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STREAM SURVEYS IN VICINITY OF URANIUM MILLS III. AREA OF URAVAN, SLICK ROCK, AND GATEWAY, COLORADO - AUGUST 1960 INTRODUCTION Purpose This is a report of one of three short-term field studies carried out in the vicinity of uranium processing mills in western Colorado and eastern Utah during August 1960. These studies were the initial undertaking of the Colorado River Basin Water Quality Control Project and were made for the pur- pose of determining the pollutional constituents contained in uranium mill discharges and the effects of these discharges on receiving waters in certain specific areas of the Colorado River Basin. The results of the other studies "are contained in reports of the Colorado River Basin Project (1)(2). General Description of the Area and Mill Processes Both the Dolores and San Miguel Rivers rise in the San Juan Mountains of fouthwestern Colorado. The San Miguel flows generally northwest some 80 miles from its headwaters to its c~nfluence with the Dolores. The Dolores takes a more "circuitous route, flowing southwest, northwest, and finally north for about 130 miles before the confluence. From this point, it flows north and northwest 67 miles to its meeting with the Colorado River south of C~sco~ Utah. Both rivers in the upper reaches flow through high mountain valleys which grad- "ually narrow into canyons in the downstream reaches. For much of the 60 miles between Slick Rock and its meeting with the San Miguel River, the Dolores River flows through canyons which make access difficult to impossible. Below the confluence its course meanders through a series of valleys and canyons with varying degrees of accessibility. Figure I indicates the immediate area in which this survey was conducted. River mileages for pertinent locations in the area are given in Table I along with population figures. The mouth of the Dolores River is in Utah at Colorado River mile 1024, 36 miles above Moab, Utah, the first community downstream from the mouth. In general appearance, the San Miguel River in the survey area above Uravan"might be considered as a typical mountain stream, swift, shallow, cool, and clear. Below Uravan its c@lor ranged from red-brown to yellow-brown. By contrast, the Dolores River from Slick Rock to the confluence of the two rivers wa"s -almost dry for part of the survey period. Public Health Service engineers making the survey felt that a large portion of the flow at Slick Rock was in underground strata. Below the confluence, the channel widens out, average water velocity is lower, and the stream is warmed somewhat in its journey to Gateway, Colorado. Both mills presently operating in the area under study are owned by Union Carbide Nuclear Company. The Uravan mill extracts uranium and vanadium from feed ores. Uranium recovery is by an acid leach and ion exchange process.