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2. STUDY AREA CHARACTERISTICS service area are available for a number of heavy metals that are harmful to aquatic life, such as zinc, cadmium, chromium, copper, lead, mercury, and nickel. Above a certain concentration, these metals have been determined to be toxic to aquatic life; thus, the Oregon DEQ has established a set of water quality standards for their protection. These are specified in OAR 340-41. When applicable, the standards consider water hardness (a measure of mineral salts dissolved in the water). A discussion of the heavy metals found in the Willamette River within the MWMC service area is presented below. Mercury has been found in some species of fish caught in the Willamette River and its major tributaries. The mercury in the fish is believed to come from natural volcanic and mineral sources and mining wastes in the headwaters of the Willamette River, and from human sources along the river. Fish with high levels of mercury are resident fish that eat other fish, such as largemouth bass and northern pike minnow. Anadromous fish that spend most of their adult life in the ocean do not have high mercury levels in their bodies. Potential sources of human-derived mercury include household products, food products, dental waste, wrecking yards (mercury-based automobile switches), fluorescent and compact lamps, and deposition of air-borne particles. In Lane County, perhaps one of the largest single sources of mercury in the Coast Fork Willamette River is runoff from the Black Butte mine, which was once the second largest mercury mine in Oregon until operations ceased in 1968. It is estimated that mine tailings on the site contain about 90,000 pounds of mercury, and that between 180 and 1,800 pounds of mercury is potentially mobilized into the environment each year (Weiss and Wright, 2001). The Oregon DEQ is currently conducting a TDML study of mercury in the Willamette basin. The Oregon Health Division has issued a health advisory for mercury in fish for the Willamette River. Ambient water quality monitoring of the Willamette River at four stations above, within, and below the Eugene-Springfield urban growth boundary suggests minimal mercury discharges from urban stormwater runoff and permitted point-source discharges. The average total mercury concentration upstream of the urban growth boundary is 0.00217 #g/L, while the average downstream of the urban growth boundary is 0.00232 #g/L. Effluent from the Eugene-Springfield wastewater treatment plant averages 0.00553/zg/L of mercury. These values are lower than the state chronic criteria standard of 0.012 #g/L. Flow-weighted averages for those days on which samples were collected are 60 grams per day (g/day) of mercury in the Willamette River, and 0.71 g/day of mercury in effluent from the treatment plant. The City of Eugene reported no statistically significant difference between mercury concentrations detected upgradient and downgradient of the urban growth boundary. An evaluation of the long-term concentration trends for metals by the City of Eugene found that arsenic was decreasing over time. This was the only analyte demonstrating a statistically significant trend. Arsenic, a metalloid, is included in this discussion because it is toxic to aquatic organisms. Its chronic criterion is 48 #g/L and it is hardness- dependent. The decreasing trend is significant at 1 percent; that is, there is a 1 percent probability that the observed trend is caused by random sample variability. The cause for the decreasing trend is unknown, although changes in land use or practices within the drainage basin could lead to this phenomenon. MWMC_2.0_REV23.DOC 2-25