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' AN ANALYSIS OF POSSIBLE GROUND WATER AND SURFACE WATER IMPACTS ' RESULTING FROM THE LYONS - ROCKIN' WP GRAVEL PIT ' CHAPTER 1 -INTRODUCTION ' 1.1 Overview The Lyons -Rockin' WP Sand and Gravel Pit is operated by Western Mobile, Inc. (WMI), located southeast of Lyons, Colorado as shown in Figure 1. The Lyons -Rockin' WP Pit is an on-going sand ' and gravel mining operation. WMI previously received permits from the Colorado Department of Minerals and Geology (DMG) to mine certain areas defined as the Rockin' WP Nortn Pit (Permit ' No. M-74-015) and the Miller Pit (Permit No. M-32-034). In June, 1999, WMI filed art amendment to the existing permit with the DMG to allow mining on new lands adjacent to tl;e previously t pem~itted lands. The boundazies of the existing and new permitted lands aze shown in Figure 1. The Lyons -Rockin' WP Pit (both the existing and new permitted lands) is situated upon the alluvial ' plain of the St. Vrain River. As such, the mined area is comprised of alluvial material, deposited over time by the surface water stream system. In the area of the pit, the alluvial material is ' hydrologically connected to the St. Vrain River and the South Branch of the St. Vrain River (South Branch). The alluvial material has formed a shallow aquifer, capable of storing v<ater which is ' periodically rechazged by the streams during periods of high flows and which periodicrlly discharges water back to the streams during periods of low flows. In addition to serving a storage function in relationship to the stream system, this local aquifer provides a water supply to a number of residences in the area which utilize low capacity wells to supply their water needs. ' 1.2 The Mining Operation t The amended permit application for the Lyons -Rockin' WP Pit calls for a portion cf the alluvium ' to be dewatered and removed during the mining process. Portions of the alluvium have been or will i 1 /li.,/rr~p /frr,~ri.i„ioinia'. /ar.