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City of Redwood (]it)' Proposal No. 03-187 September 18, 2003 Page No. 2 2) The documentation reviewed indicates that emergency grading immediately after the slide occurred included the removal of about 2,500 to 3,000 cu. yds. of soil from behind the residences on Farm Hill Blvd. Among the documentation are two drawings titled "From Hill Blvd. - Nob Hill Rd. Area, Subdrainage Project" (dated Dec. 1968) showing a drainage gallery and horizontal drains to be installed above the slide area, and a plan titled "Grading Plan for Farm Hill Disaster Area" (dated 3-10-67) showing the proposed grading for the slide area. The grading shown on the latter plan does not include a buttress fill as tentatively recommended by Shannon & Willson. In addition, a communication from the Public Works Director to the City Manager, dated April 5, 1967, "strongly recommended that no grading of this slide mass be done in the near future." 3) Recently, an offer has been made to purchase the two lots in conjunction with performing stabilization grading of the old slide. Mr. Mahoney, a Geotechnical Engineer, stated that he has "seen logs of the soils test drilling done in the street and remember(s) the existence of a shear plane at a depth of approximately 25feet below the street level" and concluded the slide could re-activate affecting Nob Hill Rd as well as the houses above. On Monday, July 21, 2003, we visited the site to visually observe conditions. The topography of the City's two lots are generally similar to the contours shown on Shannon and Wilson's plot plan (see also Plate 1, Proposed Boring Locations, attached to this proposal), except the slide scarp is no longer vertical, but at roughly 1½:1 (horizontal to vertical). Although the scarp area appears steeper than the 2:1 shown on the"Grading Plan for Farm Hill Disaster Area," it is assumed this was a result of implementing the referenced grading plan, rather than the normal slumping of an over-steepened slope. A concrete drainage swale (not shown on the "Grading Plan") has been constructed immediately above the old scarp area, crossing the two lots and draining into a drop inlet in the northeast comer of Lot 15. The concrete ditch shows no signs of movement, with the exception of the extreme northern end, where a couple cracks have developed and have been partially filled with a foam-like compound; however, no cracks in the ground surface were evident adjacent to the cracks in the concrete ditch. As this area is generally at the edge and beyond the original slide area, and because we also did not find any other evidence of recent soil movements on or near the two lots, it appears this is likely a combination of settlement of loose soils immediately beneath the ditch, and/or the lifting of the concrete swale by reots of adjacent trees. Within the street, there is a patched area that generally corresponds with the location of the drainage gallery shown on the referenced plan (also shown on the attached plate). Because the outlets to the horizontal drains shown on the Subdrainage Plan are located on adjacent private property, we could