Planning commission approves permits for Coastside County Water District to replace six wells

The San Mateo County Planning Commission on Aug. 13 approved permits for the Coastside County Water District to replace six municipal wells in its Pilarcitos Creek well field (county file PLN2025-00126).

Planner Mike Schaller told the commission the project would remove aging well casings and concrete pads, drill new wellbores 10–15 feet from existing bores, and install stainless-steel casing and modern pumps, controls and appurtenances. The district said the work will maintain existing pump capacities and not increase the amount of water it is allowed to withdraw under its state permit.

Mary Brogren, general manager for Coastside County Water District, said the district serves about 19,000 people in Half Moon Bay and nearby unincorporated coastside communities and that the Pilarcitos well field historically supplies roughly 20% of the district’s supply in normal years. District engineer John Sutter said the wells are operated under a water-right permit that limits instantaneous diversion to 1.5 cubic feet per second and an annual volume of 360 acre-feet; pumping is limited to Nov. 1–March 31 under that permit.

Schaller and the applicant said the six replacement wells are needed because the existing wells — constructed between the 1960s and 1990s — are nearing the end of their useful life, with corrosion, fouling and increasing maintenance costs. The project design calls for corrosion-resistant materials (stainless steel casings and screens), variable-frequency drives, SCADA integration and manual transfer switches for generator hookups to improve emergency resiliency.

Biological studies identified three special-status plant species and four special-status animals in the area; staff recommended, and the applicant committed to, standard avoidance and minimization measures including preconstruction surveys, exclusion fencing, worker training and on-site biological monitoring during construction days. The applicant said most replacement pads will be adjacent to or overlap existing cleared pads; one former pad will be converted to a monitoring well and the rest will be demolished and removed.

Construction sequencing requires at least three production wells to remain in service during pumping season to avoid customer interruptions; the applicant said the contract allows about 200 calendar days for the work (roughly five to six months). The applicant also said the project would not change treatment processes: raw water from the wells is conveyed to the district’s Nunes Water Treatment Plant and treated as it has been.

Commissioner Hansen moved to approve the coastal development permit, plan agricultural development permit and use permit as conditioned; Commissioner Gupta seconded. Commissioners voted aye; the motion carried.

Votes at a glance: Motion to approve PLN2025-00126 (Coastside County Water District wells) — Mover: Commissioner Hansen; Second: Commissioner Gupta; Outcome: approved (unanimous).

The commission’s approval is subject to the findings and conditions in Attachment A of the staff report; construction will proceed under standard county permit conditions and biological mitigation measures.