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8-1-3 Groundwater Monitoring Guidelines for Water Wells

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Version: 07/11/2023 | 12/03/2020 | 05/18/2004


The purpose of this policy is to provide groundwater monitoring guidelines and procedures for permits with requirements for groundwater monitoring, volunteer monitors, and other monitoring entities. Procedures are written for permittees with requirements for metering and monitoring. Volunteer monitors should consider these guidelines as best management practices, but not mandatory requirements.


Use Permit holders, cannabis permits, and well permits commonly require ongoing metering of groundwater use and measurement of groundwater levels. Requirements are often specific to the permit, and the permit holder is advised to review the specific terms of their permit. These guidelines outline groundwater metering and monitoring requirements and also provide basic instruction related to meter specifications and how to make depth to water measurements. For additional information, please contact:

Water Use Categories for Groundwater Monitoring

Projects are generally categorized by the amount of proposed groundwater use:

  1. "Very Low Use” projects use less than 0.5 acre-feet per year (AFY) (formerly known as "small" projects);
  2. "Low Use" projects use less than 2.0 acre-feet per year (AFY);
  3. "Moderate Use" projects use less than 5.0 acre-feet per year (AFY) (formerly known as "large" projects);
  4. "High Use" projects use greater than 5.0 acre-feet per year (AFY) (formerly known as "very large" projects).

Estimates of groundwater use, used to categorize projects for monitoring purposes, must be developed in accordance with Policy and Procedure 8-2-1 Water Supply, Use and Conservation Assessment Guidelines.

Metering and Monitoring Requirements

Metering and monitoring requirements vary depending on the permit type and water use category. In addition, project-specific conditions of approval, mitigation measures in California Environmental Quality Act (CEQA) documents, or other prescriptive standards in County code, may specify alternative or more stringent groundwater monitoring requirements (e.g., frequency, parameters, methods) which must be complied with. Table 1 below provide the most common requirements.

Table 1. Frequency of groundwater use and water level measurements required for various permit types dependent on water use category (acre-feet per year or AFY).

Permit Type Very Low Use
(0 – 0.5 AFY)
Low Use
(0.5 – 2 AFY)
Moderate Use
(2 – 5 AFY)
High Use
(5 – 10 AFY)

Well Permit – Residential



Monthly water meter readings

Monthly water meter readings and groundwater levels

Well Permit – Nonresidential

Monthly water meter readings

Monthly water meter readings

Monthly water meter readings

Monthly water meter readings and groundwater levels

Use Permit

Annual water meter readings

Quarterly water meter and groundwater levels

Quarterly water meter and groundwater levels

Monthly water meter readings and groundwater levels within a dedicated monitoring well

Cannabis Permit

Quarterly water meter and groundwater levels

Quarterly water meter and groundwater levels

Quarterly water meter and groundwater levels

Monthly water meter readings and groundwater levels within a dedicated monitoring well

Measurement of Groundwater Use

Each project shall be equipped with a totalizing water meter, meeting American National Standards Institute (ANSI) Cold-Water standards, to measure groundwater use. Typically, the meter will be installed at the well head and measure all extraction from the well. Additional meters may also be required for monitoring the water use of separately regulated or permitted facilities or operations. Water meters must be calibrated at least once every five years. See Appendix A for additional information related to water meters.

In addition to recording groundwater use, a photograph of the face of the water meter with sufficient resolution to read the meter value shall be taken on the date of the last meter reading of each year.

Groundwater pumped shall be reported in gallons.

Measurement of Groundwater Level

Groundwater level (depth to water) is the depth from a reference point on the well casing to the water surface within the well. For Very Low, Low, and Moderate Use projects, depth to water is measured within the water supply well itself. High Use projects approved through a Use Permit may be required to install a dedicated monitoring well.

Water supply wells that will be used for depth to water measurements shall be equipped to enable regular measurements of depth to water. There are a variety of methods and technologies available. Most often, a sounding tube, port, or other device is installed by a well contractor to enable accurate depth to groundwater measurements. For wells under artesian conditions (where the water level is above the well head) the well head must be tightly sealed and a pressure gauge with units of feet installed at the well head.

In all cases, the well being used for depth to water measurements must be marked with a measuring reference point on the well casing from which depth to water measurements will be made. The monitoring well’s latitude and longitude must be surveyed, measured using a GPS device, or derived from digital map, and provided in decimal degrees to at least 5 decimal places using the WGS 84 coordinate system. The ground surface at the monitoring well and elevation of the monitoring well’s reference point must be provided in feet above sea level in NAVD88 datum.

Depth to water is measured by first turning the pump off, allowing the well to stabilize and equilibrate to static water level, and then, before restarting the pump, recording the depth to water. Equilibration to static water level can be considered achieved if the depth to water has not changed by more than 0.1 feet over a one (1) hour period. Typically, a twelve (12) hour non-pumping period is required to achieve equilibration.

Prior to turning off the well pump, the following fire response precautions shall be taken:

  1. Prior to turning off the pump, inspect fire storage tank(s) on the site to ensure that tanks are full.
  2. When the pump is turned off, a sign with written instructions on how to turn the pump back on in case of emergency must be placed on or immediately adjacent to the pump’s on‑off switch. The instruction sign shall be made of metal or plastic with letters shall be at least two (2) inches tall and written in contrasting colors, with words visible from at least 25 feet away.

Dedicated Monitoring Wells. A dedicated monitoring well is a well used solely for the purpose of monitoring groundwater. Similar to a production well, a well permit must be obtained before construction of the monitoring well. A water supply well may be converted to a monitoring well by removing the pump. The monitoring well shall be the same depth and contain the same screened interval as the water supply well, and be representative of the geologic and hydrologic conditions of the water supply well. The monitoring well will be located as far from other water wells, streams, waste water disposal fields and ponds as the parcel will allow, yet be located within the same geologic formation(s) as the primary water well.

See Appendix B for additional discussion of depth to water measurements.

Reporting Requirements

Groundwater metering and monitoring data must be submitted annually to Permit Sonoma by January 31 of the year following the year being reported through Permit Sonoma’s online data submittal process.

Permit Sonoma establishes and uses a Water Resources Monitoring record (WRM Record) for each project following submittal of WRM Application, and groundwater reporting data is managed under the WRM Record.
PJR-147 Water Resources Monitoring Application form (PDF)

Upon receipt of an annual email from Permit Sonoma with instructions and a link to the online reporting form, the WRM Record contact will complete the online form, and submit to Permit Sonoma.

The online reporting form requires the following information:  annual water use, water meter readings at the required interval (annual, quarterly, monthly), a photograph of the water meter face at the end of the monitoring year, and measurements of depth to water at the required interval. Any additional water-related monitoring reports or studies that are required to be submitted for the project must also be submitted through the online reporting form or by email.

If the permitted use has not yet commenced, the use has ceased, or groundwater monitoring data is unavailable for another reason, a signed statement to this effect must be submitted using PJR-122 Groundwater Monitoring Program Affidavit (PDF).

If the property has transferred ownership, the WRM Record contact should return the affidavit form indicating property transfer, its date, and other relevant information requested by the form related to changes in ownership.


Sonoma County General Plan Water Resources Element, Sonoma County Code Section 26-88-254 and 25b-12

Approved By

Approved By:  Tennis Wick, Director

Reviewed By Department Manager:  John Mack, Division Manager

Reviewed By County Counsel:  Jennifer Klein, Chief Deputy County Counsel

Lead Author:  Robert Pennington, Professional Geologist

Appendix A – Water Meters

Totalizing water meters are devices used to measure and record the cumulative volume of water that has passed through the meter. For the purposes of this document, a water meter refers to a device that measures, at a minimum, the total volume of groundwater extracted from a well.

Permit Sonoma requires a totalizing water meter that meets specifications of ANSI Cold-Water standards be used. Meters should have a “odometer” that presents the total amount of water that has passed through the meter. Totalizing meters are commonly used for residential, commercial, and agricultural water system.

Totalizing flow meters can commonly be found at your local water pump supplier or from online equipment suppliers. Each flow meter should have a manufacturer’s seal and should be installed, operated, and maintained to manufacturer’s standards, instructions, and recommendations. Water meters are generally installed by well contractors or plumbers, but may be installed by others handy with basic plumbing. Amongst other factors, meter selection should consider minimum and max flow rate, expected annual use, and whether automatic meter reading (AMR) is desired. AMR technology has many user benefits but adds up front costs.

Meters vary primarily in size, measurement technology, material, and registration and encoding elements. Water meters used for residential service connections are typically between 5/8 and 2 inches in size, and employ one of the following measurement technologies: positive displacement (either nutating disc or oscillating piston), single jet, multi-jet, or fluidic-oscillator. Meters for agricultural uses are typically larger and usually employ propeller, ultrasonic, or electromagnetic technology.

The registration and encoding elements convert the signal generated by the measurement technology into quantitative information that reflects the volume of water that has passed through the meter in a standard unit of measure. The most common units for residential and commercial uses are gallons.

totalizing water meter
Figure 1. Typical appearance of a totalizing water meter. Source: Hialeah Meter

The water meter must meet the following requirements:

  • Meet ANSI Cold-Water standards.
  • Warranted to register not less than 98% and not more than 102% of the actual volume of water passing the meter for all rates of flow within the meter size’s range of flow.
  • Equipped with a direct reading rate-of-flow indicator showing instantaneous flow in gallons per minute or a sweep hand indicator for which rate-of-flow can be determined by timing.
  • Equipped with a visual, volume-recording totalizer recorded in gallons, cubic feet, or acre-feet.
  • Calibrated prior to installation.
  • Installed near the well (upstream of all connections to the main discharge line) to measure the entire flow from the well, or installed upstream of the metered use (such as upstream of a winery building)
  • Installed such that there is full pipe flow at all times. Full pipe flow can be achieved by elevating a downstream section of pipe, or constructing a gooseneck in the downstream pipe. Pressurized systems will normally have full pipe flow.
  • Installed with a specific minimum length of unobstructed straight run of pipe without valves or elbows upstream and downstream of the meter, based on manufacturer’s recommendations. Such recommendations may be as much as 10 pipe diameters upstream and 5 pipe diameters downstream, so that for a 12 inches discharge pipe, 120 inches would be required upstream and 60 inches would be required downstream. Usage of straightening vanes may be used to reduce the lengths. Lengths are generally longer for propeller meters than other types of meters.

Methods for Collecting Meter Measurements

  • Inspect the groundwater well and surrounding area. Note any new or changed conditions.
  • Refer to previous well meter readings to estimate the expected reading.
  • Record the totalized volume from the meter face on a standardized form.
  • Note if the meter has “rolled over” and started counting from zero again.
  • Take a photo of the meter face that legibly shows the totalizer numbers.

Meter Calibration

Calibration and validation of each meter must be conducted once every five years. Proof of calibration must be submitted to Permit Sonoma upon request. Note that installing filters ahead of the meter units help make the water cleaner and minimize fouling and wear on propeller and other mechanical meters; however, these filters may require periodic backwashing and/or replacement per manufacturer’s instructions to maintain their effectiveness.

Additional Information Related to Metering

Department of Ecology, State of Washington. Liquid Flowmeters – A Guide for Selecting a Flowmeter for Pressurized Systems.

Department of Ecology, State of Washington. The Basics: How to Read Your Meter.

Appendix B – Depth to Water Measurements

Depth to Water is the depth from a reference point on the well casing to water within the monitoring well. Depth to Water will increase when a water supply well is pumping and recover slowly to equilibrium or “static water level” when the well is turned off and allowed to rest.

The intent of Permit Sonoma’s monitoring program is to measure static water level. Thus, operators that use a water supply well as a monitoring well are asked to turn off the well pump the night before and measure the Depth to Water in the morning after water levels have had time to recover. Operators that have a dedicated monitoring well, that is not used to pump water, generally do not need to worry about turning off well pumps before taking measurements.

Methods to Take Depth to Water Measurements

There are many ways to measure depth to water. The method you choose will depend on the configuration of your well, cost, and ease. Permit Sonoma advises that you consult with an experienced well contractor or other qualified professional and have them either take measurements on a regular interval as required or provide you or your staff detailed training.
The most common methods for measuring Depth to Water include those below:

  1. Sonic Well Sounders

    Sonic well sounders use sound waves to measure the depth to water level by bouncing sound waves off the surface of the water. Sonic well sounders are simple to use and provide instant data. There is no risk of contaminating the well because nothing touches the water and there are no probes or wires to hang up.

    Note, we recommend periodically checking the Depth to Water measurement with an alternative direct method, such as an Electric Water Level Probe, to verify that the sonic well sounder is working correctly.

  2. Electric Water Level Probes

    Electric water level probes consist of a spool of dual conductor wire, with graduated markings like a long tape measure, with a probe attached to the end and an indicator. When the probe contacts the water, the circuit closes and a light or audible signals contact.

    Note, disinfect the measuring device with a dilute chlorine bleach solution before using it to prevent well contamination. Make sure the instrument is working by dipping the probe into a bucket of clean water.

    Slowly lower the probe through a port or sounding tube at the well head and down the well casing. If the probe gets caught up on wires, pipes or other material in the well, pull back and try again. You may need to try several times before finding a free path down to the water. When the indicator light or buzzer signals that you have reached the water, mark the cable at the reference point at the well casing, and record the Depth to Water result.

  3. Wetted Steel Tape

    A wetted steel tape is simply a long measuring tape with a chalk coating applied to the bottom end. You can measure the Depth to Water by lowering the steel tape into the well until the lower part of the tape is under water. When you remove the tape, the section of the tape that was submerged will be evident from removal of the chalk. The wetted distance and total length of tape that was lowered can be subtracted to find the Depth to Water.

    Note, disinfect the tape with dilute chlorine bleach solution before using it to prevent contaminating your well. Food grade chalk should be applied to the lower end of the tape after disinfection.

    This method is limited by the length of the tape, and usually used on wells where the Depth to Water is shallower than about 50 feet.

  4. Air Line Device

    A well contractor can install an airline device with a pressure gauge that can be used to measure Depth to Water. Once installed, this system does not require opening the well to make measurements. An experienced well contractor or other qualified professional should provide detailed training on how to make measurements using this system.

  5. Pressure Gauges

    For artesian wells where the static water level is above the top of the well head, a pressure gauge in units of feet can be installed that measures equivalent depth of water above the pressure gauge. In this case, the Depth to Water would be above the well and should be reported as a negative value.

  6. Pressure Transducers

    Pressure transducers are submersible sensors that measure the pressure of the depth of water above the sensor in the well and send information to above-ground data loggers or transmitters. Once installed, this system does not require opening the well to make measurements. The system will continuously record water levels, and can be setup to transfer data to the cloud or a computer for real-time monitoring. An experienced well contractor or other qualified professional should install this type of system.