1). During the summer, runoff is usually not present, but treated STP discharges are present. Low river flows can concentrate contaminants in the water. Total phosphates reach moderately high concentrations during the summer, but these conditions are infrequent. As a result, average OWQI scores in the South Santiam River are excellent during summer (Table 1).

North Santiam Subbasin

Like the South Santiam Subbasin, the North Santiam Subbasin drains lands primarily used for agriculture and logging operations. DEQ Laboratory routinely monitors water quality at the most downstream bridge in the subbasin, the North Santiam River at Greens Bridge. Water quality at this site represents the cumulative affects of upstream nonpoint and point sources of pollution, including the Stayton STP. Water quality in the North Santiam River is occasionally impacted by moderately high levels of fecal coliforms and biochemical oxygen demand. This indicates the introduction of organic materials to the water. High levels of fecal coliform can be associated with the presence of untreated human or animal waste. These high concentrations occur primarily in the wet fall, winter, and spring seasons, indicating runoff from fields, ditches, and storm drains carrying organic material to streams and rivers in the subbasin. Due to the low frequency and low severity of these impacts, water quality in the North Santiam River is generally excellent throughout the year (Table 1).

Yamhill Subbasin

Water quality in the Yamhill Subbasin is influenced by logging, intensive agricultural operations, municipal sewage treatment plants, and natural hydrological conditions. Because of the flat gradient of the primary streams in the subbasin, water flows slowly. Point and nonpoint source pollution is slowly moved to the Willamette and is not readily assimilated.

Salt Creek drains the hills north of Dallas and meanders through Amity and Whiteson before entering the South Yamhill River. The Amity STP discharges to Salt Creek upstream of the monitoring site in Whiteson at Highway 99W. Salt Creek contains naturally high levels of dissolved solids, or salts. This naturally occurring concentration affects OWQI results. However, other impacts on water quality are so severe that total solids impacts are moderate in comparison. During summer, flows decrease and pollutants tend to concentrate. During dry years, these conditions can extend into early November. Very high concentrations of total phosphates fuel eutrophication at the monitoring site on Salt Creek at Whiteson, producing algae. Respiration and die-off of the algae contribute to high levels of biochemical oxygen demand and extremely low concentrations of dissolved oxygen. Precipitation in the fall, winter, and spring brings field runoff, loading the creek with nutrients. High concentrations of total phosphates and nitrate nitrogen in the creek may reflect the loss of fertilizer from agricultural operations. The Amity STP may also contribute to high concentrations of nutrients (phosphates and nitrogen) throughout the year. On the average, water quality is very poor throughout the year (Table 1).

The South Yamhill River drains the Coast Range west of Willamina, receiving impacts from nonpoint sources (logging operations) and point sources (log ponds and Sheridan STP) before meandering across the valley floor. Agricultural operations are the primary source of pollution from Sheridan to the mouth of the South Yamhill River east of McMinnville. The McMinnville STP was a significant source of pollution in the lower South Yamhill River and mainstem Yamhill River throughout the reporting period (water years 1986-1995). DEQ Laboratory routinely monitors water quality in the South Yamhill River at Highway 99W, upstream of McMinnville. This site measures non-point pollution in the South Yamhill River. Monitoring of the South Yamhill River indicates that water quality is frequently impacted during the fall, winter, and spring. High levels of total phosphates and fecal coliform regularly impact water quality, indicating the presence of fertilizers and/or untreated human or animal waste. Land use in the area indicates that runoff from agricultural operations impacts water quality. Occasional high concentrations of nitrate and ammonia nitrogen support this conclusion. High concentrations of total solids also impact water quality at this site, but this may be due to influence from Salt Creek. Low precipitation levels and low flows in the summer mean less impact from the above sources. However, high temperatures and high concentrations of total phosphates and total solids occasionally impact summer water quality conditions. On the average, OWQI scores are poor in the fall, winter, and spring and fair in the summer (Table 1).

The North Yamhill River drains similarly used lands but in a smaller area than the South Yamhill River. The North Yamhill River meanders past the cities of Yamhill and Carlton before converging with the South Yamhill River east of McMinnville. Water quality is occasionally impacted by the Yamhill and Carlton STPs during wet weather. Non-point sources of pollution associated with agricultural operations have a greater and more consistent impact on water quality in the North Yamhill River at the monitoring site at Poverty Bend Road. Consequently, high levels of fecal coliforms, total phosphates, nitrate and ammonia nitrogen, total solids, and biochemical oxygen demand depress water quality throughout the year. High temperatures also limit water quality during the summer. On the average, OWQI scores are poor throughout the year (Table 1).

Water quality results from the Yamhill River at Dayton reflect the cumulative impacts from the South, North, and mainstem Yamhill River. Significant point sources include the McMinnville STP, dairy operations, and fertilizer plant operations. High concentrations of fecal coliforms, total phosphates, total solids, biochemical oxygen demand, and nitrate and ammonia nitrogens impact water quality throughout the year. This indicates the presence of organic materials and untreated animal waste. Untreated human waste may also be present as a result of faulty septic systems or of STP overflows during storm events. Urban and rural runoff and erosion also contribute to these conditions. However, it is clear that point source pollution presents a serious challenge to water quality. The abundance of nutrients and high water temperatures in the summer strengthen the eutrophication process. Extremely high pH and dissolved oxygen supersaturation were measured at this site during summer months. It is likely that very low levels of pH and dissolved oxygen are present in the early morning hours as algae respire. On the average, OWQI scores are very poor in the summer and poor in the fall, winter, and spring (Table 1).

Figure 1. Trend Analysis Results for the Yamhill River at Dayton

The Yamhill River Total Maximum Daily Load (TMDL) was established in 1990 to address point and nonpoint source pollution in the Yamhill River. In 1991, the Carlton STP completed construction on a wastewater storage lagoon. This enabled the STP to store wastewater through the summer for discharge during the fall, when precipitation and North Yamhill River level rises. The severity and frequency of significant water quality impacts on the North and mainstem Yamhill Rivers noticeably lessened beginning in 1991. The North Yamhill River will likely show a significant long-term increase in water quality in the near future. Because the Yamhill River at Dayton was more severely impacted prior to 1991, a significant improvement in water quality has occurred (Figure 1). The McMinnville STP brought a new wastewater treatment facility on-line in 1996, so further improvements to water quality are expected.

Molalla-Pudding Subbasin

The Molalla and Pudding Rivers have little in common besides sharing drainage of a subbasin. The Pudding River's headwaters are in the low-lying Waldo Hills east of Salem. For nearly all of its length, the Pudding River slowly meanders through prairies that are used for intensive agricultural operations before discharging about one-and-a-half miles above the mouth of the Molalla River. Water quality in the Pudding River is poor compared to the Molalla River, which drains the Western Cascades of southwestern Clackamas County. The Molalla River descends for nearly half its length until it enters Dickey Prairie, where the river begins to meander through agricultural lands until it reaches its mouth at the Willamette River. Due to the moderate gradient of the Molalla River, the river flows faster than the Pudding River, allowing it to better assimilate water quality impacts. The Pudding River therefore receives more attention in the form of water quality monitoring.

Intensive monitoring studies were performed on the Pudding River in 1989-1992 to establish the Pudding River TMDL, which was completed in 1994. Four sites were regularly monitored during that period and two of those, Pudding River at Highway 211 in Woodburn and at Highway 99E in Aurora, remain on DEQ Laboratories' regular monitoring network. Water quality is impacted similarly at all of the monitoring sites, but the intensity and frequency of these impacts differed depending on the sources. High concentrations of nutrients (total phosphates and nitrate and ammonia nitrogen), fecal coliform, and biochemical oxygen demand throughout the year indicate the presence of organic material in the form of untreated human or animal waste and residual fertilizer in the water. High concentrations of total solids throughout the year indicate erosion processes during the wet fall, winter, and spring seasons and concentration of dissolved and suspended solids in the low-flow summer months. High temperatures and low dissolved oxygen concentrations indicate excessive eutrophication occurring in the summer. Water quality is best at the most upstream site at Highway 214 and worst at Highway 211, just downstream of the Woodburn STP. Water quality improves with distance from the Woodburn STP.

The most upstream site was the Pudding River at Highway 214, upstream of all significant point sources of pollution. On the average, OWQI scores at the Pudding River at Highway 214 were poor during the summer and very poor during fall, winter, and spring (Table 1). Agripac Industries discharges food processing waste to the Pudding River just downstream of the Highway 214 monitoring site. The river meanders through four-and-a-half river miles of agricultural lands before passing the Woodburn STP and the next monitoring site at Highway 211 in Woodburn. The Woodburn STP is a major point source of pollution to the Pudding River and is in the process of planning new sewage treatment facilities to comply with the Pudding River TMDL. The intensity and frequency of water quality impacts was greatest at this site. Average OWQI scores were lower here than for any of the other sites on the Pudding River, very poor throughout the year (Table 1). The Pudding River meanders through five more miles of agricultural lands and is joined by a major tributary, Butte Creek, before reaching the next monitoring site at Bernard Road in Whiskey Hill. Water quality at Whiskey Hill is slightly better than at the Woodburn site, although it was still very poor throughout the year (Table 1). A significant decrease in water quality in the Pudding River at Whiskey Hill was seen during the period of 1989-1992 (Figure 2). Trends are calculated and reported using a ten water year period (water years 1986-1995), therefore no significant trend is reported for the Pudding River at Woodburn. However, calculation of significant trends for the Pudding River at Woodburn during the period of 1989-1992 reveals a significant decreasing trend. Therefore, the decreasing trend at Whiskey Hill may be attributed to increasing pressure on the Woodburn STP and the consequent decreasing water quality in the Pudding River during that time. The Pudding River meanders for nine river miles between Whiskey Hill and the last monitoring site at Highway 99E in Aurora. As distance from the Woodburn STP increases, so do OWQI scores. Average OWQI scores for the Pudding River at Aurora are slightly higher than at Whiskey Hill, with poor conditions during the summer and very poor conditions during the fall, winter, and spring (Table 1).

Figure 2. Trend Analysis Results for Pudding River at Whiskey Hill

As previously mentioned, the Molalla River has better water quality than the Pudding River. The absence of major point sources and the presence of more favorable hydrologic conditions enable the Molalla River to more readily assimilate pollution. The Molalla River at Canby does experience elevated levels of total phosphates, nitrate and ammonia nitrogen, fecal coliform, and biochemical oxygen demand in the fall, winter, and spring. High temperature, high biochemical oxygen demand, and low dissolved oxygen concentration are evident in the low flow summer months. This is the result of non-point source pollution occurring in the low-lying agricultural areas in the lower half of the river. It appears that these impacts have increased over time, as water quality significantly declined during the reporting period (Figure 3). On the average, OWQI scores are good throughout the year (Table 1).

Figure 3. Trend Analysis Results for Molalla River at Canby

Middle Willamette Subbasin

Middle Willamette Subbasin water quality is primarily influenced by extensive agriculture, although municipal and industrial point sources and urban non-point sources contribute to water quality conditions as well. The most downstream site in the Upper Willamette Subbasin is at Highway 20 in Albany (see Upper Willamette Subbasin report). The Willamette River receives many inputs before reaching the most upstream site in the Middle Willamette Subbasin at Salem. After leaving the Albany monitoring site, the Willamette River receives discharges from the Albany STP and several industrial point sources, then converges with the Santiam River. The Santiam River brings drainage from the South and North Santiam Subbasins and receives discharge from the Jefferson STP. The Willamette River then receives drainage from the Luckiamute River and flows through the Ankeny and American Bottoms and around the Salem Hills, then past the cities of Monmouth and Independence, which discharge municipal wastewater to the Willamette River. The river receives discharge from Rickreall Creek, which carries discharge from the Dallas STP. The Willamette River flows past industrial waste ponds before passing the monitoring sites at the Marion Street Bridge and Salem Railroad Bridge.

During fall, winter, and spring, the Willamette River at Salem is impacted by high concentrations of fecal coliform, total phosphates, and nitrate and ammonia nitrogen. High total solids and biochemical oxygen demand also impair water quality at this site. This indicates the introduction of organic materials, untreated human or animal waste, or residue from agricultural operations. These conditions occur primarily in the fall, winter, and spring, when heavy precipitation increases erosion and runoff. Overflows frequently occur at the Dallas STP during periods of heavy precipitation. On the average, OWQI scores for the Willamette River at Salem are fair in the fall, winter, and spring and good in the summer (Table 1).

The Willamette River receives discharge from the Salem STP and passes through Mission Bottom before the crossing of the Wheatland Ferry. At this site, the river is impacted by high concentrations of fecal coliform, total phosphates, nitrate and ammonia nitrogen, and biochemical oxygen demand with additional influence from high total solids. Overflows frequently occur at the Salem STP during periods of heavy precipitation. Agricultural operations in the Mission Bottom area increase the concentration of nutrients (phosphates and nitrogen) in both surface and ground water. Both sources are likely to contribute untreated animal or human waste and other organic material during periods of heavy precipitation. Summer water temperatures are higher at Wheatland Ferry than at Salem. OWQI scores at Wheatland Ferry are fair throughout the year (Table 1).

The Willamette River continues to meander through agricultural lands and receives drainage from the Yamhill River. At this point the gradient of the Willamette River is nearly flat and flow is sluggish. This stretch of the river is known as the Newberg Pool. The pool is monitored at the Newberg Bridge (Highway 219), downstream of the Dundee and Newberg STPs and Smurfit Newsprint industrial discharge. Like the two Willamette River sites upstream, water quality is impacted by high concentrations of fecal coliform, total phosphates, nitrate and ammonia nitrogen, and biochemical oxygen demand with additional influence from high total solids. Summer water temperatures are relatively high. Because of the slow flow in the pool, the Willamette River is less likely to assimilate pollution and is more prone to variations in water quality. On the average, OWQI scores for the Willamette River at Newberg Bridge are fair in the summer and poor in the fall, winter, and spring (Table 1). Skeletal deformities and lesions have been documented in a significant number of fish in the Newberg Pool. The Oregon Water Quality Index was designed to measure general water quality conditions and does not reflect the presence of toxic compounds or other special conditions.

The Willamette River flows through Wilsonville collecting discharge from the Wilsonville STP, drains agricultural lands, and receives drainage from the Molalla River before the Canby Ferry crossing. The Willamette River at the Canby Ferry is impacted by high concentrations of fecal coliform, total phosphates, and nitrate and ammonia nitrogen. High total solids and biochemical oxygen demand also impair water quality at this site. These conditions occur primarily in the fall, winter, and spring, when heavy precipitation increases urban and rural runoff and erosion. High water temperature and high concentrations of total phosphates occur in the summer. Average OWQI scores at the Willamette River at the Canby Ferry are fair in the summer and poor in the fall, winter, and spring (Table 1).

Acknowledgment: Software used for trend analysis was the WQHydro package developed by Eric Aroner of WQHydro Consulting.

References

Oregon Department of Environmental Quality, Water Quality Division, 1988. 1988 Oregon Statewide Assessment of Nonpoint Sources of Water Pollution. Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1988. Oregon's 1988 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon. .

Oregon Department of Environmental Quality, Water Quality Division, 1990. Oregon's 1990 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1992. Oregon's 1992 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1994. Oregon's 1994 Water Quality Status Assessment Report (305 (b) Report). Portland, Oregon.

Written by Curtis Cude, Oregon Department of Environmental Quality, Laboratory Division