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Home My WebLink About04-21-2015 B1 Distributed by Ristowe Earth Systems Pacific June 4, 2014 Ms. Christine Dietrick Assistant City Attorney City of San Luis Obispo 990 Palm Street San Luis Obispo, CA 93401 (DECEIVED APR 2 2 2015 p S. ' CIS CLERK 4378 Old Santa Fe Road San Luis Obispo, CA 93401.8116 (805) 544 -3276 • FAX (805) 544 -1786 E -mail: esp@earthsys.com FILE NO.: SL- 15030 -SD COUNCIL MEETING: Vq A ITEM NO.: PROJECT: SLOPE ALONG SOUTH SIDE OF PISMO STREET BETWEEN MORRO STREET AND CHORRO STREET SAN LUIS OBISPO.. CALIFORNIA SUBJECT: Geotechnical Re- Evaluation of Slope Conditions REF: 1) Limited Geotechnical Evaluation, South Side of Pismo Street between Morro Street and Chorro Street, San Luis Obispo, California, by Earth Systems Pacific, File No.: SL- 15030 -SA, Doc. No. 0807- 073.LTR, dated July 11, 2008 2) Draft Geotechnical Re- Evaluation of Slope Conditions, Slope Along South Side of Pismo Street between Morro Street and Chorro Street, San Luis Obispo, California, by Earth Systems Pacific, File No.: SL- 15030- SC, dated January 24, 2011 Dear Ms. Dietrick: In June 2008, the undersigned Geotechnical Engineer, and Rick Gorman, Certified Engineering Geologist, both of Earth Systems Pacific (Earth Systems), conducted a visual assessment of the slope that extends along the south side of Pismo Street, between Morro and Chorro Streets in the City of San Luis Obispo. The results of the assessment were presented as a limited geotechnical evaluation report (REF. 1). We concluded that parts of the slope were unstable, and that there were several areas where there was a high potential for slope failure or rockfall. Recommendations were developed for short-term and long -term mitigation and were presented in the report. Following our assessment, K -rail barriers were installed to cordon off the slope, sidewalk and parking lane of Pismo Street as recommended in our report. Chain link fences were also installed atop the K -rail and at the toe of the slope. The fence at the toe of the slope acts to catch small rocks that fall from the slope. The fence on the K -rail effectively blocks off the sidewalk to prevent the public from accessing areas where slope failure or rockfall was considered to be a hazard to public safety. In January 2011, Earth Systems was engaged to re- evaluate and update our conclusions regarding the slope. I, along with Mr. Gorman, did the re- evaluation. We concluded that generally the slope appeared unchanged, but change that was noted since 2008 was a more pervasive growth of ivy. We commented that the ivy helps to stabilize the slope to a degree, 0 Slope along South Side of Pismo St. Between Morro St. and Chorro St. San Luis Obispo, California 2 June 4, 2014 but also fiends obscure it; making visual assessment more difficult. The easterly 60 feet of the slope (measured from the eastern end of the 3 -foot garden wall; the same datum as used in the original evaluation), was the most unstable and the slope became more stable in a westerly direction. Boulders were still in precarious positions on the slope and we concluded that for safety purposes, "it is imperative that public access continues to be restricted until more permanent stabilization measures have been implemented." A draft of that re- evaluation report was sent to your office for review and comments. As we received no comments or instructions to proceed, it remained as a draft and was never signed. On April 17, 2014, Earth Systems received a request from Mr. Matt Horn of the City Public Works Department to once again re- evaluate the slope and update our conclusions. On April 23, 2014, we received email authorization to proceed with our re- evaluation. Current Conditions As requested, the same engineer (the undersigned) and geologist (Rick Gorman) again visited the site on April 29, 2014 for the purpose of re- evaluating the slope. We observed the slope from Pismo Street; we did not gain access inside the public barricade or to the co -op residential property at the top of the slope. Since our last site visit in 2011, the most apparent change is a much denser growth of ivy on the slope face. While the ivy is very beneficial in helping to stabilize the slope via its root system, it also obscures most of the slope face, making visual assessment of the actual conditions impossible on much of the slope. However, it could be seen that, as before, the roots are helping to anchor loose boulders and rocks to temporarily prevent them from rolling or falling down the slope. In general, it appeared that the condition of the slope was not markedly changed. The initial 60 feet of the slope or so, as measured from the eastern edge of the 3 -foot garden wall (the same reference as used in the original evaluation), is still the steepest and most unstable portion of the slope. A wood yard fence at the top of the slope is undermined in the area of the main wedge failure described in the original report; an area of the slope that is vertical to overhanging. While the change in the top of the slope in this area is minor, it is indicative of slow but ongoing erosion or minor rockfalls occurring on the slope. The chain link fence at the bottom of the slope has successfully trapped several rocks that have come down from the slope. As before, they range from about fist -sized to about half the diameter of a basketball. The volume of cobbles and boulders behind the chain link fence is minimal, further indicating that the slope raveling since 2008 has been relatively minor. This conclusion assumes that boulders and cobbles have not been removed from behind the fence in the past years. Are §k w�. Slope along South Side of Pismo St. 3 June 4, 2014 Between Morro St. and Chorro St. San Luis Obispo, California The slope angle decreases in a westerly direction; however, as described in the previous reports, boulders have loosened from the face of the slope, and in many cases appear to be held in place primarily by the roots and vines of the ivy. Some boulders appear to be in more precarious positions than previously, as would be expected after the passage of time. Based upon our current observations, our conclusions regarding the stability of the slope as presented in the previous two reports remain unchanged. Much of the slope is unstable and there are several areas where slope failure or rockfall may be imminent. For safety reasons, it is imperative that public access continues to be restricted until more permanent stabilization measures have been implemented. Our conclusions as to the long -term solutions remain essentially unchanged. Despite several years of well below normal rainfall, the slope appears to be slowly eroding or otherwise retreating. At this time, the top of the slope is far enough from the buildings at the top of the slope that they are not considered to be in imminent danger. However, site improvements at the top of the slope, i.e. the fence, etc., are undermined (or nearly so) and damage to those improvements should be expected in the future, particularly in years of normal or above - normal rainfall. We appreciate the opportunity to have provided services for this project and look forward to working with you again in the future. If there are any questions concerning this letter, please do not hesitate to contact the undersigned. � "° _D� ON Sincerely, U, Earth Systems Pacific 1j,7,u �' cz° ti - Cam Dennis Sha enberger, ' . �. C, _ r. OTi- \X Principal Engineer D Gtr. Copy to: Mr. Matt Horn, City Public Works Department Doc. No.: 1406- 062.LTR /jr r ..- ........... Nl� . , 4' i Ak