Regional groundwater monitoring is generally performed at point locations via wells screened at specific depth intervals. These datasets are useful for roughly determining volumes in aquifer storage or detecting changes in groundwater quality and often used to build regional groundwater models. However, the data density for a regional assessment is considerably low; a high level of interpolation is required between measuring points both laterally and vertically.
Regional monitoring using electrical hydrogeology (regional scale electrical datasets tied to limited well data) provides multiple 2D continuous vertical planes of data on the kilometer scale, which monitor the vadose and phreatic zone to depths of hundreds of feet. Instead of requiring installation of a significant number of vertical wells to multiple depths of interest, Temporal Electrical Resistivity Imaging (TERI) only requires opening shallow (~2 foot) trenches to install monitoring cables similar to installing water lines. The installation is completed with a TERI station, where instruments are connected to collect data on a temporal basis.
TERI datasets allow aquifers to be monitored to assess changes to groundwater volume, bioactivity levels, and/or groundwater chemistry which can be incorporated into groundwater models. These monitoring datasets can provide enhanced warnings of these changes happening to the groundwater system, which would commonly be missed by solely using interpolated regional well data. This presentation will educate attendees regarding the installation of TERI cables and resulting monitoring data from a case study example of a kilometer thick carbonate aquifer monitored at the regional scale.
A city in an arid region of Oklahoma needed to increase its water supply and was pursuing development of a new wellfield for groundwater extraction and distribution as surface water resources are not a viable option in the region. Large swaths of land were available to develop to the town for a new wellfield, but sparse hydrogeologic data in the region left the project team uncertain of optimal locations for new wells which would produce sufficient yield.
A specialized electrical resistivity imaging (ERI) technology was deployed across approximately 1 square mile to scan the subsurface and identify targets for water supply wells. The results from electrical imaging data were integrated with regional hydrogeologic data to calibrate electrical signatures to known subsurface hydrogeologic structure and features. These data along with surface topography and a modeled geologic surface from borehole lithology, were integrated into a 3D visualization model to generate a robust and accurate interpretation of subsurface hydrogeologic conditions.
Seven (7) test well targets were selected based on these integrated data sets to evaluate the electrical anomalies suspected to represent groundwater zones with suitable porosity and permeability in the phreatic zone for maximum yield. Results from all 7 test wells reported satisfactory water quality and quantity and combined production rate was expected to average 14 million gallons per day (MGD). The “scan first then drill” approach used for this project allowed the project team to save money on the test well process, maximize yields via targeting, and develop the well field in less time and at lower cost and with higher levels of certainty throughout the process.
