Paleolandslide Investigation Building 25 Lawrence Berkeley National Laboratory Berkeley, California Submitted to: Mr. Jerome Ohearn Project Manager, Facilities Division Lawrence Berkeley National Laboratory One Cyclotron Road, MS 76-225 Berkeley, CA 94720 [email protected] Prepared by: William Lettis & Associates, Inc. 1777 Botelho Drive, Suite 262 Walnut Creek, CA 94596 August 31, 2009 SIGNATURE PAGE Paleolandslide Investigation, Building 25, Lawrence Berkeley National Laboratory, Berkeley, California William Lettis & Associates, Inc. Project No. 2072.001 This investigation and report were prepared by the following qualified William Lettis & Associates, Inc. personnel: ______________________________________ ___August 31, 2009___ John N. Baldwin, C.E.G. 2167 Date Principal Geologist Project Manager 2072.001 Paleolandslide Study i 8/31/09 TABLE OF CONTENTS 1.0 Introduction.................................................................................................................. 1 1.1 Project Description................................................................................................... 1 1.2 Purpose..................................................................................................................... 2 1.3 Previous AKA/WLA Investigations ........................................................................ 2 1.4 Limitations ............................................................................................................... 3 2.0 Scope of Work ............................................................................................................. 4 2.1 Data Review, Site Reconnaissance, and Geologic Mapping ................................... 4 2.2 Personal Communications ....................................................................................... 5 2.3 Subsurface Exploration............................................................................................ 5 3.0 Regional Geologic and Seismic Setting....................................................................... 7 3.1 Berkeley Hills Geology............................................................................................ 7 3.2 Bay Area Active Faults............................................................................................ 7 3.3 Bay Area Seismicity ................................................................................................ 8 4.0 Local Geologic Conditions ........................................................................................ 10 4.1 Local Geomorphology ........................................................................................... 10 4.2 Bedrock Units ........................................................................................................ 11 4.2.1 Cretaceous Great Valley Group...................................................................... 11 4.2.2 Tertiary Orinda Formation.............................................................................. 11 4.2.3 Tertiary Moraga Formation............................................................................. 12 4.2.4 Unconsolidated Deposits ................................................................................ 13 4.3 Building 25 Geologic Conditions ......................................................................... 14 5.0 Origin of Moraga Formation in Old Town ................................................................ 15 5.1 Paleolandsliding..................................................................................................... 15 5.2 Faulting .................................................................................................................. 17 5.3 Depositional ........................................................................................................... 17 6.0 Results of Subsurface Investigation........................................................................... 18 6.1 Exploratory Trench WLA T-1 ............................................................................... 18 6.1.1 Stratigraphic Relations in Trench T-1............................................................. 18 6.1.2 Structural Relations in Trench T-1 ................................................................. 19 6.2 Test Pit T-1 ............................................................................................................ 20 6.3 Exploratory Trench T-2 ......................................................................................... 20 6.3.1 Stratigraphic Relations of Trench T-2 ............................................................ 21 6.3.2 Structural Relations of Trench T-2 ................................................................. 22 6.4 Estimated Ages of Deposits................................................................................... 23 7.0 Discussion.................................................................................................................. 25 7.1 Paleolandslide Model............................................................................................. 26 8.0 Conclusions................................................................................................................ 28 9.0 References.................................................................................................................. 29 2072.001 Paleolandslide Study ii 8/31/09 LIST OF TABLES Table 1. Aerial Photography Reviewed............................................................................. 4 LIST OF FIGURES Figure 1. Location Map Figure 2. Map of Regional Geology Figure 3. LBNL Geologic Map from the RFI (Parsons, 2000) Report Figure 4. 1935 Oblique Aerial (View from Southwest) with Primary Local Creeks Figure 5. 1935 Oblique Aerial Photography Showing Schematic Geology Figure 6. Historical Seismicity of San Francisco Bay Area Figure 7. Section A-A’ Figure 8. Section B-B’ Figure 9. Section C-C’ Figure 10. Core Photograph of Borehole 430 (AKA-2) Figure 11. Core Photographs of Borehole 429 (AKA-1) Figure 12. Core Photograph Borehole 431 (AKA-3) LIST OF PLATES Plate 1. Geologic Map of Building 25 Area Plate 2. Trench T-1 (South Wall) Plate 3. Trench T-2 (South Wall) Plate 4. Test-Pit TP-1 (South Wall) LIST OF PHOTOGRAPHS Photograph 1 View to the northwest showing the trench T-1 location in a narrow lawn area sloping southwest toward Building 42 (not shown). Photograph 2 View to the east showing the location of trench T-1. Photograph 3 View of the southwall of trench T-1 near Station 16 feet. Photograph 4 View of the zone of folding and faulting in Tertiary sediments near Station 22 feet. Photograph 5 Photomosaic of a portion of soil profile SP-1 evaluated at Station 24 feet. 2072.001 Paleolandslide Study iii 8/31/09 Photograph 6 View of the geologic contact between the Tertiary sediments and sheared Moraga Formation near Station 38 feet in trench T-1. Photograph 7 View looking west of the abrupt and sheared contact between the Tertiary sediments and the Moraga Formation near Station 38 feet in trench T-1. Photograph 8 A close-up of calcium carbonate lining the shear zone between the Tertiary sediments and Moraga Formation at Station 42 feet near note b. Photograph 9 View looking west and upslope toward the southern Building 25 parking lot showing the location of trench T-2. Photograph 10 View of the geologic contact between Moraga-derived colluvium and Moraga formation and the underlying Orinda Formation near Station 38 feet. Photograph 11 View of the south wall of trench T-2 showing the geologic contact between the Moraga Formation and the Orinda Formation near Station 34 feet. Photograph 12 Close-up of the geologic contact between the Moraga and Orinda Formations at Station 34 feet showing the absence of shearing. LIST OF APPENDICES Appendix A-Soil Data Sheets SP-1 through SP-4 2072.001 Paleolandslide Study iv 8/31/09 1.0 INTRODUCTION William Lettis & Associates, Inc. (WLA), under subcontract to Alan Kropp and Associates, Inc. (AKA), presents the results of a paleolandslide investigation for a proposed redevelopment of the Building 25 area of Lawrence Berkeley National Laboratory (LBNL). The approximate site location is shown on Figure 1 and the site geologic map (Plate 1). 1.1 Project Description The Building 25 site is located in the "Old Town" area of the LBNL facility in an area of moderately steep slopes. The proposed re-development would include: (1) the demolition of LBNL Buildings 25 and 25A; (2) the construction a General Purpose Laboratory (GPL) building; and (3) a building or building(s) unrelated to the GPL project. The exact location of the proposed building footprints and site improvements are unknown at the time of this report but are assumed to be near Building 25 and its adjacent parking lots. The "Old Town" area of LBNL includes some of the earliest buildings constructed at the LBNL campus. The natural topography of the area has been extensively modified by grading; however, it is apparent that Building 25 is situated atop a north-south trending ridgeline that extends down into Strawberry Canyon (Figure 1). Old topographic maps of this area generally show the ridgeline and adjacent swales sloping down toward the south at declinations between 2:1 (horizontal to vertical) and 4:1. The general area of Building 25 has been graded to an approximately level pad near Elevation +940 feet (LBNL datum); the nose of the ridgeline intersects the floor of Strawberry Canyon at about 500 feet below the level of the building pad.