A three-layer superposition MODFLOW model was created to simulate the 100-year effects of pumping a community water supply well near Santa Fe, New Mexico for the purpose of subdivision plan approval.
The model was designed to conservatively predict the drawdown in the on-site community well and estimate off-site effects on wells of other ownership. The model is a simplified representation of the groundwater flow system near the subject well.
A 96-hour pumping test was conducted on the subject well. Results revealed a limiting boundary in the aquifer which is interpreted to be the termination of the fracture zone in which the well is located, creating a compartmentalized aquifer.
Examination of drill cuttings from the well and evaluation of outcrops in the area indicate generally low permeability in sediments, with significant anisotropic character due to interbedding of sand, silt and clay. The fractures observed in outcrops are generally in a NE or NW orientation, as is seen in the major mapped faults of the area.
These field observations were incorporated into the construction of the groundwater model with anisotropic zones of hydraulic conductivity. The degree of anisotropy in the model was determined by trial and error to best simulate the 96-hour pumping test on the subject well. The best-fit model construction produced an elliptical drawdown pattern centered on the well and parallel to the fracture zone.
Hodgins, M., Chudnoff, M.., 2003, MODFLOW Simulation of Pumping Test Data in a Fractured Sedimentary Rock Aquifer: MODFLOW and More 2003, Understanding through Modeling, Proceedings Volume II, International Ground Water Modeling Center (IGWMC), Colorado School of Mines, September 16-19, pp. 570.
Rancho San Lucas model grid showing drawdown from examined wells.