Mi l l er Pac i fic E N G I N E ERI NG GR O UP 504 Redwood B l vd. Suite 220 Novato, Ca l i f o rnia 94947

Transcription

1 Mi l l er Pac i fic E N G I N E ERI NG GR O UP 504 Redwood B l vd. Suite 220 Novato, Ca l i f o rnia T 415 / F 415 / PRELIMINARY GEOTECHNICAL REPORT RIVERFRONT RESIDENTIAL DEVELOPMENT 500 HOPPER STREET PETALUMA, CALIFORNIA March 23, 2006 Project Prepared For: Basin Street Properties 201 First Street Petaluma, California CERTIFICATION This document is an instrument of service, prepared by or under the direction of the undersigned professionals, in accordance with the current ordinary standard of care. The service specifically excludes the investigation of radon, asbestos, toxic mold, other biological pollutants and hazardous materials. The document is for the sole use of the client and consultants on this project. Use by third parties or others is expressly prohibited without written permission. If the project changes, or more than two years have passed since issuance of this report, the findings and recommendations must be reviewed by the undersigned. MILLER PACIFIC ENGINEERING GROUP (a California corporation) REVIEWED BY Timothy J. Reynolds Scott A. Stephens Geotechnical Engineer No Geotechnical Engineer No (Expires 12/31/06) (Expires 6/30/07)

2 PRELIMINARY GEOTECHNICAL REPORT RIVERFRONT RESIDENTIAL DEVELOPMENT 500 HOPPER STREET PETALUMA, CALIFORNIA TABLE OF CONTENTS I. INTRODUCTION Page 1 II. PROJECT DESCRIPTION 3 III. SITE CONDITIONS 4 A. Regional Geology 4 B. Seismicity 4 C. Surface Conditions 7 D. Subsurface Conditions 7 E. Groundwater 8 IV. GEOLOGIC HAZARDS EVALUATION 9 A. Summary 9 B. Fault Surface Rupture 9 C. Seismic Shaking 9 D. Liquefaction Potential and Related Impacts 10 E. Seismic Induced Ground Settlement 11 F. Lurching and Lateral Spreading 12 G. Erosion 12 H. Seiche and Tsunami 12 I. Expansive Soil 13 J. Settlement Under Static Loads 13 K. Flooding 14 V. CONCLUSIONS AND DISCUSSION 15 A. Conclusion 15 B. Settlement 15 VI. ADDITIONAL GEOTECHNICAL SERVICES 17 LIST OF REFERENCES 18 FIGURES Site Location Map Figure 1 Site Plan 2 Fault Map 3 TABLE OF CONTENTS (CONTINUED)

3 APPENDIX A SUBSURFACE EXPLORATION AND LABORATORY TESTING Soil Classification Chart Figure A-1 Boring Logs A-2 to A-7 CPT Data Interpretation Chart A-8 CPT Data A-9, A-10

4 PRELIMINARY GEOTECHNICAL REPORT RIVERFRONT RESIDENTIAL DEVELOPMENT 500 HOPPER STREET PETALUMA, CALIFORNIA I. INTRODUCTION This report summarizes the results of our preliminary geotechnical investigation for the planned Riverfront residential development in Petaluma, California. As shown on Figure 1, the site is located in southern Petaluma, West of U.S. Highway 101 and north of the Petaluma River. The purpose of our preliminary investigation and report is to provide our professional opinion regarding overall project feasibility, identify and address potential geotechnical and geologic hazards at the project site (in particular settlement, liquefaction, and seismic ground shaking), develop feasible mitigation options for the identified hazards, and summarize the results in this report for use in planning and preliminary design of the project. Our scope of services is described in our proposal letter dated November 23, 2005 and includes several phases to match project development. This report completes the Phase 1 services, which included the following: 1. Review of readily available geologic reference information to describe geologic setting and local geologic conditions. 2. A site reconnaissance to observe surface conditions. 3. Subsurface exploration with two CPT probes and three borings, ranging in total depth from approximately 35 to 50 feet below existing ground surface. 4. Limited laboratory testing of representative samples to determine in-place moisture and density. 5. An evaluation of geologic hazards that could impact the planned site development and development of preliminary recommendations to mitigate the identified hazards. 6. Description of other geotechnical constraints that should be addressed during project design and preliminary recommendations for probable foundation types. 7. Preparation of this report with a summary of geologic hazards and preliminary geotechnical recommendations. 1

5 Future phases of our work will include a design-level geotechnical investigation(s) and report(s), supplemental consultation and geotechnical plan review, and geotechnical observation and testing services during construction. 2

6 II. PROJECT DESCRIPTION The Riverfront project site is located directly west of Highway 101 and north of the Petaluma River within the City of Petaluma, as shown on Figures 1 and 2. The approximately 40-acre site is currently undeveloped. Previous grading activities at the site appear to have included placement of three to five feet of artificial fill over the northern one third to one half of the site. Several large stockpiles have been placed on top of this fill area. We understand that the project will include development of approximately 440 new homes, along with associated new infrastructure, utilities, and park/open space areas. A southerly extension of Caulfield Lane is planned through the center of the site, leading to a possible future bridge crossing of the Petaluma River beyond the south edge of the project. New residences will be a combination of two- and three-story single family homes, three-story town homes, live/work spaces (town homes with ground floor workspaces), and mixed use (four-story housing over retail). We anticipate foundation loads associated with this planned residential construction will be light to moderate. Preliminary grading plans prepared by Steven J. Lafranchi and Associates indicate up to approximately 10 feet of new fill will be placed over portions of the southern half of the property, principally along the proposed alignment for the Caulfield Lane extension. Planned fill for the residential building pads typically ranges from zero to five feet. 3

7 III. SITE CONDITIONS A. Regional Geology The site is located within the Coast Range Geomorphic Province of California. The regional bedrock geology consists of complexly folded, faulted, sheared, and altered sedimentary, igneous, and metamorphic rock of the Jurassic-Cretaceous age (65 to 190 million years ago) Franciscan Complex. Northwest-southeast trending mountain ridges formed from previous tectonic activity characterizes the regional topography. Extensive faulting during the Pliocene Age (1.8 to 7 million years ago) formed the uneven depression that is now the San Francisco Bay. More recent tectonic activity is concentrated along the San Andreas Fault zone, a complex group of generally parallel faults. Regional geologic mapping by the California Geological Survey (CGS 2002) and California Division of Mines and Geology (CDMG 1980) indicate the site is underlain by highly compressible Bay Mud deposits over as much as 300 feet of unconsolidated alluvium. This mapping shows the bay mud beginning near the north end of the property and thickening towards the Petaluma River. B. Seismicity The project site is located within a seismically active area and will therefore experience the effects of future earthquakes. Earthquakes are the product of the build-up and sudden release of strain along a fault or zone of weakness in the earth's crust. Within north coastal California, faults are concentrated along the San Andreas Fault zone. The movement between formations along either side of a fault may be horizontal, vertical, or a combination and is radiated outward in the form of energy waves. The earthquake force is transmitted through hard rock in short, rapid vibrations, while this energy movement becomes a long, high-amplitude motion when moving through soft ground materials. Long, high amplitude motions are typically more destructive. An active fault is one that shows displacement within the last 11,000 years and, therefore, is considered more likely to generate a future earthquake than a fault that shows no sign of recent rupture. The locations of the currently known active faults relative to the project site are shown on 4

8 Figure 3. The Richter or Moment Magnitude Scale provides a method to deduce the magnitude of an earthquake from seismologic instruments. The measurement of magnitude provides a rating that is independent of the place of observation and thus allows a comparison of seismic events. Magnitude is measured on a logarithmic scale; every one-unit increase indicates an increment of roughly 30 times the energy. For example, an 8.0 magnitude earthquake would have an energy level 30 times that of a 7.0 magnitude and 900 times that of a 6.0 magnitude earthquake. Historic Fault Activity Numerous earthquakes have occurred in the region within historic times. The results of our computer database search indicate that 28 earthquakes (Richter Magnitude 5.0 or larger) have occurred within 100 kilometers of the site area between 1735 and Using empirical attenuation relationships, the maximum historic acceleration at the ground surface (median peak) at the project site is approximately 0.25g. The five most significant historic earthquakes to affect the project site are summarized in Table A. 5

9 TABLE A SIGNIFICANT EARTHQUAKE ACTIVITY BASIN STREET RIVERFRONT PETALUMA, CALIFORNIA Fault Historic Richter Magnitude Year Distance Peak Site Acceleration San Andreas km 0.25 g Rodgers Creek km 0.24 g Rodgers Creek km 0.16 g Rodgers Creek km 0.15 g West Napa km 0.13 g References: Sources: USGS (2004), Seed, et al (1997), Boore, Joyner, Fumal (1994) The calculated site accelerations should only be considered as reasonable estimates. Many factors (soil conditions, orientation to the fault, etc.) can influence the actual ground surface accelerations. Significant deviations from the values presented are possible due to geotechnical and geologic variations from the typical conditions used in the empirical correlations. Probability of Future Earthquakes The historical records do not directly indicate either the maximum credible earthquake or the probability of such a future event. To evaluate earthquake probability in this region, the USGS has assembled a group of researchers into the Working Group on California Earthquake Probabilities to estimate the probabilities of earthquakes on active faults. Potential sources were analyzed considering fault geometry, geologic slip rates, geodetic strain rates, historic activity, and microseismicity, to arrive at estimates of probabilities of earthquakes with a Moment Magnitude greater than 6.7 by The probability studies focus on seven fault systems within the Bay Area. Fault systems are composed of different, interacting fault segments capable of producing earthquakes within the 6

10 individual segment or in combination with other segments of the same fault system. The probabilities for the individual fault segments in the San Francisco Bay Area are presented on Figure 3. In addition to the seven fault systems, the studies included probabilities of background earthquakes. These earthquakes are not associated with the identified fault systems and may occur on lesser faults (i.e., West Napa) or previously unknown faults (i.e., the 1989 Loma Prieta and 2000 Mt. Veeder - Napa earthquakes). When the probabilities on all seven fault systems and the background earthquakes are combined mathematically, there is a 62 percent chance for a magnitude 6.7 or larger earthquake to occur in the Bay Area by the year Smaller earthquakes (between magnitudes 6.0 and 6.7), capable of considerable damage depending on proximity to urban areas, have about an 80 percent chance of occurring in the Bay Area by 2032 (USGS, 2003). Additional studies by the USGS regarding the probability of large earthquakes in the Bay Area are on going. These current evaluations include data from additional active faults and updated geological data. C. Surface Conditions The site is bounded to the west by the existing Waste Water Treatment Plant (WWTP) for the City of Petaluma and other industrial development, to the east by Highway 101, to the south by the Petaluma River, and to the North by Northwestern Pacific Railroad tracks and industrial development beyond. The site is relatively level, with a very gentle gradient towards the south. Based on review of a site topographic map provided by Steven J. Lafranchi and Associates (SLA), current elevations range from approximately 10 to 15 feet (MSL). D. Subsurface Conditions We explored subsurface conditions by means of two Cone Penetration Test (CPT) probes on January 23, 2006 and three exploratory borings on February 14, 2006 at the approximate locations shown on Figure 2. The borings were drilled using track-mounted drilling equipment with solid-stem augers. Our subsurface exploration program is discussed in more detail in Appendix A. 7

11 Our probes and borings generally confirm the mapped geology. To the depths explored, the subsurface profile consists of artificial fill (at the CPT probe locations only), bay mud, and alluvial soils consisting of sand, silt, and clay with minor intermittent gravels. Logs of our borings and CPT probes are presented in Appendix A. Over the northern one third to one half of the site, our CPT probes encountered approximately five feet of sandy artificial fill over the natural bay mud and alluvial soil. The thickness of the compressible bay mud layer varies across the site. Our exploration indicates that the mud is between 15 and 20 feet thick beneath the northern half of the site and thickens to between 35 to 40 feet at the southern end of the site, adjacent to the Petaluma River. An approximately nine-foot thick layer of loose, natural sandy soil was encountered above the bay mud near the center of the site (Boring 3). This deposit is likely a filled-in old stream meander, which are occasionally found in bay mud and can leave isolated deposits of saturated sands. E. Groundwater We did not measure groundwater depth in our probes or borings. However, we anticipate that ground water at the site would be very near to the elevation of the adjacent Petaluma River, approximately 10 to 15 feet below current ground surfaces. Groundwater levels in the area will likely fluctuate throughout the year, and will likely be relatively close to the ground surface during and immediately after the wet winter rain season. 8

12 IV. GEOLOGIC HAZARDS EVALUATION A. Summary We evaluated potential geologic hazards that could effect the site and their significant adverse impacts as they would effect structures for human occupancy. The principle geologic hazards are total and differential settlement and strong seismic ground shaking. Localized liquefaction and moderate expansive potential of near-surface soil are also potential hazards. Shallow groundwater may be present during and after construction and should be considered in planning and design of any underground (or below current ground surface) structures and/or utilities. Other commonly-considered geologic hazards are judged to be of minor concern. Commonly considered geologic hazards, their potential impacts, and mitigation measures are described below. B. Fault Surface Rupture The proposed development area is not located within an Alquist-Priolo Earthquake Fault Zone 1. We therefore judge the potential for fault surface rupture in the development area to be low. No mitigation measures are required for structures in the development area. C. Seismic Shaking The site will likely experience seismic ground shaking similar to other areas in the seismically active Bay Area. Earthquakes along several active faults in the region could cause moderate to strong ground shaking at the site. The intensity of earthquake motion will depend on the characteristics of the generating fault, distance to the fault and rupture zone, earthquake magnitude, earthquake duration, and site specific geologic conditions. Deep and relatively soft soil deposits underlie the site. Therefore, a CBC soil Type of SOE (soft soil profile) should be applied to the site for seismic analysis. Empirical relations developed for soft soil sites (Seed, et al 1997) provide approximate estimates of median peak ground accelerations. A summary of the principle active faults affecting the site, their closest distance to the development area, moment 1 The Alquist-Priolo Earthquake Fault Zoning Act prohibits most structures for human occupancy across known traces of active faults. These fault zones are shown on maps issued by the 9

13 magnitude of characteristic earthquake, and probable peak ground accelerations at the site are shown in Table B. TABLE B ESTIMATED PEAK GROUND ACCELERATION FOR PRINCIPLE ACTIVE FAULTS BASIN STREET RIVERFRONT PETALUMA, CALIFORNIA Moment Magnitude Closest Estimated Median for Characteristic Distance Peak Ground Fault Earthquake (kilometers) Acceleration (g) Rodgers Creek San Andreas Hayward Maacama West Napa REFERENCE: USGS (1996); Seed, et al (1997); Boore, Joyner, Fumal (1994) The potential for strong seismic shaking at the project site is high. Due to their close proximity, the Rodgers Creek and San Andreas faults present the highest potential for severe ground shaking. The significant adverse impact associated with strong seismic shaking is potential damage to structures and improvements. Seismic Shaking Mitigation Measures - Mitigation measures should include, at a minimum, designing the improvements and structures in accordance with the most recent version of the California Building Code. D. Liquefaction Potential and Related Impacts Liquefaction refers to the sudden, temporary loss of soil strength during strong ground shaking. This phenomenon can occur where there are saturated, loose, granular (sandy) deposits subjected to seismic shaking. Liquefaction-related phenomena include settlement, flow failure, and lateral spreading. California Department of Conservation s Division of Mines and Geology. 10

14 Bay mud is not the type of soil that is susceptible to liquefaction. However, ancient stream meanders are occasionally found in bay mud and can leave isolated deposits of saturated sands that could liquefy during strong seismic shaking. One channel meander was encountered during our subsurface exploration, therefore the potential for liquefaction beneath portions of the site exists. However, given the localized nature of the channel meanders, widespread liquefactionrelated settlements and other related phenomenon are not anticipated at the project site. Liquefaction Potential Mitigation Measures Preliminary recommendations for mitigation of liquefaction hazard are discussed in Section V of this report. Once specific building layouts are established, our design-level geotechnical investigation(s) will include additional exploration and laboratory testing to determine extent of liquefiable deposits. Detailed geotechnical recommendations for grading and foundations will then be developed, as needed, to mitigate impacts to structures and improvements. Deep foundations or stiffened mat-slabs may be appropriate systems to mitigate liquefaction hazard potential, depending on the final building location and design foundation loads. Foundation options are discussed in Section V of this report. E. Seismic Induced Ground Settlement Ground shaking can induce settlement of loose granular soils above the water table. Boring 3 did encounter the channel meander deposit discussed above, which depending on the time of year could be unsaturated. Otherwise, we did not encounter these types of soils at the site. Seismicinduced ground settlement is considered to be a minor potential hazard at the site. Seismically-Induced Ground Settlement Mitigation Measures Our design-level geotechnical investigation(s) will include additional exploration to determine extents of loose granular soils above the water table and laboratory testing to evaluate degree of potential settlement. Appropriate geotechnical recommendations for grading and foundations should be developed, if needed, to mitigate impacts to structures and improvements. Mitigation measures (if needed for liquefaction) should also be appropriate for hazards associated with seismic induced ground settlement. 11

15 F. Lurching and Lateral Spreading Lurching and lateral spreading can occur during strong ground shaking. Lateral spreading generally occurs on slopes and near the tops of slopes where stiff soils are underlain by soft liquefiable deposits. Lurching and spreading along the bank of the Petaluma River, directly adjacent to the southern end of the property, is a potential hazard. However, preliminary plans show an approximately 100-foot wide Civic Space parkway zone between the river and new development. We judge that this level of setback from the river should effectively mitigate any lurching or spreading hazard. Lateral Spreading Mitigation Measures Our design-level geotechnical investigation(s) will include additional exploration, and laboratory testing and analysis to evaluate degree of potential spreading. Appropriate geotechnical recommendations for grading and foundations will then be developed, if needed, to mitigate impacts to structures and improvements. G. Erosion Sandy soils on moderate slopes or clayey soils on steep slopes are susceptible to erosion when exposed to concentrated surface water flows. Because site topography is generally relatively flat, and we did not observe evidence of significant erosion problems currently, we consider the potential hazard to the site from erosion to be low. No Mitigation Measures are required. However, the Project Civil Engineer should design the site drainage system (including roof downspouts) to minimize the risk of erosion. H. Seiche and Tsunami Seiche and tsunamis are short duration earthquake-generated water waves in enclosed bodies of water and the open ocean, respectively. The site is located several miles north of San Pablo Bay. Additionally, the site is at an elevation of at least 15+ feet and located sufficiently inland so that the potential for a seiche or tsunami to damage the development area is considered to be low. No mitigation measures are required. 12

16 I. Expansive Soils Moderate and highly plastic silts and clays, when located near the ground surface, can exhibit expansive characteristics (shrink-swell) that can be detrimental to structures and flatwork during periods of fluctuating soil moisture content. Our probes and borings do not indicate the presence of highly plastic silts or clays near-surface soil at the site, although some pockets of moderate plasticity clays and/or silts with low to moderate expansive characteristics may exist. Expansive soils are therefore not considered to be a significant site hazard. Expansive Soil Mitigation Measures Highly expansive soils are not anticipated at the site, however subsequent design-level geotechnical investigation should include exploration and laboratory testing to more precisely determine extent and degree of potential expansion of near surface soil within the chosen building pad area. Appropriate geotechnical recommendations for grading and foundations will then be developed, if needed, to mitigate impacts to structures and improvements. J. Settlement Under Static Loads Compressible bay mud deposits of variable thickness are present below the entire site. Therefore, site improvements will be subject to settlement due to consolidation of the bay mud under new foundation and/or fill surcharge loads. A surcharge load from 10 feet of new fill, as planned at the south end of the site for the Caulfield Lane extension, would generate as much as two feet of total settlement over the life of the project. Where fills of three feet or less are planned, lesser total settlements, up to one foot could still be expected. Consolidation of bay mud occurs at a decreasing rate over several decades. For mud of this thickness and loading of this type, we anticipate that as much as 50 percent of the total settlement would likely occur within the first five years after the fill load was applied. Settlement Mitigation Measures - More detailed analysis of settlements and rates of settlement will be required during our Design Level Investigation(s) for the site. These analyses will be based upon more detailed logging, sampling, and laboratory testing along with more precise loading data, as available. Possible settlement mitigation measures include pre-loading future development areas to surcharge loads in excess of the final design loads in order to force the settlement to occur at an accelerated rate prior to construction (if enough time is available before 13

17 start of construction) or use of structural foundation systems (such as matt slabs) which can withstand the potential total and differential settlements. Ground improvement, such as with the use of Rammed Aggregate Piers (RAP,) may also be appropriate at certain locations within the site. Due to excessive costs, traditional deep foundations such as driven pile or Cast-In-Drilled- Hole piers are not judged to be a likely foundation option for the planned new residences. Settlement mitigation options are discussed in more detail in Section V-B. K. Flooding Based on review of USGS quad maps, the site is located at approximate elevation +15 feet, or greater. The site is not mapped within a FEMZ 100-year or 500-year flood zone. The project Civil Engineer is responsible for site drainage and should evaluate local flooding potential and provide appropriate mitigation. Flooding Mitigation Measures - The project Civil Engineer should evaluate site drainage and localized flooding potential and provide appropriate mitigation measures and a recommended finished floor elevation. 14

18 V. CONCLUSIONS AND DISCUSSION A. Conclusion Based on our preliminary geotechnical investigation, we conclude the proposed project is geotechnically feasible. However, there are geologic and geotechnical hazards at the project site that will require some level of mitigation for the proposed development. As discussed briefly in the previous section, these hazards are settlement, strong seismic ground shaking, and isolated layers of liquefiable soil. We discuss these hazards in more detail below. B. Settlement As much as two-feet of total settlement could occur under planned new loading of the bay mud deposits on this site. The total amount of settlement will vary across the site and settlements will occur, at decreasing rates, over several decades. The principal hazards associated with this anticipated settlement include distress to new residential structures, disruption of underground gravity flow utilities (storm drain and sanitary sewer), and distress to new pavements and flatwork. Common mitigations for settlement of new improvements on soft soil include: use of deep foundations (driven piles of drilled piers) which gain support below the compressible layer, preloading (with stockpiles for example) of the development area to force the estimated settlement in an accelerated time frame in advance of construction, improvement (use of Rammed Aggregate Piers (RAP) or other densification method) of the compressible soil layer to limit future settlements to tolerable levels, use of stiffened foundation systems to withstand the effects of the anticipated settlement, or a combination of two or more of the above. The rate of settlement can be significantly increased through the use of vertical wick drains installed through the bay mud layer. The wick drains reduce the drainage path distance for the dissipation of pore water pressure and accelerate the consolidation of the bay mud. Based on our understanding of site conditions, planned development, and previous experience, we do not judge that the use of deep foundations will be a cost-effective option for the planned residential structures. A combination of the three other options will likely provide the most practical solution for the settlement hazard. Which option or combination will be most effective will vary across the site. Most buildings will likely require structural foundation systems, such as matt slabs or rigid interconnected grade beams, able to resist the anticipated strong ground shaking and potential for differential movement caused by liquefaction and/or consolidation of the bay mud. 15

19 For the northern portion of the site, where current plans call for removal of the previously placed fill and possibly some of the native soil to make design grades, we anticipate the settlement hazard will be lessened but not eliminated. Ground improvement with RAP may be a cost-effective option for this area. RAP are compacted aggregate base columns, constructed in pre-drilled holes. Hole diameters are typically 20 to 30 inches and maximum practical depths for RAP are on the order of 20 to 30 feet. If properly designed and constructed, RAP can improve a Weak near-surface soil layer, effectively mitigating settlement, providing an improved ground surface for construction activities, even through the winter months, and possibly provide a somewhat improved seismic ground shaking condition. Over the southern half of the site, where new fills are planned and bay mud thickness increases to near 40 feet, preloading with a surcharge in excess of the planned new fill loads could be advantageous, if the development timeline of the project allows. If it is possible, phasing of the project build-out to allow for development for the southern portions of the project after development of the north could provide an advantage in mitigating settlement hazard. If phased properly, material excavated from the north of the site, along with imported material if necessary, could be stockpiled to provide the surcharge at the south while construction of the first phase(s) proceeds. Again, use of wick drains to accelerate the settlement can be considered to better fit desired development timetables. Monitoring of actual settlement during this pre-loading could be performed so that actual settlements could be factored into design of these latter phase improvements. RAP would likely not be able to reach the bottom of the mud layer at the south half of the site. However, improving a potion of the bay mud layer could still provide some advantage. 16

20 VI. ADDITIONAL GEOTECHNICAL SERVICES This report provides preliminary geotechnical and geological information, and is therefore suitable for planning purposes only. Further detailed geotechnical exploration, testing, and engineering analysis will be required to develop design criteria for project design. Due to the overall size of the project, we anticipate that it will be developed in phases. When sequencing, phasing, and other details of project development have been determined, we will perform additional subsurface exploration and lab testing to provide the basis for our final foundation design criteria. We further anticipate that separate design-level geotechnical investigations may be required for the separate phases of the project development and build-out. We must consult with the design team and project professionals during design. When the project improvement plans have been prepared, we must review the documents to confirm that the intent of our recommendations has been understood and incorporated. Supplemental recommendations can be prepared during the design phase as needed. During construction we must inspect all site preparation, grading work, construction of building foundations, pavement construction, and utility trench backfills to observe that subsurface conditions are as expected and are consistent with geotechnical design criteria. 17

21 LIST OF REFERENCES Abrahamson, N. and Silva, W., Empirical Response Spectral Attenuation Relations for Shallow Crustal Earthquakes, Seismological Research Letters, Vol. 68, No. 1, Jan/Feb 1996, pp Boore, Joyner, and Fumal, Ground Motion Estimates for Strike- and Reverse-Slip Faults (1994), Lecture Notes from CE 275, Fall Semester 1997, University of California at Berkeley. California Department of Conservation, Division of Mines and Geology, Maps of Known Active Fault Near-Source Zones in California and Adjacent Portions of Nevada to be Used with the 1997 Uniform Building Code, International Conference of Building Officials, Whittier, California, February California Department of Conservation, Division of Mines and Geology, "Fault Activity Map of California and Adjacent Areas," California Department of Conservation, Division of Mines and Geology, Fault-Rupture Hazard Zones in California, Publication 42, revised California Department of Conservation, California Geologic Survey, Geologic Map of the Petaluma River 7.5 Quadrangle, Kunkle, Fred and Upson, J.E., Geology and Ground Water in Napa and Sonoma Counties, California, Engineering Group, Geotechnical Evaluation, Caulfield Lane Crossing Alternatives, March 24, Mitchell, J.K. and Wentz, F.J., Performance of Improved Ground during the Loma Prieta Earthquake, Earthquake Engineering Research Center (EERC) and College of Engineering, University of California at Berkeley, Report No. UCB/EERC-91/12, October Ritter, John R., and William R. Dupre, Maps Showing Areas of Potential Inundation by Tsunamis in the San Francisco Bay Region, California, U.S. Geological Survey Miscellaneous Field Studies Map MF-480, Scale 1:125,000, Seed, R.B., Chang, S.W., Dickenson, S.E., and Bray, J.D., Site-Dependent Seismic Response Including Recent Strong Motion Data, 1997 Wagner, D.L. and Bortungo, E.J., Geologic Map of the Santa Rosa Quadrangle, 1982, CDMG Regional Map Series No. 2A. Youd, T., Hansen, C., and Bartlett, S., Revised MLR Equations for Predicting Lateral Spread Displacement, Proceedings, 7 th U.S.-Japan Workshop on Earthquake Resistant Design of Lifeline Facilities and Countermeasures Against Liquefaction, Seattle, Washington, MCEER ,

22

23

24

25 APPENDIX A SUBSURFACE EXPLORATION AND LABORATORY TESTING 1.0 Subsurface Exploration Auger Borings We explored subsurface conditions over southern portions of the site by drilling three test borings on February 14, 2006 utilizing a track mounted drilling rig and 6-inch solid stem augers. The boring location is also shown on Figure 2. The borings were drilled to maximum depths of 41 feet below the ground surface. The soils encountered were logged and identified by our Field Geologist in general accordance with ASTM Standard D 2487, "Field Identification and Description of Soils (Visual-Manual Procedure)." This standard is briefly explained on Figure A-1, Soil Classification Chart and Key to Log Symbols. The Boring Log is presented on Figures A-2 to A-7. We obtained undisturbed samples using a 3-inch diameter, split-barrel modified California sampler with 2.5 by 6-inch brass tube liners. The sampler was driven with a 140-pound hammer falling 30 inches. The number of blows required to drive the samplers 18 inches was recorded and is reported on the Boring Log as blows per foot for the last 12 inches of driving. The samples obtained were examined in the field, sealed to prevent moisture loss, and transported to our laboratory. 2.0 Cone Penetration Test The Cone Penetration Test (CPT) is a special exploration technique that provides a continuous profile of data throughout the depth of exploration. It is particularly useful in defining stratigraphy, relative soil strength and in assessing liquefaction potential. We performed four CPTs at the locations shown on the Site Plan, Figure 2. The CPT is a cylindrical probe, 35 mm in diameter, which is pushed into the ground at a constant rate of 2 cm/sec. The device is illustrated on Figure A-1. It is instrumented to obtain continuous measurements of cone bearing (tip resistance), sleeve friction, and pore water pressure. The data is sensed by strain gages and load cells inside the instrument. Electronic signals from the instrument are continuously recorded by an on-board computer at the surface, which permits an initial evaluation of subsurface conditions during the exploration. The recorded data is transferred to an in-office computer for reduction and analysis. The analysis of cone bearing and sleeve friction (i.e. friction ratio) indicates the soil type, the cone bearing alone indicates soil density or strength, and the pore pressure indicates the presence of clay. Variations in the data profile indicate changes in stratigraphy. This test method has been standardized and is described in detail by the ASTM Standard Test Method D3441 "Deep, Quasi-Static Cone and Friction Cone Penetration Tests of Soil." The interpretation of CPT data is illustrated on Figure A- 8, and the CPT data logs are presented on Figures A-9 and A Laboratory Testing We conducted laboratory tests on selected intact and bulk samples to verify field identifications A-1

26 and to evaluate engineering properties. The following laboratory tests were conducted in accordance with the ASTM standard test method cited and results are shown on the exploratory Boring Logs. Laboratory Determination of Water (Moisture Content) of Soil, Rock, and Soil-Aggregate Mixtures, ASTM D 2216; and, Density of Soil in Place by the Drive-Cylinder Method, ASTM D 2937; The exploratory Boring Log, description of soils encountered, and the laboratory test data reflect conditions only at the location of the boring at the time they were excavated or retrieved. Conditions may differ at other locations and may change with the passage of time due to a variety of causes including natural weathering, climate, and changes in surface and subsurface drainage. A-2

27

28

29

30

31

32

33

34

35

36