1985-12-22_HYDROLOGY - M1984049 - Laserfiche WebLink

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consist of lenses of angular talus material intercalated in • a matrix of silts and fine sands. These fine sediments appear to be consist mainly of old tailings which have been deposited by flood waters from Eurel<a and possibly as far away as Animas Forks. The characteristic grey and ochre color and the ubiquitous presence of carbonate evaporite tends to confirm the identity as tailings, (sodium carbonate and time are used extensively in selective flotation). The SunnYside Mill was located at Eureka, 3.6 miles upstream. This mill processed as much as 1000 tons of ore per day for more than 20 years, yet little tailings remain in evidence at the site. Indeed, sediment collected from monitor well M- 20, located near the east shore of the Animas River 300 feet west of the new pond, is deep ochre yellow, strongly resembling or.idized mill tailings. The high metal and sulfate content of water samples collected from this well support the conclusion that this area is underlain by old mill tailings. Bedrocl: was not encountered in any of the 41 borings. These test holes averaged 30 feet in depth with two being drilled to depths in er.cess of 50 feet. Graphic logs of the current test holes are found on Plate II. INJECTION WELLFIELD • The wellfield consisted of 12 injection wells and 12 monitor wells clustered in 4 patterns of 3. Three patterns were located on the new pond and one on the old pond. (Refer to Plate I, in pocket). Monitor wells were spaced 150 feet apart along a north-south line. An injection well was placed 10 feet east of each monitor well. The injection monitor wells were identified as MIA, M16, M1C, M2A, M2B, M2C, M3A, M3B, M3C, M4A, M4B and M4C. The injection wells were drilled 5 feet deep and cased with 4" diameter perforated pvc pipe (SDR). This was later replaced with 1 1/4" diameter slotted pvc casing. The pvc casing had 0.020" slots on 0.25" spacings providing 4% open area. The annulus between the well bore and the casing was packed with -#B mesh washed sand. The monitor wells were constructed by drilling with 6 5/8" diameter hollow stem augers to a point estimated to be 5 feet above the base of the tailings. This estimate was based upon the logs of the drilling completed in 1980 by Sutherland, Ricketts and Rindahl. When the required depth was reached, the center bit of the auger was removed leaving the auger flights in the hale to serve as temporary casing. A casing string consisting of a 2" diameter stainless steel • -5-