GMA selects alternate approach for yield study modeling, approves Dudek contract increase to complete yield study

The Fox Canyon Watermaster presented a preferred alternative on June 25 for completing the Las Posas Valley basin optimization yield study after the agency was unable to secure timely access to modeling services from an adjacent district. The board approved staff's recommended approach and separately authorized a contract modification with consultant Dudek for additional modeling tasks.

Dr. Farai Kasseke and hydrologist Robert Hampson outlined three modeling approaches considered: continue to await United Water Conservation District modeling services; develop a new numerical groundwater flow model (time-consuming); or estimate the basin optimization yield by using United's periodic evaluation model files to run new scenarios. Staff and Dudek recommended the third approach as the best available science given schedule constraints. PAC and TAC both provided recommendation reports supporting the preferred alternative, while asking for additional documentation and clarity on calibration and model validation steps.

Counsel advised that United's modeling files are subject to a protective order in the Oxnard Plain adjudication and that United has not granted access, which constrained the Watermaster's options. The preferred alternative preserves the original technical methodology, maintains consistency with the Groundwater Sustainability Plan and periodic evaluations, and is expected to allow a timely completion of the yield study.

Because the West Las Posas management-area model work remained to be completed, staff asked the board to authorize a professional services contract modification with Dudek to perform additional modeling tasks on the west side. The board approved a $90,500 increase, raising the contract maximum to $303,000, to complete the yield study tasks for both east and west model areas.

Board members emphasized the need to proceed expeditiously with the best available science. Some members urged continued outreach to United for access to its calibrated files, though counsel explained access remains subject to the protective order. A member of the public requested that certain local aquifers (Grimes Canyon Aquifer) be included; agency staff confirmed that the Grimes Canyon Aquifer is included in the model and will be part of the exercise.

The board voted to authorize the contract modification and to proceed with the preferred modeling approach and related schedule and reporting. (Motion carried; voice vote and roll-call for contract authorization.)