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•~ ~ <br />Suite 200, 740 50. Cobratlo BhG. <br />P. O. Boi 37583, Terminal Anne= <br />Denver, Cobratlo 80217 <br />--. Tekylwne 303.753-8600 <br />December 11, 1980 <br />Northern <br />Coal <br />Company <br />Mr. Jim Herron <br />Colorado Division of Mined Land Reclamation <br />723 Centennial Building <br />1313 Sherman Street <br />Denver, Colorado 80203 <br />RE: Hydrologic Monitoring of Curtis Creek <br />Dear Mr. Herron: <br />J <br />We have been reviewing the hydrologic situation relative to mining <br />under Curtis Creek and have developed a program for hydrologic and <br />subsidence monitoring which we feel will satisfy your requests. <br />First, I would like to outline what we perceive to be, as a result <br />of our meeting with the CMLR staff, the four primary issues to be <br />addressed in this monitoring program. They are: (1) subsidence <br />monitoring; (2) monitoring of volume of water encountered in the <br />mine; {3) surface water flow monitoring above the subject area; and, <br />(4) ground water monitoring. I would like to take each of these <br />issues and discuss in detail why it is important and how Northern <br />intends to address each particular monitoring parameter. <br />r~ <br />I. Subsidence Monitoring <br />As we have stated earlier, initially four main entries will be <br />advanced to the east under State Highway 13 and Curtis Creek, <br />The main entries will be used to transport people and materials <br />for the life of the mine. In order to maintain the integrity <br />of the entries, large barrier pillars will be left on either <br />side of the main entries. In a normal situation, main entry <br />pillars would be removed after mining is completed as the equip- <br />ment is pulled from the mine. Aowever, in this instance, in <br />order to insure that the geologic structure underlying Curtis <br />Creek is not altered, pillars will not be removed under Curtis <br />Creek or State Highway 13/789. {See attached map ME-7960-10-1/2 <br />which depicts the location of pillars under Curtis Creek and <br />State Highway 13/789.1 <br />~, <br />The concept of leaving the pillars in place under Curtis Creek <br />and the highway will insure that no subsidence will occur in <br />this area which will adversely affect either Curtis Creek or <br />the State Highway. In order to monitor for even the slightest <br />