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Permit Sonoma › Divisions › Engineering & Construction › Well and Septic Systems › Water Wells › Dry Weather Testing
Well and Septic Systems

Dry Weather Well Testing

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Testing Dates – 2023 Season is CLOSED

The dry weather testing season for well pump tests (well yields) is usually from July 15 to October 1 of each year. The dry weather testing season may be extended by the director of Permit Sonoma as authorized by Sonoma County Code Section 7-12 (c).

Springs and Shallow Wells

Closed as of Sunday, October 1, 2023

Shallow wells are wells that are equal to or less than 50 feet deep. Dry weather testing for springs and shallow wells ends on October 1.

Deep Wells

Closed as of Tuesday, December 19, 2023

Deep wells are wells that are greater than 50 feet. The dry weather testing season for deep wells may be extended beyond October 1 up until the County-wide average rainfall is between five and six inches.

Rainfall Totals

The County-wide average rainfall is based on the rainfall totals reported in the Press Democrat at the 12 rain gauge locations identified in the table below. Dry weather testing for deep wells shall close after the County-wide average rainfall exceeds five inches (5").

Rainfall totals for the 2023 season:

Updated: Monday, December 19, 2023

County-Wide Average: 5.93  inches

Rain Gauge Locations Total Rainfall to Date (inches)
Bodega Bay 5.47"
Cazadero 8.87"
Cloverdale 7.27"
Guerneville 4.48"
Healdsburg 5.90"
Petaluma 5.09"
Rohnert Park 7.80"
Santa Rosa 5.41"
Sea Ranch 7.03"
Sebastopol 4.50"
Sonoma 3.64"
Windsor 5.66"

Background & Requirements

Sonoma County Code, Sections 7-12, 25-17, 25-56, and 26-88-060H, require dry weather well testing for issuance of building permits for new dwellings located in marginal or scarce water zones (PDF 409 KB). The testing must demonstrate a sustained yield of one gallon per minute per dwelling from a well, spring, or multiple wells or springs combined.

Water yield tests performed on springs are allowed only if the spring has been developed to capture and convey water, such as with a spring box or as a horizontal water well.

Dry weather testing is required for the following:

  • New or replacement dwelling in scarce water zone four (4) or,
  • Accessory dwelling unit (ADU) in marginal water zone three (3), and scarce water zone four (4),
  • As required to comply with Natural Resource or Health and Safety Conditions.

Pump tests shall be performed by or under the direction of a licensed water well drilling contractor (C57), pumping contractor (C61/D21), a registered civil engineer, or a registered geologist who shall report test results to Permit Sonoma. Property owners that are not any of the licensed professionals listed or are not working directly for or under a licensed professional cannot perform well pump tests.

Any pump test that does not comply with the pump test requirements will not be approved.

Application Process

A permit is required for each well or spring in advance. The following is required for a permit:

  1. WLS-006 Request for Well & Septic Service Form (PDF) and
  2. Site map showing well(s) and spring locations.

Licensed contractors conducting the well yield must notify Permit Sonoma 24 hours in advance of testing. Completed well yield reports submitted for review must be signed by a licensed professional and include a copy of the driller’s well report or other supporting documents.