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Project Title: |
1699 Alameda Diablo Two-Lot Minor Subdivision |
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County File(s): |
CDMS24-00013 |
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Applicant/Owner: |
Alexander Mehran (Applicant and Owner) |
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Zoning/General Plan: |
R-20 Single-Family Residential District, -UE Urban Farm Animal Exclusion Combining District / RL Residential Low Density |
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Site Address/Location: |
1699 Alameda Diablo in the Diablo area of unincorporated Contra Costa County (Assessor’s Parcel Number: 195-151-009) |
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California Environmental Quality Act (CEQA) Status: |
Mitigated Negative Declaration, SCH 2025030612 |
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Project Planner: |
Diana Lecca, Project Planner (925) 655-2869 |
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diana.lecca@dcd.cccounty.us |
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Staff Recommendation: |
Approve (See Section II for Full Recommendation) |
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I. PROJECT SUMMARY
The applicant requests approval of a Vesting Tentative Parcel Map for a two-lot Minor Subdivision application to subdivide a 5.89-acre residential parcel into a 2.59-acre Parcel A and a 3.29-acre Parcel B. No development is proposed with this application. The applicant is also requesting authorization of an Exception to the requirements and regulations of County Code Section 914-2.004 (Offsite Collect and Convey).
II. RECOMMENDATION
Department of Conservation and Development, Community Development Division (CDD) staff recommends that the Zoning Administrator:
A. ADOPT Mitigated Negative Declaration/Initial Study (MND), SCH 2025030612, and the March 14, 2025 Mitigation Monitoring and Reporting Program (MMRP), based on the attached findings, and specify that the Department of Conservation and Development (located at 30 Muir Road, Martinez, CA) is the custodian of the documents and other materials, which constitute the record of proceedings upon which this decision is based.
B. GRANT the exception to the drainage improvements required under County Code Section 914-2.004 (Offsite Collect and Convey), as detailed in the attached findings.
C. APPROVE the Vesting Tentative Parcel Map for the Two-Lot Minor Subdivision of a 5.89-acre residential lot (County File CDMS24-00013), based on the attached findings and subject to the attached conditions of approval.
D. DIRECT staff to file a Notice of Determination with the County Clerk.
III. GENERAL INFORMATION
A. General Plan: RL Residential Low Density.
B. Zoning District: R-20 Single-Family Residential District; -UE, Urban Farm Animal Exclusion Combining District.
C. California Environmental Quality Act (CEQA): A draft Mitigated Negative Declaration/Initial Study, State Clearinghouse Number (SCH) 2025030612, was prepared and published for the application. The public review period for the draft MND started on March 18, 2025, and ended on April 18, 2025. No comments were received in response to the publication of the draft MND.
D. Tribal Cultural Resources: In accordance with Section 21080.3.1 of the California Public Resources Code, a Notice of Opportunity to Request Consultation was both mailed and sent via email on March 7, 2025 for the Minor Subdivision CDMS24-00013 application to the Confederated Villages of Lisjan and the Wilton Rancheria, the California Native American tribes that have requested notification of proposed projects within unincorporated Contra Costa County. Pursuant to Section 21080.3.1(d), there was a 30-day time period from receipt of the Notice for the Native American tribes to either request or decline consultation in writing for this project. On March 7, 2025, the Confederated Villages of Lisjan submitted an email requesting any cultural resource or archaeological reports. On March 7, 2025, the Wilton Rancheria submitted an email with no comments on the project.
On March 10, 2025. staff send a request for information on cultural resources related to the project site, to the Northwest Information Center of the California Historical Resources Information System (CHRIS). On March 24, 2025, CHRIS submitted a letter stating that there was no record of previous cultural resource studies for the project area. The letter from CHRIS is included as Attachment D. In its letter, CHRIS also stated that given the proximity of known archaeological sites located in similar environments, they recommend that a qualified archaeologist conduct further archival and field study of the project area to identify cultural resources. The possibility of discovery of previously undiscovered archaeological resources was identified as a potentially significant adverse environmental impact in the MND, which includes mitigation measure Cultural Resources 3 to address this potential impact. Cultural Resources 3 is included as Condition of Approval #19.
On March 25, 2025, the Confederated Villages of Lisjan submitted an email stating that it wished to be contacted if any cultural resources or burial sites are encountered during ground disturbance. Mitigation measures Cultural Resources 3 and Cultural Resources 4 in the MND respond to this request and are included as Conditions of Approval #19 and #20.
E. Previous Applications:
1. CDLL24-00011: This Lot Line Adjustment to transfer 954 square feet of land from Assessor Parcel Number 195-151-007 (Parcel 1) to Assessor Parcel Number 195-151-002 (Parcel 2) was approved by the Zoning Administrator on August 2, 2024. Resultant Parcel 1, which was assigned new Assessor’s Parcel Number 195-151-009, is the current project site.
2. CDTP20-00007: This Tree Permit to remove three code protected trees, including one Walnut Tree and two fruit trees, and to work under the drip line of one Walnut tree for the construction of a new 20-foot-wide private driveway was approved by the Zoning Administrator on April 22, 2020.
3. CDTP14-00039: Tree permit to remove one code-protected Valley Oak tree due to tree failure, with no proposed development, was approved by the Zoning Administrator on October 23, 2014.
4. CDTP10-00002: Tree permit to remove one code-protected Canary Island Pine tree due to tree hazard was approved by the Zoning Administrator on March 4, 2010.
IV. SITE/ AREA DESCRIPTION
The 5.89-acre project site at 1699 Alameda Diablo is located on the north side of Alameda Diablo and Diablo Road, and is east of Calle Arroyo and south of Hole 17 of the Diablo Country Club Golf Course. The property is bisected by the East Branch of the Green Valley Creek that runs (north-to-south) through the property.
Buildings and structures located east of the creek include one single-family residence built in 1916, a carriage house, a pool house and a bridge leading to the west side of the creek. Buildings and structures located west of the creek include a stable, hay barn, tack room, a shed, a water tower, and four Doric columns with a trellis. The residence, carriage house, stable, hay barn, tack room, water tower, Doric columns, and bridge are located on the 3.29-acre Parcel B and the property has been identified as a contributor to the Diablo Historic District. Parcel A is a 2.59-acre vacant area of the project site located west of Parcel B.
The project site is located along the northern boundary of the Town of Danville along Diablo Road. Access to Parcel B is from Alameda Diablo, a privately maintained road within the Diablo community. Future access to Parcel A would be from either Diablo Road and/or Calle Arroyo. The topography of the project site is fairly level. The only significant sloping occurs on either side of the creek.
The project site is adjacent to developed single-family residential lots to the southeast, east and west, the Diablo Country Club Golf Course to the north, and an undeveloped hillside south of Diablo Road. The immediate vicinity generally consists of parcels to the southeast, east, and west in the R-20 Single-Family Residential District and the -UE Urban Farm Animal Exclusion Combining District, and Golf Course parcels to the north in the F-R Forestry Recreational District. The entirety of the property is within a RL Residential Low Density General Plan land use designation.
V. PROJECT DESCRIPTION
The applicant requests approval of a Vesting Tentative Parcel Map for a two-lot Minor Subdivision application to subdivide a 5.89-acre residential parcel into a 2.59-acre Parcel A and a 3.29-acre Parcel B. As described above, Parcel B is already developed with a single-family residence and accessory structures. Parcel A is the vacant portion of the property. There is no development associated with this application and future development is not contemplated. The project site is in the R-20 Single-Family Residential District wherein a single-family residence is permitted use. Therefore, it is possible that there would be a new single-family residence on Parcel A at some future time. This future possibility was evaluated in the MND, which is included as Attachment F.
With the existing topography of the project site, stormwater runoff flows generally towards the west. The East Branch of the Green Valley Creek intercepts the runoff from the eastern portion of Parcel B. West of the creek, the site slopes gently towards Calle Arroyo; however the stormwater falling in the property is generally retained onsite. Given that the project proposes no development, there will be no development on Parcel A for the foreseeable future. Thus rather than construct drainage improvements now, the applicant is also requesting authorization of an Exception to the requirements and regulations of County Code Section 914-2.004 (Offsite Collect and Convey) to retain Parcel A in its undeveloped state.
VI. AGENCY COMMENTS
An Agency Comment Request packet was sent on June 24, 2024, to a number of public agencies, including Building Inspection Division, Advanced Planning Section, Housing Programs Section, Environmental Health Division of the Health Services Department, Engineering Services and Flood Control Divisions of the Public Works Department. San Ramon Valley Fire Protection District, Central Contra Costa Sanitary District, East Bay Municipal Utility District, City of Danville, San Ramon Unified School District, Diablo Municipal Advisory Council, and Diablo Community Services District. Comments received by staff are included in Attachment E. Following are summaries of the comments received.
A. Housing Programs Section: On June 27, 2024, Housing Programs returned the agency comment request form with no comments.
B. Diablo Municipal Advisory Council (MAC): On July 16, 2024, the Diablo MAC returned the agency comment request form stating that it had no objection to the subdivision, and that any future permit application for Parcel A be submitted to the Diablo MAC for review and comment.
C. San Ramon Valley Fire Protection District: On July 17, 2024, the Fire Protection District submitted a letter stating that it had no comments.
D. East Bay Municipal Utility District (EBMUD): On July 22, 2024, EBMUD submitted a memorandum stating that separate meters for each parcel will be required, and that the project sponsor should contact EBMUD regarding new water service.
E. Department of Public Works, Engineering Services Division: On April 22, 2025, the Engineering Services Division submitted a memo describing the regulatory programs that applied to the project site and included a number of conditions of approval and advisory notes to be applied to the proposed project. The Division recommended approval of the request for an exception to County Code County Code Section 914-2.004 (Offsite Collect and Convey).
The April 22, 2025 Public Works conditions of approval and advisory notes are incorporated in the Conditions of Approval and the Advisory Notes.
VII. ENVIRONMENTAL REVIEW
A draft Mitigated Negative Declaration/Initial Study, State Clearinghouse Number (SCH) 2025030612, was prepared and published on March 18, 2025. Potentially significant impacts were identified in the draft MND, related to possible future construction, including: construction period air pollutant emissions, odors, and release of hazardous emissions; construction impacts on nesting birds; adverse changes to a historical resource, uncovering previously unknown cultural remains, burial sites, and paleontological resources during construction, including potential tribal cultural resources; potential liquefaction, effects of expansive and corrosive soils, and construction period noise. The public review period for the draft MND started on March 18, 2025, and ended on April 18, 2025. No comments were received in response to the publication of the draft MND, and therefore, preparation of a final MND is not necessary. The draft MND constitutes the MND for the application and is included as Attachment F.
A Mitigation Monitoring and Reporting Program (MMRP) was prepared for MND, SCH 2025030612, that addresses all of the mitigation measures recommended in the draft MND. The MMRP is included as Attachment G. If approved, the MND mitigation measures will be applied to Minor Subdivision CDMS24-00013 as Conditions of Approval.
VIII. STAFF ANALYSIS AND DISCUSSION
A. General Plan Consistency: The proposed two-lot Minor Subdivision is consistent with the General Plan, as discussed below.
1. Land Use Element: The 5.89-acre residential lot is located within the RL Residential Low Density General Plan land use designation. Uses in the RL designation typically include single-family residences on lots approximately 15,000 square feet to 1 acre in size. The RL designation also has residential densities of between 1 and 3 residential units per acre. The existing density of the project site is 1 unit per 5.89 acres. The project is proposed to subdivide the project site into two smaller parcels, a 2.59-acre Parcel A and a 3.29-acre Parcel B. Parcel B already sites an existing residence and does not propose any development. Currently, there is no proposed development for Parcel A; however, the future development of one potential new residence on Parcel A would result in a density of 1 unit per 2.95 acres for the project site, which will not exceed the maximum density allowed under the RL land use designation.
2. Transportation and Circulation Element: The Transportation Element of the General Plan shows designated arterials and expressways that are part of the County roadway network. The project site is located on Alameda Diablo, which intersects with Diablo Road, which, in turn, merges with Blackhawk Road. Both Diablo Road and Blackhawk Road are County-designated arterials. At some point in the future, residential development of Parcel A would create a new driveway accessing Diablo Road and/or Calle Arroyo. The Engineering Services Division has included Condition of Approval #30 that requires a code-compliant access from Parcel A. Thus the new driveway would not create a substantial adverse effect on the County-designated arterials.
3. Noise Element: The General Plan Health and Safety Element includes Table HS-3, Maximum Allowable Noise Exposure by Use, which shows levels of 60 dB or less are normally acceptable and 70 dB or less are conditionally acceptable for residential land uses. As evaluated in the MND, no development is associated with the project and therefore, activities at the project site will not change and are not expected to expose persons to, or generate noise levels in excess of hose shown in Table HS-3 for residential uses. At some time in the future, there may be a new residence on Parcel A; however, the types and levels of noise generated from future residential use on Parcel A would be similar to noise levels from existing surrounding residential development. Therefore, the subdivision and potential future residential development of the site would meet the acceptable single-family residential noise level standards of the Health and Safety Element of the General Plan.
As identified in the MND, during grading and construction of a future single-family residence on Parcel A, there may be periods of time when there would be loud noise from construction equipment, vehicles, and tools. The construction period noise could disturb occupants of nearby residences. The MND includes mitigation measure Noise 1 that details noise reduction measures to be implemented during project construction. This mitigation measure is included as Condition of Approval #25, which would limit disruptions due to noise, in compliance with the policies and restrictions of the Health and Safety Element.
B. Zoning Compliance: The project site is located in the R-20, Single-Family Residential District, which requires a 20,000 square-foot minimum lot size, a minimum average lot width of 120 feet, and a minimum lot depth of 120 feet. As shown on the Vesting Tentative Parcel Map, both Parcel A and Parcel B would meet these minimum requirements for a R-20 lot. At some time in the future, Parcel A may be developed with a single-family residence. At the time of submittal of a development application for Parcel A, CDD staff will review the application for compliance with applicable R-20 zoning standards.
The project site is also in the -UE Urban Farm Animal Exclusion Combining District. The project does not include or contemplate raising any urban farm animal, and therefore, the project is not in conflict with the -UE Combining District.
C. Diablo Historic District: As discussed in the MND, the Diablo Historic District is listed in the Contra Costa County Historic Resources Inventory as a historic district, and the property at 1699 Alameda Diablo is identified as a contributor to the District. A Historic Resources Evaluation (Historic Resources Assessment and Project Evaluation, 1699 Alameda Diablo, Diablo, CA; Valerie Nagel, Architect, February 12, 2025) was prepared for the project. As described in the evaluation, the Parcel B includes a number of contributory buildings and structures, including a single-family residence built in 1916, a carriage house, a stable, hay barn, tack room, a water tower, four Doric columns with a trellis, and a bridge. The non-contributor buildings and structures include a pool house, shed, various greenhouse buildings, and a pool. There is no proposal to alter any existing buildings or structures. The vacant portion of the project site that will become Parcel A was obtained after the period of significance for the Diablo Historic District, and therefore, separating Parcel A from the rest of the property will not impact the integrity of the resource. Thus, the proposed project has no impact on any known historical or culturally significant resources.
Regarding possible future development on Parcel B, the MND includes mitigation measure Cultural Resources 1 that requires CDD approval of any modification to the listed contributory buildings or structures, and requires submittal of a Secretary of the Interior’s Standards report to CDD for review and approval. This mitigation measure is included as Condition of Approval #17.
Because the project site is in the R-20 Single-Family Residential District, there could be a new single-family residence constructed on Parcel A at some time in the future. The MND includes mitigation measure Cultural Resources 2 that requires review and approval of architectural plans by the CDD prior to the submittal of a building permit application, to verify that the design will not deter from the character defining features of the contributor buildings of Parcel B. The mitigation measure also requires submittal of as-built photos to the CDD for review and approval prior to final building inspection. This mitigation measure is included as Condition of Approval #18.
Thus, as conditioned, the project would be compatible and consistent with the Diablo Historic District.
D. Request for Exception: County Code Section 914-2.004 (Offsite Collect and Convey). requires that runoff from any subdivision be conveyed without diversion to an adequate storm drainage facility.
Based on County elevation data, surface runoff of the property flows westerly. The East Branch of Green Valley Creek intercepts the runoff from the eastern portion of Parcel B. The remainder of the site gently slopes towards Calle Arroyo but since Parcel A is undeveloped, the stormwater falling on the property is generally retained. In the event that Parcel A is developed at some time in the future, the development may not comply with County Code Section 914-2.004 since there is no apparent infrastructure in the vicinity of Parcel A to collect the runoff and convey it to an adequate storm drainage facility.
Given the cost and logistical constraints of designing and constructing off-site drainage infrastructure to accommodate development on Parcel A that is not proposed or contemplated, pursuant to County Code Chapter 92-6, the applicant has requested an exception to the offsite collect and convey requirements specified in County Code Section 914-2.004.
Future development of Parcel A will be subject to permitting by the Department of Conservation and by the Public Works Department. Moreover, the Engineering Services Division has included Condition of Approval #33 that requires the property owner to record a deed disclosure stating that future development of Parcel A is subject to the drainage requirements of the County Ordinance Code, or to mitigate storm water runoff so as to not concentrate runoff or increase peak flow rates in excess of that for the current undeveloped condition of Parcel A. Accordingly, the granting of the exception would not be detrimental to the public welfare. For these reasons, staff recommends granting the requested exception.
E. Appropriateness of the Use: Subdivision of the 5.89-acre residential lot would result in two lots, a 2.59-acre Parcel A and a 3.30-acre Parel B. Parcel B is already developed in a manner consistent with the General Plan and the R-20 Single-Family Residential District. The development on Parcel B is a contributor to the Diablo Historic District. Parcel A is undeveloped and no development is proposed or contemplated. Development of Parcel A at some time in the future will be subject to compliance with the goals, policies, and implementing actions of the General Plan, the development standards and regulations of the R-20 District, the Diablo Historic District, and the Conditions of Approval and Advisory Notes herein. Thus, future development of Parcel A would not conflict with the General Plan, the R-20 regulations, or the Diablo Historic District.
IX. CONCLUSION
The proposed Two-Lot Minor Subdivision, as conditioned, would be compatible with existing residential development in the surrounding vicinity, would be consistent with the General Plan and in compliance with all applicable R-20 District regulations. Staff recommends approval of the Vesting Tentative Parcel Map for the Two-Lot Minor Subdivision of the 5.89-acre residential parcel into a 2.59-acre Parcel A and a 3.29-acre Parcel B, based on the attached findings and subject to the attached conditions of approval.