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SECTION 5 - INITIAL DEWATERING RATE ESTIMATES <br /> Quantitative evaluation of groundwater flow conditions was evaluated using three methods: (1) <br /> groundwater underflow calculation based upon groundwater mapping prepared in the 2014 CGS <br /> Report and 2015 CGS Report,(2)calculations based upon the water budget mass balance presented <br /> in the 2015 Brown and Caldwell Report and (3) superposition well drawdown analysis. These <br /> analytical methods allowed the study team to estimate the magnitude of dewatering rates required <br /> to achieve the Town's target depths and identify optimal dewatering sites. Estimated dewatering <br /> rates were refined through groundwater model analysis, summarized in Section 6. Aquifer <br /> characteristics were evaluated to support the dewatering rate estimates. The results of the analyses <br /> are presented in Tables 5.1 and 5.2, and discussed further below. <br /> AQUIFER CHARACTERISTICS <br /> Aquifer characteristics of saturated thickness, hydraulic conductivity and specific yield strongly <br /> influence groundwater flow and dewatering rates required to achieve the Town's depth to <br /> groundwater targets. Long-term aquifer pumping tests are the best source for data regarding <br /> aquifer characteristics, however there are limited aquifer pumping test data available in the <br /> immediate vicinity of the Town. <br /> Based upon reported depth to bedrock and mapped groundwater levels in the vicinity of the Town, <br /> the average aquifer saturated thickness ranges from approximately 75 to 95 feet. Aquifer hydraulic <br /> conductivity was estimated to range from 400 to 800 ft/d in the vicinity of the Town based upon <br /> the 2014 CGS Report. The nearest controlled long-term aquifer pumping was completed 3 miles <br /> north of Town near the intersection of County Road 35 and U.S. Highway 85 in 1957, identified <br /> in Figure 5.1. That test is documented in Circular 11 (Pumping Test in Colorado, USGS, 1965) as <br /> B4-66-11adc, and shows a hydraulic conductivity of 1,270 ft/d, a transmissivity of 370,000 gpd/ft <br /> and storage coefficient of 0.03. During September 17 through November 1, 2015 water levels and <br /> pumping rates monitored near-continuous operation of the Lorenz well. Analysis of water level <br /> data from observation wells located near the Lorenz well indicate a hydraulic conductivity of <br /> approximately 150 ft/d and a transmissivity of approximately 100,000 gpd/ft. <br /> Based upon published values and analysis of well pumping test data, a transmissivity (product of <br /> hydraulic conductivity and saturated thickness) ranging from 100,000 to 300,000 gpd/ft was used <br /> for groundwater analyses for the Town. That range is based upon an average saturated thickness <br /> of approximately 90 feet and a hydraulic conductivity ranging from 150 to 470 ft/d. Specific yield <br /> was assumed to be 20%, which is the same value used in regional groundwater models and in <br /> support of numerous water court decrees. <br /> 18 <br />