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Superior Court of Washington for King County 8 Ryan M 1 HONORABLE ROGER S. ROGOFF 2 3 4 5 6 7 SUPERIOR COURT OF WASHINGTON FOR KING COUNTY 8 RYAN M. PSZONKA, et al., 9 No. 14-2-18401-8 SEA 10 Plaintiffs, 11 PRELIMINARY EXPERT REPORT OF 12 v. DR. J. DAVID ROGERS, Ph.D., P.E., P.G., C.E.G., C.HG. 13 SNOHOMISH COUNTY, et al., DR. MARVIN R. PYLES, Ph.D., P.E. 14 Defendants. DR. JONATHAN D. BRAY, Ph.D., P.E., NAE 15 TIM WARD, et al. DR. ARNE SKAUGSET, Ph.D., RPF 16 Plaintiffs, DR. RUNE STORESUND, D.Eng., P.E., G.E. 17 v. 18 SNOHOMISH COUNTY, et al., 19 Defendants. 20 GREGORY REGELBRUGGE, et al., 21 Plaintiffs 22 v. 23 STATE OF WASHINGTON, et al., 24 Defendants 25 26 27 28 29 30 31 32 PRELIMINARY EXPERT REPORT OF ROGERS, PYLES, BRAY, SKAUGSET, & STORESUND PAGE 1 1 Executive Summary 2 The SR 530 Landslide of March 22, 2014 was a tragedy of unparalleled proportions in this country. 3 Nearly the entire long-term average annual loss of life from landslides in the continental United States 4 occurred in this one event in the State of Washington for 2014. A few facts are not in question. The 5 landslide was a deep seated landslide with an elevation difference from crest to toe of just over 600 feet, 6 and portions of the slide mass traveled to a point just over a mile from the scarp. This report is the first 7 of what will be a series of reports that will arise out of an effort to fully understand the causes of the 8 landslide. It is a joint report prepared by an expert team assembled by the Attorney General of the 9 State of Washington. This joint report is a preliminary document in which we review the hypotheses 10 either directly listed or implied in the complaints regarding the proximate causes of the SR 530 Landslide 11 of March 22, 2014. 12 13 Hypotheses that we discuss herein include: 14 Hypothesis 1 – Clear-cut timber harvesting will result in increased through-fall that results in a 15 direct increase in groundwater; 16 Hypothesis 2 – The SR 530 Landslide failure mechanism was driven by unconfined gravitational 17 seepage; 18 Hypothesis 3 – Erosion by the Stillaguamish river at the toe of the slope destabilized the slope 19 and resulted in the SR530 landslide; 20 Hypothesis 4 – Construction of settling ponds near the toe of the slope for the purpose of 21 reducing sediment input to the river to benefit fisheries destabilized the slope; and 22 Hypothesis 5 – Stability analysis done before the SR 530 Landslide with subsurface information 23 available at the time demonstrated within the standard of practice that the landslide was going 24 to occur and endanger the Steelhead Haven neighborhood. 25 26 This must be considered a preliminary document because, in the opinion of the authors, we believe 27 there is insufficient factual information available at the present time to offer an informed opinion. It 28 is not possible to evaluate the March 22, 2014 SR 530 Landslide and to form defensible opinions 29 regarding its causative mechanisms and to identify potentially important contributing factors to its 30 instability without subsurface investigations and monitoring that help define the landslide 31 geometry, the engineering properties of the key geologic units, and the groundwater conditions 32 within and below the landslide. PRELIMINARY EXPERT REPORT OF ROGERS, PYLES, BRAY, SKAUGSET, & STORESUND PAGE 2 1 2 A subsurface exploration program coupled with a geotechnical testing program will provide factual 3 information on which to base an informed opinion. While it is not our desire to slow the legal 4 process in this case, we believe we have an obligation to maintain the standards of our professional 5 practice in civil engineering and forestry. PRELIMINARY EXPERT REPORT OF ROGERS, PYLES, BRAY, SKAUGSET, & STORESUND PAGE 3 1 Table of Contents 2 3 Executive Summary ....................................................................................................................................... 2 4 Nature of Involvement .................................................................................................................................. 6 5 Credentials and Compensation ..................................................................................................................... 6 6 Available Information ................................................................................................................................... 8 7 Aerial Imagery (1947-2014) ...................................................................................................................... 8 8 Aerial LiDAR Data Sets (2003-2014) .......................................................................................................... 9 9 Existing Reports/Documents................................................................................................................... 10 10 Eyewitness Accounts ............................................................................................................................... 11 11 Historic Topographic Surveys .................................................................................................................. 11 12 Precipitation Records .............................................................................................................................. 12 13 Streamflow Records ................................................................................................................................ 12 14 Rainfall Monitoring Program .................................................................................................................. 12 15 WDOT Subsurface Exploration Program ................................................................................................. 15 16 Site Context ................................................................................................................................................. 15 17 Overview ................................................................................................................................................. 15 18 Geology & Stratigraphy ........................................................................................................................... 16 19 Prehistoric Landslide Events ................................................................................................................... 19 20 Historic Landslide Events ........................................................................................................................ 20 21 Groundwater “Compartments” .............................................................................................................. 25 22 Seismic Signals ........................................................................................................................................ 30 23 Discussion of hypotheses to be tested ....................................................................................................... 36 24 Hypothesis 1 - Clear-cut timber harvesting will result in increased through-fall which results in a direct 25 increase in groundwater ......................................................................................................................... 36 26 Hypothesis 2 – The SR 530 Landslide failure mechanism was driven by unconfined gravitational 27 seepage ................................................................................................................................................... 37 PRELIMINARY EXPERT REPORT OF ROGERS, PYLES, BRAY, SKAUGSET, & STORESUND PAGE 4 1 Hypothesis 3 – Erosion by the Stillaguamish river at the toe of the slope destabilized the slope and 2 resulted in the SR530 landslide............................................................................................................... 38 3 Hypothesis 4 – Construction of settling ponds near the toe of the slope for the purpose of reducing 4 sediment input to the river to benefit fisheries destabilized the slope ................................................. 38 5 Hypothesis 5 – Stability analysis performed before the SR 530 Landslide with subsurface information 6 available at the time demonstrated within the standard of practice that the landslide was going to 7 occur and endanger the Steelhead Haven neighborhood ...................................................................... 39 8 Proposed Field and Laboratory Program .................................................................................................... 47 9 Purpose and influence on slope stability analyses ................................................................................. 47 10 Exploratory Borings ................................................................................................................................. 51 11 Piezometers ............................................................................................................................................ 51 12 Geophysical Surveys ............................................................................................................................... 51 13 Reservation ................................................................................................................................................. 52 14 Works Cited ................................................................................................................................................. 54 15 Appendix A – Aerial Image Catalog ............................................................................................................. 56 16
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