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Home My WebLink About3.1ITEM 3.1 TOWN OF LOS ALTOS HILLS December 6, 2012 Staff Report to the Planning Commission RE: APPROVAL OF A FINAL MAP AMENDMENT TO SHOW A CORRECTED GEOLOGIC FAULT TRACE: LANDS OF WALLACE, STONEBROOK DRIVE (ASSESSOR PARCEL NUMBERS 336-23-020 & 021). FILE #137-11 MISC. FROM: Cynthia Richardson, Consulting Planner (T-. APPROVED BY: Debbie Pedro, AICP, Planning Director 3R RECOMMENDATION That the Planning Commission: Forward a recommendation that the City Council approve the requested Final Map Amendment, based on the findings in Attachment #l, subject to the conditions . in - Attachment #2. PROJECT DESCRIPTION The applicant is requesting approval of a Final Map Amendment of Parcel Map. 445 maps 56 as it relates to only his parcel in the two lot subdivision. The Subdivision was approved in 1978 (PM 445 M56, Recorded July 18, 1978). The map originally located the Monta Vista Fault bisecting the property in an east west direction, further to the north than currently found. During the Town Geologist review it became clear that test trenches located in the area of the former location, found that Franciscan Bedrock materials were not present as previously thought and no fault contacts were found. - New trenches located further south, bisecting the panhandle, show materials consistent with the Monta Vista Fault trace. FINAL MAP AMENDMENT REVIEW A property owner can submit an application to proceed with a map amendment. under Government Code Section. 66469(f). The code section provides that a final map may be amended to correct the map as long as it does not impose any additional burden on the present owners of the property and does not alter any right, title, or interest in the real property reflected on the record map. In order to approve the map, the Planning Commission must determine that the project is consistent with the General Plan, Subdivision and Zoning Regulations, .and that this modification does not alter any right, title, or interest in the property and that the map as modified conforms to the provisions of Government Code Section 66474. Neighboring residents and property owners within 500 feet of the site have been notified of the public hearing. Lands of Wallace December 6, 2012 Page 2 of 3 Geotechnical Review The Town's Geotechnical Consultant, Cotton, Shires and Associates reviewed the proposed Final Map Amendment and Supplemental Geologic Assessment (letter -report) prepared by John T. O'Rourke, dated December 13, 2011. Cotton, Shires and Associates reported that the Project Geotechnical Consultant has adequately completed the additional subsurface investigation suggested in their previous review and based on the site data they have no geologic objections to the depiction of the proposed Morita Vista fault zone modification and associated setback illustrations (Attachment #2) Public Comments The neighbor to the west of the project site, Mr. Wilkerson, has contacted staff with questions about the relocated fault trace however no written correspondence has been submitted at this time. CONCLUSIONS Staff has concluded that, as documented in the recommended findings of approval, the proposed subdivision is in compliance with the General Plan and Subdivision Ordinance. ENVIRONMENTAL REVIEW This project is categorically exempt under Section 15305, Class 5 consists of minor alterations in land use limitations in areas with an average slope of less than 20%. The property has been determined to have a 14% slope. ATTACHMENTS 1. Recommended Findings for map amendment 2. Recommended Conditions of approval 3. Cotton, Shires and Associates report, July 13, 2011 4. Final Map Amendment plan set (Commission only) Lands of Wallace ATTACHMENT 1 December 6, 2012 Page 3 of 3 ATTACHMENT 1 RECOMMENDED FINDINGS FOR AMENDMENT TO FINAL MAP PM445 M56. LANDS OF WALLACE, STONEBROOK DRIVE (APN #'S 336-23-020 & 021) FILE #137-11-MISC 1. The modifications to the Final Map, Parcel Map 445 maps 56, which modify the Monta Vista Fault trace, are appropriate and necessary due to the Town Geologist review where he found that Franciscan Bedrock materials were not present as previously thought and new trenches located further south, bisecting the panhandle, show materials consistent with the Morita Vista Fault trace. 2. The property owner is not subjected to additional burdens on the property by this Final Map Amendment. A .Fault trace currently exists on the property and has been determined to not be in the original location. The new location is within the panhandle and is less of a burden to the overall development of the property.,. 3. The modification to the Final Map does not alter any right, title or interest in the property. No change in property ownership will occur with this project. 4. The map as modified is consistent with the Town of Los Altos Hills. General Plan and Subdivision Ordinance. ATTACHMENT 2 ��a�i�� 1�► RECOMMENDED CONDITIONS FOR THE FINAL MAP AMENDMENT LANDS OF WALLACE, STONEBROOK DRIVE ASSESSOR PARCEL NUMBER 336-23-020 & 021 FILE #137-11-MISC. PLANNING DEPARTMENT: 1. Any changes or modifications to the approved map shall first be reviewed and approved by the Planning Commission and City Council, depending upon the scope of the changes. ENGINEERING DEPARTMENT: 2. This approval shall be of no force or effect until such time as the applicants submit a mylar amended final map to be reviewed and approved by the Town of Los Altos Hills City Engineer. GEOTECHNICAL 3. Future design of a residence shall be based on a geotechnical investigation that provides a basis for foundation design as well as other geotechnical criteria needed for the design of site improvements. The project Geotechnical Engineer shall review the findings of site the geologic investigation and provide a letter to the Town. ATTACHMENT 3 COTTON, SHIRES AND ASSOCIATES, INC. CONSULTING ENGINEERS AND GEOLOGISTS August 24, 2011 L3208B TO: Brian Froelich RECENED Planning Department TOWN OF LOS ALTOS HILLS AUG 2 7 2012 26379 Fremont Road Los Altos Hills, California 94022 TOWN OF LOS ALTOS HILLS SUBJECT: Supplemental Geotechnical Peer Review RE: Lands of Wallace, Proposed Fault Map Correction #137-1.1-MISC _ _ .. .... _..... _ _ .. 12400 Stonebrook Drive (previously 12309) At your request, we have completed a geotechnical peer review of the proposed Fault Map Correction using: • Tentative Map (sheet TM -1) prepared by TS, Civil End eenng, dated August 15, 2012; • Supplemental Geologic Assessment (letter -report) prepared by John T. O'Rourke, dated December 13, 2011; • Geologic Assessment of Potential Fault Risk (report) prepared by Hydro -Geo Consultants, dated August 1, 2006; • Geologic and Seismic Hazard Investigation (partial report) prepared by Burkland and Associates, dated April 7,1977; and • Supplemental Geotechnical Investigation (report) prepared by Burkland and Associates, dated May 23,1977. In addition, we have reviewed pertinent documents and technical maps. from our office files and observed site test pit exposures. DISCUSSION. We understand that the applicant proposes to modify mapped fault trace alignments across the subject property. Specifically, the applicant proposes to remove a previously identified fault trace in the central portion .of 'the property (based on Buckland and Associates, 1977) and add a new fault trace in the western portion of the Northern California Office Central California Office Southern California Office 330 Village Lane 6417 Dogtown Road 550 St. Charles Drive, Suite 108 Los Gatos, CA 95030-7218 San Andreas, CA 95249-9640 Thousand Oaks, CA 91360-3995 (408) 354-5542 a Fax (408) 354-1852 (209) 736-4252 • Fax (209) 736-1212 (805) 497-7999 • Fax (805) 497-7933 I Brian Froelich Page 2 August 24, 2012 L3208B property ("proposed amended fault zone' ori TM -1). Proposed 50 -foot wide building setbacks (HHBSBL) are depicted from the edges of the amended fault alignment. In our previous geotechnical peer review (letter dated July 13, 2011) regarding the subject property, we evaluated the referenced 2006 Geologic Assessment of Potential Fault Risk (report). We noted that the associated Tentative Map did not illustrate recommended 50 -foot fault setbacks, and we concluded that additional site subsurface exploration was needed to potentially eliminate the fault trace depicted by Buckland and Associates in the central portion of the property. RECENT GEOLOGIC FINDINGS The Project Geologist has completed three additional test pits across the fault trace alignment mapped by Burkland and Associates. Test pits encountered colluvial soils and unfaulted bedrock materials of the Santa Clara and Monterey Formations. No Franciscan Complex bedrock was identified as previously logged by Burkland and Associates. The current Project Geologist recommends that the previously mapped central fault trace be removed from the subject .property. Based on completed site subsurface exploration, the consultant concludes that a single trace of the Monta Vista fault has been identified crossing the western portion of the property (where the pan handle connects to the main portion of the property). Subsurface exploration has not been conducted along the central portion of the pan handle driveway. CONCLUSIONS AND RECOMNIENDED ACTION The Project Geologist has adequately completed the additional subsurface investigation suggested in our previous geotechnical review. Based on collected site data, we do not have geologic objections to the depiction of the proposed Monta Vista fault zone modification and associated setbacks illustrated on the referenced Tentative Map. However, the bar scale and stated 1 inch equals 20 feet scale of the Tentative Map is not correct. It appears that the correct scale of the property on the Tentative Map may be 1 inch equals 40 feet. We do not have geotechnical objections to the depicted Tentative Map if the map scale is corrected. Future design of a residence at the subject property should be based on a geotechnical investigation that provides a basis for foundation design as well as other geotechnical criteria needed for the design of site improvements. The Project Geotechnical Engineer should review the findings of site geologic investigation. LL MTATIONS This supplemental geotechnical peer review has been performed to provide technical advice to assist the Town with discretionary permit decisions. Our services have been limited to review of the documents previously identified, and a visual review of the property. Our opinions and conclusions are made in accordance with generally ■ ilTTI1XT CTTTTT-I- A X- A --V •- -IT Brian Froelich Page 3 August 24, 2012 L3208B accepted principles and practices of the geotechnical profession. This warranty is in lieu of all other warranties, either expressed or implied. TS:DTS:kd Respectfully submitted, COTTON, SHIRES AND ASSOCIATES, INC. TOWN GEOTECHNICAL CONSULTANT Ted Sayre Principal Engineering Geologist CEG 1795 David T. Schrier Principal Geotechnical Engineer GE 2334 %'/ITTAAr Q"T"TC . - A --v & -roc• .,..�