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III IIIIIIIIIIIIIIII o0~0~,2~,12t,o, • LORENCITO CANYON MINE ALLUVIAL VALLEY FLOOR INVESTIGATION SECTION 1 -INTRODUCTION Lorencito Coal Company is proposing to perform surface coal mining operations east of Weston, Colorado at the Lorencito Canyon Mine site. Operations will include multiple underground mines and one surface mine above Jeff Canyon. Streanilaid deposits of the South Fork of the Purgatoire River and the Purgatoire River circumscribe the operation on the west and the north of the proposed permit area. Colluvial/alluvial deposits are found along Lorencito Canyon, Cow Canyon, and in limited locations along Little Pine, Chimney, and Alamosa Canyons. There are no planned disturbances from the proposed operation in the watersheds contributing to the South Fork of the Purgatoire River. Consequently, this investigation is not evaluating the South Fork. The main access road enters the permit area crossing the Purgatoire before ascending into Lorencito Canyon to the load-out. The rail spur will run southwest across the Purgatoire River alluvium above the confluence of Lorencito Canyon and the river before running approximately 2600 feet along terraces on the west side of Lorencito Canyon. The PI and P2 portals are located approximately three miles south of the confluence of Lorencito Canyon and the Purgatoire River. A haul road will connect this site and the ]oadout. Two portal areas, and the • haul road connecting them, are proposed in Cow Canyon: the P3 portal is located less than a mile from the confluence with the Purgatoire while the Rl and R2 portals are located more than three mites upstream. Colluvial-alluvial deposits of limited extent in Little Pine, Chimney, and Alamosa Canyons underlie portions of the Pl mine. Colluvial-alluvial deposits underlie development mining in P2 in the upper reaches of Lorencito Canyon. The R3 and R4 portals proposed for the second permit term are located in an upper tributary of Chimney Canyon and underlie the upper reaches of this canyon. This investigation evaluates the Purgatoire River and Lorencito, Cow, Alamosa, Chimney, Puertecito, and Jeff Canyons for alluvial valley floor status. Information has been compiled from the geologic and soils literature and 1996 field investigations on subsurface stratigraphy, surface water, groundwater, soils, vegetation and land use. SECTION 2 -METHODOLOGY Streamlaid deposits were mapped from the Little Pine and Weston USGS 7.5 minute quadrangles and field-verified October 7 though 10, 1996. Alluvial wells were established in March 1996. Four wells were drilled in Lorencito Canyon, two wells were drilled in Cow Canyon, and one well each was drilled near the mouths of Alamosa, Chimney, Puertecito and Jeff Canyons. Lithologic and well completion logs can be reviewed in the Geology and Groundwater Technical Reports. Field parameters (water level, pH, EC, and temperature) were being acquired monttily. Full suite • water quality characterization occurred quarterly. .4vL4751December 13, 1996