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a INTRODUCTION As part of the on-going development of the Deepe Pit, Flatiron Sand and Gravel Company plans to remove sand and gravel from areas designated as Stages 4 and 6 (as shown on Plates 1 and 2 ) . Each stage will be mined separately, with Stage 4 mined first. r Currently, most of the sand and gravel underlying these stages is J below the water table. To facilitate extraction of the sand and gravel, a dewatering trench will be constructed around the perimeter of each stage. This method of dewatering has been successfully used to dewater Stage 1 without adverse impacts . Stage 1 is immediately north of Stage 4 and east of Stage 6 . Because the depth to water in the vicinity of the new stages will be increased and because there are wells in the area, Leonard Rice Consulting Water Engineers, Inc. investigated .the magnitude and lateral extent of dewatering. This report presents the results of that investigation. EXISTING GROUND WATER CONDITIONS The Deepe Pit is being developed in the water saturated unconsolidated sand and gravel alluvium deposited by South Boulder Creek. The alluvium is underlain by impermeable non-water producing shale. The alluvium ranges in thickness from zero to about 20 feet thick and has been deposited in a valley approximately 4,000 feet wide parallel to South Boulder Creek. The alluvium is moderately permeable with a hydraulic conductivity that ranges from 80-1200 gpd/ft2 and averages about 200 gpd/ft2. The depth to water varies seasonally and from year to year due to fluctuations in precipitation in the drainage basin and local irrigation practices. The annual variation is up to 3 feet. Depending on location, the depth to water is generally 1 to 6 feet below ground level. The water table slopes to the north about 80 y feet per mile. 1 Leonard Rice Consulting Water Engineers,Inc.