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Kern GSAs outline technical fixes in 2025 GSPs — monitoring expansion, stricter thresholds, new mitigation and subsidence actions
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Summary
GSA technical teams and State Water Board staff described substantial 2025 GSP revisions: expanded monitoring networks, higher minimum thresholds, a 60‑day independent exceedance investigation and a new degraded‑water mitigation track; staff still flagged a few outstanding issues for verification.
Technical representatives from the Kern County groundwater sustainability agencies detailed substantial revisions to the subbasin’s 2025 Groundwater Sustainability Plan on Sept. 17, saying the changes address many of the State Water Board’s prior concerns and lay out clear steps for implementation.
Staff and GSA presenters reported they expanded the groundwater‑level monitoring network to about 187 representative wells (with plans to reach up to 197) and increased the groundwater‑quality monitoring network by about 30 wells, narrowing data gaps identified in a hexagon‑based analysis. The GSAs said these expansions will improve spatial and vertical coverage so domestic wells are better represented; the GSA team said the goal is to have most monitoring gaps filled with existing wells by the end of the year and to install new monitoring wells by the end of next year.
Minimum thresholds (MTs) were raised at 35 wells on average (about 29 feet in many cases and more than 100 feet in isolated instances) to avoid MTs within certain geologic layers (e.g., the Corcoran Clay) and to reduce subsidence risk. The GSAs also tightened the undesirable‑result definitions for water levels and dry‑well impacts: one trigger is 25% of representative monitoring wells reaching MTs within a single year, and the plan includes a well‑impact analysis that reduced the number of potentially impacted domestic wells compared with the 2024 plan.
On groundwater quality, the GSPs identify six constituents of concern — arsenic, nitrate/nitrite, uranium, 1,2,3‑TCP and total dissolved solids — and set 330 minimum thresholds across 55 representative monitoring wells, 93% of which are set at drinking‑water standards. The subbasin created a consolidated groundwater quality appendix, a 14‑factor independent exceedance investigation to be performed by a qualified professional and reported within 60 days to a Coordinating Committee, and a separate degraded water‑quality mitigation program (a ‘‘2.0’’ program) that ties notification, investigation and mitigation together.
For mitigation, GSAs described two mitigation tracks and a technical assistance track. The mitigation track for domestic wells (less than five service connections) was described as providing up to $90,000 per well for replacement or mitigation and emergency water; a technical assistance track for public supply wells provides up to $50,000 for planning or feasibility; and GSAs said they are developing a separate funding assistance track for state small water systems that could provide up to $100,000 per well and emergency drinking water.
On subsidence, GSAs revised action timelines to be more proactive: an exceedance investigation would start after two consecutive quarterly exceedances at a representative monitoring site and targeted projects or management actions would be considered after four consecutive quarterly exceedances. GSAs commit to coordinate with DWR’s California Aqueduct Subsidence Program and other agencies to quantify GSA vs non‑GSA subsidence causes and to refine critical‑head analyses.
Board staff acknowledged these technical improvements but listed a small set of remaining priorities for verification — the mitigation program for drinking‑water wells (including 1,2,3‑TCP), mitigation for state small water systems, and removal of the KINDLA JPA sunset — before recommending the referral to DWR. Both staff and GSA technical teams emphasized that the next critical phase is implementation and that the Board will continue to monitor progress.
