July 10, 2024
Job No. 24-5181
3. The review of plans, titled “Benda-Spenker Residence Bayview RoadCalera Terrace, Pacifica, CA 94044, APN: 022-062-550” prepared by JC Engineering, dated December 3, 2018 with a latest revision date of October 16, 2023;
4. The review of a previous Geotechnical Report and updated report by Summit Engineering, dated March 9, 2011 and September 14, 2022, respectively;
5. Retaining Earth Focus Geology to prepare a report by Certified Engineering Geologist, Patrick Drumm. The report is dated July 9, 2024 and is appended to this report;
6. Discussions with Javier Chavarria, JC Engineering;
7. A review of available published geologic maps and literature;
8. Marking the street and sidewalk in front of the property and then contacting USA (Utility Service Alert) to locate where buried utilities enter the property prior to logging test borings;
9. Filing the appropriate forms with San Mateo County in accordance with our Annual Drilling Permit, as required by the County Department of Health;
10. Logging three exploratory test borings that were advanced by continuous sampling the subsurface soil and bedrock materials;
11. The recovery of samples from the borings, and the performance of a variety of engineering tests upon the various soil and bedrock layers encountered;
12. Backfilling the boreholes with appropriate grout (by Access Soil Drilling of San Mateo);
13. The performance of geotechnical engineering analysis utilizing the above items; and,
14. The preparation of this report.
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Packet Pg. 870 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
FIELD INVESTIGATION AND LABORATORY TESTS
In order to evaluate the geotechnical engineering characteristics of the soil and bedrock layers which underlie the site, three borings were advanced at the approximate locations indicated on the attached Existing and Proposed Site Plans, Figures 2A and 2B, respectively. The borings were advanced by Access Soil Drilling of San Mateo on May 29, 204 by continuous sampling of the subsurface soil and bedrock materials.
Relatively undisturbed samples were recovered in thin brass tubes from the borings at selected intervals with a free-falling, 140-pound hammer (with a 30- inch drop) advancing modified California, and in some cases standard penetration, drive samplers up to 24 inches into the subsurface soil and bedrock layers. The brass tube encased samples were labeled in the field and carefully sealed to preserve their in-situ moisture content. They were ultimately transported to our laboratory.
As the borings were excavated, logs of the materials encountered were prepared based upon an inspection of the recovered samples as they emerged from each borehole. The final boring logs, as presented on the attached Figures 3 through 5, are based upon the field logs with occasional modifications based upon further close laboratory examinations of the recovered samples as well as the laboratory test results.
Laboratory tests were performed upon samples that were extruded from the brass tubes. These tests, which are useful in evaluation of the general strength properties of the materials tested, included the determinations of moisture content, dry density and unconfined compressive strength (in accordance with ASTM D2166) of selected samples. The results of these tests, along with the resistance to penetration of the sampler, are listed opposite the corresponding sample location on the final Boring Logs, Figures 3 through 5. A Boring Log Key is also included as Figure 6.
We also performed plastic index testing (in accordance with ASTM D4318) upon a representative sample of the surface soil that was encountered in Boring 3 (near the proposed driveway entrance). The results of this test are useful in evaluating the shrink/swell properties of the material and are included on Figure
7. We have also prepared a Typical Profile of the site showing the proposed improvements along with our interpretation of the subsurface soil and bedrock conditions as the attached Figure 8.
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Packet Pg. 871 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
SITE CONDITIONS
The subject property is currently accessible via an over-grown private driveway easement that extends towards the southeast off of the southeast side of Bayview Road between the properties at 171 and 125 Bayview Road. The access driveway easement is shown in the following Photo 1.
Photo 1: View towards the southeast of the access driveway easement for the street along Bayview Road.
Our observations suggest that an old stream channel likely drained from the northeast towards the southwest beneath Bayview Road prior to mass grading to develop the roadway.
The subject property is surrounded by residences along Bayview Road to the northwest and along Rockaway Beach Avenue to the southwest and southeast.
There is also a “paper” roadway easement (referred to as Calera Terrace) that extends along the northeast side of the property. The location of the property is shown on the attached Site Vicinity Map, Figure 1.
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Packet Pg. 872 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
The subject property is an irregularly-shaped vacant lot that is currently covered with dense seasonal grasses, shrubs and trees. Several photos showing the existing conditions at the time of our study follow.
Photo 2: View towards the southeast of the dense vegetation covering the site at the time of our study.
Photo 3: View towards the northeast looking up the slope of the existing conditions in the area of the proposed new residence.
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Packet Pg. 873 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
Photo 4: View towards the northwest of the existing conditions at the time of our study in the area of the proposed future residence.
The site topography slopes steeply downward generally towards the south and southwest at an average inclination that is on the order of 1.75 horizontal to 1 vertical with locally steeper areas. There also appears to have been some minor past grading in the middle of the property at the southeast end of the private driveway easement, where the slope was levelled out. The area is shown on the attached Existing Site Plan, Figure 2A between the Summit Engineering Borings 2 and 3.
PREVIOUS REPORTS BY SUMMIT ENGINEERING
Summit Engineering previously issued a geotechnical report for the site dated, March 9, 2011 for the then proposed new residence project. The report contained the logs of three test borings (shown on Figure 2 as SEB-1 through SEB-3), the logs of which are appended to the end of this report. In general, their borings encountered between 0 and 3 feet of weak native topsoil, which was underlain by stiff to hard gravelly clay and material they classify as weathered gravel conglomerate to possible greenstone at about 6 to 8 feet below grade.
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Packet Pg. 874 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
The report contained seismic criteria and geotechnical recommendations for site grading, drilled pier foundations, shallow foundations, retaining walls, slab on grade and pavement preparations.
The 2011 report did not contain reference to or discussion regarding the potential for seismic-induced landsliding on the property, based on the State’s 2019 seismic hazard map of the Montara Mountain Quadrangle.
Summit Engineering followed up their 2011 geotechnical report with an update letter dated September 14, 2022, which indicated that since no grading had been done at the site since issuance of their 2011 report, the recommendations in the 2011 report remained applicable, and they also updated the seismic criteria.
We understand that their report and update letter did not satisfy the City of Pacifica requirements.
SOIL AND BEDROCK CONDITIONS
In order to evaluate the soil and bedrock conditions at the site, three borings were advanced at the approximate locations shown on the attached Existing and Proposed Site Plans, Figures 2A and 2B, respectively. Borings 1 and 2 were advanced in the area of the proposed new residence, and Boring 3 was advanced in the area of the driveway easement. We should note that the three borings completed by Summit Engineering are also shown on both of our site plans, and the logs have been appended to the end of this report, for reference.
Borings 1 and 2 encountered about 2-1/2 feet (Boring 2) to 3 feet (Boring 1) of relatively weak native soil at the ground surface, which generally consisted of loose to medium dense mottled clayey fine to medium sand with rock fragments. In both borings, the native soil was underlain by about 2-1/4 feet (Boring 1) to 3 feet (Boring 2) of residual soil (soil that results from the in-place weathering of the underlying bedrock material) that consisted of stiff to very stiff abundantly fine to medium mottled sandy silt to sandy clay with rock fragments. Deeply weathered Franciscan greenstone bedrock was encountered beneath the residual soil at a depth of 5-1/4 feet in Boring 1 and 5-1/2 feet below grade in Boring 2. Both borings were advanced to depths of 8 feet below grade.
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Packet Pg. 875 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
The soil conditions in Boring 3 were significantly different than those found in Borings 1 and 2. As noted, there appears to have been an old stream channel that likely drained from the northeast towards the southwest beneath Bayview Road. Boring 3 encountered about 5 feet of firm artificial fill from the ground surface that consisted of silty fine sandy clay with rock fragments. The fill was likely placed during mass grading for the roadway, and the fill likely extended onto the front portion of the adjacent properties in addition to the driveway easement that will service the subject property. The fill in Boring 3 was underlain by about 5 feet of soft compressible native soil that consisted of fine sandy to silty clay with rock fragments. About 10 feet of alluvial deposits consisting of firm to stiff fine sandy to silty clay with rock fragments/pebbles were encountered beneath the native soil in Boring 3; the alluvial deposits extended to a depth of 20 feet below grade, at which depth the boring was terminated.
We performed plasticity index testing on a representative sample of the fill encountered in Boring 3 collected between depths of 2 to 4 feet below grade and found that the material was moderate in expansion potential. The results of our plasticity index test are shown on the attached Figure 7.
Groundwater was not encountered in any of the borings at the time of drilling.
Groundwater and perched groundwater levels, however, tend to fluctuate seasonally, and could rise to the depths explored in the future.
A survey of the existing site features is included on the Existing Site Plan, Figure 2A. The proposed conditions are shown on the attached Proposed Site Plan, Figure 2B. For a more complete description of the soil and bedrock layers encountered in the borings, refer to the final Boring Logs included as Figures 3 through 5 and the Boring Log Key included as Figure 6. We have also prepared a Typical Profile of the site showing the proposed improvements along with our interpretation of the subsurface soil and bedrock conditions as the attached Figure 8.
* Expansive soils are generally clay-rich soils that swell when their moisture content increases and shrink as it dries out. Expansive soil can cause problems with foundations, pavements, and other site features. The effects of expansive soil can be mitigated as will be described later in this report.
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Packet Pg. 876 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
SITE GEOLOGY
The site has been mapped by Brabb, Graymer and Jones (1998) and Pampeyan (1994) to be underlain by Franciscan greenstone bedrock (KJg). Pampeyan describes the Franciscan greenstone as dark-green to red, altered basaltic volcanic rocks, including flows, pillow lava, breccia, tuff, and minor related intrusive rock. The material is friable to hard and dense depending upon rock type and degree of weathering. We should note that both geologic maps also indicate that slope wash deposits are mapped on the slopes further to the south beyond the subject property. We encountered deeply weathered Franciscan greenstone bedrock in Borings 1 and 2 of our study. Our interpretation of Summit Engineering’s Borings also suggests that Franciscan greenstone bedrock was encountered in their borings as well. A scan of the relevant portion of Bonilla’s geologic map follows.
Map1: Pampeyan (1994)
The State of California has published a series of maps, which depict areas may be subject to seismically induced liquefaction (the bluish-green colored areas) and seismically induced slope instability (the light-blue colored areas). The official map of the Montara Mountain Quadrangle (released on April 4, 2019) covers the subject site area, and the map indicates that the all or a portion of the subject site is mapped in an area that may be susceptible to seismic-induced landsliding.
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Packet Pg. 877 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
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Job No. 24-5181
As noted, we did observe a centrally-located area where past grading appears to have been conducted on the slope. Our observations of the property suggest that the area previously graded appeared to be stable. In general, the slopes appeared to be relatively stable, and we did not observe any indications of deepseated or shallow slope movement on the property or on the visible portions of the adjacent properties. A scan of the state seismic hazard map follows.
Map 2: Montara Mountain Quadrangle (2019)
California law (commonly referred to as “Alquist-Priolo”) specifies that zones around active and potentially active faults be established, and that geologic studies be conducted to delineate the locations of these faults to preclude the siting of structures for human occupancy across the traces of such faults. Our review of the official revised map of the Montara Mountain Quadrangle (issued on January 1, 1982) revealed that the site does not lie within a State mandated Alquist-Priolo Earthquake Fault Zoning Act "Special Studies Zone" for active faults (California Division of Mines and Geology, 1974). A scan of the relevant portion of the Alquist-Priolo map of the Montara Mountain Quadrangle follows.
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Packet Pg. 878 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
Map 3: Montara Mountain Quadrangle (1982)
There are no indications of active faulting at the site. The closest mapped active fault to the site is the San Andreas Fault located approximately 2.6 miles (4.2 kilometers) to the northeast. The San Andreas Fault, and numerous active and potentially active Bay Area faults are capable of producing moderate to major earthquakes that could cause severe ground shaking at the subject site in the future. This hazard is shared in some degree by all land and structures in the San Francisco Bay Area.
An engineering geologic report dated July 7, 2024 has been prepared by Patrick Drumm, of Earth Focus Geological Services (EFGS). The report, which did not identify significant geologic hazards, is appended.
CONCLUSIONS
Based upon our study and the EFGS report, it is our opinion that the project can be developed as planned, provided that the recommendations contained within this report are followed. The primary geotechnical consideration will involve supporting planned improvements within the dense bedrock or strong alluvial deposits that were encountered in the test borings. Therefore, the most appropriate foundation would be spread footings in areas where bedrock or competent alluvium is exposed by the planned excavation, or drilled piers, where these materials occur at depth.
Specific recommendations follow.
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Packet Pg. 879 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
RECOMMENDATIONS
The following recommendations are contingent upon our firm being retained to review the development plans and to observe the geotechnical aspects of construction. We should also be provided the opportunity to “fine-tune” our recommendations as plans are being prepared. Supplemental recommendations may also be necessary based upon conditions exposed during construction.
A. Seismic Criteria Per The 2022 CBC
It is our opinion that the subject site can be classified as Site Class “D” for the purpose of structural engineering calculations as defined in Chapter 20 found in ASCE 7-16.
It is important that the structural engineer verify the coefficients indicated on the following seismic criteria data sheet.
Seismic Design Criteria: Presented at https://siesmicmaps.org (OSHPD 2024)
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Packet Pg. 880 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
B. Grading
All grading should be performed under the observation of a representative from our firm. Prior to the commencement of grading, the areas to be graded should be stripped to remove all grass, weeds, and other deleterious materials. In addition, brush and trees should be removed, along with their root systems. In areas where trees are removed, it will be necessary to carefully backfill the excavations with engineered fill.
After the site has been stripped to our satisfaction, a key should be excavated at the toe of any planned fill (or behind any retaining wall that is to support fill).
Actual key widths should be determined when grading commences, as it will vary slightly depending upon the width of the compaction equipment used. Generally, a 12- to 15-foot-wide key will accommodate most compaction equipment. Fill can then be brought into the key in thin lifts, moistened or aerated as required, mixed, and compacted. All fills should be compacted to a minimum degree of 90 to 95 percent based upon ASTM D1557, latest revision*.
The downhill side of any key excavation in the area of the residence and ADU should have a minimum depth of 12 inches into strong residual soil or bedrock.
All horizontal benches should remove the surface soil and extend into strong residual soil or dense bedrock as approved by our representative. The maximum finished fill slope inclination should not exceed 2 ½ horizontal to 1 vertical. Any cut slopes should also not exceed 2 horizontal to 1 vertical in bedrock.
As the level of the fill rises, horizontal benches should be excavated into the hillside, so that a strong bond is maintained between the newly placed engineered fill and strong residual soil or bedrock.
It may be necessary to place subdrainage beneath fills that have a thickness greater than 4 feet, or in areas were seepages are encountered.
Any areas to receive flatwork, pavements, or slabs on grade should also be underlain by at least 8 inches of select granular engineered fill (such as class II baserock). The select granular fill should be compacted to a minimum degree of 95 percent, based upon ASTM D1557, latest revision.
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Packet Pg. 881 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
In the area of the access driveway any weak fill or underlying soil, may require over excavation and replacement with engineered fill. A determination regarding this requirement should be based upon planned grades and conditions encountered during grading. The soil conditions vary in the area of the planned access driveway and we may provide supplemental recommendations for the driveway when plans are available (which indicate retaining wall locations and heights).
* The degree of compaction of a soil is determined by first gathering a representative bulk sample of the material that is to be compacted and returning it to our laboratory where a “compaction test” in accordance with ASTM D1557, latest revision, is performed. This establishes a maximum density (which varies for soil types…thus a lab compaction test is needed for different soils at the site or that are imported). Field density tests are taken (usually with a porta-probe nuclear density testing device) after an attempt has been made to compact the soil at the project site. The density obtained in the field is then compared with the maximum laboratory density and when expressed a ratio is the degree of compaction. A 90 percent degree of compaction is needed for fine-grained soils (silty and sandy clays), and a 95 percent degree of compaction is needed for granular soils (sandy, gravelly, or rocky materials) in order for the soil to maintain sufficient strength to minimize settlement.
C. Foundations
In our opinion, the proposed structures (in areas where weak surficial soils are not removed by the planned excavations) should be constructed upon drilled, cast-in-place, reinforced concrete pier and grade beam foundations. In areas where strong alluvium (driveway), or residual soil and bedrock are exposed, spread footings or drilled piers may be used.
Drilled piers should be designed on the basis of a skin friction value of 500 psf beginning at the top of supporting material. In this case, the top of supporting material should be assumed to begin at a depth of 2 feet below finished grade, 12 inches below the top of residual soil or bedrock (which may be estimated from our boring logs) or as defined by the "Rule of Ten" criteria illustrated on the attached Figure 9, whichever is deeper. The depth may be modified by our representative during construction, especially if very dense bedrock areas are encountered.
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Packet Pg. 882 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
In addition to vertical loading, the piers should be designed to resist a horizontal "creep" load equal to a fluid weighing 45 pounds per cubic foot, projected over 2-1/2 pier diameters. The load should begin at the ground surface and extend to the top of supporting material, as described above. The piers can resist the lateral load through a passive resistance of 400 pounds per cubic foot, projected over 2 pier diameters. The creep load will not apply in areas that the surface soil has been excavated, or in areas that piers are to extend through engineered fill, as the weak soil will have been removed. It is suggested that the structural engineer contact us during the design phase, so that a specific lateral load criteria can be developed for each pier location.
Reinforcing for the piers should be determined by the structural engineer based upon anticipated loading.
It is possible that water may accumulate in the pier excavations. Therefore, provisions for casing may be necessary. Any water that accumulates in the piers should be pumped out prior to concrete placement. Alternatively, concrete may be placed by the “tremmie technique”.
Spread footings may be used in areas where the required excavation exposes alluvium (driveway), or bedrock. The footing should extend to a minimum depth of 18 inches, 12 inches below the top of bedrock (which may be estimated from our boring logs) or as illustrated by the "Rule of Ten" criteria illustrated on the attached Figure 9, whichever is deeper. The "Rule of Ten" takes into account the reduction in bearing capacity that shallow foundations experience when located on or near sloping terrain.
At the minimum depth, the footings can be designed for an allowable bearing pressure of 2500 psf for dead plus live loads. This value may be increased by 33 percent to account for all loads, including transient loading such as wind and seismic.
D. Retaining Walls
Retaining walls should be constructed upon foundations designed in accordance with Section C above. All retaining walls should be designed to resist the active equivalent fluid pressures tabulated below.
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Packet Pg. 883 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
WALL BACKSLOPE EQUIVALENT FLUID
INCLINATION (H:V) PRESSURE (pcf)
Level 45
4h: 1v 50
3h: 1v 55
2h: 1v 60
Interpolation can be used to determine pressures for intermediate inclinations.
When walls are to be rigidly restrained from rotation, a uniform surcharge pressure of 75 psf should be added to the design values.
In addition to static soil earth pressure as outlined above, the retaining walls could (if code or local jurisdiction required) be designed to resist short-term seismic loading. The retaining walls should be designed for a seismic loading increment (in pounds per foot) equal to 8 times the height of the wall (in feet) squared. The seismic component, as defined above, should be considered as a line load acting at a point 0.33 times H above the base of the retaining wall, where H is the wall height. It is noted that the seismic component should be added to the static earth pressure loading. In our opinion, it is acceptable to use a factor of safety of 1.1 for overturning and sliding when considering the combined effect of static and seismic loading.
Passive resistance can begin at the top of supporting material, as defined above, and can be taken as a value of 400 pcf. If drilled piers are used to support the wall this value can be projected over 2 pier diameters. In areas where spread footings are appropriate, a friction factor of 0.35 can be incorporated into the design.
It is important that adequate subdrainage be constructed behind retaining walls.
We have included a Typical Subdrain Detail as the attached Figure 10. In addition, moisture proofing should be provided in areas where moisture migration through retaining walls would be undesirable.
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Packet Pg. 884 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
E. Slab-On-Grade Construction
It is anticipated that slab-on-grade construction will be used for the garage floor.
The slabs should be reinforced with steel bars and cast upon strong residual soil, rock, or engineered fill. It is recommended that some type of moisture retardant be provided beneath the slabs. We have included a commonly used treatment as the attached Figure 11, however the project architect, or moisture control consultant should provide the final plan. It is also important that adequate provisions be provided (drainage improvements) to prevent moisture from seeping into any vapor barrier soils.
F. Surface Drainage
We recommend that the site be fine-graded to direct water to flow away from the building foundations. As a general requirement, storm water should not be allowed to pond or flow in concentrated streams or channels on the site.
It is further recommended that all roof downspouts be led into tightline disposal pipes that deposit water well away from building foundations and into a suitable disposal area. Disposal requirements vary from building department to building department and some require disposal into on site “dry well” or other facilities.
We should be further consulted if there is such a requirement for this project.
G. Subdrainage
As noted, subdrainage should be constructed behind retaining walls as illustrated on Figure 11. Subdrains should also be placed beneath engineered fills that have depths greater than 4 feet and in areas where any seepage zones (or potential seepage zones) are encountered.
In order to mitigate the potential for water to seep into the building "crawl areas" or slab vapor barrier soils, it is also recommended that a foundation drain be constructed along all sides of the structures as illustrated on the attached Figure 12. Material specifications are also included on Figure 11. If the uphill foundation wall is a retaining wall, the wall subdrain will serve this purpose.
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Packet Pg. 885 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
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Job No. 24-5181
H. Pavements
Final pavement design will be dependent upon the anticipated traffic and the materials exposed at the subgrade levels. For preliminary design purposes, a pavement section of 3 inches of asphaltic concrete underlain by 8 inches of Class II baserock can be anticipated for the roadway. The subgrade should be prepared in accordance with the Grading Section, above.
I. Review of Plans and Construction Observations
It is important that all of the plans related to our recommendations be submitted to our office for review. The purpose of our review will be to verify that our recommendations are understood and reflected on the plans, and to allow us to provide supplemental recommendations, if necessary. We should be provided the plans well in advance of construction. We will provide plan review letters as appropriate.
It is important that our firm be retained to provide observation and testing services during construction. Our observations and tests will allow us to verify that the materials encountered are consistent with those found during our study, and will allow us to provide supplemental, on-site recommendations, as necessary.
We will require at least 72 hours notice so that the appropriate personnel may be scheduled. If we are not called to the site prior to the completion of items that require our observation or testing, our recommendations should be considered voided.
LIMITATIONS
The conclusions and opinions expressed in this report are based upon the exploratory borings that were drilled on the site, spaced as shown on the Site Plan, Figure 2. While in our opinion these borings adequately disclose the soil conditions across the site, the possibility exists that abnormalities or changes in the soil conditions, which were not discovered by this investigation, could occur between borings.
This study was not intended to disclose the locations of any existing utilities, septic tanks, leaching fields, hazardous wastes, or other buried structures. The contractor or other people should locate these items, if necessary.
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Packet Pg. 886 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
July 10, 2024
Job No. 24-5181
Michelucci & Associates, Inc. does not practice in the field of moisture vapor transmission evaluation/mitigation. Therefore, we recommend that a qualified person/firm be engaged/consulted with to evaluate the general and specific moisture vapor transmission paths and any impact on the proposed construction. This person/firm should provide recommendations for mitigation of potential adverse impact of moisture vapor transmission on various components of the structure as deemed appropriate.
The passage of time may result in significant changes in technology, economic conditions, extraordinary weather events, global warming, sea level rises, or site variations that could render this report inaccurate. Accordingly, neither John Spenker and Robert Benda nor any other party shall rely on the information or conclusions contained in this report after 12 months from its date of issuance without the express written consent of Michelucci & Associates, Inc. Reliance on this report after such period of time shall be at the user's sole risk. Should Michelucci & Associates, Inc. be required to review the report after 12 months from its date of issuance, Michelucci & Associates, Inc. shall be entitled to additional compensation at then-existing rates or such other terms as may be agreed upon between Michelucci & Associates, Inc. and John Spenker and Robert Benda.
This report was prepared to provide engineering opinions and recommendations only. It should not be construed to be any type of guarantee or insurance.
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Packet Pg. 904 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Earth Focus Geological Services, Inc.
www.earthfocusgeology.com
115 Orchard Drive, Fremont, CA 94536
Tel/Fax (510) 794-7495
Engineering Geology • Fault and Landslide Investigations • Urban Geology • Forensic Studies July 7, 2024
Project No: S24-01978
Attention: Joseph Michelucci, G.E.
Michelucci & Associates, Inc.
1801 Murchison Drive, Suite 210
Burlingame, CA 94010
RE: Evaluation of Potential Landslide Hazards
Proposed New Residential Construction
Vacant Lot; APN: 022-062-550; Access from Bay View Road Between Rockaway Beach Avenue and Calera Terrace (unimproved) Pacifica, California
Dear Mr. Michelucci:
As requested, we have prepared this evaluation to assess the potential for Earthquake-Induced Landslide Hazards to impact the proposed new residential construction within the vacant lot identified as APN: 022-062-550 in Pacifica, California (Figure 1). We understand that Michelucci & Associates has recently explored the subsurface conditions within the site by drilling and sampling a series of exploratory borings and are in the process of preparing a geotechnical report for the project. We also understand that a previous geotechnical study for the site was undertaken by Summit Engineering and the findings summarized in their report dated March 9, 2011.
The property is located within a State of California Seismic Hazards Zone for EarthquakeInduced Landslides (State Geologist, 2019a; Figure 2). This engineering geologic evaluation follows general guidelines established by the California Geological Survey (1997 and 2008) to prepare a screening investigation of the project site to assess the potential for EarthquakeInduced Landslide Hazard. Our work presented here is to supplement your geotechnical investigation for the project.
SCOPE OF WORK
The scope of work for this project was generally as follows. • Perform a geologic reconnaissance of the property.
• Review historic aerial photographs of the site area.
• Review published geologic maps of the site area.
• Prepare this report presenting findings and conclusions.
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Packet Pg. 905 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Evaluation of Potential Landslide Hazards Page 2
Vacant Lot; APN: 022-062-550, Pacifica, CA
July 7, 2024
Project No: S24-01978
Engineering Geology • Fault and Landslide Investigations • Urban Geology • Forensic Studies Earth Focus Geological Services, Inc.
SITE DESCRIPTION
The site is located in the Rockaway Beach portion in the City of Pacifica within San Mateo County. Access to the property is from an unimproved easement connected to Bay View Road to the west of the property. An unimproved street that exists only on paper, Calera Terrace, is along the north portion of the lot. The area is within a prominent northwest-draining canyon accessed by Rockaway Beach Avenue that runs along the canyon bottom. The neighborhood is characterized by older residences along Rockaway Beach Avenue and concentrations of hillside homes overlooking the canyon.
The site is a vacant hillside lot along a relatively steep slope to the north of and overlooking Rockaway Beach Avenue. From our review of historic aerial photographs, the lot has never been developed. There are existing neighboring residences to the northwest and west that front onto Bay View Road. Bay View Road was constructed in the late 1960s and associated residential development began in the early 1970s. Downslope to the south, there are neighboring residences along Rockaway Beach Avenue.
The center of the property is at approximate elevation of 300 feet above mean sea level (U.S.
Geological Survey, 2022; see Figure 1). The site in on a relatively steep southwest-facing slope that begins at the canyon bottom near Rockaway Beach Avenue. The average slope gradient within the site is approximately 1.8:1 (horizontal to vertical). The vertical relief within the site is approximately 80 feet. The slope continues above the site to the northeast for approximately 400 vertical feet to reach the prominent ridgetop. There is no development above the site to the northeast.
PROPOSED DEVELOPMENT
We understand that a new two-story residence with attached garage, separate ADU, and driveway turnaround are proposed for the site. The proposed development of the lot will require significant excavations into the existing hillside supported by retaining walls. Pier supported foundations are anticipated for the proposed structures. Access to the new residence will be along an easement between existing neighboring residences that front onto Bay View Road.
GEOLOGY
Regional Geologic Setting
The site is located within the San Francisco Bay portion of the Coast Ranges geomorphic province of California. Extending from the Transverse Ranges in central California to Oregon, this region is characterized by northwest-trending mountain chains and intervening valleys. The structural grain of the Coast Ranges is generally controlled by the San Andreas fault zone and related major fault zones. The property is located on the geologically complex San Francisco Peninsula, which is bisected by the San Andreas fault, bounded by the San Gregorio fault along the Pacific Ocean, and internally complicated by a series of fault blocks containing individual bedrock terranes. These bedrock terranes comprise a variety of related rocks collectively known as the Franciscan Complex or Assemblage of Jurassic to Cretaceous age. These rocks are overlain by younger sedimentary rocks and generally concealed by a veneer of various surficial deposits, including alluvium, colluvium, and landslides. There are areas underlain by artificial fill from human development (Wagner and others, 2005).
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Packet Pg. 906 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Evaluation of Potential Landslide Hazards Page 3
Vacant Lot; APN: 022-062-550, Pacifica, CA
July 7, 2024
Project No: S24-01978
Engineering Geology • Fault and Landslide Investigations • Urban Geology • Forensic Studies Earth Focus Geological Services, Inc.
Site Geology
Bedrock
The various published geologic maps reviewed for this evaluation suggest that the site and the hills above the site are underlain by greenstone belonging to the Franciscan Complex of Jurassic to Cretaceous age (see Figure 3). The formation may include altered basalt rocks, consisting of flows, pillow lavas, breccias, tuffs, and minor relative intrusive bodies. These rocks are generally hard and difficult to excavate when fresh. The greenstone may also include minor amounts of chert and limestone. The predominate bedrock structure, presumably layering between flows, within the site vicinity is shown as dipping to the northeast and east from 45 to 80 degrees (Brabb and others, 1998; Brabb and Pampeyan, 1972 and 1983; Pampeyan, 1994; Ellen and Wentworth, 1995; Graymer and others, 2006; and Wentworth and others, 1985).
We did not observe any bedrock outcrops within or adjacent to the project site during our recent geologic reconnaissance. The ground surface was littered with greenstone rock fragments suggesting that bedrock is near the surface. We observed greenstone bedrock samples retrieved during the exploratory borings at the site during drilling.
Surficial Deposits
The published geologic maps do not show surficial deposits of any significant thicknesses within the site or on the slopes above the site. Alluvium generally consisting of unconsolidated silt, sand, and gravel has been mapped at the west end of the northwest-draining canyon to the west of the site (Brabb and others, 1998; Helley and Lajoie, 1979; and Pampeyan, 1994).
Upstream of the alluvium, most of the remainder of the main canyon as well as the southwestflowing drainage along Bay View Road has been mapped as slope wash and ravine fill deposits.
These slope wash and ravine fill deposits are generally shallower than the alluvial sediments and consist of unconsolidated clay, silt, and sand with rock fragments the represent erosional detritus from upslope areas. No artificial fill areas have been mapped near the site (Brabb and Pampeyan, 1972; and Pampeyan, 1994).
We understand that alluvial deposits were recently encountered in an exploratory boring drilling within the access easement near Bay View Road. We also understand that these alluvial deposits were capped by a layer of artificial fill.
Debris Flows and Deep-Seated Landslides
According to the landslide maps published by the U.S. Geological Survey, no debris flows or deep-seated landslides have been mapped within or adjacent to the subject property. Several relatively small landslides have been mapped throughout the hillslopes within the site vicinity.
Most of these landslides appear to be relatively shallow failures (Brabb and Pampeyan, 1972; and Pampeyan, 1994). None of these small mapped landslides impact the site.
Similar to the other published landslide maps reviewed for this evaluation, the California Geological Survey (State Geologist, 2019b; Plate 1.2) has mapped several relatively small landslides throughout the hills of the site area. A landslide is mapped along the west-facing slope above the site. The reactivation of this mapped landslide would likely fail into the
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Packet Pg. 907 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Evaluation of Potential Landslide Hazards Page 4
Vacant Lot; APN: 022-062-550, Pacifica, CA
July 7, 2024
Project No: S24-01978
Engineering Geology • Fault and Landslide Investigations • Urban Geology • Forensic Studies Earth Focus Geological Services, Inc.
southwest-flowing drainage and possibly impact the residences along Bay View Road bypassing the site.
The California Geological Survey has created and maintains an online Landslide Inventory and Deep Landslide Susceptibility Map for areas throughout California. The online map is being periodically updated as additional information becomes available. The map shows several types of landslides identified based on geomorphic characteristics and history of movements (http://www.conservation.ca.gov/cgs/landslides). No landslides have been mapped within or near the site (see Figure 4).
The rainstorms of January 3–5, 1982 triggered many landslides and debris flows in the San Francisco Bay area resulting in 24 fatalities and widespread property damage estimated to be in the millions of dollars (Smith and Hart, 1982). The U.S. Geological Survey mapped the various slope failures resulting from this event over an eleven-county area. No such landslides were mapped within the site or above the site as a result of the 1982 rainstorms (Ellen and Wieczorek, 1988).
The Pacifica area experienced significant damage from the 1982 storms that were responsible for causing approximately 475 landslides. One of the most notable debris flows and tragic events occurred approximately 1.5 miles to the southeast of the site within a residential subdivision. This debris flow resulted in the death of three children and the destruction of two residences along Oddstad Boulevard. The failure occurred within a colluvial-filled swale within the bedrock slopes high above the site. The failure occurred at the top of the bedrock surface.
Apparently, the colluvial-filled swale had not been mapped and the potential hazard was not recognized (Howard and others, 1988; and Shlemon and Wright, 1987).
FAULTING AND SEISMICITY
The site is within the seismically active San Francisco Bay area where small earthquakes (Magnitude <4) are frequent, moderate earthquakes (Magnitude 4–6) are sometimes felt, and large earthquakes (Magnitude >6) occur, but are rare. The San Francisco Bay area is dominated by the northwest-striking strike-slip San Andreas fault and related seismically active1 faults, such as the San Gregorio fault along the west side of the San Francisco Peninsula and the Hayward–Rodgers Creek, Calaveras, Concord–Green Valley, and Greenville– Marsh Creek faults located in the East Bay (Jennings and Bryant, 2010; see Figure 5).
The site is not within a designated Earthquake Fault Zone as established by the State of California for seismically active faults (Hart and Bryant, 1997). The closest active fault to the site is the San Andreas fault, approximately 2.6 miles to the northeast. The onshore portion of the San Gregorio fault is located approximately 5.7 miles to the south-southwest (State Geologist, 1982). The Hayward–Rodgers Creek fault and other East Bay faults are more than 20 miles away to the east (Jennings, 2010).
REVIEW OF AERIAL PHOTOGRAPHS
We have reviewed selected vertical stereo pairs of historical aerial photographs of the site and vicinity for the years 1946, 1955, 1958, 1963, 1969, 1977, 1983, 1991, 2000, and 2005. The 1 An “active” fault is defined as one that has had surface displacement within Holocene Time or about the last 11,000 years (California Code of Regulations, Title 14, Division 2, Appendix B, Section 3601).
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Packet Pg. 908 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Evaluation of Potential Landslide Hazards Page 5
Vacant Lot; APN: 022-062-550, Pacifica, CA
July 7, 2024
Project No: S24-01978
Engineering Geology • Fault and Landslide Investigations • Urban Geology • Forensic Studies Earth Focus Geological Services, Inc.
horizontal scales of the aerial photographs reviewed range from 1:7,200 to 1:36,000. A complete list of photographs reviewed and their sources is provided in the back of this report.
The following paragraphs are a brief summary of observations and interpretations of the site and vicinity, based on a review of aerial photographs.
The earliest aerial photographs reviewed from 1946 show the site area within a prominent and relatively narrow northwest-flowing canyon that outlets into the Pacific Ocean. The sides of the canyon were relatively steep and covered with sparce vegetation. Rockaway Beach Avenue was present at that time along with scattered house throughout the canyon. Bay View Road and the adjacent properties, including the project site, were not developed as observed on the 1946 aerial photographs. An incised drainage flowing toward the southwest into the main canyon can be seen passing to the northwest of the project site and along the southeast side of the future Bay View Road alignment. We did not observe any obvious signs of slope instability or erosion within or above the site on the 1946 aerial photographs.
There were no significant developmental changes to the site area as seen on the aerial photographs reviewed from 1955, 1958, and 1963. The project site, areas adjacent to the site, and the Bay View Road alignment remained undeveloped during this time period. The low altitude 1958 aerial photographs suggest that the southwest-flowing drainage passing between the future Bay View Road alignment and the project site was incised into alluvial fan deposits and not bedrock. Therefore, alluvial deposits may underlie the area to the west of the site.
Sometime between 1963 and 1969, Bay View Road was constructed. The road appeared as recent construction as seen on the 1969 aerial photographs. There were no houses along Bay View Road at that time. The 1969 aerial photographs suggest that approximately 50 percent of the properties along Rockaway Beach Avenue were developed with houses at that time. The incised southwest-flowing drainage remained present and parallel to the southeast side of Bay View Road as observed on the 1969 aerial photographs. We did not observe any evidence of erosion, slope instability, or colluvial-filled swale within the site or above the site as seen on the 1969 aerial photographs.
Residential development increased significantly within the site neighborhood in the early and middle 1970s such that approximately 75 percent of the once vacant properties were now developed, based on our review of the aerial photographs. Between 1969 and 1977, the two existing residences at the north end of and on opposite sides of Bay View Road were present, including the residence along the north side of the site easement. The residence along the south side of the site easement had not been constructed at that time and there were several other undeveloped lots along Bay View Road. Although none of the aerial photographs reviewed captured the grading, it appeared that the old incised southwest-flowing drainage had been backfilled during that time to accommodate residential construction along the southeast side of Bay View Road.
The 1977 aerial photographs show that a narrow bench had been excavated into the slope within the central portion of the site that was connected to the easement from Bay View Road.
The approximately alignment of Calera Terrace above the site has been brushed and a narrow dirt path has been excavated across the slope at that time. The remainder of the slopes above the site were covered with low vegetation as seen on previous aerial photographs. There were no indications of slope instability or colluvial-filled swales within or near the site as observed on the 1977 aerial photographs.
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Packet Pg. 909 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Evaluation of Potential Landslide Hazards Page 6
Vacant Lot; APN: 022-062-550, Pacifica, CA
July 7, 2024
Project No: S24-01978
Engineering Geology • Fault and Landslide Investigations • Urban Geology • Forensic Studies Earth Focus Geological Services, Inc.
Most of the once vacant properties along Bay View Road were developed with houses by the early 1980s. However, the lot along the south slide of the site easement and along the southeast side of Bay View Road remained vacant throughout the late 1970s and the 1980s, and was eventually developed by 1991 as seen on the aerial photographs. The alignment of Calera Terrace can be seen above the site as a relatively narrow dirt trail on the 1983 and 1991 aerial photographs that extends along the topographic contours to the north of the site.
The 1991, 2000, and 2005 aerial photographs show a possible debris flow scarp high on the slope above the northeast terminus of Bay View Road. The scarp was arcuate-shaped, but there was no obvious disruption in the vegetation. If this was a debris flow scarp, the failure would have likely impacted the neighboring property to the north that fronts onto Bay View Road. The project site would not have been impacted by this potential failure.
GEOLOGIC RECONNAISSANCE
We visited the site on May 29, 2024 to observe the property and the surroundings during the exploratory drilling. Access to the site is an unimproved grass-covered easement between two existing residences along the southeast side of Bay View Road. The property is vacant of any structures and overgrown with low vegetation and bushes. Some of the areas within the site were recently cleared so that drilling equipment could access the property.
There is a hint of a narrow terrace area within the central portion of the lot that was seen on the aerial photographs. The ground surface is littered by hard greenstone rock fragments. The site slopes steeply down to the southwest to the back yards of the houses the front onto Rockaway Beach Avenue. The property slope steeply up to the northeast to a prominent ridgetop. Runoff appears to sheetflow uncontrolled down the slopes within the site. We did not observe any obvious signs of landsliding within the site or above the site during our geologic reconnaissance.
We did not observe any bedrock exposures within or adjacent to the site. No seepage areas or springs were identified within or adjacent to the site during our geologic reconnaissance.
DISCUSSION AND CONCLUSIONS
The property is along a relatively steep slope underlain by hard greenstone bedrock concealed by a thin veneer of surficial soils. The bedrock becomes progressively harder with depth as was evident from the recent exploratory drilling and the previous exploratory drilling by Summit Engineering (2011). An old incised drainage passing through alluvial fan deposits was backfilled to the west of the site along the southeast side of Bay View Road. The fan deposits or backfill of the old drainage do not affect the proposed development within the site.
No landslides have been mapped within or above the property as shown on published geologic maps and none have been identified from our review of historic aerial photographs and observations during our recent geologic reconnaissance. No colluvial-filled swales have been previously mapped or identified from our research within or above the site. There were no seepages or springs observed along the site slope. The proposed site development would likely improve the overall surface and subsurface drainage conditions at the project site by the installation of subdrains, wall drains, and surface drainage facilities.
In following the general guidelines established for a screening investigation for EarthquakeInduced Landslide Hazards according to the California Geological Survey Special Publication
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Packet Pg. 910 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
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Packet Pg. 911 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Evaluation of Potential Landslide Hazards Page 8
Vacant Lot; APN: 022-062-550, Pacifica, CA
July 7, 2024
Project No: S24-01978
Engineering Geology • Fault and Landslide Investigations • Urban Geology • Forensic Studies Earth Focus Geological Services, Inc.
REFERENCES
Brabb, E.E., Graymer, R.W., and Jones, D.L., 1998, Geology of the Onshore Part of San Mateo County, California: A Digital Database: U.S. Geological Survey Open-File Report 98-137.
Brabb, E.E., and Pampeyan, E.H., compliers, 1983, Geologic Map of San Mateo County: U.S.
Geological Survey Miscellaneous Investigations Series Map I-1257-A, map scale 1:62,500.
Brabb, E.E., and Pampeyan, E.H., compilers, 1972, Preliminary Geologic Map of San Mateo County, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-328, map scale 1:62,500.
Brabb, E.E., and Pampeyan, E.H., 1972, Preliminary Map of Landslide Deposits in San Mateo County, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-344, map scale 1:62,500.
California Geological Survey, 1997, Guidelines for Evaluating and Mitigating Seismic Hazards in California: Special Publication 117, 74 p.
California Geological Survey, 2008, Guidelines for Evaluating and Mitigating Seismic Hazards in California: Special Publication 117A, 98 p.
Ellen, S.D., and Wentworth, C.M., 1995, Hillside Materials and Slopes of the San Francisco Bay Region, California: U.S. Geological Survey Professional Paper 1357, 215 p., 7 pls.
Ellen, S.D., and Wieczorek, G.F., eds., 1988, Landslides, Floods, and Marine Effects of the Storm of January 3-5, 1982, in the San Francisco Bay Region, California: U.S. Geological Survey Professional Paper 1434, 310 p., 14 pls.
Graymer, R.W., Moring, B.C., Saucedo, G.J., Wentworth, C.M., Brabb, E.E., and Knudsen, K.L., 2006, Geologic Map of the San Francisco Bay Region: U.S. Geological Survey Scientific Investigations Map 2918.
Hart, E.W., and Bryant, W.A., 1997 (revised), Fault-Rupture Hazard Zones in California:
California Geological Survey Special Publication 42, 38 p.
Helley, E.J., and Lajoie, K.R., 1979, Flatland Deposits of the San Francisco Bay Region, California – Their Geology and Engineering Properties, and Their Importance to Comprehensive Planning: U.S. Geological Survey Professional Paper 943, 88 p., 3 pls.
Howard, T.R., and Baldwin, J.E., II, and Donley, H.F., 1988, Landslides in Pacifica, California, Caused by the Storm: in Ellen, S.D., and Wieczorek, eds., Landslides, Floods, and Marine Effects of the Storm of January 3-5, 1982: U.S. Geological Survey Professional Paper 1357, pp. 163-183.
Jennings, C.W., compiler, 2010, Fault Activity Map of California: California Geological Survey, Geologic Data Map No. 6, map scale 1:750,000.
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Packet Pg. 912 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Evaluation of Potential Landslide Hazards Page 9
Vacant Lot; APN: 022-062-550, Pacifica, CA
July 7, 2024
Project No: S24-01978
Engineering Geology • Fault and Landslide Investigations • Urban Geology • Forensic Studies Earth Focus Geological Services, Inc.
Pampeyan, E.H., 1994, Geologic Map of the Montara Mountain and San Mateo 7-1/2’ Quadrangles, San Mateo County, California: U.S. Geological Survey Miscellaneous Investigations Series Map I-2390, map scale 1:24,000.
Shlemon, R.J., and Wright, R.H., 1987, Anatomy of a Debris Flow, Pacifica, California: in Costa, J.E., and Wieczorek, eds., Debris Flows/Avalanches: Process, Recognition, and Mitigation: The Geological Society of America Reviews in Engineering Geology, Volume VII, pp. 181-199.
Smith, T.C., and Hart, E.W., 1982, Landslides and Related Storm Damage, January 1982, San Francisco Bay Region: California Geology, v. 35, pp. 139-152.
State Geologist, 2019a, Seismic Hazard Zones, Montara Mountain Quadrangle: California Geological Survey Official Map Released April 4, 2019, map scale 1:24,000.
State Geologist, 2019b, Seismic Hazard Zone Report for the Montara Mountain 7.5-Minute Quadrangle, San Mateo County, California: California Geological Survey Seismic Hazard Zone Report 128, 33 p.
State Geologist, 1982, Earthquake Fault Zones, Montara Mountain Quadrangle: Official Map, Released January 1, 1982, map scale 1:24,000.
Summit Engineering, 2011, Geotechnical Report for the Proposed Residence at Parcel 55, Bay View Road, Pacifica, California: Unpublished Consultants Technical Report, Dated March 9, 2011, 16 p., one appendix.
U.S. Geological Survey, 2022, Montara Mountain 7.5’ Quadrangle, California: Map scale 1:24,000.
Wagner, D.L., Bortugno, E.J., and McJunkin, R.D., 2005, compliers, Geologic Map of the San Francisco-San Jose Quadrangle: California Geological Survey Regional Geologic Map Series Map No. 5A (Geology), map scale 1:250,000.
Wentworth, C.M., Ellen, S., Frizzell, V.A., Jr., and Schlocker, J., 1985, Map of Hillside Materials and Description of Their Engineering Character, San Mateo County, California: U.S. Geological Survey Miscellaneous Investigations Series Map I-1257-D, 2 sheets, map scale 1:62,500.
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Packet Pg. 913 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Evaluation of Potential Landslide Hazards Page 10
Vacant Lot; APN: 022-062-550, Pacifica, CA
July 7, 2024
Project No: S24-01978
Engineering Geology • Fault and Landslide Investigations • Urban Geology • Forensic Studies Earth Focus Geological Services, Inc.
AERIAL PHOTOGRAPHS REVIEWED
Date Flight Line Frames Scale Type
07-29-46 AV-9 13-1 & 2 1:23,600 B & W Stereo
05-10-55 AV-170 02-24 1:10,000 B & W Single
04-23-58 AV-279 02-32 & 33 1:7,200 B & W Stereo
07-09-63 AV-550 04-27 & 28 1:36,000 B & W Stereo
10-29-69 AV-933 03-22 & 23 1:12,000 B & W Stereo
05-27-77 AV-1356 02-22 & 23 1:12,000 B & W Stereo
06-06-83 AV-2265 02-23 & 24 1:12,000 B & W Stereo
07-02-91 AV-4075 2-21 & 22 1:12,000 B & W Stereo
08-15-00 AV-6600 3-23 & 24 1:12,000 B & W Stereo
10-17-05 AV-9200 32-3 & 4 1:7,200 B & W Stereo
All photographs available for review at Pacific Aerial Surveys in Novato, California.
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Packet Pg. 914 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Evaluation of Potential Landslide Hazards
Vacant Lot; APN: 022-062-550, Pacifica, CA
July 7, 2024
Project No: S24-01978
Figure 1 – Site Location Map
Figure 2 – Earthquake Zones of Required Investigation
Figure 3 – Regional Geologic Map
Figure 4 – California Geological Survey Landslide Inventory Map Figure 5 – Regional Fault Map
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Packet Pg. 915 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Earth Focus
Geological Services, Inc.
www.earthfocusgeology.com
115 Orchard Drive
Fremont, CA 94536
Phone/Fax 510-794-7495
SITE LOCATION MAP
Evaluation of Potential Landslide Hazards
Proposed New Residential Construction
Vacant Lot, APN 022-062-550
Pacifica, California
Project No.
S24-01978 July 2024 Figure 1
Map Source: U.S. Geological Survey, 2022, Montara Mountain, California, 7.5’ Quadrangle, Scale 1:24,000.
N
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Packet Pg. 916 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Map Source: State Geologist, 2019, Earthquake Zones of Required Investigation, Montara Mountain Quadrangle: California Geological Survey Official Map, Released November January 1, 1982 (Earthquake Fault Zones), April 4, 2019 (Seismic Hazard Zones), Scale: 1:24,000.
Earth Focus
Geological Services, Inc.
www.earthfocusgeology.com
115 Orchard Drive
Fremont, CA 94536
Phone/Fax 510-794-7495
STATE OF CALIFORNIA
SEISMIC HAZARD ZONES MAP
Evaluation of Potential Landslide Hazards
Proposed New Residential Construction
Vacant Lot, APN 022-062-550
Pacifica, California
Project No.
S24-01978 July 2024 Figure 2
N
EXPLANATION
MILE
0 0.5 1.0
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Packet Pg. 917 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Earth Focus
Geological Services, Inc.
www.earthfocusgeology.com
115 Orchard Drive
Fremont, CA 94536
Phone/Fax 510-794-7495
REGIONAL GEOLOGIC MAP
Evaluation of Potential Landslides Hazards
Proposed New Residential Construction
Vacant Lot, APN 022-062-550
Pacifica, California
Project No.
S24-01978
July 2024 Figure 3a
Map Source: Pampeyan, E.H., 1994, Geologic Map of the Montara Mountain and San Mateo 7-1/2' Quadrangles, San Mateo County, California: U.S. Geological Survey Miscellaneous Investigations Map I-2390, Scale 1:24,000.
N
0 0.5 1
MILE
EXPLANATION
See Figure 3b for nomenclature and description of map units.
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Packet Pg. 918 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Map Source: Pampeyan, E.H., 1994, Geologic Map of the Montara Mountain and San Mateo 7-1/2' Quadrangles, San Mateo County ,
California: U.S. Geological Survey Miscellaneous Investigations Map I-2390, Scale 1:24,000.
Earth Focus
Geological Services, Inc.
www.earthfocusgeology.com
115 Orchard Drive
Fremont, CA 94536
Phone/Fax 510-794-7495
REGIONAL GEOLOGIC MAP
Evaluation of Potential Landslide Hazards
Proposed New Residential Construction
Vacant Lot, APN 022-062-550
Pacifica, California
Project No.
S24-01978
July 2024 Figure 3b
DESCRIPTION OF MAP UNITS
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Packet Pg. 919 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) MILE
0 0.2 0.4
N
SITE
EXPLANATION
Debris flow, active/historic
Debris flow track, active/historic
Small debris flow scarp or track, active/historic
Map Source: California Geological Survey, 2015, Landslide Inventory (Beta) Online Mapping Application: available at https://maps.conservation.ca.gov/cgs/lsi/, accessed 07/06/2024.
Earth Focus
Geological Services, Inc.
www.earthfocusgeology.com
115 Orchard Drive
Fremont, CA 94536
Phone/Fax 510-794-7495
CALIFORNIA GEOLOGICAL SURVEY
LANDSLIDE INVENTORY MAP
Evaluation of Potential Landslide Hazards
Proposed New Residential Construction
Vacant Lot, APN 022-062-550
Pacifica, California
Project No.
S24-01978
July 2024 Figure 4
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Packet Pg. 920 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal) Map Source: Jennings, C.W., and Bryant, W.A., compilers, 2010, Fault Activity Map of California: California Geological Survey Data Map No. 6, Scale 1:750,000.
Earth Focus
Geological Services, Inc.
www.earthfocusgeology.com
115 Orchard Drive
Fremont, CA 94536
Phone/Fax 510-794-7495
REGIONAL FAULT MAP
Evaluation of Potential Landslide Hazards
Proposed New Residential Construction
Vacant Lot, APN 022-062-550
Pacifica, California
Project No.
S24-01978
July 2024 Figure 5
N
MILES
0 12 24
SITE
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Packet Pg. 921 Attachment: Attachment F - Micheluccci Associates Geotechnical Report-24-07-10 (6153 : Bay View Rd Appeal)
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Packet Pg. 922 Attachment: Attachment G - Amendment to Grant of Easement (6153 : Bay View Rd Appeal)
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Packet Pg. 923 Attachment: Attachment G - Amendment to Grant of Easement (6153 : Bay View Rd Appeal)
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Packet Pg. 924 Attachment: Attachment G - Amendment to Grant of Easement (6153 : Bay View Rd Appeal)
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Packet Pg. 925 Attachment: Attachment G - Amendment to Grant of Easement (6153 : Bay View Rd Appeal)
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Packet Pg. 926 Attachment: Attachment G - Amendment to Grant of Easement (6153 : Bay View Rd Appeal)
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Packet Pg. 927 Attachment: Attachment G - Amendment to Grant of Easement (6153 : Bay View Rd Appeal)
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Packet Pg. 928 Attachment: Attachment G - Amendment to Grant of Easement (6153 : Bay View Rd Appeal)
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Packet Pg. 929 Attachment: Attachment G - Amendment to Grant of Easement (6153 : Bay View Rd Appeal)
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Packet Pg. 930 Attachment: Attachment G - Amendment to Grant of Easement (6153 : Bay View Rd Appeal)