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5I Al 1' OI COI ~)I1 AIlp DUI IInNU 11. I AIl.M. <l.~v nova III III III III IIII III <br />DEPARTMENT OF NATURAL RESOURCES I I 999 <br />D. Monte Pascne, Executive Dn ecla. <br />11~IIN1~;1) I.ANU lil';(:I.AMA'I'lI1N <br />423 Centennial Building. 1313 Sherman Street <br />Denver, Colorado 80203 Tel. (303) 839-3567 <br />David C. Shelton <br />Director <br />March 20, 1981 <br />Mr. E. B. CribbS <br />460 S. Marion Parkway, Apt. 1304-C <br />Denver, Colorado 80209 <br />Dear Mr. Cribbs: <br />At your request we are forwarding the comments by the Division concerning <br />the alluvial valley floor determination for the Dorchester N1 Mine before <br />the entire adequacy statement is finished. <br />The Division must have a reconnaisance Level map at the unconsolidated stream <br />Laid deposits in the life of mine area and the adjacent area to fulfill this <br />main requirement. Yo1>r geologist could use a USCS topo, mapping alluvium <br />deposits greater than 50 feet in width. <br />Specifically the comments on the ACF determination were as follows: <br />1. Geomorphic Characteristics <br />Dorchester must identify the surface extent of all flood plains and associated <br />terraces underlain by unconsolidated material, in which are also found identifiable <br />stream channels. (Jarrow deposits along stream channels should be mapped until <br />they are no longer distinguishable on the base map. The mapping may exclude <br />isolated higher terraces that are separated aerially from the main valley floor. <br />The study area should be approximately 2 miles in radius of the permit area or <br />less if the applicant can justify. In general the study must include all areas <br />that could be impacted due to changes in quality and quantity of surface and <br />ground water. <br />2. Water Availability - Subirrigation <br />A map of the study area must be included that delineates the vegetation <br />types that would suggest Subirrigation. The map can be limited to those areas <br />identified as unconsolidated stream laid deposits. The map submitted indicates <br />"grassland" and "Riparian woodland". We need a list of the species that these <br />categories include. Depending on the species present, riparian woodland may <br />indicate that Subirrigation is taking place. <br />(cont'd) <br />