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Wet-Weather Testing for Septic Permits

Are you buying or selling an undeveloped rural property? Are you currently in the process of developing a rural parcel located outside of the city sewer district? If so, now is the time to pursue wet-weather groundwater testing.

Limited Testing Window

Wet-weather groundwater testing is often a crucial and time-sensitive step toward applying for a septic permit in Sonoma County. The testing window is limited and unpredictable, depending on rainfall patterns at the beginning of the year and agency discretion in extending the season. Missing the window means testing can’t be conducted until the following rainy season – a significant delay for development projects.

As we enter the rainy season, we are monitoring rainfall totals in Sonoma County and tracking the wet-weather groundwater season testing dates. Site and septic development in Sonoma County are typically dependent on the confirmation of separation to the winter groundwater table via wet-weather groundwater testing. For undeveloped sites with shallow slopes, groundwater testing is often the first step toward maximizing the septic potential onsite.

What is Wet-Weather Groundwater Testing & Why is it Needed?

Engineer testing groundwater levels for septic permitWet-weather groundwater testing determines the depth from the surface to the groundwater table of your property during the rainy season. The purpose of groundwater testing is to ensure there is enough separation between where wastewater is discharged into the soil and the groundwater table. The minimum depth required for a passing groundwater test hole is 24 inches. Groundwater testing is required on parcels with shallow slopes (5% or less) and when an indirect observation cannot be made – and test results must be measured by a registered Civil Engineer or Registered Environmental Health Specialist. (contact Adobe Associates to determine your property’s requirements). 

When does the Wet-Weather Groundwater Testing Season Open in Sonoma County?

The wet-weather test period opens after 50% of the seasonal rain has fallen. A storm of 0.8 inches within 48 hours will open a 10-day window to conduct required testing and coordinate a review of the results with the County. The wet-weather groundwater season typically ends by March 1st, but the County can extend this date into early April if rain continues.

When will the testing season open in 2024?

As of 4/24/24, the area-wide totals are as follows:

2024 Wet Weather Groundwater Season – CLOSED
Town Total Rain Required Rain to Date
Cloverdale 20” 41.32″ (CLOSED)
Guerneville 25” 43.56″ (CLOSED)
Healdsburg 20” 46.73″ (CLOSED)
Petaluma 12.5” 26.89″ (CLOSED)
Santa Rosa 15”  36.38″ (CLOSED)
Sebastopol 17.5” 30.31″ (CLOSED)
Sonoma 15” 31.26″ (CLOSED)

Sonoma County sporadically updates its website with rainfall totals here:

Avoid Delays, Secure Testing Today

Adobe Associates’ Wastewater Department has decades of experience performing wet-weather groundwater testing in Sonoma County. Our staff consistently conducts testing in an efficient and targeted manner to maximize the septic potential of each site.

If you are interested in scheduling testing or learning more about this service & how Adobe Associates can help, please Contact us Today.

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