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1 1 CHAPTER 2 -EXECUTIVE SUMMARY Analyses were performed to determine the fuhue hydrologic impacts brought about by the amended mining permit for the Lyons - Rockin' WP Pit. These analyses were conducted to determine both impacts during the mining operation and afrer mining has ceased. The analysis was split into two general parts: (1) changes in ground water levels and possible impacts to local wells; and (2) impacts to the alluvial aquifer -stream system relationship and the timing of flows in the St. Vrain Rivet. The key findings of both components of the analysis are presented below. 2.1 Changes in Ground Water Levels and Possible Impacts to Nearby Wells • Aground water level impact analysis was completed to estimate changes in ;;round water levels in the aquifer and possible impacts to nearby wells resulting from the plumed mining and reclamation activities. • The analysis included a computerized ground water model which was based on a "worst- case" mining scenario in which the entire mined area is mined and dewatered at once. The model was also based on winter-time conditions when historic recharge is nct occurring. • Twenty one existing production wells were identified near the boundaries of the proposed mine, all of which aze low-yielding domestic wells (permitted pumping rates ,are 15 gallons per minute or less). There were not any high capacity (municipal or irrigation) wells identified in the vicinity of the mine. • Ground water level changes in nearby wells will range from a slight rise in water level to a decline of about 1.33 feet. Ten of the 21 wells may experience a water level decline greater titan 0.1 feet; only one well may experience a water level decline greater than one foot. Water level changes of these amounts will not limit the ability of properly constructed wells to produce their permitted amounts. -5- 1 /1iJnp lfni,~dn~.l.~~ni id/rr. ln..