1. Interconnected Surface Water Analysis Supports Current Groundwater Level Thresholds Woodard & Curran presented a detailed technical analysis showing that historical groundwater pumping in the Modesto Subbasin causes approximately 60,000 acre-feet per year of stream depletions — water that would otherwise flow between rivers and the aquifer. Using five pumping scenarios and modeling, the consultants demonstrated a correlation between average groundwater levels at interconnected surface water (ISW) monitoring wells and stream depletions. They stated the modeled correlation indicates the 60,000 AFY depletion level corresponds to an average ISW groundwater level of about ~53–54 feet (approx., uncertainty-adjusted), and also stated the existing minimum thresholds averaging ~57 feet are protective. The consultants recommended continuing to use the existing minimum thresholds as the GSP proxy approach; no board action was taken at this meeting. The GSA is not required to eliminate historical depletions, only to prevent them from getting worse.
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