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8-2-1 Water Supply, Use and Conservation Assessment Guidelines
Version: 01/07/2020
Purpose
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 development of an accessory dwelling unit in a Class 4 groundwater area where zero net increase in groundwater use is required.
Authority
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.
Procedure
The following information is required for all Assessments unless indicated otherwise by Permit Sonoma:
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Introduction
- Name and credentials of the individual preparing the Assessment
- Project description;
- 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;
- Photographs of the site.
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Site Plan
Prepared in accordance with Sonoma County’s Site Plan Requirements for Planning Applications (PJR-129) and includes the following:
- Delineation of the study area;
- Water-related infrastructure including wells, pools, reservoirs, ponds, water tanks, rainwater catchment surfaces, stormwater features, leach fields, wetlands, springs, streams, and drainage ways;
- Delineated irrigated landscape and irrigated agricultural areas.
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Water Use Estimates
- Estimate existing and proposed water uses of the project, parcel, or study area, as applicable to the Assessment;
- 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;
- Distinguish water uses, including but not limited to: residential domestic, employee, project-related irrigation, landscape irrigation, agricultural irrigation, other water uses;
- Identify the water source(s) for each use;
- Provide tables of annual and monthly water use for each use and each source.
Note: Water use estimates by month may be required of discretionary permit applications.
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Water Conservation
- Describe water conservation measures applicable to the proposal that guarantee with reasonable certainty that water conservation will be achieved:
- Plumbing fixtures;
- Graywater or process water reuse;
- Landscape alterations;
- Other.
- Describe water conservation measures applicable to the proposal that guarantee with reasonable certainty that water conservation will be achieved:
The following information should be provided, as applicable to the Assessment
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Water Wells
- Provide all available well completion reports for existing wells, abandoned wells, or attempted wells on the project parcel;
- Provide available yield tests for wells that provide water for the project or parcel.
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Surface Water And Springs
- Describe surface water diversion and storage systems for the project or parcel;
- Provide available surface water rights or registration documentation;
- Provide available yield tests for springs that provide water for the project or parcel;
- If proposed, provide preliminary design details and grading plans for surface water impoundments or diversions.
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Rainwater Capture
- Preliminary design specifications related to rainwater catchment. Rainwater catchment systems shall meet the specifications of California Plumbing Code chapters 15 and 16;
- 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)
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Trucked Water
- Provide the trucking company name, source, and letter or contract with the supplier.
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Recycled Water
- Describe offsite recycled water source, availability, and letter or contract with the supplier;
- Describe graywater or process water reuse.
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Enhanced Groundwater Recharge Plan
- Prepared and certified by a Qualified Professional;
- Numeric estimate of recharge to groundwater under existing and proposed conditions;
- Conceptual design details and grading plan;
- Increased recharge to groundwater may be used to offset increased groundwater use at a ratio of 2 to 1.
Definition
- 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
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
Appendix A
Default Water Use Guidelines
Residential
Type of Water Use, Volume in Acre-feet per Year
Primary dwelling indoor water use (no landscaping) | 0.2 |
---|---|
Primary dwelling with unspecified landscaping | 0.5 |
Accessory dwelling indoor water use (no landscaping) | 0.1 |
Accessory dwelling with unspecified landscaping | 0.25 |
Landscape
Type of Water Use, Volume in Acre-feet per Year
Lawn | 3.6 per acre |
---|---|
Other Landscaping | 1.8 per acre |
Pools and decorative water features | 0.1 per 1000 square-feet |
Agricultural
Type of Water Use, Volume in Acre-feet per Year
Vineyard irrigation | 0.6 per acre |
---|---|
Irrigated pastures | 3.6 per acre |
Irrigated orchards | 1.8 per acre |
Cannabis: Indoor or mixed light | 4.0 per acre canopy |
Cannabis: Outdoor | 2.0 per acre canopy |
Livestock (sheep or cows) | 0.05 per acre |
Winery
Type of Water Use, Volume
Process water |
2.15 acre-feet per 100,000 |
---|---|
Tasting room visitation | 3 gallons per visitor |
Events with onsite catering | 15 gallons per visitor |
Commercial and Industrial Uses
Type of Water Use, Volume
Food processing | 31.0 acre-feet per employee per year |
---|---|
Brewery process water | 7 gallons of water per gallon of beer produced |
Printing/Publishing | 0.60 acre-feet per employee per year |
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.