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INTRODUCTION <br /> <br />The Eagle #5 and #6 Mines are underground coal mines, located approximately seven miles south of Craig, <br />Colorado (Figure 1). The aerial extent of the underground workings in the #5 Mine was approximately 2,040 <br />acres at the end of 1990 and since active mining in the #5 Mine ceased in 1990 this acreage has not <br />changed. Approximately 275 acres had been mined in the #6 Mine at the end of 1991. The #5 Mine is still <br />used for access to the #6 Mine. The coal extraction is from the Cretaceous Age Williams Fork Formation, <br />"F" Seam in the #5 Mine and the "E" Seam in the #6 Mine. <br />Hydrologic monitoring has been conducted a[ the mine site since 1980. This report presents the results of <br />year 1991 monitoring. The complete 1983 through 1991 monitoring is presented in the respective Annual <br />Reports for each calendar year. <br />The hydrologic monitoring is divided into two parts: 1) groundwater, and 2) surface water. The monitoring <br />locations are shown in Figure 2 and summarized in Table 1. The water quality monitoring Includes field <br />parameters (fable 2), water quality parameters (fable 3), and NPDES parameters (fable 4). The water <br />quality samples are analyzed by ACZ Laboratories, Inc., Steamboat Springs, Colorado, a USEPA certified <br />laboratory. This report includes data collected specifically to meet requirements of the Colorado Mined Land <br />Reclamation Division (CMLRD), as well as data collected to meet the requirements of the Colorado <br />Wastewater Discharge Permit System (NPDES permits). A complete listing of atl the water quality data is <br />submitted separately. <br />GROUNDWATER MONITORING <br />Bedrock <br />Three sandstone aqu"rfers are monitored at the site. There are, in ascending order: Trout Creek Sandstone <br />(2 wells), Middle Sandstone (6 wells), and Twentymile Sandstone (3 wells). The #5 and #6 Mines are <br />• 1 <br />