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002521 1. Introduction ',,~ " i. INTRODUCTION The San Juan River Seven Year Fisheries Research Plan was initiated in 1990 to guide the collection of data believed necessary for the conservation of the San Juan River's native fish fauna. Included among the Plan's goals was a long-tenn water-quality program, the first step of which was a water quality and contaminants review. The review was to synthesize existing water quality and contaminants infonnation for the San Juan River and its tributaries in order to identify research needs. Specifically, the review was designed to meet the following objectives: 1) To compile and interpret existing water quality and contaminants information into a single document to guide investigations of chemical hazards to San Juan River endemic fishes. 2) To determine any geographic variation in water quality parameters and contaminants in the San Juan River basin. 3) To identify important water quality and contaminant data gaps as a focus for determining needed water quality and contaminant assessments in the San Juan River basin. The review was undertaken as a joint effort between the University of New Mexico (UNM) and the New Mexico Ecological Services Office of the U.S. Fish and Wildlife Service (FWS). UNM assumed responsibility for the compilation of data related to contaminants and water quality, while the FWS was responsible for interpreting the data, identifYing any important water quality and contaminants needs, and providing advice which may direct future research in this area. This report constitutes the first portion of the review, the compilation of existing information. 2. STUDY AREA Data included in this review were collected in the San Juan River basin, which is located within the Upper Colorado River basin and comprises a drainage area of 24,900 mF (Figure 1) (loms et al. 1965, Melancon et al. 1979). For this report, the basin included the area drained by the San Juan River from its headwaters to Lake Powell, as well as all of the river's tributary streams. Major tributaries are Navajo, Piedra, Los Pinos, Animas, La Plata, Chaco, and Mancos rivers; McEhno, Montezuma, and Chinle creeks; and Cottonwood Wash (Figure 2) (Bureau of Reclamation et al. 1992). The states from which data were included are New Mexico, Colorado, and Utah; Arizona contains only the headwaters of Chinle Creek, whose effect on the basin's water quality was deemed negligible. It is important to note that the watershed termed the San Juan River basin is not eqnivalent to the geologic San Juan basin, which is a larger structural depression covering approximately 30,000 mi2 of northwest New Mexico and southwest Colorado (Figure 3) (Melancon et al. 1979, Stone et al. 1983). In this report all references to the basin will refer to the San Juan River basin unless otherwise noted. 2.1 SOILS AND GEOLOGY The soils of the San Juan River basin have been principally developed by weathering of the underlying rocks. As a resnlt of the arid climate, the soils are poorly developed, retaining many of the geochemical characteristics of the parent rocks. The San Juan Mountains, where the San Juan, Animas, Los Pinos, Piedra, and Navajo rivers head, are composed chiefly of Tertiary age volcanic rocks. The rest of the basin is principally underlain by late Paleozoic to Recent sedimentary rocks (Ioms et al. 1965).