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Butte County moves to align septic rules with state ADU law, proposes interim one‑bedroom ADU policy
Summary
Public health staff presented an interim policy to allow one‑bedroom accessory dwelling units up to 750 sq ft without a two‑bedroom septic sizing requirement and to use certified designers and flexible system plans; the board directed staff to return with a draft ordinance and continue coordination with the Regional Water Quality Control Board.
Butte County public health staff on Feb. 25 presented an interim policy designed to close a gap between state housing law and local wastewater regulations and to make accessory dwelling units (ADUs) easier to build in unincorporated areas.
Nick Ostrovsky, senior program manager for environmental health, said the county's Local Agency Management Program (LAMP) provides tailored septic standards and that staff's interim approach would allow one‑bedroom ADUs up to 750 square feet without enforcing the older two‑bedroom septic minimum. "To bridge this gap, we're introducing our interim policy for EDUs," Ostrovsky said, describing options to use certified designers, flexible design plans and combined systems where appropriate.
The policy responds to a mismatch staff described between state law (which facilitates ADUs up to 750 sq ft) and Butte County's existing wastewater code, which historically treated second dwellings as requiring a two‑bedroom sizing. Elaine McSpadden, Environmental Health Division director, said the LAMP framework considers local soils, groundwater and public health risks such as nitrate contamination and must remain consistent with California water code requirements.
Supervisors raised operational questions about how the county would assess connections to existing systems, test‑pit timing, and owner‑builder exceptions. Ostrovsky said staff often must review records and, where previous systems are undersized, require upgrades such as additional leach line or a larger tank. He said staff surveyed nearby counties and found roughly half already allow one‑bedroom sizing while half still require two‑bedroom minimums.
Public commenters, including a local resident and water interests, asked staff to explicitly allow use of surplus capacity in older tanks and to clarify rules for small‑lot neighborhoods where separate septic systems are infeasible. John Stonebreaker urged rules that permit efficient use of existing tanks on small lots so ADUs remain affordable in communities such as Magalia.
Next steps: staff said any ordinance change will require Regional Water Quality Control Board review and that a draft ordinance will return to the board for further direction and possible adoption.
