Hydrogeologic Investigations at the Cholla Power Plant
M&A helps APS relocate a major wellfield, settle a land-lease dispute, and model aquifer conditions in a fractured rock system.
Client: Arizona Public Service (APS)- Time frame: 2005–present
- Location: Cholla Power Plant, Joseph City, Arizona
M&A has been involved in several investigations at the Cholla Power Plant to support water supply and other projects. When a long-term land lease was terminated, threatening Cholla’s wellfield, M&A provided a range of services to ensure that the plant would maintain continuity for its water supply. In addition to relocating production wells, M&A conducted analyses to support land-condemnation negotiations. We have also been involved in various modeling studies for Cholla, including a review of a groundwater flow model prepare by another consultant as part of the Black Mesa EIS.
Services
- Launched an exploration program to identify the best locations for new production wells
- Assessed water quality relationships
- Assembled technical, regulatory, and economic data sets, integrating the results into a GIS platform to display various aquifer characteristics in relation to property ownership
- Developed a groundwater flow model to simulate drawdown impacts from historical pumping and evaluate the potential for increasing production
- Conducted a critical review of an EIS model to assess the validity of projected base flow reductions
- Logged boreholes to assess the distribution and density of fractures within the sandstone aquifer
- Installed 11 new production wells and modified two existing wells to meet demand requirements
- Oversaw well drilling and testing
- Deployed downhole explosives in some wells to enhance fracture connectivity to increase yields to more than 3,000 gpm
- Selected and managed the contractors who installed all the pipeline, wellhead, and pumping infrastructure under extremely tight deadlines
- Installed about 20 monitoring wells in the shallow alluvial and the deeper sandstone aquifers
- Equipped monitoring wells with data loggers and pressure transducers to continuously record the aquifers’ response to pumping and streamflow runoff
- Characterized the relationship between groundwater and surface water resources
- Assembled technical, regulatory, and economic data sets, integrating the results into a GIS platform to display various aquifer characteristics in relation to property ownership
- Assessed the value of the leased land where the Cholla wells were located, relative to the landowner’s property
- Equipped monitoring wells with data loggers and pressure transducers to continuously record the aquifers' response to pumping and streamflow runoff
Outcome
Under an expedited deadline, M&A not only shifted production to other wells, but we also helped APS expand the wellfield and develop redundancy to provide reliable backups. In addition, we helped replace the monitoring network, to the extent possible, on APS land and supported land-condemnation negotiations by providing a valuation of the leased land.
Our review of the EIS model found it lacking the structure, detail, or accuracy required to validate the projection that pumping “…in the vicinity of Holbrook and Joseph City” would cause significant declines in the base flow of lower Chevelon and Clear Creeks.
Work is underway to identify the best approach for updating our original groundwater flow model for the region.
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