Wet Weather Percolation & Groundwater Testing
Rainfall Totals and Testing Open/Closure Dates
2021 Wet Weather Testing Season – Closed
Testing is closed in all areas for the season.
The information in the table below is updated when open dates change or when new rainfall totals data are collected. The latest updates to the data are displayed in bold below. Data and open/closure information were updated on April 30, 2021.
The Memorandum of Understanding with the State of California Regional Water Quality Control Board allows for wet weather percolation and groundwater testing between January 1 and March 1, and after having received 50% of the average rainfall.
Depth to groundwater determinations can be conducted within ten (10) calendar days following a rainfall of 0.8 inches in a 48 hour period. Sonoma County is divided into 7 geographic areas for this purpose. The amount of rainfall will be posted for each area.
Visit our Inspection Scheduling page to make inspection requests for wet weather percolation/groundwater tests.
Wet weather percolation test: 384
Wet weather groundwater test: 386
View inspection codes for the Well & Septic section