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Public Trust Review

Applications for water wells submitted after October 4, 2022, located within the Public Trust Review Area (PTRA) may require a Discretionary Public Trust Review. A Public Trust Review involves the evaluation of impacts to streams and rivers caused by the impacts of existing and proposed groundwater extraction in the local watershed.

The PTRA is shown in Section 25B-14 of the Sonoma County Code and is viewable through the Well Ordinance Map. For information on how the PTRA was established, please see the Well Ordinance Update and the Sonoma County Well Ordinance Public Trust Review Area Delineation study.

For well permits that are subject to Public Trust Review, the well construction permit will not be issued until the additional review is complete.

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Which Well Permits Require a Public Trust Review?

Certain classes of wells located in PTRA are exempt from Discretionary Public Trust Review, as listed in Sec. 25B-4(e). Staff will review permit applications to determine whether the proposed well falls within one of the exemptions. Exempt wells are reviewed ministerially unless they are part of a larger discretionary project. Exempt well classes include:

Wells outside the PTRA Proposed wells outside the PTRA will not be subject to discretionary public trust review. If the PTRA bisects a parcel, the review requirements are determined by the proposed location and well class.
Public Water Well A public water well for which environmental review under the California Environmental Quality Act is complete.
Water Board Regulated Well Water wells that will serve as a point of diversion associated with an appropriative water right regulated by the CA State Water Resources Control Board, Division of Water Rights.
Low Water Use Well Water wells where total groundwater use of the parcel is limited to 2.0 acre-feet per year (651,702 gallons).
Well for Existing Land Use Water wells where total groundwater use of the parcel is limited to and does not exceed the amount of groundwater used as of the date of ordinance adoption for legally established land uses. Existing use is based on average use from 2018-2022.
Zero Net Increase Well

Water well where the proposed use would not result in a net increase in groundwater use on-site through the implementation of water conservation measures, rainwater catchment or recycled water reuse system, water recharge project, or local groundwater management project.

How is Water Use Estimated?

Water use will be estimated by staff using standard use rates detailed in Appendix A of Policy and Procedure 8-2-1, Water Supply, Use, and Conservation Assessment Guidelines. An applicant-prepared assessment may be submitted to support the water use determination.

What Does a Discretionary Public Trust Review Entail?

Discretionary review of impacts on public trust resources involves evaluating how “public trust resources” of local streams and rivers may be harmed by groundwater pumping. In practice, the analysis is focused on the reduction in streamflow during the summer and fall caused by the combined pumping of all existing wells, surface water diversions, and the proposed well. Typically, the water use of the proposed well is a tiny fraction of the total use, yet the additional use may exacerbate an existing impact.

The discretionary review process involves both watershed scale and site-specific analysis. Existing hydrologic models will be used to estimate the reduction in flow in streams that support salmonids caused by groundwater pumping. Available information indicates that streamflow reduction is highly variable across the County during the summer dry season. Remote watersheds with little development have minimal flow reduction, while lowland streams in alluvial valley bottoms often have the highest levels of streamflow depletion.

Unless the applicant hires a private hydrogeologic consultant, the public trust analysis will be completed by Permit Sonoma staff or a consultant under contract with Permit Sonoma. Regardless of who performs the hydrologic analysis, Permit Sonoma will consider available information and make written findings regarding impacts before issuing the well permit.

What is an “Adverse Impact” on Public Trust Resources?

The Sonoma County Well Ordinance does not define adverse impact on public trust resources. However, the Outcomes and Recommendations Report developed by the Well Ordinance Technical and Policy Working Groups recommended that cumulative reductions in streamflow of 10 percent or more in Coho-bearing streams, and cumulative reductions in streamflow of 20 percent or more in Steelhead-bearing streams should constitute an adverse impact. Permit Sonoma will use these percentages as guidance; however, what constitutes an adverse impact may vary depending on flow, habitat conditions, and available information for a particular stream and is looked at on a case-by-case basis.

Timeline and Process

For those permits that require discretionary review, Permit Sonoma will inform the applicant, request additional information (as needed) and assess the at-cost Discretionary Well Permit Review fee. This new review process is anticipated to take three to six months to complete if the project is CEQA exempt or CEQA is already complete. Once fees are paid, and additional information is submitted, staff will refer permit application materials to owners of neighboring parcels within 300 feet, local groundwater sustainability agencies, resource agencies, and other interested parties. To be added to the distribution list, please subscribe to the “Permit Sonoma – Public Trust Review” email list. A 30-day response period will be provided.

After the initial response period, Permit Sonoma will conduct the analysis and make preliminary findings. If analysis indicates that the proposed well will cause or exacerbate an existing impact, Permit Sonoma will convey this information to the owner and applicant. Options for additional information, analysis, and mitigation measures will be considered at this time. Permit Sonoma will also determine the appropriate CEQA pathway at this stage of the permit process.

Once analysis is complete and any necessary mitigation measures developed, Permit Sonoma will then make written findings and a determination to either (1) approve the well permit, (2) approve the well permit with conditions and/or mitigation, or (3) deny the well permit. Written findings, supporting information, and the determination will be distributed to interested parties. The decision may be appealed within ten days or as required by CEQA. The public trust review would be brought to the Board of Supervisors for final approval or denial if appealed.

Once the Public Trust Review is complete and approved, the well construction permit will be issued, where all other requirements and construction standards for issuance are met. Water conservation, metering, and monitoring requirements may apply and would be required as specified in permit terms.