8-2-1 Water Supply, Use and Conservation Assessment Guidelines

Version: 05/01/2024

On this page:

• Purpose
• Authority
• Procedure
• Definition
• Approved By
• Appendix A: Default Water Use Guidelines and Site-Specific Water Use Rates
• Appendix B: Agricultural Water Conservation Practices

The purpose of this policy is to provide guidance to applicants and their representatives on how to prepare a Water Supply, Use, and Conservation Assessment (henceforth, the “Assessment”). The Assessment may be a standalone document, or supplemental to a hydrogeologic study, Zero Net Use report, or other water supply related report. These guidelines are intended for discretionary and ministerial projects.

Discretionary projects that are dependent on groundwater or surface water will typically require an Assessment with the use permit application. The Assessment will inform the environmental review process and conditions of approval.

An Assessment may also be required for non-discretionary projects, such as a well permit that must comply with Level II conservation requirements, or development of an accessory dwelling unit in a water scarce area where zero net increase in groundwater use is required.

Sonoma County General Plan, Water Resource Element Goals WR-2 and WR-4, Objective WR-4.1, WR-4.2, and WR-4.3, and Policies WR-2c, WR-2d, WR-2e, WR-4b, and WR-4f.

Sonoma County Code Section 25B-13.

The following information is required for all Assessments unless indicated otherwise by Permit Sonoma:

1. Introduction

   1. Name and credentials of the individual preparing the Assessment
   2. Project description;
   3. Study area description. Generally, the study area will be the project parcel, but may extend to the local groundwater basin or recharge area, subject to approval by the Director;
   4. Photographs of the site.

2. Site Plan

   Prepared in accordance with Sonoma County’s Site Plan Requirements for Planning Applications (PJR-129) and includes the following:

   1. Delineation of the study area;
   2. Water-related infrastructure including wells, pools, reservoirs, ponds, water tanks, rainwater catchment surfaces, stormwater features, leach fields, wetlands, springs, streams, and drainage ways;
   3. Existing and proposed irrigated landscape and irrigated agricultural areas.

3. Water Use Estimates

   1. Estimate existing and proposed water uses of the project, parcel, or study area, as applicable to the Assessment;
   2. Water use estimates should be from default water use rates and/or methods (Appendix A). Note, similar methods and assumptions of water use should be used for existing and proposed conditions;
   3. Distinguish water uses, including but not limited to: residential domestic, employee, project-related irrigation, landscape irrigation, agricultural irrigation, other water uses;
   4. Identify the water source(s) for each use;
   5. Provide tables of annual and monthly water use for each use and each source.

4. Water Conservation Measures

   1. Describe water conservation measures applicable to the proposal that guarantee with reasonable certainty that water conservation will be achieved:
      1. Water efficient landscaping;
      2. Plumbing fixtures;
      3. Water efficient cleaning and sanitation equipment;
      4. Water use meters including sub-meters with leak detection monitoring;
      5. Graywater or process water reuse;
      6. Agricultural water conservation practices – see Appendix B;
      7. Other.
      Note: Water conservation measures reliant on adjustment of personal habits will not be approved.

The following information should be provided, as applicable to the Assessment:

5. Water Wells

   1. Provide all available well completion reports for existing wells, abandoned wells, or attempted wells on the project parcel;
   2. Provide available yield tests for wells that provide water for the project or parcel.

6. Surface Water And Springs

   1. Describe surface water diversion and storage systems for the project or parcel;
   2. Provide available surface water rights or registration documentation;
   3. Provide available yield tests for springs that provide water for the project or parcel;
   4. If proposed, provide preliminary design details and grading plans for surface water impoundments or diversions.

7. Rainwater Capture

   1. Preliminary design specifications related to rainwater catchment. Rainwater catchment systems shall meet the specifications of California Plumbing Code chapters 15 and 16;
   2. Maximum available rainwater volume shall be estimated using the formula below:
      
      Max Volume = 0.6 x 0.62 x Roof Catchment Area x Ave Annual Precip
      
      Max Volume is in gallons
      Roof Catchment Area is the contributing area of the roof in square feet
      Ave Annual Precip is in inches as available through the Sonoma County Cannabis Viewer
      0.6 is a factor of safety multiplier to account for drought years and system efficiency
      0.62 is a unit conversion
      
      Note: Rainwater storage tanks of larger size may be proposed, but additional volume beyond the (Max Volume) may not be used to credit water uses during the dry season (April 1 - October 31)

8. Trucked Water

   1. Provide the trucking company name, source, and letter or contract with the supplier.

9. Recycled Water

   1. Describe offsite recycled water source, availability, and letter or contract with the supplier;
   2. Describe graywater or process water reuse.

10. Enhanced Groundwater Recharge Plan

    1. Prepared and certified by a Qualified Professional;
    2. Numeric estimate of recharge to groundwater under existing and proposed conditions;
    3. Conceptual design details and grading plan;
    4. Increased recharge to groundwater may be used to offset increased groundwater use at a ratio of 2 to 1.

Qualified Professional

A professional geologist, engineer, or landscape architect, acting within the scope of their license. A qualified professional must hold a valid license in the State of California.

Approved By: Tennis Wick, Director

Reviewed By Department Manager:  John Mack, Division Manager

Reviewed By County Counsel:  Christa Shaw, Deputy County Counsel IV

Lead Author:  Robert Pennington, Professional Geologist

Default Water Use Guidelines

Residential

Type of Water Use, Volume in Acre-feet per Year

Landscape

Type of Water Use, Volume in Acre-feet per Year

Agricultural

Type of Water Use, Volume in Acre-feet per Year

Winery

Type of Water Use, Volume

Commercial and Industrial Uses

Type of Water Use, Volume

Employees

15 gallons per shift

Other Uses

See Sonoma County Onsite Wastewater Treatment System Regulations and Technical Standards (OWTS Manual), or another published reference.

Site-Specific Water Use Rates

Site-specific landscape water use should be estimated in accordance with Sonoma County’s Water Efficient Landscape Ordinance (WELO).

Water use rates may deviate from the above listed default use rates with site-specific data or published reference, and approval of the review authority.

Agricultural Water Conservation Practices

Agricultural water conservation plans must include sections and components listed below.

Note, for well permit applicants subject to Level II Conservation requirements, enrollment in an agricultural practices monitoring and certification program, approved by the Director, shall fulfill the requirement for a agricultural water conservation practices plan. Approved programs are listed on Permit Sonoma’s Water Wells – Water Conservation and Best Management Practices page.

1. Soil Amendments for Soil Permeability and Water Holding Capacity. Soil properties, including organic carbon concentrations, influence soil permeability and water holding capacity. The agricultural water conservation practices plan must include the following components:
   1. Monitoring methods, frequencies and locations that will be used to monitor soil properties. Monitoring should include a combination of direct permeability testing, soil sampling, and tracking of soil inputs and outputs.
   2. Description of objectives for permeability, organic carbon concentration, water holding capacity, and other monitored components.
   3. Description of how monitoring results will guide agricultural practices or alterations including soil amendments, cover crops, buffer strips, and tillage.
2. Cover Crops and Groundcover. Cover crops offer a practical and cost-effective means of protecting soils from erosion and supplying the organic matter needed to maintain and improve soils and increase recharge. Sites with cover crops may use more water compared with sites without. However, cover crops increase water infiltration, potentially offsetting this difference. Some sites may choose to use other types of groundcover such as hay or mulch. The agricultural water conservation practices plan must include the following components:
   1. Type and coverage of groundcover.
   2. Groundcover application rates such as pounds of seed per acre or tons of straw per acre.
   3. Schedule for groundcover application. Groundcover must be applied prior to onset of winter rains.
   4. Groundcover maintenance including re-seeding, mowing, and tillage.
   5. Cover crop germination and growth should rely predominantly on rainfall or recycled water.
   6. Groundcover monitoring plan with clear objectives. The plan should clearly define how monitoring results will guide management actions including application of additional groundcover, seed, or other temporary erosion control measures.
3. Irrigation Management Strategy and Water Budget. Each site must have an irrigation management strategy that includes goals for irrigation water efficiency and monitoring methods. Management strategies should include monitoring of plant vigor, soil moisture, and climate conditions, and may include delayed onset of irrigation, regulated deficit irrigation, or dry farming. Monitoring must allow the operator to estimate evapotranspiration and inform the volume of irrigation water applied. Multiple monitoring tools should be used, including use of climate station data, onsite monitoring of plant stress or vigor, soil moisture, stomatal conductance, or other methods. The agricultural water conservation practices plan must include:
   1. Locations and schedule of observations or sampling needed to effectively characterize the site and calculate prescribed irrigation volumes.
   2. How monitoring results will guide irrigation practices including timing and volumes of irrigation water.
   3. For sites using delayed onset irrigation, clearly specify the methods used to determine when irrigation should commence.
   4. For sites using regulated deficit irrigation, clearly specify the fraction of crop evapotramspiration that irrigation water and soil water should provide by irrigation cycle (e.g. month, week, etc.). The water-holding capacity of the soil and soil water depletion rate must be factored into the water budget to allow for calculation of the amount of soil water available and irrigation water required to meet objectives.
4. Irrigation System Design and Maintenance. The agricultural water conservation practices plan must include:
   1. A site-scale irrigation schematic with irrigation zones, storage tanks, pumps, and water meters.
   2. Irrigation system details, including:
      • Irrigation system type (e.g. drip irrigation, overhead sprayer, etc.);
      • Emitter or sprinkler flow rates and spacing;
      • Filter specifications;
      • Pressure compensation devices and specifications.
5. Irrigation Maintenance. System testing, maintenance methods, and schedule.
   1. Objective flow rates and/or pressure ranges.
6. Measuring Water Use and Groundwater Elevations. Water use metering and monitoring is required to verify irrigation volumes and check for leaks. The agricultural water conservation practices plan must describe the following components in detail:
   1. Meter specifications including make and model.
   2. Meter reading and depth to water measurement methods and schedule.

Additional Agricultural Resources

• Gold Ridge Resource Conservation District
• Sonoma Resource Conservation District
• California Sustainable Winegrowing Alliance
• Fish Friendly Farming Program
• UC Cooperative Extension Sonoma County
• Natural Resources Conservation Service