Pleasanton and Zone 7 find joint groundwater wells feasible; staff to return with cost comparison

Pleasanton city staff and Zone 7 officials told the City Council on Feb. 3 that a joint groundwater facility in the Bernal Subbasin is technically feasible and could replace lost production from Wells 5, 6 and 8.

Public Works Director Su Chin Yang and Utilities Planning Manager Todd Yamelo summarized the Phase 1 feasibility study, saying test wells at Tennis Park, Hansen Park and Del Prado Park produced water that met California Title 22 requirements and were non-detect for the primary PFAS contaminants PFOS and PFOA. Yamelo said two of four evaluated build alternatives met a mandatory reliability threshold of 7,000 acre-feet in a drought year (3,500 acre-feet for Pleasanton and 3,500 for Zone 7). The preferred option is two wells at Tennis Park and Hansen Park, which scored highest on a six-factor feasibility rubric, including capital cost, O&M, resilience, schedule, community impacts and treatment risk.

Zone 7 General Manager Valerie Pryor and Water Resources Manager Ken Min described the groundwater modeling used to test worst-case scenarios, including running candidate wells continuously for 20 years under stressed conditions. Min said the model showed no PFOS migration to the facilities within that 20-year horizon under current plume data; he characterized the model’s fit as high (on the order of 0.97–0.98 for statistical measures used). Pryor and Min emphasized that the modeling is conservative and that contingency planning for future treatment remains possible.

City staff reported the joint project’s preliminary, level‑4 cost estimate is approximately $42.3 million (joint cost to construct wells, piping and treatment upgrades). Staff noted the city’s share will be determined through draft terms with Zone 7, and that additional city distribution upgrades (turnouts, upsized piping) would be required and costed separately. Earlier project funding included a State Water Board grant of $1,000,000 applied to the study; Pleasanton’s enterprise fund share for Phase 1 was $280,000, and the city’s earlier council-approved cash share for the feasibility agreement was $1,000,000 (later increased by amendment to a $1,280,000 not‑to‑exceed figure).

Council members pressed Zone 7 and staff on model assumptions, the risk that pumping could mobilize PFAS, and the potential cost of future treatment. Zone 7 acknowledged uncertainty and said the modeling used particle-tracking and empirical data; they also said the model is validated against observed basin data and that, while future treatment remains an option, facilities would be sited with room for treatment if needed. Staff said they will perform a comparative analysis of a joint project versus a Pleasanton-only project (costs, distribution impacts, unit cost of water and schedule) and return with recommendations targeted for March or April.

The council did not take action to commit to construction at this meeting. The near-term direction is for staff and Zone 7 to negotiate draft terms and for Pleasanton to complete its internal cost/benefit and distribution impact analysis before seeking council direction on whether to proceed.