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Mr. Peter V. O'C. .ior Page 5 September 23, 1985 5. The use of underground mine workings to store process water is e common practice in the minerals industry. Many of the mining and milling operations that are currently active in Colorado use under- ground mine workings for this purpose, as well as to dispose of mill tailings. The decision to store water for milling purposes in under- ground mine workings during the period between November 1 and March 31 was arrived at after considering the geology and hydrology of this area. Among the geologists with many years of field experience and working knowledge of the surface and sub- surface geology of this area who were consulted are: Russell R. McLellan (BSc., MSc.), Charles A. Steen (BSc.), Richard T. Heard (BSc.), Allan G. Bird (BSc., MSc.) and William W. Atkinson (BSc., MSc., Ph.D.). Afield examination of this entire area was under- taken by Theodore M. Zorich (BSc., MSc., Ph.D.) and Martin A. Sailus (BSc., MSc.), who are experienced water engineers and hydrologists. The underground water storage plan was also reviewed by the Board of Directors of the Hand Ditch Company and their legal representatives. The Gold Hill Ventures Limited Partnership did not purchase these shares in the Lett Hand Ditch Company with the intention of building a costly pumping station and water pipe- line in order to observe how fast this exper-sive water can flow out of underground mine workings. In fact, the proposed underground storage areas represent a secure and discrete location for storing the water that will be necessary to carry this milling operation through the winter months. The alternative to this plan is the construction o[ several costly and aesthetically unattractive metal or concrete water tanks that will be built on the north sid4 of County Road No. 52. The accompanying geologic map of this area was taken from E.N. Goddard's "Preliminary Report on the Gold Hill Mining District, Boulder County, Colorado". It indicates the location of the Wynona, Who Do, and Cash veins (shown in blue) in relation to the Hoosier Reef (shown in red). The following geologic summary was taken from E.N. Goddard's works on this mining district. The Gold Hill Mining district is almost entirely within the northern part of a small oval shaped batholith that has an areal extent of about 100 square miles. The batholith ranges in composition from quartz monzonite through granodiorite to granite. The Precambrian Boulder Creek~e is the chief wallrock of t veins ~ '~ distriof, an~the foliation in~it a g~anTte has had an important influ- 1 coca on the Vend of many of the fissure veins in the district. ~` ~' Within the Boulder Creek granite are strong, persistent Laramide faults or breccia reefs which are known locally as "dikes". The importance of the breccia reefs on the distribution of the ore deposits has long been recognized. The Hoosier Reef is the. most important structural feature in the district. It is prominently exposed east of Gold Hill in Cash Gulch, and on Hoosier Hill south of Summerville. in Cash Gulch the reef strikes N35°W and dips from 68° to 70° to the northwest and forms resistant, silicified outcrops