Alameda County supervisors deny Zone 7 appeal, certify EIR and approve Arroyo Lago subdivision

Alameda County supervisors on Feb. 10 denied an appeal from Zone 7 Water Agency and approved the Arroyo Lago subdivision, certifying the final environmental impact report and approving a 190‑unit vesting tentative tract map.

Planning staff and the county’s environmental consultant told the board the record supports upholding the Planning Commission’s earlier 6–1 approval. Aubrey Rose of the Alameda County Planning Department summarized the case (PLN2022‑00193) and recommended that the board deny the appeal, certify the final EIR and approve the vesting tentative map. County consultant Rachel Krasinowski described site design changes, mitigation measures and monitoring conditions including relocation of agricultural spray fields (Condition 71) and extensive operational safeguards for a modular membrane‑bioreactor (MBR) wastewater treatment plant.

Zone 7’s presentation focused on proximity to the Livermore groundwater basin and the chain of lakes. Colleen Weine, a senior geologist for Zone 7 Water Agency, said the proposed wastewater and recycled‑water spray fields are “right adjacent to the lake” and warned the project could pose a risk to municipal groundwater supplies and the agency’s planned surface‑water projects. She told the board Zone 7’s concerns center on the chance that an upset, flooding or maintenance shortfall could compromise water quality and that PFAS in wastewater effluent is a particular worry.

The applicant and technical experts pushed back. An applicant representative said the EIR and technical studies justify approval and that the project team has made voluntary concessions to reduce neighborhood impacts. “This facility is not gonna contaminate the water,” the representative said, adding the MBR design, monitoring, automatic shutdowns and lined recycled‑water storage meet state requirements. Consultant Bert Mihalczyk said MBR systems are widely used and noted that state and regional review produced no adverse comments.

Supervisors pressed staff and Zone 7 on alternatives and residual risk. Several members noted that annexation to the City of Pleasanton — the applicant’s stated pathway — would move the project onto municipal sewer infrastructure and likely address many of Zone 7’s concerns, but staff and Zone 7 said annexation had not yet been completed and could not be guaranteed. Zone 7 emphasized it is not opposed to development but urged the board to require municipal connection if feasible.

After deliberation, the board adopted staff’s recommendation: deny the Zone 7 appeal, certify the EIR, adopt the findings of fact and statement of overriding considerations, and approve the vesting tentative tract map. The motion passed on a roll call vote (yes 4, abstain 1). The county attorney and staff noted adopting the decision carries litigation risk under the Housing Accountability Act but said the record did not contain the level of evidence needed to deny the project under that statute.

Next steps: with the county action in place, the applicant anticipates pursuing annexation and project approvals with the City of Pleasanton; the State Water Board and the Regional Water Quality Control Board remain the permitting authorities for any on‑site wastewater treatment facility.