County of Sonoma PRMD required testing for septic development for an onsite septic disposal system.
A Wet-Weather Groundwater Determination Test is used to observe the groundwater table level during the rainy season, through a series of test holes. A test hole will be dug to a minimum depth of 24” from grade and a perforated test pipe will be installed to monitor the groundwater depth.
This test is typically conducted between January 1st and March 1st, after having received 50% of the average seasonal rainfall for each defined geographic area, as listed in the County of Sonoma Onsite Wastewater Treatment System Regulations and Technical Standards.
Once an area has received the required 50% average seasonal rainfall and 0.8” or more or rainfall within a 48-hour period, a 10-day testing window is open to officially document the onsite groundwater table depth with the County of Sonoma.
Throughout the County leading up to a geographic area receiving the required rain amounts, Qualified Consultants will begin the work of installing groundwater test pipes in anticipation of the season opening. Testing hole depths change from site to site, but all pipes must be at least 24” in depth to prove the site has septic potential. If trying to upgrade an existing system, a much deeper depth may be required in order to meet the County requirements of 3’ separation from trench bottom to the groundwater table.
Addressing County Requirements for Groundwater Testing for Your Project
BC Engineering Group has performed this test on countless properties across Sonoma County and understand the process and specific timelines the work must be completed in. As a leading civil engineering design firm, feel free to reach out to us with any questions you may have regarding the process of documenting the groundwater table on your property.
For more information on groundwater testing and other septic planning and design services, please contact us at 707-542-4321. You can also stay up to date with civil engineering and land planning issues by subscribing to our blog.