Calistoga Road Emergency Repair Project at PM 16.91


SCH Number
Public Agency
Sonoma County
Document Title
Calistoga Road Emergency Repair Project at PM 16.91
Document Type
NOE - Notice of Exemption
Document Description
PROJECT DESCRIPTION: Existing Conditions The proposed project area occurs along a 30- to 40-foot long stretch of Calistoga Road that was damaged by heavy rains during the 2017 storm events. Damage to this portion of Calistoga Road consists of slope failures on the downslope portion of roadway, that extends from the roadway shoulder to an unnamed stream which is a tributary to Porter Creek. The unnamed stream is located at the toe of the failed slope, approximately 20 feet below the roadway. The slip out is also located adjacent to a private driveway that crosses the creek by means of a pipe culvert with concrete headwalls. The concrete headwalls are leaning severely and are extensively cracked. The culvert outlet is severely undercut, and it appears stream downcutting is ongoing and is likely contributory to the long-term slope instability. Proposed Conditions The Project would require limited excavation of unstable soil along the slip out and may require trimming of low hanging branches, removal of portions of the existing storm damaged roadway, and clearing and grubbing of understory vegetation. The slope repair work would then install a short soldier pile wall in conjunction with reconstructing the shoulder. The Project would also place rock slope protection (RSP) along the face of the wall above the ordinary high-water mark. Once the shoulder reconstruction has been completed, surface drainage elements would be installed along the roadway to divert existing side run-off towards existing drainages. Upon completion of Project construction, the slope would be treated with erosion control measures and the disturbed areas would be revegetated. Utilities There are several utilities at the Project site; however, no utility relocations are anticipated to be necessary during the construction of the Project. The temporary deenergizing of the overhead electric lines may occur during construction in order to construct the soldier pile wall. Right-of-Way No permanent right-of-way or temporary easements will be required to construct the project. 2300 COUNTY CENTER DRIVE, SUITE B 100 SANTA ROSA, CA 95403 ? PH: 707.565.2231 ? FAX: 707.565.2620 Traffic Handling The average daily traffic (ADT) along Calistoga Road is 4,400 vehicles. A temporary lane closure will be required along Calistoga Road at the Project site to complete project construction activities. The proposed temporary lane closure will require the implementation of day-time traffic control measures to maintain safe vehicular access in both directions along Calistoga Road. Upon the completion of daily construction activities, metal plates will be laid down at the slip out location and night-time vehicular traffic will resume using both lanes along Calistoga Road. Construction Activities Clearing and Grubbing Portions of hardscape and vegetation in conflict with proposed project construction will be removed. Areas around the slip out location will be cleared of vegetation, or other obstacles to gain access for constructing the new improvements. The work will occur within the approved project limits of disturbance. Erosion Control and Water Quality Temporary Best Management Practices (BMPs) and erosion control measures will be installed and maintained during construction. Unloading Failed Slope Loose and eroded soils within the slip out location above the ordinary high-water mark will be removed to construct project improvements. Reconstructing Shoulder The existing shoulder will be reconstructed by installing a short soldier pile wall. The soldier pile wall will be approximately 30 feet long and 4 feet above grade and will extend approximately 30 feet downstream of the existing headwall. Holes will be drilled approximately 32 feet deep, soldier piles placed and concreted in place. The area between the existing road and soldier wall will be reconstructed. The reconstructed area will include a drainage system along the face of the wall with new embankment material placed and compacted. The portion of reconstructed area between the edge of the shoulder and the wall will be hydroseeded. Placing RSP Rock slope protection (RSP) will be installed along the face of the soldier pile wall. The RSP will be placed in a trench measuring approximately 3’ wide by 3’ deep and 30’ long along the front face of the wall. Grading the slope Beyond the northerly end of the Rock slope protection (RSP), approximately 25’ of the existing channel slope will be regraded in order to tie back into the existing slope. The impact area is outside of the OHWM. Repairing Drainage Elements The drainage ditch along the inboard slope will be cleaned out. The existing underdrain located approximately 50-feet to the north of the failed area will be evaluated to determine if it is still intact and the existing damaged over side drain will be replaced. If the underdrain is determined to be damaged, it will be replaced in kind. RSP will be replaced at the end of the new over side drain to help dissipate the flows and to minimize future erosion of the channel bank caused by the flows exiting the over side drain. Installing Drainage Elements Surface drainage elements, such as asphalt concrete dikes, will be placed along the edge of the shoulder to divert the water towards the existing over side drainage located approximately 50-feet from the end of the failed area. Construction Schedule and Timing Construction of the Project is anticipated to take one construction season to complete. The approximately 3-4-month construction period is scheduled to begin as early as Spring 2022. 2300 COUNTY CENTER DRIVE, SUITE B 100 SANTA ROSA, CA 95403 ? PH: 707.565.2231 ? FAX: 707.565.2620 Construction Equipment List Table 1 provides a description of the type of equipment likely to be used during the construction of the Project. Table 1. Construction Equipment Construction Purpose Air compressor Finishing work Backhoe Soil manipulation, drainage work Bobcat Fill distribution Compaction equipment Earthwork Concrete truck Placing concrete Drill Rig Construction of soldier pile wall Dump truck Fill material delivery Excavator Soil manipulation Flatbed truck Material handling and delivery Front-end loader Dirt or gravel manipulation Generators Power hand tools Haul truck Earthwork construction, clearing Jack Hammer Demolition, asphalt concrete removal Paver Asphalt concrete construction Pump Truck Placing concrete Truck with seed sprayer Landscaping Water truck Earthwork construction, dust control

Contact Information

Cindy Rader
Agency Name
Sonoma County Transportation and Public Works Dept
Job Title
Senior Engineer
Contact Types
Lead/Public Agency


Other Location Info
Calistoga Road at Post Mile 16.91

Notice of Exemption

Exempt Status
Emergency Project
Type, Section or Code
15269 (a) and (b); Section 15301(c)
Reasons for Exemption
This is designated ‘Emergency Project’ with signed ‘Proclamation of Emergency’ by the State Governor. It is the maintenance of an existing public facility involving no expansion of use.
County Clerk


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