2621 ROCKEFELLER AVE Geotech Report 2022-10-25

• Decreasing runoff velocities. • Preparing drainage ways and outlets to handle concentrated or increased runoff. • Confining sediment to the project site. 1 • Inspecting and maintaining control measures frequently. In addition, we recommend that sloped surfaces in exposed or disturbed soil be restored so that surface runoff does not become channeled. Some sloughing and raveling of slopes with exposed or disturbed soil should be expected. Temporary erosion protection should be used and maintained in areas with exposed or disturbed soils to help reduce erosion and reduce transport of sediment to adjacent areas and receiving waters. As temporary erosion protection, we recommend the use of straw, jute matting, rolled erosion control products, heavy plastic sheeting or other forms of ground cover on areas disturbed by construction. Permanent erosion protection should be provided by establishing vegetation by hydroseeding or landscape planting. 11 Until the permanent erosion protection is established and the site is stabilized, site monitoring should be performed by qualified personnel to evaluate the effectiveness of the erosion control measures and to repair and/or modify them as appropriate. Provisions for modifications to the erosion control system based on monitoring observations should be included in the erosion and sedimentation control plan. Permanent Slopes We recommend that permanent cut and fill slopes be constructed no steeper than 2H:1V. To achieve uniform compaction, we recommend that fill slopes be overbuilt slightly and subsequently cut back to expose properly compacted fill. To reduce erosion,newly constructed slopes should beplanted or hydroseeded shortlyafter completion Y p of grading. Until the vegetation is established, some sloughing and raveling of the slopes should be expected. This may require localized repairs and reseeding. Temporary covering, such as clear heavy plastic sheeting, jute fabric, loose straw, excelsior matting or other rolled erosion control products should be used to protect the slopes during periods of rainfall. Drainage Considerations 11 We recommend that the ground surface be sloped to drain away from the proposed building such that surface water runoff is collected and routed to suitable discharge points. EXCAVATIONS Excavations for the parking level will require cuts up to about 8 feet deep on the west side of the site. These cuts can likely be made as temporary open cut slopes depending on site constraints. Excavations are also required for underground utilities. The stability of open cut slopes is a function of soil type, groundwater seepage, slope inclination, slope height and nearby surface loads. The use of inadequately designed open cuts could impact the stability of adjacent work areas, existing utilities, and endanger personnel. File No.12547-001-00 February 3.2006 Page 8 GEoENG{NEERS g