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Kern GSPs add monitoring, raise water‑level thresholds and outline mitigation pathways for dry and contaminated wells
Summary
State Water Board staff told members Sept. 5 that the Kern subbasin’s 2025 draft GSPs raise many groundwater thresholds, expand monitoring coverage, and outline mitigation pathways that include up to $90,000 per domestic well replacement and a proposed up to $100,000 pathway for small public systems.
State Water Board staff told members on Sept. 5 that the 2025 draft GSPs for the Kern subbasin contain substantive technical changes intended to reduce the risk of undesirable results, expand the monitoring network and clarify mitigation steps for impacted wells.
Key technical changes described by staff include higher minimum groundwater‑level thresholds at many monitoring locations, clearer quantitative definitions of “undesirable results” for groundwater level, quality and subsidence, and more prescriptive minimum‑threshold action plans. Staff said minimum thresholds were raised at roughly 35 monitoring wells in the representative network and that some thresholds increased by tens of feet in specific places to reduce the risk of subsidence and protect beneficial uses.
Monitoring network and data gaps: The GSAs subdivided the basin into 111 hexagons to test representativeness of domestic wells and the monitoring network; staff said the representative network for groundwater‑level monitoring currently covers about 187 wells and the plan would expand that to roughly 197 representative wells and proposes to add 30 additional monitoring wells to close confirmed data gaps. GSAs told staff they would prioritize filling gaps and aim to use existing wells where feasible by the end of the year and to install new monitoring wells the following year.
Water‑quality procedures and mitigation: The draft 2025 plans set quantitative conditions that constitute an undesirable result for water quality. Staff highlighted three illustrative conditions: (1) 25 percent of representative monitoring wells reaching their minimum quality thresholds in a single year; (2) 15 domestic drinking wells drying in a single year with a cumulative cap (staff cited a plan‑level cumulative number through 2040); and (3) a GSA’s inability to meet mitigation needs for affected wells. Using the basin inventory (about 2,300 domestic wells, some 300 small public and community supply wells, and roughly 4,200 agricultural wells), staff’s analysis estimated the number of domestic wells that could be affected under different threshold scenarios and reported a reduction in projected affected wells from the 2024 draft under the 2025 revisions.
Mitigation pathways: Staff described two primary assistance tracks. The mitigation track for domestic wells (typically fewer than five service connections) can include replacement wells and emergency potable water and — under draft plan terms presented to the board — offers up to $90,000 per well for replacement or similar measures. A technical assistance track for small public supply wells offers up to $50,000 for grant development or feasibility support; staff said GSAs are developing a separate financial assistance option for small state systems that could fund up to $100,000 per affected system.
Subsidence: The GSPs include minimum subsidence thresholds and an “exceedance” policy that triggers investigation and potential mitigation when single‑year or multi‑quarter thresholds are surpassed. One GSA currently has a moratorium on new extraction and new or replacement well drilling within 2.5 miles of a segment of the California Aqueduct (mileposts about 195–215) to limit local contributions to subsidence near the canal. Staff asked GSAs to improve methods to separate subsidence caused by groundwater extraction from subsidence caused by oil and gas operations and urged clearer plans tying measured subsidence levels to specific infrastructure risk thresholds.
Next steps in implementation: Staff recommended that GSAs fill monitoring gaps as a priority, finalize the domestic and small‑system mitigation finance tracks, and clarify several minimum‑threshold adjustments for a small number of wells where local conditions warrant deeper thresholds. Staff also recommended continued coordinated technical workshops to resolve data gaps and to refine methods for attribution and mitigation.
Speakers in the record for the technical presentation included multiple State Water Board staff presenters and technical leads from the Kern GSAs; the record includes staff slides summarizing monitoring counts, mitigation dollar limits and subsidence policy details.
