— February 1, 2018
High-production municipal water well fields can depress water levels, cause land subsidence, and disturb subsurface aquifer temperatures. As an example, the City of Santa Fe’s Buckman well field located along the Rio Grande, was pumped at high rates from 1989 to 2003. This high-rate pumping led to a precipitous drop in water level (>100 m), caused measureable ground subsidence over a 25 km2 area (based on 1995-1997 InSAR [satellite-based] data), and created a land-surface fissure with 20 cm of vertical displacement. Pumping rates were reduced after 2003 and water levels have since risen ~120 m.
Students attending the Summer of Applied Geophysical Experience (SAGE) field school in Santa Fe had a unique opportunity to collect temperature data in monitoring wells in the Buckman well field between 2013 and 2016. Repeat measurements of thermal profiles and discharge temperatures in monitoring and production wells in the Buckman field record the complex interplay of cooling in aquifers during times of high production and warming during recovery. During high production, water levels drop near the wells, which cause cool water to move horizontally toward the wells, thus decreasing the temperature of the aquifer system. When production decreases, water levels near the wells rise, and vertical groundwater flow warms the aquifer.
One of the most significant discoveries to come out of this study was made by former SAGE and current NM Tech hydrology student, Matthew Folsom. Matt has been intrigued with the changes associated with recovery of Buckman since he was a student at SAGE, so he conducted a repeat InSAR analysis using data from 2007-2010 as a project in Ronni Grapenthin’s geodesy class last fall. He documented land surface rebound on the west side of the field caused by the changing water levels. The observed non-uniform patterns of uplift and subsidence across the field reveal buried geologic features (faults and ancient river channels) that interestingly coincide with measured variations in geothermal gradient. The temperature measurements made by the SAGE students have identified a previously unrecognized area with high geothermal gradients (76-79°C/km) in the field that correlates with the area of maximum uplift. Matt is in the process of writing up his findings for the journal Water Resources Research.