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• +~ III IIIIIIIIIIIII III <br />999 <br />CanonleEnvironmental <br />January 22, 1994 <br />Mr. Luke Russell <br />Corporate Manager, Environmental Affairs <br />650 California Street <br />San Francisco, CA 94108 <br />RE:Buildog ~~iine Hvurolooic Evaiuation <br />Dear Luke: <br />Cancn~? En nronm=oral Se r::ces C,:.r <br />333 Haggert, Lane <br />Bo-eman. Pdo nr.ana 597 LS <br />Phon? 306 686~5~k96 <br />Fa:: 4G6~686 972~t <br />This letter responds to a January 5, 1994 correspondence from Allen Sorenson, State <br />of Colorado Division of Minerals and Geology, regarding the Hydrologic Evaluation of <br />Bulldog Mine, File No. M-77-215. In his letter, Mr. Sorenson requested justification <br />for the selection of a Curve Number of 55 used in the hydrologic evaluation. <br />During a September 9, 1993 telephone conversation with Mr. Ron Rigenbaugh, Soil <br />Conservation Service, Monte Vista office (719-852-5114), I was informed my Mr. <br />Rigenbaugh that there is not a published soil survey for the Bulldog Mine area. <br />However, he did tell me that the information he had in his office indicated that the <br />hydrologic soil group in the general area of the Bulldog Mine is a type "B". <br />Using this information and field reconnaissance of the land use and condition of <br />vegetation, I referred to the SCS Engineering Field Manual, Section 2, Table 2-3c <br />(copy attached) to determine the Curve Number. Using the Pinyon-juniper and grass <br />understory cover type, average runoff condition, and good hydrologic condition <br />(greater than 70 percent ground covers, the Curve Number for a type "8" soil group <br />shown in Table 2-3c is 41. Allovring fcr small areas of fair and poor hydrologic <br />condition and a safety factor, I increased the curve number to 55. <br />If you or Mr. Sorenson have any other questions regarding this evaluation, please <br />contact me at (406) 586-9496. <br />Sincerely, <br />~,r~~ <br />U c~• ~'/ / ~~\/ <br />Scott Benowitz. P.E. <br />