USING THE ANALYTIC-ELEMENT METHOD MODEL TO CHARACTERIZE GROUNDWATER FLOW IN A KARST AQUIFER IN COLORADO, USA

Six artesian wells in Manitou Springs, Colorado, are part of an ongoing study by the U.S. Geological Survey to better understand groundwater flow, residence times, and sources of recharge in the Manitou Springs aquifer. Statistical analysis of long-term pressure-transducer measurements using the Mann-Kendall test indicate a mixed behavior of steady-state and transient hydraulic conditions. Hydraulic-head and geochemical data from the wells indicate groundwater flow in the Manitou Springs aquifer originates as recharge in the western part of the Manitou Formation outcrop area and flows to the east. Hydrologic data were used to create a two-layer analytic-element method model, and geochemical data may be utilized to calibrate the flow rates based on rates of carbonate mineral dissolution. Additionally, sources of groundwater recharge were evaluated using measured streamflow gains and losses over multiple seasons and years. Evaluating the hydrology within the Manitou Springs aquifer could provide an understanding of future groundwater availability given changing recharge conditions and land use, as well as an understanding of groundwater flow paths and solute transport.