Wet-Weather Testing Period Opens for Humboldt Septic Systems, Jan-April

Humboldt County officials opened the annual wet-weather testing period for individual onsite wastewater treatment systems (OWTS) on Jan. 5, the Division of Environmental Health announced on Jan. 6. Under normal rainfall, the testing window will run through April 1. The county said the period is designed to determine depth to seasonally high groundwater and performance in soils of low permeability, both key factors in approving new or replacement septic systems.

The tests are required where soils do not readily transmit water or where the seasonal high groundwater level must be established for system design. Testing is mandatory within Humboldt County’s Variance Prohibition Areas, locations where standard variances to setback and depth requirements are not permitted. The notice also clarifies how the testing window may be adjusted if rainfall is insufficient to produce representative wet-weather conditions, protecting both applicants and the public-health intent of the measurements.

For residents proposing new septic systems, repairs, or replacements, the testing period can affect permit timelines and contractor scheduling. Consultants and system designers will need to plan infiltration and percolation assessments within the county’s window or arrange for an adjusted test period if dry conditions prevent reliable results. For property buyers and sellers, pending approvals tied to OWTS testing may influence closing schedules and required contingencies.

The county provided references to its OWTS regulations and the technical manual to guide applicants and consultants on procedural and technical requirements. Applicants are advised to consult those materials and coordinate with the Division of Environmental Health early in project planning to avoid delays. Timely testing is particularly important in rural parts of Humboldt County that rely on onsite treatment rather than municipal sewer systems, where improper sizing or siting can lead to system failure or groundwater contamination.

Seasonal wet-weather testing is a standard practice in areas where groundwater and soil conditions vary through the year; the requirement reflects an effort to protect groundwater resources and public health while ensuring wastewater systems are appropriately designed for local conditions. With rainfall patterns increasingly variable, the county’s provisions for adjusting the test window aim to balance scientific rigor with practical flexibility for applicants and consultants.