TO: Napa County Planning Commission
FROM: Brian D. Bordona, Director of Planning Building and Environmental Services
REPORT BY: Kelli Cahill, Planner III
SUBJECT: Diamond Creek Vineyards Winery Use Permit Major Modification No. P19-00177-MOD
RECOMMENDATION
title
DIAMOND MOUNTAIN VINEYARD COMPANY INC/ DIAMOND CREEK VINEYARDS / MAJOR MODIFICATION NO. P19-00177 - MOD & REQUEST FOR EXCEPTION TO THE NAPA COUNTY ROAD AND STREET STANDARDS
CEQA STATUS: Consideration and possible adoption of a Mitigated Negative Declaration and a Mitigation Monitoring and Reporting Program (MMRP) (SCH#2025120440). According to the proposed Mitigated Negative Declaration, the proposed project would not have any potentially significant environmental impacts after implementation of mitigation measures. Mitigation measures are proposed for the following area: Biological Resources. The project site is not included on a list of hazardous materials sites compiled pursuant to Government Code Section 65962.5.
The project was scheduled to be heard at the Planning Commission Hearing of January 7, 2026. However, due to an unannounced closure of the Governor’s Office of Land Use and Climate Innovation, the posting of Initial Study-Mitigated Negative Declaration prepared for this project was delayed, Since the project was not posted in a timely manner that would allow State or public review for the required 30 day review period prior to the hearing, the item was continued to January 21, 2026. In accordance with Section 15105(b) of the California Environmental Quality Act (CEQA) Guidelines, Napa County submitted the proposed Initial Study/Mitigated Negative Declaration to the State Clearinghouse for a 30-day review period beginning December 10, 2025, and running through January 9, 2026.
REQUEST: This application was submitted to participate in the County's Code Compliance Program as described in Resolution No. 2018-164 adopted by the Napa County Board of Supervisors on December 4, 2018. The proposal is to modify an existing winery Use Permit and subsequent modifications to recognize and approve items that are out of compliance with the permitted entitlements and for expansion beyond existing entitlements such as construction of a new winery building and agricultural storage building, increase in annual wine production, number of employees, weekly visitation, on-premises consumption of wine produced on-site, additional parking, decrease in the number of marketing events, necessary infrastructure improvements and upgrades to the wastewater system, and conversion of the existing winery building to a single-family residence with parking. The request also includes an Exception to the Napa County Road and Street Standards. The project is located on a 78.12-acre holding within the Agricultural Watershed (AW) zoning district and General Plan designated as Agriculture, Watershed, and Open Space (AWOS) at 1500 Diamond Mountain Road, Calistoga, CA 94515. APN 020-440-004 (Winery Parcel) and 020-400-012 (Residential Parcel).
STAFF RECOMMENDATION: Adopt the Mitigated Negative Declaration/MMRP and approve an Exception to the Napa County Road and Street Standards (RSS), and a Winery Use Permit Modification subject to the recommended conditions of approval.
STAFF CONTACT: Kelli Cahill, Planner III, (707) 265-2325 or kelli.cahill@countyofnapa.org
APPLICANT AGENT CONTACT: Lester Hardy, Attorney; (707) 480-8093; lester@lfhardy.com
CONTINUED FROM JANUARY 7, 2026 PLANNING COMMISSION MEETING.
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EXECUTIVE SUMMARY
Proposed Actions:
That the Planning Commission:
1. Adopt the Mitigated Negative Declaration and the MMRP based on Findings 1-7 in Attachment A;
2. Approval of an Exception to the Road and Street Standards, based on Findings 8-9 of Attachment A; and,
3 Approval of Use Permit Major Modification No. P19-00177, based on Findings 10-14 of Attachment A and subject to the recommended Conditions of Approval in Attachment B.
DISCUSSION:
Due to The project was scheduled to be heard at the Planning Commission Hearing of January 7, 2026. However, due to an unannounced closure of the Governor’s Office of Land Use and Climate Innovation, the posting of Initial Study-Mitigated Negative Declaration prepared for this project was delayed, Since the project was not posted in a timely manner that would allow State or public review for the required 30 day review period prior to the hearing, the item was continued to January 21, 2026.
This application was submitted to participate in the County's Code Compliance Program as described in Resolution No. 2018-164 adopted by the Napa County Board of Supervisors on December 4, 2018. On March 29, 2019, this application was submitted to participate in the County’s Code Compliance Program as described in Resolution No. 2018-164. The request is for approval of a modification to previous project approvals for an existing 10,000 gallons per year winery and an Exception to the Napa County Road and Street Standards (RSS) to allow the following:
A. COMPONENTS NECESSARY TO REMEDY EXISTING VIOLATIONS:
1) Recognition and approval of by-appointment visitation for tours and tastings for a maximum of 22 daily and 47 weekly visitors (approved for 10 daily and 10 weekly) six (6) days a week from 9:00 a.m. to 6:00 p.m. (approved for five days a week);
2) Recognition and approval of six (6) full-time and two (2) part-time employees (approved for five (5) full-time employees);
3) Recognition and approval of on-premises consumption of wines produced on site in outdoor areas on the terrace in accordance with Business and Professions Code Sections 23358, 23390 and 23396.5(this was not allowed at the time of the entitlements); and
4) Recognition and approval of retail sales at the winery and removal of COA No.1 under Permit #96378 restricting retail sales of wine to invited marketing guests.
B. EXPANSION BEYOND EXISTING ENTITLEMENTS:
1) Increase annual wine production from 10,000 gallons to 25,000 gallons;
2.) Increase weekly tours and tastings from 47 persons per week (recognized above) to 60 persons per week maximum. Reduce daily visitation from 22 (recognized above) back to 10 persons per day with a weekly maximum of 60 persons.
3) Revise the existing marketing plan to include catered food prepared off-site and the number of events be increased from five (5) events with a maximum of 100 guests each to:
• Ten (10) annual events with no more than 12 one way vehicle trips as follows:
• Five (5) events to occur between 10:00 am and 2:00 pm
• Five (5) events to occur between 6:00 pm and 10:00pm
• One (1) annual event with no more than 20 one way vehicle trips to occur between 6:00 pm and 10:00 pm
4) Increase the number of employees from six (6) full-time (as recognized above) to eight (8) full-time and two (2) part-time employees;
5) Convert the existing 7,540 sf winery into a single-family residence with four (4) private parking spaces;
6) Construct a new 23,245 sf winery structure (18,600 sf production, 3,960 sf hospitality, 685 sf enclosed patio);
7) Construct a new 2,170 sf agricultural shop building;
8) Install twenty-two (22) new parking spaces will be constructed at the new winery structure (approved for five (5) parking spaces at the existing winery), with four (4) being required EV charging stations;
9) Install improvements to the driveway that will include:
• Improve the existing winery driveway to meet the 22 foot wide Napa County Road and Street Standards for commercial driveways, with the exception of 233 feet of access and driveway as detailed below.
• Improve the existing vineyard avenue to construct a new private one-way loop that will serve the proposed residence and the existing vineyard.
10) Addition of two (2) 30,000-gallon fire suppression tanks;
11) New domestic and winery wastewater systems, including a 40,000-gallon treated process wastewater tank for onsite vineyard irrigation;
12) Increase Production hours during the non-harvest season to six (6) days a week from 7:00 am to 6:00 pm;
13) Increase daily by appointment-visitation hours to six (6) days a week from 9:00 am to 6:00 pm; Monday through Saturday;
14) On-premises consumption of wines produced on site in outdoor areas at the new winery structure in accordance with Business and Professions Code Sections 23358, 23390 and 23396.5;
15) Prior to increasing production volume from 10,000 to 25,000 gallons, construction of the new winery building and/or agricultural storage building, the following shall be completed:
a. The property owner shall submit and obtain approval of a Lot Line Adjustment through the Public Works Department to adjust the parcel boundaries to have all winery uses on the same parcel as the existing winery which is proposed to be converted to a single-family residence, the existing residence would remain on its own parcel;
b. Install a new domestic wastewater system for the existing and proposed residence (converted existing winery structure), and process wastewater treatment and disposal system; and
c. Installation of road improvements including widening, the new looped driveway to the new residence, emergency pull outs and repairs to the historic bridge foundation and shared access off of Diamond Mountain Road.
16) A total of 120 trees are proposed to be removed or limbed to maintain adequate access for emergency vehicle access, and the preservation of 4.8 acres of vegetation canopy cover will be deed restriction.
The request also includes an exception to the Napa County Road & Street Standards (RSS) from the commercial driveway width standard of 22-feet where the proposed roadway width requested is 13-15 feet within an area totaling 233 feet to limit earthmoving and grading on steep slopes and limiting vegetation removal within the setback of an ephemeral drainage, while still providing access for emergency vehicles.
The holding is 78.12 acres located on the west side of State Highway 29 and north of Diamond Mountain Road. The project driveway is located approximately 270 feet north at the intersection of Diamond Mountain Road and the shared driveway, and 0.75 miles northwest of the intersection of Diamond Mountain Road and State Highway 29. The proposed project is in an area that is relatively flat to moderately flat adjacent to the existing winery. The project site comprises two parcels, APN 020-400-012 is currently developed with a single-family residence, and APN 020-440-004 is currently developed with a winery, associated outbuildings, approved existing vineyards, a reservoir permitted for recreation only, two additional small landscape pond features, and an existing driveway accessed by an existing historic bridge crossing an ephemeral drainage. As part of the project, the driveway will be improved and the existing bridge will include repairs to the footings as the stream bed has eroded, which will require permitting through the California Department of Fish and Wildlife. As there are no proposed modifications to the bridge width, the County has no permitting requirements.
Staff has reviewed the proposed project and supports granting approval. Staff prepared an Initial Study/Mitigated Negative Declaration and MMRP that evaluated the potential environmental impacts of the proposal as presented by the applicant. Staff determined that the applicant’s proposal would not have any potentially significant environmental impacts with incorporation of mitigation measures, based upon the existing conditions of the parcel and given that the proposed physical improvements are limited, generally occurring in already disturbed areas. Therefore, staff recommends adoption of the Mitigated Negative Declaration and MMRP. Furthermore, staff found the requests to be consistent with the Zoning Ordinance, the Napa County Road and Streets Standards, and applicable General Plan policies including the County’s current groundwater requirements.
ENVIRONMENTAL IMPACT
ENVIRONMENTAL DETERMINATION: Consideration and possible adoption of a Mitigated Negative Declaration and a Mitigation Monitoring and Reporting Program (MMRP) (SCH#2025120440). According to the proposed Mitigated Negative Declaration, the proposed project would not have any potentially significant environmental impacts after implementation of mitigation measures. Mitigation measures are proposed for the following area: Biological Resources. The project site is not included on a list of hazardous materials sites compiled pursuant to Government Code Section 65962.5.
The project was scheduled to be heard at the Planning Commission Hearing of January 7, 2026. However, due to an unannounced closure of the Governor’s Office of Land Use and Climate Innovation, the posting of Initial Study-Mitigated Negative Declaration prepared for this project was delayed, Since the project was not posted in a timely manner that would allow State or public review for the required 30 day review period prior to the hearing, the item was continued to January 21, 2026 . In accordance with Section 15105(b) of the California Environmental Quality Act (CEQA) Guidelines, Napa County submitted the proposed Initial Study/Mitigated Negative Declaration to the State Clearinghouse for a 30-day review period beginning December 10, 2025, and running through January 9, 2026.
BACKGROUND AND DISCUSSION
PROJECT INFORMATION:
Owner: Diamond Mountain Vineyard Company Inc.
DBA Diamond Creek Vineyards
383 Fourth Street Suite 400, Oakland, CA 94607
Owner Representative: Nicole Carter, President
1500 Diamond Mountain Road, Calistoga, CA 94515; Phone: (707) 328-8353; email: nicolecarter@diamondcreekvineyards.com
Project Representative: Lester Harder, Esq.; Phone: (707) 480-8093; email: lester@lfhardy.com
General Plan Land Use Designation: Agriculture, Watershed and Open Space (AWOS)
Zoning District: Agricultural Watershed (AW)
Filed: April 2, 2019
Resubmittals Received: October 14, 2019, November 14, 2022, July 10, 2023, February 20, 2024, August 27, 2024, February 7, 2025, May 12, 2025, May 29, 2025
Application deemed complete: July 23, 2025
Courtesy Notice Sent: August 31, 2020, and January 5, 2023
Project site size: 78.12 acres
WINERY CHARACTERISTICS
Approved and Proposed Winery Characteristics
Winery Development Area Approved/Existing: 5,998 sf or 0.14 acres.
Winery Development Area Proposed:14,656 sf or 0.34 acres.
Winery Coverage Approved/Existing: 34,122 sf or 0.78 acres, approximately 1.1% of the property.
Winery Coverage Proposed: 58,634 sf or 1.35 acres, approximately1.8% of the property.
Maximum permitted 25% or approximately 15 acres permitted, whichever is less.
Production Capacity Approved/Existing: 10,000 gallons per year.
Production Capacity Existing: 6,720 gallons per year.
Production Capacity Proposed: 25,000 gallons per year (A portion will be subject to the Winery Definition Ordinance 75% Rule - See Discussion Below).
Winery Building Approved/Existing:7,540 sf to be converted to a single-family residence
Winery Building Proposed: 23,245 sf (18,600 sf production, 3,960 sf hospitality, 685 sf enclosed patio
Agricultural storage Building Proposed: 2,170 sf
Cave: None existing or proposed
Accessory/Production Ratio Approved/Existing: 3,740 sf accessory/3,800 sf production - approximately 98%
Accessory/Production Ratio Proposed: 3,960 sf accessory/18,600 sf production - approximately 21%
Maximum permitted 40% accessory uses to production uses.
Number of Employees Approved: five (5) employees including the owner
Number of Employees Existing: six (6) full-time employees, two (2) part-time employees for a total of eight (8) Employees
Number of Employees Proposed: eight (8) full-time and two (2) part-time employees for a total of ten (10) Employees.
Visitation By-Appointment - Approved: Maximum of 10 visitors per day with 10 visitors per week
Visitation By-Appointment - Existing: Maximum of 22 visitors per day with 47 visitors per week
Visitation By-Appointment - Proposed (expansion beyond approved and beyond existing unpermitted levels):10 per day with 60 visitors per week.
Marketing Program - Approved: five (5) events per year with a maximum of 100 people.
Marketing Program - Existing: no changes from approved marketing program.
Marketing Program - Proposed: Revise the existing marketing plan to include catered food prepared off-site and the number of events be increased from five (5) events with a maximum of 100 guests each to:
• Ten (10) annual events with no more than 12 one-way vehicle trips as follows:
• Five (5) events to occur between 10:00 am and 2:00 pm
• Five (5) events to occur between 6:00 pm and 10:00 pm
• One (1) annual event with no more than 20 one-way vehicle trips to occur between 6:00 pm and 10:00 pm
Days and Hours of Hospitality - Approved: Days and Hours were five (5) days a week 10:00 a.m. to 4:00 p.m.
Days and Hours of Hospitality -Existing: six (6) days per week 10:00 a.m. to 4:00 p.m.
Days and Hours of Hospitality - Proposed: six (6) days a week 9:00 a.m. to 6:00 p.m.
Hours of Operation for Production - Approved: unspecified
Hours of Operation for Production - Existing: Five (5) days a week on Monday through Friday, 7:00 a.m. - 6:00 p.m.
Hours of Operation for Production - Proposed: Six (6) days a week 7:00 a.m. to 6:00 p.m.
Parking - Approved: five (5)
Parking - Existing: five (5)
Parking - Proposed: 22 new spaces constructed with the new winery structure (project will comply with California building code related to accessible parking and electric vehicle charging stations), four (4) additional parking spaces will be dedicated for residential use only.
Setbacks
Required Property Line setbacks: 20 feet.
Existing Property Line setbacks: The existing and proposed winery structure exceeds 20 feet from side and rear property lines.
Required Road Setback: 600 feet from State Highway 29 and 300 feet from Diamond Mountain Road and shared road off Diamond Mountain Road
Approved/Existing Road Setback - Winery Building: Approximately 4200-feet from the centerline of the highway, approximately 450 feet from Diamond Mountain Road, and over 1,250 feet from the shared road.
Proposed Road Setback: The proposed winery will be constructed approximately 3,600 feet from State Highway 29, approximately 300+ from Diamond Mountain Road, and over 370 feet from the shared road.
Adjacent General Plan Designation / Zoning / Land Use:
North: AWOS General Plan Designation / AW Zoning - properties range in size from six (6) to 40 acres, with the Calistoga City Limits being less than 1,000 feet north where the Calistoga Hills Resort property is located, the properties include residential, winery and vineyards.
South: AWOS General Plan Designation / AW Zoning - properties range in size from seven (7) to 32 acres with residential, one non-producing winery, and vineyard.
West: AWOS General Plan Designation / AW Zoning - properties range in size from 40 to 270 acres with residential and vineyard one the largest parcel and the smaller parcel being undeveloped.
East: AWOS General Plan Designation / AW Zoning - site properties ranging in size from five (5) to 20 acres with residential, vineyard and wineries.
Nearby Wineries located within one (1) mile of the project:
There are nine (9) wineries within one mile of the project, including three (3) that are currently not yet producing and one (1) within the Calistoga City Limits. Please refer to Attachment L.
Parcel History:
October 1963, a License for Diversion and Use of Water was granted for twenty-six (26) acre feet to be collected from an unnamed stream (aka Diamond Creek). The creek has since been named Kortum Canyon Creek (County GIS Layer - Blue Lined Streams). The License is restricted to Recreational Use only.
April 3, 1972, a use permit (U-437172) was approved by the Planning Commission to construct small limited production winery of 5,000 gallons per year, with no public tours or tastings, or retail sales. All sales were approved to be by mail, and the winery was to be located on the ground level of the residence.
July 20, 1977, a modification (U-447677) to the use permit was approved by the Planning Commission to store, bottle and ship wine in the garage and storage room adjacent to the dwelling and a minimum of five (5) parking spaces.
March 5, 1980, a modification (U-567879) to the use permit was approved by the Planning Commission allowing the increase in wine production from 5,000 gallons to 10,000 gallons per year and construction of two new structures totaling 5,000 sf and the construction of five (5) off street parking spaces.
February 19, 1997, a modification (96387) to the use permit was approved by the Planning Commission, expanding the existing winery to construct a 4,000 sf second story office and storage; there were no changes to the winery operations proposed. The modification included the following which were previously not allowed:
• A marketing plan with:
o Five (5) annual events with a maximum attendance of 100 people
o Retail wine sales to invited guests during marketing events;
• Five (5) employees including the applicant/owner;
• All winery uses, including office and storage, shall be relocated to the existing winery parcel. The area of the owner’s residence presently used for the winery to be used only for personal wine storage and wine library;
• Tours and tastings limited to wine trade only, by prior appointment and shall not exceed a maximum of 10 visitors a day and 10 visitors per week; and
• Retail sales of the wines produced on the site are not permitted, except as noted as part of the marketing plan.
March 3, 1997, an appeal to Use Permit Request 96387 was filed; however, the parties came to a settlement, and the appeal was withdrawn on March 27, 1987, ahead of the April 8, 1987, Board of Supervisors hearing.
October 3, 1997, a modification (97093) to the use permit was approved by the Planning Commission limited to modification of the exterior elevation of the winery building with no changes in size, except for an additional 80 sf of cellar area. No changes to operations.
May 1996 an Agricultural Erosion Control Plan (99138) was approved by the Conservation, Development and Planning Department for 1.4 acres of vineyard development. The majority of vineyard development occurred prior to 1980.
April 2004 an Agricultural Erosion Control Plan Track II replant was approved by the Conservation, Development and Planning Department for the replant of 21.0 acres of the 24.0 acres vineyard development.
Code Compliance History:
December 2018 - The Board of Supervisors approved Resolution No. 2018-164, in part allowed property owners to apply for a permit to voluntarily remedy violations of their approved Use Permits through the County Code Compliance Program.
On March 29, 2019, this application was submitted to participate in the County’s Code Compliance Program as described in Resolution No. 2018-164. Pursuant to that Resolution, a site inspection was conducted by Code Compliance, Planning, Fire, and Environmental Health staff to identify any potential health and safety issues, as well as to review the existing use and proposed changes. Life safety issues included minor Fire and Building Code issues including 17 items such as installing fire extinguishers, posting the winery address, installing an illuminated exit signage in the winery and removal of improper exit door hardware. All issues were resolved, and a final inspection was conducted on July 23, 2023, which found all health and safety issues were addressed.
Discussion Points:
As part of this application, staff analyzed the following requested application types:
1) An Exception to the Napa County Road and Street Standards (RSS); and
2) A Winery Use Permit Major Modification.
Road and Street Standards Exception Request: The Engineering Division and the Fire Department received a request for an Exception to the RSS dated August 20, 2024 (Attachment F), for the access roadway design criteria as part of the proposed project. As identified in the Engineering memo dated July 23, 2025 (see Attachment B), the parcel is served by an existing paved road that starts at the intersection of a private easement with access from Diamond Mountain Road, the road and meanders up the hill for approximately 1,280 feet terminating at the existing winery. The RSS requires a 22-foot minimum width for roads serving commercial uses such as the proposed winery. The majority of the existing road does not meet the minimum width requirement due to environmental and physical constraints that prevent compliance with the standards. Specifically, an RSS Exception Request is requested for two segments of the road: Station 0+50 - 1+80, and Station 2+40 - 4+73.
STA 0+50 to 1+80 - The existing historic bridge has a 13.7’ clear width. This 130‐foot linear section of existing roadway is adjacent to a natural blue line stream. Widening the roadway to a minimum of 22 feet would result in earth disturbance and grading within the stream setback. The applicant is proposing turnouts with clear sight lines on either side of the bridge.
STA 2+40 to 4+73 - The existing road in this area is approximately 15’ clear and includes an existing access gate that has a clear width opening of 15.5’. This 233‐foot linear section of existing roadway is adjacent to a steep slope and several large mature native trees. Widening the roadway to a minimum 22 feet would result in the grading on slopes over 50% and earthwork near the stream setback.
Winery Major Modification Proposal:
Winery Proposal - The project proposes the recognition and approval of existing operations beyond entitlements that would remedy the existing violations, and requests expansion beyond existing entitlements that includes increasing production, visitation, employees, hours of hospitality, decrease the number of marketing events, installation of a new domestic and winery wastewater system, improvements to the existing driveway including increased parking and repairs to a historic bridge crossing, and conversion of the existing winery to a single-family residence.
Visitation and Marketing - The Use Permit Modification approved in 1997 authorized tours and tastings by appointment for a maximum of 10 daily visitors and 10 weekly visitors five (5) days a week from 10:00 a.m. to 4:00 p.m As part of the compliance program, the applicant has provided by-appointment visitation for tours and tastings Logs provided that in 2018-2019, 22 daily and 47 weekly six (6) days a week from 10:00 a.m. to 4:00 p.m. were occurring. The applicant is proposing ten (10) daily visitors with a weekly maximum of 60. The approved Marketing Plan includes five (5) annual events with a total of 100 guests. The proposed project would reduce the number of marketing events to one (1) annual event with 100 guests and one (1) annual event with 50 guests. No impacts were identified in the Initial Study/Mitigated Negative Declaration associated with the requested increases to visitation. The winery comparison chart shows that this winery would be above average in marketing and visitation levels for a 25,000-gallon winery; however, this is due in part to several wineries having few to no visitation or marketing events.
On-Premises Consumption - The applicant requests recognition and approval of on-premise consumption on outdoor terraces of the existing winery, and approval to allow for on-premise consumption at the proposed new winery building within an enclosed outdoor patio on the north side of the winery.
Parking - The winery is entitled with five (5) parking spaces, As part of the proposed project, the new winery will include 22 spaces and the existing winery converted to a single-family residence will have four (4) dedicated spaces. Parking for Marketing Events will be located onsite unless sufficient parking is not available, and shuttle service shall be used in accordance with COA No. 4.3 (Attachment B). The new parking spaces are subject to compliance with the County’s Road and Street Standards per Engineering Conditions of Approval dated July 25, 2025. The proposed parking supply is anticipated to be sufficient to accommodate the increase in the number of employees and visitors.
Water Availability Analysis (WAA) - The WAA (Attachment G) was prepared by RSA Civil, dated January 6, 2026, which replaced the May 23, 2025 report that was analyzed in the Initial Study/Mitigated Negative Declaration to provide clarification of groundwater calculations resulting in a further reduction in water demand. RSA Civil also provided a Supplemental WAA dated January 6, 2026, for the Winery’s “Interim Program” which addresses continued operation of the existing winery until the expansion occurs. Pursuant to CEQA Guidelines Article 6, Section 15073.5, the revisions made to the WAA does not require recirculation of the Initial Study/Mitigated Negative Declaration as the new information would not result in new significant impacts. The discussion herein is based on the January 6, 2026, WAA and Supplemental WAA for Interim Program.
The existing domestic residential, winery, vineyard and landscaping water uses are supplied by two existing groundwater wells. Well #1 provides water for the winery, domestic use and irrigation of 8.2 acres of the 25 acres onsite. The remaining 13.3 acres of vineyard are irrigated with water from Well #2. Well #2 was recently replaced with a new well (Well #3) under a separate permit which will also be discussed below under Tier 3 analysis. Due to concerns about the integrity of the casing within Well #2, an application was approved to abandon and replace in a location approximately 193 feet from Kortum Canyon Creek, which is 172 feet further from the creek than Well #2. The project site is not located within the Napa Valley Subbasin and is subject to a Tier 1 parcel specific recharge based on an area of 73.26 acres where slopes range from 5 to 30%, with the remaining 4.86 acres of the holding are on slopes in excess of 30%. The groundwater recharge rate has been determined by examining the annual rainfall, runoff and species-specific evapotranspiration during winter months. Napa County’s new 10-year PRISM data was used to determine the annual rainfall amount and site runoff volumes. It was determined that the average annual rainfall amounts to 32.52 inches per year. The Diamond Creek Vineyards property has an annual rainfall of 32.52 inches per year, equating to 198.54 acre-feet per year (af/yr) for the parcels. Total evapotranspiration volume that occurs through the vineyard, grassland, and oak tree areas is 21.85 af/yr. The stormwater runoff from the parcels totals 130.60 af/yr. The total average evapotranspiration and runoff is 152.45 af/yr. This equates to a groundwater recharge rate of 46.15 af/yr for the 73.26 acre parcel (or 0.63 acre feet per acre per year). A Tier 2 analysis was not required because there was no identified offsite neighboring wells located within 500 feet or a natural spring within 1,500’ from the two existing wells.
The Tier 1 analysis considered existing uses onsite to include the winery, domestic uses including the addition of single-family residence through conversion of the existing winery building, landscaping and vineyard irrigation. An onsite water audit was completed, and the existing water use based on existing entitlements associated with the winery and vineyards is estimated to be 11.92 acre-feet/year (af/yr). Prior to initiating the winery expansion, the interim water demand is estimated to be 10.83 af/yr. Although there is an increase in production, employees and weekly hospitality guests, the total water use for proposed uses would be 11.54 af/yr before proposed reductions, which is 0.38 af/yr less than the existing usage. The project proposes operational changes to further reduce the proposed water demand, including but not limited to dry farming, reduction in pumping duration, as well as installing water efficient models for pressure and barrel washing, and triggers control for hoses, as well as water conservation and efficient fixtures in employee and public areas. These operational changes would reduce proposed demand by an additional 0.79 af/yr from water demand of 11.54 af/yr to 10.75 af/yr under the proposed reduced usage shown in the following table.
Overall, the proposed project would implement operational changes to reduce water use as follows:
|
Usage Type |
Existing Usage (af/yr) |
Proposed Interim Usage (af/yr) |
Proposed Standard Usage (af/yr) |
Proposed Reduced Usage (af/yr) |
|
Vineyard |
|
|
|
|
|
Irrigation - well |
10.75 |
9.66 |
9.66 |
8.95 |
|
Irrigation - Recycled process Wastewater (credit) |
0 |
0 |
-0.46 |
-0.46 |
|
Landscaping |
0.05 |
0.05 |
0.13 |
0.13 |
|
Residential |
|
|
|
|
|
Existing |
0.75 |
0.75 |
0.75 |
0.75 |
|
Proposed |
0 |
0 |
0.75 |
0.75 |
|
Winery |
|
|
|
|
|
Process Water |
0.22 |
0.22 |
0.54 |
0.46 |
|
Domestic Water |
0.15 |
0.15 |
0.17 |
0.17 |
|
Totals (af/yr) |
11.92 |
10.83 |
11.54 |
10.75 |
|
Estimated Water Recharge (af/yr) |
46.15 |
46.15 |
46.15 |
46.15 |
A Tier 3 Analysis was required as both wells are located within 1,500 feet of a significant stream. Well #2 which provided water for vineyard irrigation only, is located 21 feet from the stream. Therefore, RSA Civil assumed connectivity. The project proposes modification to winery operations that includes the following: 1) reduction in the overall groundwater usage of Well #1 by 0.14 af/yr and reducing a further 0.57 af/yr by year 2029 by converting to dry farming 2.4 acres that are presently irrigated with Well #1. As proposed the new process wastewater system would treat water and reuse onsite to irrigate approximately 1.36 acres with 0.46 af/yr; 2) reduction in groundwater use from Well #2 by 0.32 af/yr initially and reducing further to 0.6 af/yr by utilizing dry farming of 0.7 acres of vineyard; and 3) modification to the well operations for all existing wells by limiting well operations to their current pumping rates while reducing the pumping times for each well.
This will result in a reduction in the daily pumping rates for each well, thereby allowing greater time for aquifer recharge and therefore a reduction of impact (if any) on the stream. The proposed modifications will reduce impacts (if any) relative to existing conditions and thereby meet the requirements of the County of Napa’s January 10, 2024 Tier III Water Availability Analysis guidance memorandum. In addition, groundwater monitoring, metering of the onsite wells including a limitation of groundwater use consistent with the proposed water use detailed in Table 1 and included as conditions of approval (See Attachment B - COAs 4.20(a), 6.15(c) and 9.9 (b)), will further result in the County satisfying its duty to consider impacts to trust resources, and no further analysis is required.
Wastewater System - A Wastewater Disposal Feasibility Study, dated May 27, 2025, was prepared by RSA Civil, detailing the existing system and proposed changes to accommodate the changes in production, employees, and hospitality, and the addition of a new single-family residence. The existing winery waste treatment system consists of two 1500-gallon septic tanks - one for production waste flows and one for domestic waste flows - with both tanks connected to the leach lines. The existing domestic tank is located in a man-made pond. This tank has been inspected, and is in sound working condition. There is also a septic system serving the existing residence located on APN 020-400-012, the leach field for which is located in part where the new winery will be constructed.
The project proposes to install a new Biofiltro system or equivalent to separately treat and disperse winery process wastewater - this system will meet the General Waste Discharge Requirements for Winery Process Water.
In addition, the project proposes either (a) drain and back-fill the pond in which the domestic tank is located or (b) abandon the existing domestic tank and install a new one; and (c) use the existing winery leach lines to serve the proposed residence on the Adjusted Winery Parcel and the existing residence on the Adjusted Residential Parcel.
Biological Resources - As part of the project, approximately 120 trees will be removed, which is 12 less trees than previously documented by the engineer as Pacific Gas and Electric (PG&E) removed these trees as part of their Vegetation Management Transmission Program. The holding contains approximately 26.3 acres of mapped oak woodland, 16.5 acres of Douglas fir, and approximately 25 acres of vineyard. Mitigation Measure BIO-1 shall be implemented consistent with Napa County Code (NCC) section 18.108.020 and General Plan Policy CON-24 t to maintain, improve or restore oak woodlands.
The results of the study also included a review of databases and site reconnaissance for flora and fauna within a 5-mile radius of the project site. The record search identified the potential for 23 special status plant species, and 15 special status animal species have the potential to occur in the area; however, during the site reconnaissance no special status species observed. The project is not anticipated to result in a significant impact with incorporation of Mitigation Measure BIO-2 through Mitigation Measure BIO-5 requiring pre-construction florist surveys prior to ground disturbance, and incorporation of Mitigation Measures BIO-3 through BIO-5 during construction will reduce the potential for direct or indirect impacts to animal and bird species including nesting migratory birds, northern spotted owls and bats that may occur within the vicinity of the proposed project. The project as proposed with incorporation of mitigation measures would result in a less than significant impact to biological resources within the study area, as well as those species that have the potential to occur within nearby habitat.
Additionally, the proposes repairs to the bridge foundation that provides shared access that includes the project site. The work would occur within the ephemeral stream which is likely under the jurisdiction of State and Federal agencies. The work would not occur within the County jurisdiction; therefore, the County would have no permitting requirements. As the bridge repairs are part of the project, the County has included Condition of Approval No. 6.15 to ensure permitting is obtained prior to issuance of any building or grading permits associated with this Use Permit modification. Permits may be required through Responsible State and Federal Agencies such as California Department of Fish and Wildlife, California Regional Water Quality Control Board, and the US Army Corp of Engineers resulting in a less than significant impact to the ephemeral drainage.
Green House Gas Emissions - On April 20, 2022, the Bay Area Air Quality Management District (BAAQMD) adopted new recommended thresholds for determining the significance of individual projects’ greenhouse gas impacts under CEQA. Under the new thresholds, proposed land use projects may be analyzed for consistency with a qualified greenhouse gas (GHG) reduction strategy in the event one has been adopted. To date, Napa County has not adopted a qualified GHG reduction strategy pursuant to CEQA Guidelines section 15183.5. Absent an adopted strategy, BAAQMD recommends that a land use project include specified minimum design elements to ensure that the project is contributing its “fair share” toward achieving the state’s key climate goal of carbon neutrality by 2045. Napa County has not adopted a qualified GHG reduction strategy or an air quality plan; therefore, projects will be evaluated per the BAAQMD recommended minimum design elements. The project proposes to convert the existing winery to a single-family residence and construct a new winery structure and agricultural storage structure, which will require the conversion and new construction to comply with the current version of the California Building Code. The applicant will be required to include as part of the greenhouse gas reduction methods at the winery: VMT reduction plan to prioritize hybrid and electric vehicles, carpooling and shuttle services for marketing events, energy conserving lighting, bicycle incentives, install water efficient fixtures, recycle a minimum 75% of all waste generated, compost a minimum of 75% of food waste and garden materials, implement a sustainable purchasing and shipping program, planting shade trees within 40 feet of the south side of the building elevation, use recycled materials, locally sourced food production, education of staff and visitors on sustainable practices, use a minimum 70 to 80% cover crop in the existing vineyards. A condition of approval will be required to implement all checked Voluntary Best Management Practices Measures submitted with the project application. (See Attachment B - COA No. 6.15)
Grape Sourcing - Winery use permit U-567879 issued in 1980 increased production from 5,000 gallons to 10,000 gallons per year and was not subject to the County’s 75% rule. The existing 10,000 gallons of approved production is not subject to the County’s 75% rule as it was approved prior to the adoption of the Winery Definition Ordinance (WDO). The current request increases production to 25,000 gallons per year of which 15,000 gallons would be subject to the County’s 75% rule. There are currently 25 acres of vineyard onsite that would provide the required 75% estate grapes to be processed at the winery. At 25,000 gallons the maximum production at the winery would be 10,513 cases, the estate grapes would account for 6,307 cases which equates to roughly 15,000 gallons of wine. The increase of 15,000 gallons in production is subject to the County’s 75% rule. (See Attachment B - COA No. 4.6)
Parcel Access - The parcel is accessed via a private driveway off Diamond Mountain Road that serves five parcels, including the two that serve the project. There is a historic bridge crossing an ephemeral drainage on the private section of shared access. The streambed has eroded from under the foundation, which will require repair. A Bridge Condition Report was prepared, recommending repair of the arch foundation to regain full soil bearing support and protection from future erosion and scour. Prior to repairs as detailed in Condition of Approval 6.15(a), the applicant shall obtain all required authorization and/or permits from agencies with jurisdiction over waters of the U.S. As part of the project, the applicant proposes to continue use of the existing driveway as identified by Public Works in a memorandum that details the legal access of Diamond Creek Vineyards, dated April 30, 2025. The private road was once the original alignment of Diamond Mountain Road, which was never abandoned as a public right-of-way. The memorandum provides a graphic showing the right-of-way and an encumbered portion by 020-400-013, which Diamond Creek Vineyards relies on for legal access.
Traffic - The County maintains a set of Transportation Impact Study Guidelines (TIS Guidelines) that define situations and project characteristics that trigger the need to prepare a TIS. Per the County’s current TIS Guidelines, a project is required to prepare a TIS if it generates 110 or more net new daily vehicle trips. Based on the County’s winery trip generation assumptions, the proposed project would be expected to generate 38 daily trips on a weekday and 20 daily trips on a Saturday prior to increasing the number of employees and production levels, and 45 daily trips on a weekday and 20 trips on a Saturday following implementation of the proposed project with increased number of employees and production. This count includes vehicle trips required for 156 tons of grape haul at full buildout. Additionally, the project includes the conversion of the existing winery to a single-family residence which will generate new trips as well. The project at full buildout is anticipated to generate 14,661 annual trips, 632 less trips than currently operating under compliance levels (15,293 annual trips). The new residence is anticipated to contribute 3,471 additional annual trips, which cumulatively would still result in less than 100 new passenger vehicle trips. The project would not conflict or be inconsistent with CEQA Guidelines section 15064.3, subdivision (b). Impacts would be less than significant. All records of the Traffic Demand Management (TDM) activities and resulting data on reductions in Vehicle Miles Traveled (VMTs) will be kept and provided to the County as required.
Conditions of Approval - Site improvements are required to be completed prior to initiating the proposed project including issuance of building permits for the new winery building and agricultural storage building, increases in winery operations beyond existing and recognized levels, such as employees, visitation, marketing, and production. Improvements required to be completed prior to increasing production and the construction of the new winery structure, include recording a Lot Line Adjustment, upgrading the wastewater system and domestic systems, and repairing the foundation of the shared historic bridge crossing within the legal access. (See Attachment B - Condition of Approval (COA) 4.20.c.)
Public Comments - At the time of publication of this staff report, two (2) public comments were received. (See Attachment P)
Decision Making Options:
Pursuant to BOS Resolution No. 2018-164, Staff has provided separate decision-making options for the components of the project necessary to remedy the existing violation and the new expansions beyond existing entitlements for the winery Use Permit Modification.
Decision Making Options Regarding Remedying Existing Winery Use Permit Violations:
Option 1 - Approve Applicant's Proposal to Remedy Existing Violations
Disposition - This option would result in approval and recognition of existing unpermitted conditions. This option would result in an increase in weekly visitation levels, and employees, allow removal of Condition of Approval No. 1 under Permit #96378 restricting retail sales to invited marketing guests and allow retail sales at the winery, and on-premise consumption within the existing winery terraces.
Given that the County used the winery’s existing operations as the environmental baseline for the CEQA analysis related to this application, no potential environmental impacts have been identified with this project proposal. Furthermore, County divisions and departments have reviewed the proposal and are in support of the applicant’s request. There would be no groundwater or wastewater impacts associated with winery operations and this request was found to be consistent with the Zoning Ordinance and applicable General Plan policies.
Action Required - Follow the proposed action listed in the Executive Summary. If conditions of approval are to be amended, specify conditions to be amended at the time the motion is made. This option has been analyzed for its environmental impacts, and the project was found to have less than significant impacts.
Option 2 - Revised Project Request - Reduced Unpermitted Existing Operations
Disposition - This option would reduce unpermitted existing uses on the property that exceed the permitted levels. This could include reduction in daily and weekly visitation, number of employees, retail sales, or on-premise consumption.
Given that the County used the winery’s existing operations as the environmental baseline for the CEQA analysis related to this application, no potential environmental impacts have been identified with this applicant’s project proposal. Staff recommends no changes to the proposed visitation, employee numbers, or on-site consumption. If the Planning Commission elects to pursue this option, the recommended conditions of approval would need to reflect the revised components such as visitation, use of the existing building, and/or employee numbers.
Action Required - Follow proposed actions listed in the Executive Summary and amend scope and applicable conditions of approval to reduce the existing operations. The item may need to be continued to a future date if significant revisions to the recommended conditions of approval are desired.
Option 3 - Deny Applicant Proposal - Return to Levels in the Permitted Entitlements
Disposition - This option would deny applicant’s proposal to remedy existing violations and would require the applicant to operate the winery in compliance with its existing entitlements. This option would result in the need for unpermitted employees to be laid off, a reduction in daily and weekly visitation levels and no retail sales beyond during marketing events, and no on-site consumption on terraces. In the event the Commission determines that the project does not or cannot meet the required findings for the granting of a Use Permit Modification, Commissioners should identify what aspect or aspects of the project are in conflict with the required findings. State Law requires the Commission to adopt findings, based on the General Plan and County Code, setting forth why the proposed Use Permit modification is not being approved.
Action Required - Commission would make a motion to deny the project.
Decision Making Options Regarding Additional Expansion Beyond Existing Conditions:
Option 4 - Approve Applicant's Proposal (Staff's Recommendation for Major Modification and RSS Exception)
Disposition - This option would result in approval of expansion of operations with final buildout including lot-line adjustment between parcels APN 020-440-004 and 020-400-012, repair of the foundation of the bridge, improvements to the driveway consistent with request for exception to the road and street standards, construction of a new winery building, construction a new agricultural storage structure, conversion of the existing winery to a single-family residence, increased weekly visitation levels and levels of employees, increase in parking for the winery and dedicated parking for the new residence, a reduction in marketing events, new domestic and winery wastewater systems, and on-premises consumption on the outdoor terraces of the existing winery and upon full build out on-premise consumption within the enclosed outdoor patio. There shall be no winery activities in the existing or proposed residences. There are potential environmental impacts to biological resources as a result of the expanded project that through incorporation of mitigation measures would result in a less than significant impact. Furthermore, County divisions and departments have reviewed the proposal and are in support of the applicant’s request. There would be no groundwater or wastewater impacts associated with winery operations and this request was found to be consistent with the Zoning Ordinance, the findings for Napa County RSS exception, and applicable General Plan policies.
Action Required - Follow the proposed action listed in the Executive Summary. If conditions of approval are to be amended, specify conditions to be amended at the time the motion is made. This option has been analyzed for its environmental impacts, and the project was found to have less than significant impacts subject to Mitigation Measures.
Option 5 - Revised Project Request - Reduction to the Expansion Request
Disposition - This option would reduce all or some components of the requested expansion to production, weekly visitation, number of employees, and construction of a new winery building, new agricultural storage building, or conversion of the existing winery to a single-family residence. There are potential environmental impacts to biological resources as a result of the construction and driveway improvements related to the proposed project that through incorporation of mitigation measures would result in a less than significant impact. If the Planning Commission elects to pursue this option, the recommended conditions of approval would need to reflect the revised production, visitation, marketing, employee numbers, and/or use of the existing winery and proposed new winery structure. Improvements to the driveway and installation of the wastewater system are triggered by the increase in production and construction of the new winery structure.
Action Required - Follow proposed actions listed in the Executive Summary and amend scope and applicable conditions of approval to reduce the existing operations. The item may need to be continued to a future date if significant revisions to the recommended conditions of approval are desired.
Option 6 - Deny Applicant’s Proposal - Limit Winery Operations to Levels Recognized and Approved Above to Remedy Existing Violations or Revert to Winery’s Original Entitlements.
Disposition - This option would deny applicant’s proposal to expand winery operations, physical improvements, and visitation and employee levels beyond what was approved and necessary to remedy existing violations. This option would result in no expansion beyond approved or existing levels. In the event the Commission determines that the project does not or cannot meet the required findings for the granting of a Variance and/or Use Permit Major Modification, Commissioners should identify what aspect or aspects of the project are in conflict with the required findings. State Law requires the Commission to adopt findings, based on the General Plan and County Code, setting forth why the proposed Use Permit modification is not being approved.
Action Required - Commission would make a motion to deny the applicant’s proposal to expand the project.
Option 7 - Continuance Option
The Commission may continue an item to a future hearing date at its own discretion.
SUPPORTING DOCUMENTS
A. Recommended Findings
B. Recommended Conditions of Approval and Final Agency Approval Memos
C. Initial Study / Mitigated Negative Declaration & MMRP
D. Previous Project Conditions
E. Use Permit Major Modification Application Packet
F. Request for Exception to the Road and Street Standards
G. Water Availability Analysis and Supplemental WAA for Interim Program
H. Wastewater Feasibility Study
I. Stormwater Control Plan
J. Biological Resources Assessment
K. Trip Generation Worksheet
L. Sight Distance Report
M. Bridge Condition Report
N. Winery Comparison Analysis and Summary of Changes
O. Graphics
P. Public Comments